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A D V A N C E D
M A T E R I A L S
&
P R O C E S S E S |
N O V E M B E R / D E C E M B E R
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Metals. Hoyt describes Merica’s appear-
ance when he arrived: “One day a young
man presented himself at the laboratory
and announced he might be joining us.
His attitude seemed to say that he might
just possibly if he liked what he saw. He
wore a straw hat obviously too small
worn on the side of his head.” Merica and
Hoyt had a number of classes together
including one taught by Adolf Marten for
whom Floris Osmond named martensite
after. Here they met Guillaume Kroll,
also known as William Kroll of titanium
fame.
Upon his return, now with a Ph.D.
in physics and metallurgy, Merica
worked for a brief time at the University
of Illinois. He then joined the National
Bureau of Standards where he worked
for an older physicist and metallurgist,
George Burgess, a Massachusetts Insti-
tute of Technology graduate who also
studied under the famous Henry-Louis
Le Chatelier at the Sorbonne in Paris.
Merica led a group of metallurgists in
studying the mechanism responsible
for age hardening in duralumin. His
colleagues included Howard Scott, R.G.
Walthenberg, and J.B. Freeman.
DURALUMIN RESEARCH
PROGRAM
The Bureau’s study was designed
to examine the role of Cu and Mg in-
dependently and then combine them
in various amounts to determine how
they interacted to cause age harden-
ing. Sample alloys were made at the
New Kensington plant of the Aluminum
Company of America. They were rolled,
annealed, and rerolled until reduced to
a 0.032-in. thickness in the cold-rolled
condition. They were tested in the cold-
rolled condition and after annealing to
soften them to form a baseline mea-
surement. Other samples were solu-
tion-treated at temperatures to 520°C,
water-quenched to room temperature,
and aged for 11 days at room tempera-
ture or for three days at 100°C. All sam-
ples were tested for hardness, ultimate
tensile strength, and elongation.
Merica and his team concluded
that this supersaturated solid solution
formed a pre-precipitate that hindered
plastic deformation until higher stress
was applied to the material. Over-
aging at higher temperatures where
CuAl2 could be seen removed the pre-
precipitate, and alsodecreasedhardness.
The work showed that duralumin might
not be unique, but amechanism for hard-
ening in other alloy systems fitting the
conclusions of Merica. Any alloy with de-
creasing solid solubility with decreasing
temperature when quenched to form a
supersaturated solid solution could form
pre-precipitates at some aging tempera-
ture. The authors stated, “If the tempera-
ture of the alloy is raised to 100°C, or even
to ordinary room temperature, according
to the theory which the authors propose,
the mobility of the molecules becomes
sufficiently great that precipitation of the
CuAl2 takes place in the form of very fine
particles of colloidal dispersion.”
The authors finally concluded,
“Upon aging a quenched sample at
200°C, the hardness first increases to a
maximum and afterwards decreases.
During that aging there has been first a
formation of fine nuclei of CuAl2 followed
by coalescence of these particles into
ones of larger size. There is, therefore, a
certain average size of particle of CuAl2
for which the hardness is a maximum;
atomic dispersion of the solute is not the
dispersion that produces the maximum
hardness but some intermediate one be-
tween it and that at which the particles
become visible by ordinary means. To
this dispersion is due the hardening of
duralumin.”
Results of this study by Paul Dyer
Merica, et al., were quoted by Zay Jef-
feries as “the shot heard around the
world.” If duralumin could be hardened
by precipitation of a compound, then
this new hardening mechanism could be
applied tomany other alloy systems. The
resulting developments opened the door
to a whole newworld of strong alloys.
AWARDS AND HONORS
Merica received many awards for
his work on precipitation hardening in
duralumin including the John Fritz Med-
al, the Platinum Medal from the British
Institute of Metals, ASM’s Gold Medal,
The Franklin Institute’s Franklin Medal,
and AIME’s James Douglas Gold Medal.
Merica joined the International Nick-
el Co. in 1919 after his five years at the
National Bureau of Standards. During
the next 38 years, he advanced from re-
search metallurgist to president of the
parent company, the largest nickel com-
pany in the western world. Merica died
of a heart attack in 1957 at the age of 68.
For more information: Charles R.
Simcoe can be reached at
.
The Ford Trimotor was the first commercial plane built in the
U.S. with a duralumin type alloy produced by Alcoa. Courtesy
of .
Interior of the Trimotor, which only held a dozen passengers. Courtesy of
.