Abstract
The alloy of Ni-Al26-Cr15-Co6-Ti3-Mo2-Nb0.5-Ho0.1 (at.%) was heat-treated and studied by microstructure examination and compressive test. The results reveal that in the as-cast alloy, alpha-Cr, sigma and mu phases are segregated along the NiAl phase boundary and form into network. Small Ni(2)AlTi, Cr(2)Nb and Ni(2)Al(3)Ho particles precipitate at NiAl grain boundary. The subsequent solid solution treatment with rapid and intermediate cooling rate transforms the net-like precipitating phases into discontinuous ones, but the rapid cooling leads to micro-cracks along phase boundary. However the lower cooling rate results in spherical a-Cr particle and needle-like Ni(3)Alphase in NiAl matrix. The short-term aging after solid solution treatment promotes the coarsening of Ni(3)Al lathes and a-Cr particles, and an orientation relationship of [00 (1) over bar](beta)parallel to[(1) over bar 10](lambda), and (110)(beta)parallel to(111)(gamma), is found between lath-shaped Ni(3)Al phase and NiAl matrix. In addition, the p. phases are substituted by sigma and some Cr(3)Ni(2) phases. The long-term aging treatment reduces Ni(3)Al, sigma and mu phases and coarsens the alpha-Cr phase further. The solid solution treatment and short-term aging improve the mechanical properties of the NiAl-based multiphase alloy significantly. (C) 2011 Elsevier B.V. All rights reserved.
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