Wm. Yin et al., MICROSTRUCTURE STUDY OF A GAMMA-TIAL BASED ALLOY CONTAINING W AND SI, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 240, 1997, pp. 713-721
The phase transformations and modulated microstructures in the cast al
loy Ti-47Al-2W-0.5Si(at.%) have been studied. It has been shown that m
icrostructure is sensitive to heat treatment and composition. The stru
cture in the alloy heat treated at 1300 degrees C mainly consists of c
oarse lamellar, fine lamellar, equiaxed gamma grains and beta phase. H
omogenizing treatment at 1400 degrees C results in nearly fully-lamell
ar structure which shows colony-boundary gamma phase grains. The obser
vations showed that small increases in W content result in changes in
the amount and morphology of beta phase. For the alloy containing 2.1
at.% W, the beta phase has been observed in three types of morphology:
blocky beta phase containing gamma needles and fine silicide particle
s inside; rod-like beta phase and fine needle-like beta phase. For the
alloy variant containing 1.5 at.% W, only a very small amount of rod-
like beta phase appeared. Different mechanisms are proposed to explain
the occurrence of three types of beta phase, in that W may stabilize
it by extending the primary beta phase to lower temperature as well as
by yielding new phase zones. A few primary silicide particles have be
en found in the interdendrite region in the alloys containing more tha
n 0.5 at.% Si, while coherent secondary silicides generally nucleated
at the interfaces. (C) 1997 Elsevier Science S.A.