starship-design: Computer models make "super-alloys"

["L. Clayton Parker" <lparker@cacaphony.net>]

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From: L. Clayton Parker [mailto:lparker@cacaphony.net]
Sent: Sunday, April 27, 2003 1:12 PM
To: Starship-Design (E-mail)
Subject: Computer models make “super-alloys”


Useful in a re-entry vehicle perhaps?

Computer models make “super-alloys”
22 April 2003

Researchers in Japan have created a new group of "super-alloys" with
superior properties. Takashi Saito and colleagues at the Toyota Research and
Development Laboratories and the University of Tokyo used a novel
computational approach to make the materials. The alloys, whose properties
include ultra-high strength and super-elasticity, could be used for
high-precision instruments and medical equipment (T Saito et al. 2003
Science 300 464).

Advances in metal alloying techniques are largely made by trial and error.
Costly, time-consuming experiments result in only small improvements in
physical and mechanical properties. Materials scientists rely on
experimentally determined phase diagrams to design new alloys, but it takes
millions of such diagrams to produce new multi-element structures- even for
common metal combinations.

Now, Saito and co-workers have used three electronic "magic numbers" to make
a novel set of alloys. The numbers are: the electron-to-atom ratio; the
"bond order", which represents the average bonding strength between atoms;
and the d electron-orbital energy level, which represents the average
electronegativity.
The researchers produced alloys based on titanium that also contained
tantalum, niobium, zirconium, vanadium and oxygen in a simple body-centred
cubic structure. Superior properties were observed only when all three of
the magic numbers had specific values - 4.24 for the electron-to-atom ratio
for example. The alloys do not expand on heating and are very strong.
Moreover, they are super-elastic and super-plastic because they can be
stretched without being deformed.

The team focused on the elastic modulus of the system - the ratio of the
stress applied to the strain produced - and found a characteristic
anisotropy in the metal crystals. "This anisotropy brings a new type of
dislocation-free plastic deformation mechanism," Saito told PhysicsWeb. "The
mechanism makes it possible for the alloy to accumulate large amounts of
elastic strain energy, which leads to the exceptional properties observed."

Author
Belle Dumé is Science Writer at PhysicsWeb