IMPROVEMENT IN ROOM-TEMPERATURE DUCTILITY OF INTERMETALLIC ALLOYS THROUGH MICROSTRUCTURAL CONTROL

A summary is presented of the recent advances in the development of mu ltiphase intermetallic alloys towards improved room temperature ductil ity investigated by the present authors. The alloy systems of interest are Ni-Al-Be, Co-Al-Ni-Ti, and Co-Al-C, in which two- or three-phase alloys can be designed involving the L1(2), B2 and the primary solid s olution, hereby denoted as (Ni) or (Co,Ni) in the first two systems, w hile the B2, E2(1), and the primary solid solutions, denoted as (Co) i n the latter system. It is shown that by choosing a proper combination of phases with particular morphologies, good room temperature ductili ty can be obtained not only by compression and bending tests but also by tensile tests. Such a strategy has been so far most successful in t he Co-Al-Ni-Ti system, where room temperature ductility of near to 20% is achieved in a B2/L1(2)/(Co,Ni) three-phase alloy. It is pointed ou t that keys to design ductile multi-phase intermetallic alloys would b e: (1) refinement of the microstructure utilizing solid state phase tr ansformations such as an invariant reaction; (2) adjustment of amounts and compositions of the constituent phases, which is not possible in the binary system, but is in a multi-component system, and (3) hot fab rication to reduce solidification defects. Copyright (C) 1996 Elsevier Science Ltd.