Comparative Electron-Microscopic Study of Shape Memory Alloys of Systems Cu-Ni-Al and Ni-Mn-Al

Abstract

Thermoelastic martensitic transformations (TMTs) were observed in many binary and multicomponent intermetallic atomic-ordered alloys based on titanium, nickel, and copper: Ti-Ni, Ni-Mn, Ni-Al, Cu-Al, Ti-Ni-Me, Ni-Mn -Me, Ni-Al-Me, Cu-Al-Me and others [1-13]. Doping with third chemical elements allows one to control their critical temperatures Ms, Mf, As, Af and to design alloys with specified TMT parameters. At the same time, many aspects of the effect of doping on the features of TMT and the mechanisms of destruction in such alloys remain unexplored. The most important problem that impedes the practical application of many polycrystalline alloys based on most intermetallic compounds is their relatively low strength, plastic and fatigue characteristics and their tendency to brittle fracture. Thus, polycrystalline Cu-Ni-Al and Ni-Mn-Al alloys experience brittle intercrystalline failure after deformation by 2-3%. The main reasons for this destruction include: a very large elastic anisotropy of their metastable austenite; large grain sizes; the presence of grain-boundary segregations and precipitates of embrittling phases.