single grain experiment

Stephen Mouton Babcock and the Babcock Test

Babcock Test Machine

On July 2, 1931, American agricultural chemist Stephen Moulton Babcock passed away. He is best known for his Babcock test in determining dairy butterfat in milk processing, for cheese processing, and for the “ single-grain experiment ” that led to the development of nutritional science as a recognized discipline. He worked for 43 years at the University of Wisconsin, where he established a laboratory where he carried out pioneering research in nutrition and in the chemistry of vitamins .

Stephen Babcock – Early Years

Stephen Babcock was born on a farm in Bridgewater, New York, USA, to Peleg and Cornelia Babcock. He earned his bachelor’s degree from Tufts College in 1866 and his master’s degree from Cornell University in 1875. At the University of Göttingen , Babcock studied organic chemistry and received his Ph.D. in 1879 under the supervision of Hans Hübner. He became an agricultural chemist at the New York State Agricultural Experiment Station in Geneva, New York, where his first assignment was to determine the proper feed ratios of carbohydrate, fat, and protein using chemical analysis of cow excrement. After finding out that the excrement’s chemical composition was similar to that of the feed, the only major exception being the ash content, the scientist wondered what would happen if cattle were fed a single grain, e.g. barley , corn, or wheat. However, that test would not be carried out for nearly twenty-five years.

Stephen Moulton Babcock (1843-1931)

The Babcock Test

Stephen Babcock accepted a position at the University of Wisconsin–Madison Agricultural Experiment Station in 1888 as chair of the Agricultural Chemistry department. Two years later, he developed the famous Babcock test which determines the butterfat content of milk. He then worked with bacteriologist Harry L. Russell in developing the cold-curing process for ripening cheese. The Babcock test set the worldwide standard for butterfat determination of milk, while the cold-curing process enabled Wisconsin to become the leading cheese producer in the United States. Before the Babcock test, dishonest farmers could water down their milk or remove some cream before selling it to the factories because milk was paid for by volume. Honest farmers on the other hand, as well as those that produced naturally rich milk, were not being compensated fairly.

How it works

In order to research and solve the problem, Babcock developed a test in which milk was measured into a test tube, 17.6 milliliters were usually taken. Then, 17.6 milliliters of 90-92% sulfuric acid were added and centrifuged at 50°. In the end, the fat floating on top of the liquid in the test tube could be measured. The principle behind the process is that everything in milk except the fat dissolves in sulfuric acid and the centrifuge ensures complete separation with no bubbles in the fat, and the fat content can be measured using the graduations on the test tube and knowing the initial amount of milk used.

Fair Compensation for Dairy Farmers

After the development of the test, it was much easier for a dairy operation to not only compensate farmers fairly, but to produce a consistent product that consumers could depend on. The Babcock test was also utilized by farmers to selectively breed for cows who produced milk with higher butterfat content — the tests were usually done monthly by an employee of the local Dairy Herd Improvement Association.

The Vitamin Concept

Babcock’s most important contribution arose from his skepticism regarding the biological equivalency of chemically similar feeds from different crops. In 1907 four of his younger associates — E.B. Hart, E.V. McCollum, H. Steenbock, and G. Humphrey began a cattle-feeding experiment using chemically equivalent rations, each derived from a different plant. The experiment not only confirmed Babcock’s skepticism but led to studies that helped develop the vitamin concept. Babcock also studied metabolic water in insects and, in his later years, sought to investigate the structure of matter and its relation to energy.

Stephen Babcock died in 1931, in Madison, Wisconsin, at age 87, from a heart attack suffered during a heat wave. In 1948, the Institute of Food Technologists created the Stephen M. Babcock Award (now the Babcock-Hart Award ) in honor of Babcock’s achievements.

References and Further Reading:

• [1]  Short Biography of Stephen Babcock
• [2]  How does a Babcock Tester work?
• [3] “ Babcock, Stephen Moulton “. Encyclopedia.com.
• [4] Stephen Babcock at Wikidata
• [5]    “Famed Man of Science Heat Victim at 87” .   Wisconsin State Journal . July 2, 1931. p. 1
• [6]  “Prof. Babcock Dies; Heat Victim. World Famous Scientist Passes Away, Aged 88” .  The Capital Times . July 2, 1931. p. 1 .
• [7] HISTORICAL ESSAY, Babcock, Stephen, 1843-1931, Wisconsin Historical Society
• [8] Timeline of American Nutritionists , via DBpedia and Wikidata

Tabea Tietz

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2017 Marks Centennial of Two Significant Department Discoveries

The year 1917 — 100 years ago — was a big year for the Department of Biochemistry at the University of Wisconsin–Madison, then called the Department of Agricultural Chemistry. Now in 2017 the department is celebrating the centennial of two major achievements: the discoveries of vitamin B and the link between goiter and iodine.

Elmer McCollum and Marguerite Davis were responsible for the discovery of “fat-soluble A” (which was eventually resolved into vitamins A, E, D, and K), and E. B. Hart and Harry Steenbock confirmed that iodine can alleviate goiter. These two important scientific achievements, as well as the stories, personalities, and even controversies that accompanied them, changed the field of biochemistry at UW–Madison and around the world.

The department’s work with vitamins began with what is called the single grain experiment with cows from 1907-1911. The experiment, done by Stephen Babcock, Hart, McCollum, and Steenbock, fed groups of cows only a single grain, either corn, wheat, or oats, and then a last group a combination of all three. They found that the cows that ate corn were healthier than the others.

This finding told the researchers there was something essential in corn that wasn’t present in wheat or oats and they began supplementing the other two with different additions, like parts of milk, to find what would make a diet complete.

To further develop the experiment, McCollum asked his dean if he could have some money to study rats instead of cattle because it would be cheaper and produce better results. In a funny twist in the story, McCollum was laughed out of the office. Rats were a nuisance on Wisconsin farms, causing thousands of dollars in damage each year.

“If the farmers of this state ever figured out that the dean was spending their taxes to learn how to nourish rats there would be trouble,” the dean reportedly told McCollum as he denied his request. Dave Nelson, a Biochemistry Emeritus Professor and defacto department historian, recounted these historical conversations at a recent lecture for  Wednesday Nite at the Lab .

Instead McCollum drove to Chicago to buy some mating pairs of white rats, and Wisconsin actually became a leading breeder of rats used as model organisms in science in a short time. Using these experiments in cattle and rats, McCollum and Davis found that there were components in milk that were extremely potent and fixed the insufficient diet. They described two fractions, fat soluble A (which was eventually resolved into vitamins A, E, D, and K), and water-soluble B (eventually shown to consist of vitamins B 1 , B 3 , B 6 , and B 12 ).

Conrad Elvehjem and coworkers discovered that tiny amounts of niacin (vitamin B 3 ) cure “black tongue” disease in dogs, thought to be the canine equivalent of pellagra in humans. Niacin was quickly shown to cure pellagra in humans. This finding resolved the debate about whether pellagra was due to a nutritional deficiency in some foods or to toxins present in certain foods. This was coupled with research during this time from the United States Public Health Service.

“This stuff is extremely potent and it’s interesting to imagine how these scientists must have felt when giving a tiny amount helped a dog recover from black tongue,” says Nelson. “A normal aspirin tablet weighs about half a gram. These researchers gave dogs a fraction of that weight of niacin. Just 10 mg helped dogs recovery very quickly. It must have been very exciting to witness.”

At about the same time, scientists in the Department of Agricultural Chemistry (which later became the Department of Biochemistry) discovered that the disease goiter is caused by a lack of iodine in the diet. Because iodine is an essential part of the thyroid hormone, its absence from the diet causes excessive growth of the thyroid gland — the disease goiter.

Nelson explains that seafood provides a lot of iodine since the ocean is rich in the element. Before the advent of refrigerated transport of seafood, goiter was uncommon on the East and West Coasts, but common in the Midwest.

In 1917, Hart and Steenbock confirmed this link between iodine and goiter. In 1939, Hart and colleagues also devised a way to get iodine into people’s everyday diet. The solution was to add trace amounts of iodine to the ubiquitous staple in every kitchen — table salt. Iodized table salt is still in use today.

These two discoveries and the department’s work in vitamins are just one example of the ground-breaking research that exemplifies the department’s history and makes up the modern research occurring today.

“There really isn’t a vitamin or mineral that’s been discovered that wasn’t somehow touched by a UW–Madison researcher,” Nelson says. “And while we have lots of diverse research taking place in the department, some are still working in this area. For example, we now have visualized at the molecular level how vitamin D works.”

The top left thumbnail is a photo by Robin Davies of Harry Steenbock depicted in murals by John Steuart Curry  that are located in the Hector F. DeLuca Biochemistry Building. The murals showcase the societal benefits of biochemistry. 

Research Highlights 1900 – 1949

1900 – University of Wisconsin–Madison is one of 14 institutions from across the nation to meet in Chicago to discuss graduate education, resulting in the creation of the Association of American Universities.

1904  – The UW–Madison Graduate School is created, with astronomer G.C. Comstock as its director (title changed to dean in 1914). Total graduate student enrollment is 115.

1911 – The Single-grain Experiment demonstrates the importance of trace nutrients (later identified as vitamin) for optimal health. The discovery lays the groundwork for modern nutritional science. The experiment was conceived by Stephen Babcock, overseen by Edwin B. Hart, and assisted by Elmer McCollum, Harry Steenbock and George Humphrey.

1913 – Following out of the nutrition research of Babcock and Hart, experiments performed in the labs of biochemistry professors Davis, Elvehjem, Hart, McCollum and Babcock finds undiscovered components in diets. The researchers demonstrate the existence of vitamins A and B and their roles in nutrition, including the causes of pellagra and beriberi (vitamin B3 (niacin) and B1 (thiamin) deficiency, respectively). These discoveries foster development of vitamin synthesis, helping to eliminate diseases stemming from some vitamin deficiencies. Commemorative historical markers about these and other events can be found throughout the Agricultural and Life Sciences campus (Henry Mall/Babcock Drive area).

1914 – Communication Sciences and Disorders is the first speech pathology department (Dept of Speech Correction, at that time), 1914, and is the first doctoral program in the United States.

1915 – Professors McCollum and Davis isolate a water-soluble substance later to be named vitamin B.

1916 – Cornelia Kennedy, graduate student in biochemistry, is the first to use the letters “A” and “B” for trace nutrients, which establishes a precedent for naming vitamins.

1917 – The Research Committee is formed. Its initial mission was to raise funds and to coordinate national defense research during World War I. The committee grew to one dedicated to providing resources for faculty research.

1920s – Biochemists in the 1920s conducted studies leading to improved understanding of the roles of minerals in animal and human diets. The labs of Professors Hart, Elvehjem, and Steenbock discover that copper, in addition to iron, is necessary for making hemoglobin, a component of blood that carries oxygen from the lungs to tissues, and carbon dioxide from tissues to lungs. This led to the use of copper to treat iron deficiency anemia.

1922 – Sara Stinchfield receives first PHD. in Communicative Disorders in the United States.

1924 – Professor of Agricultural Chemistry Harry Steenbock discovers the process of irradiating food to enrich its vitamin D content. In 1921 E.V. McCollum discovered a substance that cured rickets – vitamin D. The discovery of vitamin D by Steenbock’s lab is a hallmark contribution to science and society made during the university’s history. Steenbock not only discovered vitamin D but also invented a way to produce it and applied the invention eliminate rickets as a major medical problem. Proceeds from the invention were applied in the form of a Wisconsin Alumni Research Foundation (WARF) to support research at UW. WARF contributes approx. $130M annually to support research at the university.

Cut into a rusted-steel panel, the molecular model of Vitamin D is featured at Alumni Park. Harry Steenbock discovered how to enrich foods with Vitamin D, thus ending the scourge of rickets. (Photo by Jeff Miller / UW-Madison)

1925 – Professor Harry Steenbock, Graduate Dean Charles Slichter, Agriculture Dean Harry Russell, and a group of UW alumni found The Wisconsin Alumni Research Foundation. Steenbock’s vitamin D patents establish a portfolio of inventions and investments used to support and fund additional research by university faculty, staff and students.

1928 – Fermentation methods that lead to large-scale preparation of antibiotics such as penicillin are developed by the labs of Biochemistry Professors W.H. Peterson and M.J. Johnson. Without their work and the work of other scientists at UW–Madison, penicillin could not have been used during World War II in the preparations that it became available. The methods developed by the fermentation group were applied by industry and academic institutions, affecting the entire antibiotic industry. https://www.wispolitics.com/2017/uw-madison-d-day-invasion-was-bolstered-by-uw-madison-penicillin-project

1929 – Edwin B. Hart develops a method for stabilizing iodine in table salt to cure goiter.

1929 – The School of Business establishes the country’s first graduate program in public utilities.

1932 – Animal behaviorist Harry Harlow founds the Harlow Primate Laboratory, including the nation’s first monkey-breeding colony.

1932 – UW Arboretum is founded.

1933 – UW Arboretum begins its first forest plantings.

1933– Farmer Ed Carlson brought to Biochemistry Professor Karl P. Link sweet clover hay that he thought might be involved in the death of his cattle from uncontrollable bleeding. Link’s lab isolates and identifies dicumarol as the anticlotting agent in the spoiled hay. They then synthesized comparable compounds including Warfarin , which is widely used to treat thrombosis and other clotting disorders. It also proved to be a highly effective rodenticide. Compound synthesis was performed by Link, Mark Stahmann, and Miyoshi Ikaw ( https://publichistoryproject.wisc.edu/travel-permit-to-madison-wi-for-miyoshi-ikawa-text-description/). The American Chemical Society honored the development of the blood thinner warfarin with the National Historic Chemical Landmark designation in a ceremony at UW–Madison on Oct. 12, 2022.

1934 – UW Arboretum is dedicated.

1934 – Although they may not have anticipated it when the Arboretum was founded, the University of Wisconsin’s Arboretum committee’s foresight resulted in the Arboretum’s ongoing status as a pioneer in the restoration and management of ecological communities. In focusing on the re-establishment of historic landscapes, particularly those that predated large-scale human settlement, they introduced a whole new concept in ecology: ecological restoration — the process of returning an ecosystem or piece of landscape to a previous, usually more natural, condition.

1937 – Conrad Elvehjem leads UW researchers who find that niacin supplementation prevents pellagra, a disease that killed 5,000 people a year at the time.

1937 – Tuition and fees for graduate study are $55 for residents and $255 for nonresidents.

1939 – As a graduate student at UW, Henry Lardy helps make possible the artificial insemination of heifers and cows through his invention of a device that helped preserve semen. Taking a practical approach, Lardy and Professor Paul H. Phillips explore media readily accessible to farmers, eventually discovering buffered egg yolk as a suitable medium for preserving semen. Their work changed the global dairy industry, allowing for relatively easy breeding of highly productive dairy cows.

1940 – Karl Paul Link and graduate assistants Harold Campbell, Ralph Overman, Charles Huebner, and Mark Stahmann first crystalize an anticoagulant substance that will lead to the development of warfarin, a widely used rodenticide and the most prescribed blood thinner in the world for human patients.

1944 – Joseph Erlanger and  Herbert Gasser win the Nobel Prize in Physiology, Medicine for the study of the differentiated functions of individual nerve threads

1945 – WARF files for a patent on warfarin (the patents is granted in 1947).

1948-50 – Graduate School takes over evaluations of applications for graduate study from the registrar. The changes were hailed as being more efficient.

1948 – UW–Madison Scientists Harry Harlow, David Grant and Esta Berg design the Wisconsin Card Sorting Test (WCST). Grant and Berg publish the now famous, patented and trademarked cognitive test in the Journal of Experimental Psychology. The test is used primarily to assess perseveration and abstract thinking, according to the American Psychological Association. It is considered a measure of executive function because of its reported sensitivity to frontal lobe dysfunction. In addition to humans, the test has been used with some animals, including rhesus monkeys in studies at the Wisconsin National Primate Research Center. https://pubmed.ncbi.nlm.nih.gov/18874598/

Stephen M. Babcock

Stephen Moulton Babcock (1843–1931) was a U.S. agricultural chemist . He is best known for his Babcock test in determining dairy butterfat in milk processing, in cheese processing, and in the "single-grain experiment" that would lead to the development of nutrition as a science. His studies helped to standardize the quality of dairy produce, where earlier there had been much variation. His work also functioned to bolster dairy production in the state of Wisconsin and secure its place as the country's leading cheese producer. Later, he was employed as a professor and leading chemist at the University of Wisconsin-Madison from 1887 to 1913. Babcock's "single grain experiment" illustrated an unquestionable connection between diet and wellness and provided the impetus for the scientific study of nutrition.

• 1 Early life and career
• 2 University of Wisconsin-Madison
• 3 "Single-grain experiment"
• 6 References
• 7 External links

Early life and career

Born on a farm in Oneida County, New York, Babcock earned degrees from Tufts College in Medford, Massachusetts and Cornell University in Ithaca, New York before earning a doctorate in organic chemistry at the University of Gottingen, Germany . Upon his return to the United States in 1881, Babcock took up the role of an agricultural chemist at the New York State Agricultural Experiment Station in Geneva, New York where his first assignment was to determine the proper feed ratios of carbohydrate , fat , and protein from cow excrement using chemical analysis. His findings determined that the excrement's chemical composition was similar to that of the feed with the only major exception being the ash. These results were tested and retested, and his results were found to be similar to German studies done earlier. This led Babcock to think about what would happen if the cows were fed a single grain ( barley , corn , wheat ) though that test would not occur for nearly 25 years.

University of Wisconsin-Madison

Seven years later, Babcock accepted a position at the University of Wisconsin-Madison Agrcultural Experiment Station (UWAES) as chair of the Agricultural Chemistry department, and immediately began petitioning Dean of Agriculture William Henry, then station director, to perform the "single-grain experiment." Henry refused. In the meantime, he discovered the Babcock test which determines the butterfat content of milk in 1890, then worked with bacteriologist Harry L. Russell in developing the cold-curing process for ripening cheese (1897). The former method is the standard for butterfat determination of milk worldwide (replacing the much more expensive and rarely utilized method employed before) while the latter led Wisconsin to be the leading cheese producer in the United States. [1]

"Single-grain experiment"

Babcock continued pressing Henry to perform the "single-grain experiment," even approaching the UWAES animal husbandry chair J.A. Craig (he refused). When W.L. Carlyle replaced Craig in 1897, Carlyle was more receptive to Babcock's idea. Initially trying a salt experiment with eight dairy cows as a matter of taste preference while eight other cows received no salt. After one of the eight cows that did not receive salt died, Carlyle discontinued the experiment and all of the remaining cows were given salt in order to restore their health.

Henry, now Dean of Agriculture in 1901, finally relented and gave Babcock permission to perform the experiment. Carlyle approved the experiment with only two cows. One cow was fed corn while the other was fed rolled oats and straw with hopes the experiement would last one year. Three months into the experiment, the oat-fed cow died, and Carlyle halted the event to save the other cow's life. The results were not published mainly because Babcock did not list how much of each grain the respective cows had consumed.

In 1906, a chemist from the University of Michigan, Edwin B. Hart (1874-1953), was hired by Babcock. Hart had previously worked at the New York State Agricultural Experiment Station and had studied physiological chemistry under Albrecht Kossel in Germany. Both worked with George C. Humphrey, who replaced Carlyle as animal husbandry professor, to plan a long-term feeding plan using a chemically-balanced diet of carbohydrates, fat, and protein instead of single plant rations as done in Babcock's earlier experiments. The "single-grain experiment" was thus born in 1907.

From May 1907 to 1911, the experiment was carried out with Hart as director, Babcock providing the ideas, and Humphrey overseeing the welfare of the cows during the experiment. Edwin V. McCollum, an organic chemist from Connecticut , was hired by Hart to analyze the grain rations and the cow excrement. The experiment called for four groups of four heifer calves each during which three groups were raised and two pregnancies were carried through during the experiment. The first group ate only wheat, the second group ate only bran, the third group at only corn, and the last group at a mixture of the other three.

In 1908, it was shown that the corn-fed animals were the most healthy of the group while the wheat-fed groups were the least healthy. All four groups bred during that year with the corn-fed calves being the healthiest while the wheat and mixed-fed calves were stillborn or later died. Similar results were found in 1909. In 1910, the corn-fed cows had their diets switched to wheat and the non-corn-fed cows were fed wheat. This produced unhealthy calves for the formerly corn-fed cows while the remaining cows produced healthy calves. When the 1909 formulas were reintroduced to the respective cows in 1911, the same gestation results in 1909 occurred again in 1911. These results were published in 1911. Similar results had been done in the Dutch East Indies (now Indonesia ) in 1901, in Poland in 1910, and in England in 1906 (though the English results were not published until 1912).

This experiment would lead to the development of nutrition as a science.

After Babcock's death in 1931, his estate was left to the University of Wisconsin-Madison College of Agriculture. By a decision of the deans, a housing cooperative for male students studying agriculture was established in the Babcock home and named in his honor. Babcock House is the oldest continuously-operating student housing cooperative in Wisconsin and is now open to male and female students of any course of study.

In 1948, the Institute of Food Technologists created the Stephen M. Babcock Award (now the Babcock-Hart Award) in honors of Babcock's achievements. Additionally, the food science department building at the University of Wisconsin in Madison was named in Babcock's honor in 1952. The Institute of International Dairy Research and Development at Wisconsin also would be named in Babcock's honor.

• ↑ Linda Anderson, "Mr. Babcock's Invention." In Wisconsin History on Stage: Scripts for Grades 4-8 , ed. Matt Blessing (Madison: The State Historical Society of Wisconsin, 1999), Mr. Babcock's Invention Retrieved December 19, 2007.

References ISBN links support NWE through referral fees

• Anderson, Linda. Mr. Babcock's Invention . edited by Matt Blessing, Madison: The State Historical Society of Wisconsin, 1999. Retrieved December 19, 2007.
• Babcock, Stephen Moulton. American National Biography, 1999
• Biographical Encyclopedia of Scientists . Oxford: Taylor & Francis, 2008 ISBN 9781420072716

External links

All links retrieved February 9, 2023.

• Babcock House

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University of Wisconsin Dairy Barn

J.t.w. jennings; arthur peabody, architects, — 1898; 1909, 1916-17 —.

• Jul 17, 2019

George Colvin Humphrey | 1935

Beloved dairy scientist and innovator in animal nutrition with his "single grain" feeding experiments at the University of Wisconsin.

1875-1947 | Artist: Robert Wadsworth Grafton (1876-1936)

Impact & Accomplishments

Born in Lenawee County, Michigan, George Humphrey graduated from the State Agricultural College of Michigan in 1901 and began teaching there after graduation.

In 1903, he accepted the position of chairman of the Department of Animal Husbandry at the University of Wisconsin, where he helped establish the strong dairy traditions of the state. From 1938 to 1942, he was professor of dairy husbandry. Professor Humphrey was active in single-grain feeding experiments and extensive studies on the influence of feed on the quality of milk, mutton, and wool.

He was an internationally recognized dairy judge. Elected president of the American Society of Animal Production in 1933, Humphrey was honored at the Saddle & Sirloin Club in 1935, with a copy of his portrait presented to the University of Wisconsin’s Agricultural Hall the following year.

Did You Know?

Humphrey was part of the team of scientists at University of Wisconsin that conducted the groundbreaking “single-grain experiment” from 1907 to 1911, determining that cows were healthier when they ate only corn instead of wheat, oats, or a combination of the three. The team’s work led to the development of the field of nutritional science.

"In recognition of faithful service and in commemoration of the 25th anniversary of his founding of the first county breeders association in Wisconsin, this testimonial is presented to GEORGE C. HUMPHREY for his vision that has made possible our association developments, for his teaching that has improved our rural homes, for his council that has brought forth rural leaders and for his ideals which have moulded the character and builded the citizenship of all who come in contact with him." - George McKerrow, Wisconsin Guerney Breeders Association 2/4/31

Sheetmetal bucket with wooden handle used to collect cow manure during nutrition experiments at the University of Wisconsin, Madison, Wisconsin, 1907-1911. These experiments overturned the conventional wisdom regarding animal nutrition and paved the way for the discovery of vitamins. Photo credit: Wisconsin Historical Society. (Museum object #1992 .103)

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About: Single-grain experiment

The single-grain experiment was an experiment carried out at the University of Wisconsin–Madison from May 1907 to 1911. The experiment tested if cows could survive on a single type of grain. The experiment would lead to the development of modern nutritional science.

Research Article

Wear mechanism of aggregated cBN grains during single-grain ultrasonic vibration-assisted grinding of γ-TiAl alloys

Jiahao Song, Biao Zhao, Wenfeng Ding, Yanjun Zhao, Jianhui Zhu, and 1 more

This is a preprint; it has not been peer reviewed by a journal.

https://doi.org/ 10.21203/rs.3.rs-4240998/v1

This work is licensed under a CC BY 4.0 License

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In this study, the wear mechanism of single aggregated cubic boron nitride (AcBN) grain during ultrasonic vibration-assisted grinding is investigated. The single AcBN grinding experiment are conducted under conventional grinding and ultrasonic vibration-assisted grinding on gamma titanium-aluminum intermetallic compounds, and the grain wear mechanism is comprehensively revealed by observing the radial wear height, normal force, average volume pile-up ratio, and morphology evolution of the grains with different maximum undeformed chip thicknesses, grinding speeds, and ultrasonic amplitudes. The experimental results show that the introduction of ultrasonic vibration produces periodic vibration of the workpiece in the tangential direction, which can produce intermittent dissociative behavior and effectively reduce normal force and average volume pile-up ratio of single AcBN grains when grinding, but also makes the instantaneous maximum undeformed chip thickness increase and introduces the periodic impact force, which accelerates the radial wear height of the AcBN grains. In addition, the ultrasonic vibration can effectively reduce the material adhesion in the AcBN grains surface and cause it to continuously undergo micro-fracture has better self-sharpening ability. In addition, excessive ultrasonic amplitude will lead to AcBN grains to occur macro-fracture and the expansion of bond cracks lead to abrasive grains pulling out, losing partial grinding ability.

wear mechanism

ultrasonic vibration-assisted grinding

self-sharpening ability

aggregated cubic boron nitride

1. Introduction

gamma titanium-aluminum intermetallic compounds ( γ -TiAl) has low density, high specific strength, high specific modulus, good antioxidant property and corrosion resistance, which makes it considered as an ideal material for cross-generation aero-engines [ 1 – 9 ]. Its plate structural components for hypersonic scramjet engines can have a potential for weight reduction of 25%-35% relative to nickel-based alloys. However, its elongation is only 2%-4% at room temperature, and its inherent brittleness limits its application [ 10 – 13 ]. Meanwhile, the excellent mechanical properties pose a great challenge for machining. Grinding is an important way to achieve its high efficiency and high surface integrity, but the process still faces problems such as fast tool wear due to high grinding forces and high grinding temperatures, and the surface is prone to adhesion, cracks, and burns [ 14 , 15 ]. Xi et al. [ 16 ] evaluated the performance of creep feed grinding γ -TiAl by electroplated diamond wheels, and the results showed that diamond wheels had better grinding results, with a lower wheel wear rate, and a maximum material removal rate up to 12 mm 3 /(mm·s), while the removal rate of cubic boron nitride (cBN) grinding wheel was only about half of it. Hood et al. [ 17 ] employed a single-layer electroplated diamond grinding wheel for finish machining γ -TiAl alloys, which could effectively remove the hardened layer up to 625 HK caused by rough machining, and the surface roughness ( R a ) was less than 0.3 µm, which is much lower than that required for aerospace parts. Conventional grinding usually ensures the machining quality by restricting the machining parameters, which results in the machining efficiency not being guaranteed. Therefore, there is an urgent need for an in-depth study of a new grinding processing technology on the removal of γ -TiAl material and the wear behavior of abrasive grains to obtain high surface quality and processing efficiency.

In recent years, the introduction of ultrasonic vibration in grinding is a new method to improve the grinding quality of difficult-to-machine materials such as titanium alloys, nickel-based high-temperature alloys, ceramics and other materials in the aerospace industry [ 18 – 26 ]. Studies have shown that ultrasonic vibration-assisted grinding (UVAG) can introduce high-frequency micro-amplitude vibration, change the relative motion trajectory between the abrasive grain and the workpiece, so that the relative percentage of abrasive grain rubbing, ploughing, cutting effect changes, which can effectively reduce the grinding force and the grinding temperature, and enhance the integrity of the surface of the workpiece [ 26 – 30 ]. Cao et al. [ 31 ] designed and fabricated an ultrasonic vibration working platform, which can realize high v s compared with traditional tool ultrasonic vibration devices and is suitable for high-speed grinding. It was applied to Inconel 718 nickel-based superalloy, and the results showed that it could reduce the grinding force by 11%-15% and effectively improve the surface quality of the workpiece. Chen et al. [ 32 ] proposed the ultrasonic vibration-assisted high efficiency deep grinding (UVHEDG) method for the problems of burns and tool degradation that are easily appeared in the grinding of γ -TiAl, and the results showed that the UVHEDG could reduce the grinding temperature by 15.4% effectively and could retard tool wear while ensuring grinding efficiency. Bhaduri et al. [ 33 ] found that the γ -TiAl surface in ultrasonic assisted creep feed grinding (UACFG) machining showed greater smearing, rubbing, plowing and overlapping traces due to its altered material removal mechanism. Wang et al [ 34 ] pointed out that UVHEDG introduces the emergence of intermittent cutting behavior between abrasive grains and the workpiece is conducive to the improvement of coolant's heat transfer capacity, and at the same time it can produce short scratches and microscopic pits on the workpiece surface and thus improve the surface quality of the workpiece. As an important method to realize and difficult-to-machine materials with high strength, high toughness, high precision and high surface integrity processing, grinding relies on a large number of abrasive grains on the surface of the grinding wheel to remove the material, so it is necessary to carry out a study for a single grain [ 35 ]. Zhao et al. [ 36 , 37 ] proposed an innovative method based on the three-dimensional reconstruction technology to track grain wear volume and volume pile-up ratio, based on which the grinding efficiency of aggregate cubic boron nitride (AcBN) was evaluated in the form of a parabolic curve, verifying AcBN has good self-sharpening and wear resistance compared to commercial monocrystalline cubic boron nitride. Dai et al. [ 38 ] performed single diamond grain grinding on Inconel 718 nickel-based superalloy, and classified the grain wear into four forms based on the residence time of rubbing, plowing, and cutting at different a gmax : crescentic depression on the rake surface, rear flank abrasion, micro-fracture and macro-fracture of the grains. Yue et al [ 39 ] employed radial ultrasonic vibration-assisted single-grinding of PTMCs materials, pointing out that the relative minimum of the pile-up ratio and the maximum material removal rate in UVAG were achieved when the v s value was controlled at about 100 m/s, the v w value was about 0.3 m/min, and the A value was 5 µm.

In this paper, a single AcBN was used as the object of study, and the single-grain grinding experiment of γ -TiAl material was carried out under CG and UVAG, respectively, with the aim of revealing the grain wear mechanism after the introduction of ultrasonic vibration. The specific content can be divided into the following sections: Section 2 describes the preparation of single grain core shaft as well as experiment parameters and steps; Section 3 quantitatively analysed grain wear through the effects of different parameters ( a gmax , v s and A ) on the radial wear ( ΔH ), normal force ( F n ), average volume pile-up ratio ( \({\overline {R} _{\text{v}}}\) ) of the AcBN, and visually analyzes the grain wear mechanism using scanning electron microscope (SEM) images.; Finally, the paper is summarized.

2. Experiment details

2.1. preparation of single-grain core shaft.

Firstly, screen out the AcBN grains with full crystal shape, ultrasonically clean and dry with single-grain core shaft. Secondly, a layer of glue was applied to the ϕ 2mm diameter on the single-grain core shaft top platform. The AcBN grain was placed in the center of the platform. Thirdly, Cu-Sn-Ti alloy powder is evenly sprinkled and moistened with acetone to ensure that the brazing material wraps the grain. The grain was exposed to one-third of their height. Finally, the single-grain core shaft was put into the VAF-20 high-temperature vacuum annealing furnace for firing, and the exposed height is measured by three-dimensional video after taking out, and the effective single-grain core shafts were screened out for spare parts.

2.2. Experiment parameters

The a gmax is one of the important factors affecting the parameters of the grinding process and the grinding results, so it is necessary to effectively control the a gmax in the single-grain griding. In CG, the size and direction of the v s and the v w are stable and unchanged, resulting in a gmax not changing over time. In UVAG, the abrasive grains reciprocate along the ultrasonic vibration direction, so that the direction and movement of the abrasive grains change with time, so the value of a gmax has a cyclic relationship with time and is not a fixed value. In this paper, the a gmax of CG and UVAG under the same parameters are labeled as the same for the convenience of comparison. According to the grinding principle, the a gmax is calculated by Eq.  1 as follows:

where λ g and d s are distance between two contiguous effective abrasive grains and single-grain grinding wheel diameter, respectively ( d s = 400 mm in this experiment). Here, λ g can be expressed as λ g  = π· d s in the single-grain grinding experiment, and the v w can be then derived as:

In this experiment, a p = 20 µm was fixed to investigate the wear morphology evolution of single grain in the presence or absence of ultrasound and at different v s , a gmax , and A, where v w was inverted by Eq.  2 . Therefore the grinding process parameters were formulated as shown in Table  1 .

2.3. Experiment procedure

As shown in Fig.  1 , the machine platform for the single-grain grinding experiment was the PROFIMAT MT-408 high-speed grinding instrument produced by the German BLOHM company. The single-grain grinding experiment was divided into three steps: i. Prior to conducting the single-grain grinding experiment, the surface of the workpiece was processed by finish grinding with silicon carbide grinding wheels to ensure that its R a < 0.4 µm. And this was done using the following grinding parameters: v s = 30 m/s, a p = 5 µm, and v w = 100 mm/min. The purpose of this was to prevent any influence from the original morphology of the workpiece on the single-grain grinding scratches. ii. replace the grinding wheel with a single-grain grinding wheel, and at the same time use the acoustic emission device for tool setting, when the acoustic emission signal appeared as the spike signal, indicating that the grain was in contact with the workpiece, on this basis one a p was dropped along the Y-axis to complete a single-grain grinding path. iii. remove the abrasive grains to record the wear condition of the AcBN grain with three-dimensional video microscope (HRX-01) and SEM (COXEM EM30). The next path was offset by 1 mm along the Z-axis to avoid interference with material pile-up on either side of the grinding scratch and steps two and three were repeated until the ΔH of the AcBN grain had reached 80% of the exposed height of the AcBN grain.

2.4. Motion trajectory of single AcBN grain

The ultrasonic relative motion trajectory of a single AcBN grain with the workpiece can be regarded as a periodic reciprocating vibration superimposed along the tangential direction in CG. According to Huang et al. [ 40 ], the equation of motion of a single AcBN grain twice adjacent in CG can be expressed as follows:

And the equation of motion for a single AcBN twice adjacent in UVAG can be expressed as

According to Eqs.  1 and 2 , the two consecutive motion trajectories schema of single AcBN grains under CG and UVAG was drawn (Fig.  2 ), and the trajectory of UVAG was projected onto CG as a sinusoidal function. Due to the existence of λ g , there is a phase difference between the two consecutive grindings, resulting in the phenomenon of “contact-separation-contact” in the UVAG.

3. Results and discussion

3.1. maximum undeformed chip thickness.

As an important parameter in the grinding process, the a gmax directly influences the wear condition of the abrasive grains. The ΔH can quantitatively reflect the wear condition of AcBN grain. As shown in Fig. 3 , the ΔH of AcBN grain varies with the specific material removal volume ( V ′) for different a gmax under CG and UVAG, respectively. Both CG and UVAG show that the value of ΔH increases and then decreases with an increasing value of a gmax . This is because there are differences in the wear condition of the grains as the grinding process transitions from rubbing, plowing, and ploughing to the cutting stage. It can be clearly seen that the AcBN grain reaches the target radial wear height volume and loses its grinding capability at a V ′ value of 2.4 mm 3 /mm for a gmax = 1.2 µm, which is 0.6 mm3/mm less compared to the V ′ with a gmax < 1.2 µm. Secondary, the ΔH is larger than that of the CG at UVAG, and its average increase is 10.8%. On the one hand this is due to the introduction of ultrasonic vibration, which brings about periodic vibration of the abrasive grain, causing an increase in the actual a gmax , which induces a cyclic impact force and accelerates the micro-fractrue of the AcBN grain. On the other hand, γ -TiAl is prone to material adhesion phenomenon in CG, which to a certain extent will make the measurement of the ΔH value of abrasive grains small. The periodic vibration can also effectively make the AcBN grain and the workpiece produce intermittent separation effect, effectively reducing the heat accumulation phenomenon in the grinding process and avoiding the influence of material adhesion on the measurement of the ΔH value.

The grain wear is an important factor affecting the grinding force, so the change of the grinding force can reflect the wear of abrasive grains laterally. Figure 4 shows the curves of the effect of a gmax on normal F n under CG and UVAG, respectively. Overall, the F n value increases with the increase of the V ′ in a class exponential function image. There exists a stage of smooth growth when the V ′ = 1.2–2.4 mm 3 /mm, during which AcBN grains are in the steady wear stage. At present, the AcBN grains are constantly micro-fracturing to form multiple micro-cutting edges, which possess excellent cutting ability, while the F n value increases gradually. After entering the severe wear stage of 2.4-3.0 mm 3 /mm, the abrasive grains are macro-fracture and pulled out, and large areas of material adhere to the AcBN grain., which leads to a sharp increase in the normal force. When a gmax < 0.8 µm, the F n increases at a faster rate with an increase in a gmax . This is because, at this stage, the grinding process involves rubbing and ploughing, and the workpiece material flows along the front blade surface and the side of the grain under the action of the sassafras force. When a gmax > 0.8 µm, grinding enters the cutting stage, and the material is removed in the form of chips. And the F n under UVAG is smaller than that under CG, with an average reduction of 10.5%. The addition of ultrasonic tangential vibration increases the percentage of the cutting stage when the abrasive grain just contacts the workpiece, and at the same time reduces the effective contact arc length, which relatively reduces the percentage of the stage of rubbing, plowing force, and increases the percentage of the cutting force increases, so that more energy is used in the material removal process, which helps to reduce the F n .

The \({\overline {R} _{\text{v}}}\) is an important parameter to characterize the abrasive grain removal capability, which also reflects the wear condition of the abrasive grain. The critical value of the a gmax in the material removal into the cutting stage is called the critical chip thickness, and from Fig. 4, a gmax = 0.8 µm is closer to the critical chip thickness, no matter it is CG or UVAG. When a gmax < 0.8 µm, that is, a gmax is less than the critical chip thickness, with the increase of a gmax , the \({\overline {R} _{\text{v}}}\) value is increasing. Meanwhile, grinding is in the stage of rubbing and ploughing, the workpiece material from a single elastic deformation to elastic deformation and plastic deformation, increasing a gmax will lead to more material pile-up, the \({\overline {R} _{\text{v}}}\) value becomes larger. When a gmax > 0.8 µm, that is, a gmax is greater than the critical chip thickness, grinding has been in the cutting stage, but with the increase of a gmax , some of the cBN grains with low height of emergence are also involved in the grinding process, making the whole AcBN grain to withstand the increasing force, and some of the cBN grains with low holding force are directly pulled out, and the holes after pulling out are filled by the chips one after another. The remaining cBN grains undergo rapid macro-fracture, resulting in a further reduction in material removal capacity and a decrease in abrasion resistance of the abrasive grains. In the mass, the \({\overline {R} _{\text{v}}}\) value increases with the V ′ value, and increases parabolically from 0.6 mm 3 /mm to 1.2 mm 3 /mm, then decreases sharply after the V ′ value is larger than 1.2 mm 3 /mm, and then slows down in the range of 2.4 mm 3 /mm to 3.0 mm 3 /mm. In addition, the \({\overline {R} _{\text{v}}}\) value is smaller than that of CG under UVAG, and its average decrease is 22.2%, indicating that ultrasonic vibration can effectively enhance the material removal ability of AcBN grain. The reasons are as follows: from Fig. 2 , it shows that the chips are longer in CG, and the AcBN grain undergoes a longer process of rubbing and plowing, which is prone to cause material pile-up on both sides of the grooves. As shown in Fig. 6 , the AcBN grain is always in contact with the grinding arc area, it causes the abrasive chip to stay on the front blade surface of the cutting edge of the AcBN grain all the time, which reduces the sharpness of the abrasive edge and increases the pile-up of the material. While in UVAG, the AcBN grain is in intermittent contact with the grinding arc area, a grinding arc area is divided into multiple regions for cutting removal, the chips are shorter, the AcBN grain undergoes a shorter process of rubbing and plowing, and the material is mostly removed by the chips. In addition, due to the presence of ultrasonic vibration, the AcBN grain and the workpiece are constantly impacted, which is conducive to the detachment of chips from the surface of the AcBN grain, maintaining the sharpness of the cutting edge of the AcBN grain, which can effectively improve the quality of surface grinding.

3.2. Grinding speed

The v s is also an important parameter affecting the grinding process, which directly influences the wear condition of the abrasive grains. As can be seen from the previous section, when a gmax > 0.8 µm, grinding is mainly in the cutting stage, so the a gmax of a single grain at each v s is controlled at 1 µm. As shown in Fig. 7, the variation curves of the ΔH of AcBN grain with the V ′ at different v s . Whether CG or UVAG, when v s ≥ 100 m/s, the ΔH of AcBN grain increases parabolically with the V ′, and the V ′ of AcBN grain only reaches 2.4 mm3/mm; while when v s ≤ 80 m/s, the ΔH of AcBN grain is closer to linear growth under UVAG, and the ΔH of AcBN grains firstly wear rapidly under CG, and then experienced steady wear, and finally severe wear, with the V ′ of the AcBN grains reaching 3.0 mm 3 /mm. This is because that an increasing v s leads to an increase in the grinding power for the same parameters, which makes the grinding temperature rise. This not only elevates the thermal softening effect on the material, but also the AcBN grains are subjected to severe thermal damage during the grinding process, resulting in rapid grain wear at v s ≥ 100 m/s, and they have lost their grinding ability by the time the V ′ value reaches 2.4 mm3/mm. Meanwhile, the ΔH of the AcBN grains is greater than CG at UVAG, and its average increase is the value varies at different v s . the average increase of the ΔH of AcBN grains at v s ≤ 80 m/s is 3.5%, 10.5%, and 12.1%. Respectively, the average difference between the two chances to be close to 0% when v s ≥ 100 m/s. As mentioned above, the addition of ultrasonic tangential vibration induces a cyclic impact force that accelerates the micro-fracture and increases the ΔH of the AcBN grains, but at higher v s , the intermittent separation of the UVAG is weakened, resulting in the ΔH of the AcBN grains being closer to the CG.

Figure 8 shows the variation curves of F n with V ′ at different v s . As mentioned before, at a gmax = 1 µm, the grinding force is mainly determined by the cutting force. At the same time, due to the increase of the v s , the workpiece material is subjected to approximately significant thermal softening, and the cutting force is even smaller, so that the F n decreases with the increase of the v s , both under UVAG and under CG. Secondly, the F n increases with V' , following an exponential-like function. There is a steady wear stage, and UVAG can reduce the F n for the same reasons described in section 3.1 . It is noted that the maximum reduction in F n varies for different v s and is 10.9%, 10%, 12.8%, 8.3% and 3.8% in descending order with v s The interrupted cutting behavior caused by ultrasonic vibration is one of the main reasons for the reduction in grinding force, but due to the increase in the v s , the separation factor of the interrupted cutting decreases, resulting in a reduction in the F n reduction at high v s .

Figure 9 illustrates that the \({\overline {R} _{\text{v}}}\) values exhibit a parabolic increase and then decrease with the V ′. Additionally, under UVAG, the \({\overline {R} _{\text{v}}}\) values are smaller than those of CG, indicating that UVAG can improve the material removal rate with an average decrease of 23.7%. Secondly, the \({\overline {R} _{\text{v}}}\) decreases and then increases with the increase of v s , and the \({\overline {R} _{\text{v}}}\) of the material is the smallest when v s = 80 m/s, i.e., the material removal ability is the strongest. At low v s , the rubbing and plowing effects are more pronounced, and the chips are more likely to adhere to the AcBN grains, which reduces the material removal ability of the AcBN grains. After increasing the v s , the effect of cutting force is more obvious, and the material removal ability is enhanced. However, continue to increase the v s , the larger grinding power causes the AcBN grains to withstand higher thermal damage, resulting in a reduction in the material removal ability. γ -TiAl has a strong viscosity in the grinding process. Therefore, whether it is UVAG or CG, low-speed grinding is more likely to cause plastic flow, resulting in uneven groove bottom morphology, grooves on both sides of the pile-up is larger, it is generally advisable to use high-speed grinding on the γ -TiAl material grinding process.

3.3. Ultrasonic amplitude

Figure 10 shows the curves of ΔH with V ′ for different A at a gmax =1 µm and v s = 80 m/s. Overall the ΔH of AcBN grains increases with the A , and its average increase ranges from 11.7–82.2%. The difference is that when A  = 0 or 3 µm, the variation curve of ΔH conforms to the general wear curve, which is divided into initial wear, steady wear, and severe wear stages. The periodic impact force leads to accelerated wear of the AcBN grains, and with the increase of A , the distance of the AcBN grains vibrating in the same cycle time increases, and the speed of the abrasive grains' movement in the vibration direction grows, which leads to an increase in the periodic impact force and exacerbates the wear of the AcBN grains.

The relationship between the change of F n with V ′ at different A is shown in Fig. 11. It can be seen when a gmax =1 µm and v s = 80 m/s, the wear curves of the F n under different A show a slow growth followed by a sharp increase with the increase of V ′. Taking A  = 6 µm as an example, specifically, the normal force increases rapidly by 0.77 N in the range of 0.6–1.2 mm 3 /mm, slowly by 1.7 N in the range of 1.2–2.4 mm 3 /mm, and sharply by 1.99 N in the range of 2.4-3.0 mm 3 /mm, which results in a final increase of 53.3% in F n compared to that at 0.6 mm 3 /mm. In addition, the F n shows a tendency to decrease and then get engaged with the increase of A , and reaches a minimum at A  = 6 µm. This is because the application of ultrasonic vibration causes micro-fracturing of the AcBN grains between the AcBN grains and the workpiece to be intensified by periodic transient impacts, thus maintaining the dynamic sharpness over a long period of time, while increasing the proportion of cutting force so that more capacity is used to remove material. So moderately increasing the A can effectively reduce the F n . However, as shown in Fig. 16 , once the ultrasonic amplitude is too large, it is easy to increase the periodic transient impact force, the abrasive grains are prone to cleavage fracture and the bond cracks lead to pull out to aggravate the wear process. At this time, the grinding performance is greatly reduced, and the F n shows a tendency to increase.

Ultrasonic vibration can accelerate the micro-fracture of the AcBN grains to a certain extent, so that the AcBN grains maintain a stable dynamic sharpness. However, it will also aggravate the degree of grain wear. In short, the AcBN grains of the material removal ability to be determined by the joint decision of the two. Figure 12 shows the relationship between the \({\overline {R} _{\text{v}}}\) and the V ′ at different A . The \({\overline {R} _{\text{v}}}\) is always lower than that of CG at UVAG, even though the ultrasonic vibration increases the grain wear of the AcBN grains, its effect on the material removal capacity is greater than that of the grain wear of the abrasive grains. Meanwhile, the \({\overline {R} _{\text{v}}}\) increases and then decreases with the increase of A , which is corroborated by the change of F n with A .

3.4. Grain wear morphology

Observing the surface morphology of abrasive grains is the most direct and intuitive way to show the wear characteristics of abrasive grains. The SEN image shows the morphology evolution of AcBN grains under UVAG and CG. The material adhesion phenomenon accompanies the whole grinding process, and AcBN grains are formed by multiple cBN grains layer by layer, which are continuously exposed and subject to the friction as well as the rebound caused by the elastic deformation of the machined surface of the workpiece, to maintain the ability to remove the material by the micro-fracture of the cutting edge. Figure 13 and Fig. 14 show the wear morphology of AcBN grains under different a gmax . Under CG, the AcBN grains are occupied by the material adhesion over a large area, and some micro-fracture phenomenon also occurs under the a gmax ≤ 0.8 µm, but it will also be adhered to by the chips and blocking. With the increase of a gmax , most of the AcBN grains are involved in the cutting stage resulting in the basic invisible, from the side of the abrasive grains can be seen with each cutting movement of the material layers accumulated on the surface of the AcBN grains, and can be seen the long chip adhering to the surface of the AcBN grains. Comparatively, under UVAG, when a gmax ≤ 0.8 µm, the AcBN grains are no longer adhered to by the material over a large area, and micro-fracture occurs in many places, which is conducive to the removal of the material. And the AcBN grains at the lower part were not involved in the grinding, and the intact single cBN grains could still be seen. When a gmax =1.0 µm, the AcBN grains were pulled out due to that the left side of AcBN grains are involved in the grinding firstly and there was not enough bond wrapped around, which leading to the cBN grains pulling out. At a gmax = 1.2 µm, the effect of ultrasonic vibration no longer counteracts the effect of increasing a gmax , and the surface of the AcBN grains is covered by the material again, with only a small amount of micro-fracture and pull-out.

The v s on the wear morphology of AcBN grains is mainly reflected in the increase of grinding temperature and the weakening of the vibration separation effect of ultrasonic vibration with the increase of v s . It can be seen from Fig. 15 that at v s = 30 m/s, some of the cBN grains are still exposed, and the surface is micro-fractured under the impact of the grinding force. As it enters the high-speed grinding stage, the workpiece material is subjected to the more significant thermal softening effect, part of which adheres to the surface of the AcBN grain, covering most of the cBN grains. The material is removed into chips, adhering to the surface of the AcBN grains, and the holes where the cBN grains are pulled out are also blocked by the chips. When v s = 120 m/s, the grinding temperature rises sharply and the material flows along the sides of the AcBN grains eventually accumulating on the AcBN grains at the end of grinding. In Fig. 16 , the wear morphology of AcBN grains with different v s under UVAG can be observed. Overall, compared to CG, AcBN grains are not extensively covered. It is evident that a considerable number of cBN grains undergo micro-fracture, and the holes formed by the pulled-out grains will not be blocked by the short chips under UVAG. At v s ≤ 80 m/s, the cBN grains are continuously micro-fracture under the reconstruction of the alternating load, and there is no chip adhesion on the surface. At v s ≥ 100 m/s, although the material adhesion is much better compared to CG, under the combined effect of increased grinding temperature and reduced vibratory separation by ultrasonic vibration, the cBN grains are adhered to the material after micro-fracture, which weakens the cutting ability of the AcBN grains.

Figure 17 shows the wear morphology of single AcBN grains at different A . when A  = 0 µm is the CG, revealing that the AcBN grain is adhered to the cutting edge by the chips, and the holes left by pulling out the cBN grains are blocked by the chips. The AcBN grains are kept free of the chips by the holes that are pulled out under the action of ultrasonic vibration at A  = 3 µm. It is also important to notice that the cBN grains shows cleavage fracture and the bond is cracked. With A  = 6 µm, the effect of ultrasonic vibration becomes more pronounced, the cBN grains on the front face have been pulled out, and the cBN grains in the middle part have been micro-fractured to produce multiple cutting edges to enhance the grinding capability. While A  ≥ 8 µm, the impact force of ultrasonic vibration becomes stronger and stronger, and the cBN grains on the front face have already been dislodged, and the cracks of the bond start to spread under the influence of shear stress on the back face.

In summary, UVAG has the following effects on the form of AcBN grain wear (Fig. 18 ): Firstly, the intermittent separation of the abrasive grains from the workpiece effectively reduces the grinding temperature and prevents the adhesion of γ -TiAl material. Secondly, UVAG frequently crushes the abrasive grains, exposing their sharp grinding edges and maintaining their sharpness, resulting in an effective increase in the self-sharpness of the abrasive grains. Thirdly, UVAG also causes periodic impacts that accelerate the expansion of cracks on the bond and the pull-out of abrasive grains.

4. Conclusion

The purpose of this paper is to reveal the grain wear mechanism of ultrasonic vibration on AcBN grains during single-grain grinding of γ -TiAl material. The main research results are as follows:

1. Compared to CG, UVAG accelerates the micro-fracture of AcBN grains by introducing periodic vibration that induces periodic impact force. This method also effectively avoids heat accumulation during the grinding process.

2. The addition of ultrasonic vibration effectively reduces the proportion of rubbing and plowing force, and increases the proportion of cutting force, so that the energy is more used for material removal, which helps to reduce the F n .

3. At low v s , chips tend to adhere to the AcBN grains, and too high v s tends to cause the AcBN grains to endure excessive thermal damage, but UVAG can effectively solve these two problems.

Declarations

Funding  Supported by the National Natural Science Foundation of China (Nos. 92160301, 92060203, 52175415, 52205475, and 52322510), the Science Center for Gas Turbine Project (No. P2023-B-IV-003-001), the Natural Science Foundation of Jiangsu Province (No. BK20210295), the China Postdoctoral Science Foundation (No. 2023T160315), and the Foundation of Graduate Innovation Centre in NUAA (No. XCXJH20230509).

Competing interests   The authors have no conflicts of interest to declare that they are relevant to the content of this article.

Availability of data and material   All data generated or analyzed during this study are included in the present article.

Authors' contributions   Jiahao Song: experimentation, data curation, and writing the original draft. Biao Zhao: manuscript revision. Wenfeng Ding: experimentation, methodology and data collection. Hailong Cui: structural and figure design. Yanjun Zhao: supervision, conceptualization. Jianhui Zhu: resources.

Ethics approval and consent to participate   The article follows the guidelines of the Committee on Publication Ethics (COPE) and involves no studies on human or animal subjects.

Consent to participate   Not applicable.

Consent for publication   Not applicable.

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Reviewers agreed at journal

02 May, 2024

Reviewers invited by journal

Editor assigned by journal

11 Apr, 2024

First submitted to journal

09 Apr, 2024