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This is the 28th volume of Memorial Tributes compiled by the National Academy of Engineering as a personal remembrance of the lives and outstanding achievements of its members and international members. These volumes are intended to stand as an enduring record of the many contributions of engineers and engineering to the benefit of humankind. In most cases, the authors of the tributes are contemporaries or colleagues who had personal knowledge of the interests and the engineering accomplishments of the deceased. Through its members and international members, the Academy...
This is the 28th volume of Memorial Tributes compiled by the National Academy of Engineering as a personal remembrance of the lives and outstanding achievements of its members and international members. These volumes are intended to stand as an enduring record of the many contributions of engineers and engineering to the benefit of humankind. In most cases, the authors of the tributes are contemporaries or colleagues who had personal knowledge of the interests and the engineering accomplishments of the deceased. Through its members and international members, the Academy carries out the responsibilities for which it was established in 1964.
Under the charter of the National Academy of Sciences, the National Academy of Engineering was formed as a parallel organization of outstanding engineers. Members are elected on the basis of significant contributions to engineering theory and practice and to the literature of engineering or on the basis of demonstrated unusual accomplishments in the pioneering of new and developing fields of technology. The National Academies share a responsibility to advise the federal government on matters of science and technology. The expertise and credibility that the National Academy of Engineering brings to that task stem directly from the abilities, interests, and achievements of our members and international members, our colleagues and friends, whose special gifts we remember in this book.
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BY JOHN ÅGREN, ZI-KUI LIU, QING CHEN, AND JI-CHENG ‘JC’ ZHAO
MATS HILDING HILLERT, one of the giants in the field of materials science, passed away on Nov. 2, 2022, at nearly 98. Born in Gothenburg, Sweden, on Nov. 28, 1924, Mats was the youngest of three sons of Anna and Hilding Hillert. The young Hillert brothers were lively and well-known in the neighborhood.
Mats grew up and completed his early education in Gothenburg before enrolling at Chalmers Technical University, where he earned his B.S. in chemical engineering in 1947. After his military service, Mats began a research career at the Swedish Institute for Metals Research in Stockholm in 1948. Initially assigned to study internal friction, he was granted considerable intellectual freedom, allowing him to pursue broader interests.
Mats wanted to register for graduate studies at the Royal Institute of Technology (KTH) in Stockholm, but first needed to complete undergraduate physics courses not included in his chemistry curriculum. For several years, he spent most of his spare time on those studies — an effort made easier because his girlfriend, Gerd, was still in school in Gothenburg.
At work, he met Sten Modin and Helfrid Modin, pioneering Swedish metallographers who used electron microscopy to study steel microstructures. Inspired by Sten, he took an additional undergraduate course at KTH, attending lectures by Axel Hultgren, a professor in physical metallurgy. Mats often credited a scientific debate with Hultgren following one of these lectures as the spark for his lifelong interest in phase transformations and thermodynamics. He challenged Hultgren’s explanation of how nickel affects the carburization of steel, arguing that it was thermodynamically incorrect. Hultgren, the grand old man of Swedish physical metallurgy, was impressed by his intuition in thermodynamics and encouraged resolving the issue through experimentation.
The results validated his reasoning, leading to a joint publication with Hultgren in 1953.1 By this time, Hultgren had developed the concept of paraequilibrium, which addressed the effect of alloying elements on transformations in steel. Their collaboration produced several manuscripts focusing on the concept of paraequilibrium, isoactivity lines in phase diagrams, and their applications to steel transformations. His original assignment on internal friction was soon overshadowed and quietly forgotten amidst this significant work.
In 1951, he married Gerd, and two years later, the young couple relocated to Boston, where Mats pursued graduate studies in physical metallurgy at the Massachusetts Institute of Technology (MIT) under the supervision of the legendary teacher Morris Cohen (NAE 1972). During this period, he also met Carl Wagner, who taught thermodynamics and gave him valuable advice on several of his manuscripts, all of which had previously been rejected.
For his master’s thesis, he conducted an experimental study of the thermodynamics of the silver-aluminum (Ag-Al) system. Inspired by one of his fellow students, Larry Kaufman — who was modelling the thermodynamic properties of the iron-nickel (Fe-Ni) system — he applied a similar model to the Ag-Al system. That project marked the beginning of his lifelong interest in the thermodynamics of alloys. Largely due to Kaufman’s efforts, this procedure eventually evolved into what is now known as CALPHAD (CALculation of PHAse Diagrams).
After earning his master’s degree, Mats was invited to pursue a doctorate. During a semester of preparation for the qualifying exam, he became intrigued by the puzzling behavior of gold-nickel (Au-Ni) alloys, which one of his roommates, Ervin Underwood, was studying. He connected the anomaly to what would later be known as spinodal decomposition and developed a theory to explain the phenomenon. Building on this work, he completed his doctorate with an experimental study of spinodal decomposition. In 1956, he earned a Doctor of Science degree from MIT and returned to the Swedish Institute for Metals Research.
An interesting coincidence followed: another of his roommates, John Hilliard, took a copy of Mats’ thesis with him when he joined General Electric in Schenectady later that year. There, Hilliard met John Cahn (NAE 1998), and together they expanded on Mats’ work, completing the theory of spinodal decomposition and opening a new field of study.
In 1959, Mats was appointed a temporary professor in physical metallurgy at KTH. Over the next several years, he published numerous papers, some of them groundbreaking. When the position of professor in physical metallurgy was formally announced, he applied and was appointed full professor in 1961. He remained in that role until his retirement 30 years later, educating thousands of students in modern materials science and engineering. His students went on to serve in industry and academia in Sweden and around the world. Even after his formal retirement, Mats continued his work as an active emeritus professor for another 30 years.
A frequent and enthusiastic participant in international conferences and symposia, he was eager to engage with everyone, regardless of position or background. His style was unpretentious, direct, and highly precise. To those unfamiliar with his manner, his forthrightness could seem harsh, but those who knew him well recognized his sincerity and dedication to advancing scientific discourse.
Mats was a fellow of the Royal Swedish Academy of Engineering Sciences and the Royal Swedish Academy of Sciences. He was also a fellow of ASM International and of the Metallurgical Society of the American Institute of Mining, Metallurgical, and Petroleum Engineers, now known as The Minerals, Metals, & Materials Society (TMS). His long list of honors includes, among others, the Robert Franklin Mehl Medal from TMS; the Bakhuis Roozeboom Medal from the Royal Netherlands Academy of Arts and Sciences; the Acta Metallurgica Gold Medal; the Murakami Gold Medal from the Japan Institute of Metals; the Björkén Award from Uppsala University; and the Hume-Rothery Award, also from TMS.
Mats is survived by his children Jan, Lena, Sven, and Nils, along with their families. Gerd predeceased him in 2018. His contributions to materials science and his unwavering dedication to education and research leave a lasting legacy.
_________________________ 1Hultgren A, Hillert M. 1953. Betingelser för bildning av cementit vid uppkolning av nickelstål. (In Swedish.) Jernkontorets Annaler 137:217.