MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF 2-PHASE ALLOYS BASED ON THE B2-TYPE INTERMETALLIC COMPOUND COAL IN THE CO-AL-NI TERNARY-SYSTEM

Various two- or three-phase alloys were prepared based on the B2 intermetallic compound CoAl in the Co-Al-Ni ternary system, in which the B2 phase forms a continuous solid solution with NiAl of the same ordered structure. Combination of the phases with the B2 phase can be the (Co, Ni) primary solid solution phase being also continuous from Co to Ni-corners, and/or the L1(2) phase based on Ni3Al. Then the relationship between microstructure and mechanical properties were systematically investigated by optical and transmission electron microscopy and by micro-Vickers hardness and compression tests. It is found that two-phase alloys of B2/Ll(2) show superior room temperature ductility with over 10% plastic strains to those of B2/(Co, Ni). The present work is based on the seemingly ever lasting motivation to provide some ductility to the intrinsically brittle CoAl compound which unless otherwise has attractive properties as a new high-temperature structural material.