MEHL, ROBERT FRANKLIN

(b. Lancaster, Pennsylvania, 30 March 1898; d. Pittsburgh, Pennsylvania, 29 January 1976)

metallurgy, chemistry.

As teacher, academic administrator, and researcher, Mehl played a major role in the broadening of metallurgical science in the mid twentieth century. The son of George H. Mehl and Sarah Ward Mehl, he received a B.S. in chemistry from Franklin and Marshall College in 1919. In 1922, after three years of teaching chemistry in small colleges, he entered Princeton University, where he earned a Ph.D. in 1924. On 27 December 1923 Mehl married Helen Charles; they had a son and two daughters. After heading the chemistry department at Juniata College (1923–1925), he spent the years 1925–1927 at Harvard University as a National Research Council fellow, working on compressibility and chemical affinity in alloys. At Harvard he came under the influence of Theodore W. Richards, Percy W. Bridgman, and Albert Sauveur, the last inspiring his lifelong interest in the relation between the physical properties and the structure of metals.

Most of Mehl’s mentors had studied in Germany, and as a result he became a disciple of the Göttingen chemist Gustav Tammann, one of whose books, Aggregatzustände, die Änderung der Materie in Abhängigkeit von Druck und Temperatur, he translated into English in 1925. From 1927 to 1931 he was superintendent of the Division of Physical Metallurgy at the Naval Research Laboratory in Washington, D.C. There he developed gamma-ray radiography for the detection of defects in large steel castings and, in association with Charles S. Barrett, commenced studies of the mechanisms of phase change in alloys, a topic that interested him throughout his life. In 1932, after a brief period in industry, he went to Carnegie Institute of Technology (now Carnegie-Mellon University) as professor of metallurgy and director of the Metals Research Laboratory.

An ambitious and energetic man, Mehl effectively combined research with administration and teaching. His associates and students were prominent in the development of the new metallurgy. At one time they constituted 25 percent of the heads of all academic departments of metallurgy in the United States and Canada.

Mehl regarded it as essential for a scientist to have sensory contact with the materials studied. This belief began in a little laboratory in his home when he was twelve. He maintained close contact with industrial operations throughout his life, once remarking, “An industrial plant is a veritable museum of fascinating phenomena.”

Most of Mehl’s research was on quantitative structural and kinetic aspects of transformations in solids. The lamellar morphology (known as the Widmannstätten structure, after its popularizer, Alois Beck von Widmannstätten) that results from oriented growth within a crystal of a second phase—the solubility of which decreases with temperature—had been observed in the huge crystals of metallic meteorites by William Thompson in 1804, By 1900 it was an accepted feature in the microstructure of man-made steel, usually attributed to mechanical cleavage planes in the parent lattice. In 1926 the English physicist J. Young first used X-ray diffraction to determine the orientation relations between the two crystalline components in a meteorite. Mehl saw the basic importance of the phenomenon and commenced a long research program based on the central belief that the character of the interface between the two phases was more important than the structure or orientation of either. Seven papers on the relations in many different alloys that emanated from Mehl’s laboratory in the years 1931 to 1935 formed a potent nucleus for the studies of intermediate levels of structure that soon thereafter came to characterize solid-state physics.

Next Mehl and his students worked on diffusion and reaction kinetics in general, studying the epitaxy of corrosion-product layers, with particular attention to distinguishing quantitatively between stages of nucleation and growth during phase change and also during the recrystallization of cold-worked metals and alloys. They also investigated the strength and ductility of steels and were pioneers in the application of statistics in scientific studies and as a means of quality control in industry. Virtually all of Mehl’s research was done in collaboration, usually with his students. Though his students regarded him as rather stern and authoritarian, they valued the experience of interactively exploring with him fruitful areas for research. The exploration was usually followed by Mehl’s benign neglect and an occasional unwillingness to accept experimental results that did not support his initial theory.

Like most metallurgists at the time, Mehl was not an especially talented mathematician, though he strongly encouraged advanced mathematical treatment on the part of his students. Neverthesess, despite his strong mental inclination toward physics, his pride in metallurgy as a profession encompassing everything from the smelting of ores to the treatment of the final product made him somewhat unsympathetic to the trends that have matured into materials science, which encompasses the nature and properties of all materials, regardless of their origin or composition.

Mehl took a keen interest in the broadest aspects of the metallurgical profession and especially of education. The curriculum that he developed at Carnegie Institute of Technology became the model for those at many other institutions. He received many medals and other honors from scientific societies throughout the world. His Brief History of the Science of Metals, published in 1948, was the first historical account to reflect the broadening of the profession beyond its traditional concern with the chemistry of smelting and refining.

In 1944 Mehl made the first of many visits to Brazil to advise on both industrial and educational aspects of metallurgy. He became dean of graduate studies at Carnegie Institute in 1953 but resigned in 1960 and moved to Zurich. Where he was consultant to the U.S. Steel Corporation. Returning to the United States in 1966, he served briefly as visiting professor at the University of Delaware and Syracuse University before returning to Pittsburgh in 1968, where he died after a long illness.

BIBLIOGRAPHY

I. Original Works. Mehl’s works include The States of Aggregation (New York, 1925), a translation of the 2nd ed. of Gustav Tammann, Aggregatzustünde, die Änderung der Materie in Abhängigkeit von Druck und Temperatur (Leipzig, 1922; 2nd ed., 1923); Metalurgia do ferro e do aço (The metallurgy of iron and steel), Vicente Chiaverine et al., trans. (São Paulo, Brazil, 1945), lectures Mehl delivered at the Polytechnic of the University of São Paulo in 1944; and A Brief History of the Science of Metals (New York, 1948). Most of his scientific contributions are published in Transactions of the American Institute of Mining and Metallurgical Engineers from 1931 to 1960. “Commentary on Metallurgy,” in Transactions of the Metallurgical Society of AIME, 218 (1960), 386–395, consists of general remarks on the history and current state of the field; “A Department and a Research Laboratory,” in Annual Review of Materials Science, 5 (1975), 1–26, is a semiautobiographical account that gives a good picture both of his own research philosophy and of the state of the field.

Cyril Stanley Smith