Schock Wave Deformation of Intermetallic Alloys

Jerzy Bystrzycki 1Robert Varin 2Andrzej Calka 3

1. Military University of Technology (WAT), Kaliskiego 2, Warszawa 00-908, Poland
2. University of Waterloo, Department of Mechanical Engineering, 200 University Ave.W, Waterloo N2L 3G1, Canada
3. University of Wollongong, Wollongong NSW, Australia

Abstract


Ordered intermetallic alloys based on aluminides are becoming a new
class of metallic materials that have unique properties for structural
application at elevated temperatures in hostile environments. One of
the major obstacles to commercialization of intermetallic alloys as
engineering materials is their low tensile ductility at room
temperature. In addition, a number of them exhibit poor fracture
resistance and possess limited fabricability. This practically makes
impossible the application of conventional cold-work routes such as
rolling, forging, extrusion etc. The present paper is an overview of
our recent studies on the explosive processing of cubic intermetallic
alloys resulting in their heavy cold-deformation: (a) shock-wave
deformation of bulk ingots and (b) shock-wave compaction of
nanocrystalline intermetallic powders (ball milled). Both of the above
processing methods result in a unique cold-worked microstructures with
corresponding increase in microhardness. Different intermetallic
alloys with cubic structure have been studied: (B2) FeAl, (B2) NiAl,
(L1[2]) titanium trialuminide based on Al[3]Ti, and (L1[2]) Ni[3]Al.
However, this work will be mainly focused on (FeAl) iron aluminide
intermetallics. Both shock-wave deformation and shock-wave compaction
of ordered (B2) and (L1[2]) intermetallic alloys result in a
substantial increase of microhardness of the material. TEM studies
show that a high density of dislocations are being formed in
shock-wave deformed bulk intermetallic ingots. Depending on the
initial chemical composition, texture, microstructure and
shock-loading conditions, usually partially disordered ingots either
recover and develop sometimes a subgrain structure or recrystallize
when subjected to subsequent annealing treatment. Kinetics of
recrystallization in shock-loaded FeAl alloys is well described by a
classical Johnson and Mehl, Avrami and Kolmogorov theory (JMAK).
Measured apparent activation energy for recrystallization in FeAl is
close to the activation energy for self-diffusion in iron and the iron
atoms in FeAl. Annealing of shock-wave deformed (B2) FeAl and NiAl
alloys prior to the onset of static recrystallization results in the
softening observed as a substantial drop in microhardness. Preliminary
tensile tests indicate that the microstructure of iron aluminides
consisting of coarse grains with the embedded network of subgrains
exhibits five to ten fold higher elongation in room temperature than
its homogenized or hot-worked conterparts. In the shock-consolidated
FeAl compacts made from the ball-milled FeAl powders some powder "core
particles", retaining their as-milled appearance, are embedded in a
heavily deformed "matrix" containing high density of deformation
microbands. Subsequent annealing treatment of the compacts induces
partial recrystallization. The first micrometer-size grains appear in
the less deformed "core particles" instead of the more heavily
deformed "matrix particles".

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Presentation: oral at High Pressure School 1999 (3rd), by Robert Varin
See On-line Journal of High Pressure School 1999 (3rd)

Submitted: 2003-02-16 17:33
Revised:   2009-06-08 12:55
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