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H U B E R T I . A A R O N S O N
Elected in 1997
“For contributions to the under
H U B E R T I . A A R O N S O N
Elected in 1997
“For contributions to the understanding of
diffusional phase transformation in commercial steels.”
BY JOHN P. HIRTH
HUBERT I. AARONSON, an international leader in the ma-
terials field, died December 13, 2005, after a lengthy illness. He
continued working as R.F. Mehl Professor Emeritus at Carnegie
Mellon University until the very end.
Born in New York City on July 10, 1924, Aaronson moved in
1936 to Jersey City, where he completed high school. Although
his father and advisors discouraged him from going into engi-
neering, his sister, Barbara, supported his goal. Hub envisioned
great advances in engineering and he enrolled at Carnegie In-
stitute of Technology (CIT), now Carnegie Mellon University,
determined to become an engineer.
At the end of his second year, Hub was called into the service.
He wanted to enter the U.S. Army Air Corps, and, helped by his
comrades and others, he was able to do so. However, when he
realized he was scheduled to enter bombardier school for B-24
Liberators, which had a poor survival rate, he showed up a week
early at the B-17 training school instead. The bureaucracy ab-
sorbed this unprecedented change, and Hub went on to fly many
B-17 missions during World War II.
When he resumed his studies after the war, he not only did
very well in his classes, but also became editor of the campus
newspaper. He completed his B.S., M.S., and Ph.D. in metallur-
gical engineering at CIT in 1948, 1954, and 1954, respectively.
4 MEMORIAL TRIBUTES
His thesis advisor was the eminent metallurgist, R.F. Mehl. Hub
remained at CIT as a research metallurgist until 1957, working
with Mehl, G.M. Pound, and C. Wells. He then became a re-
search scientist at Ford Scientific Laboratory (1958–1972), a pro-
fessor at Michigan Technological University (1972–1979), R.F.
Mehl Professor at Carnegie Mellon University (1979–1992), a
scientist at the Naval Research Laboratory (1992–1996), and fi-
nally R.F. Mehl Professor Emeritus (1996–2005).
Hub was a giant in the field of phase transformation, to which
he made many seminal contributions. One of his major contri-
butions was defining and understanding the role of microstruc-
ture in phase transformations. In 1951, F.C. Frank had demon-
strated the importance of ledges in the growth of crystals from
vapor. Hub recognized the potential for similar effects in trans-
formations in solids. In classic early work with K. Kinsman and
M. Adams, he demonstrated that bainitic and other plate-shaped
transformations proceeded by the motion of what he called
“growth ledges.” Atomic-level ledges, or steps, which had dislo-
cation content as well, relieved strains that would otherwise ap-
pear at interfaces between reactants and products. Hub called
these defects structural ledges. In later work with a number of
his students, he verified the nature of these defects by transmis-
sion electron microscopy and by computer simulations.
Hub engaged in a long, vigorous debate with J.W. Christian
on the details of bainitic transformation. Hub’s view was that
the diffusional composition change during the transformation
accompanied the motion of ledges, while Jack Christian argued
that the step structure (and accompanying shear) occurred first.
Their views have been largely reconciled in the new millennium.
Hub also made significant contributions in alloy thermody-
namics, the role of alloying elements in “hardenability” (retar-
dation or enhancement of the rate of transformation) in steels,
the mechanism of nucleation of new phases, interfacial ener-
gies, and the mechanism of massive transformation. His work
had a substantial impact on the selection of materials for auto-
mobiles and Navy ships.
Hub was elected to the National Academy of Engineering in
1997, and he received many awards in recognition of his accom-
HUBERT I. AARONSON 5
plishments. These included Fellow, R.F. Mehl Medalist, C.H.
Mathewson Medalist, Educator Award, and Hume-Rothery Med-
alist from the Minerals, Metals, and Materials Society (TMS);
Fellow and Albert Saveur Achievement Award from ASM Inter-
national; and Honorary Member of the Japan Institute of Met-
als. He participated widely in international conferences as key-
note speaker, conference organizer, and editor of conference
Hub had a tremendous influence on his students and associ-
ates, and he was beloved by all of them. A stern taskmaster, but a
friendly and helpful advisor and collaborator, his vision and
optimism were inspiring, and his supportiveness was legendary.
On three different occasions, his students organized symposia
honoring him. He regularly held lavish dinner parties for his
students, often reserving an entire restaurant for the occasion.
He held similar events to entertain visiting scientists and speak-
ers, often paying for them himself. He also funded portions of
conferences he organized, particularly to help students to at-
In a sense, his work was his hobby. He remained a bachelor
throughout his life and worked long and unusual hours. Unless
he had to attend a function or deliver a lecture, his day began at
about 3 p.m. and ended around 5 a.m. Students and colleagues
who wanted to see him had to fit in late afternoon appointments.
Even Ford Scientific Laboratory accommodated his schedule and
made special arrangements for him to work through the night.
He took vacations at posh resorts, often beaches, and lived
the high life. He read assiduously, especially in military history.
Indeed, this interest led him to work at the Naval Research Labo-
ratory for four years after his retirement from Carnegie Mellon
Hub Aaronson was an internationally respected colleague, a
valuable collaborator, a successful teacher, and a warm friend to
many in the materials field. He will be missed, but his contribu-
tions will live on.
He is survived by his sister, Barbara A. McMurray, of Lafayette,