Sl. Semiatin et al., HOT-COMPRESSION BEHAVIOR AND MICROSTRUCTURE EVOLUTION OF PRE-ALLOYED POWDER COMPACTS OF A NEAR-GAMMA TITANIUM ALUMINIDE ALLOY, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 185(1-2), 1994, pp. 45-53
The hot-compression behavior and microstructure evolution of pre-alloy
ed powder compacts of the near-gamma titanium aluminide alloy Ti-48at.
%Al-2at.%Cr-2at.%Nb were determined and compared with results for the
same alloy processed via ingot metallurgy methods. Gas-atomized powder
was by consolidated hot isostatic pressing at a low temperature (1010
-degrees-C) to retain a fine microstructure. Samples of this material
were upset isothermally at temperatures between 1000 and 1260-degrees-
C and strain rates between 10(-3) and 10(-1) s-1. The stress-strain cu
rves revealed moderate amounts of flow softening which were attributed
primarily to dynamic recrystallization and secondarily to deformation
heating (at the highest strain rate studied). The absence of large la
mellar colonies in the powder metallurgy (PM) material was deduced to
be the reason for peak flow stresses which were much lower than those
previously noted for cast plus hot isostatically pressed Ti-48at.%Al-2
at.%Cr-2at.%Nb. As for ingot metallurgy near-gamma titanium aluminides
, the flow stress and grain size showed a strong dependence on tempera
ture and strain rate. The steady state flow stresses for the PM alloy
were almost identical with those for cast plus hot isostatically press
ed and for cast plus hot isostatically pressed plus isothermally forge
d Ti-48Al-2Cr-2Nb. The PM materials also revealed a noticeable degree
of microstructure non-uniformity which persisted even after hot-compre
ssion testing at various sub-a transus temperatures.