DEFORMATION BEHAVIOUR OF SINGLE CRYSTAL OF Cu-Al MARTENSITIC ALLOYS

Abstract

Deformation behaviour and stress-induced martensite-martensite transformation of binary Cu-Al β-martensitic alloys were investigated by tensile and compression test, X-ray analysis and electronmicroscopy. Three kinds of Cu-Al alloys having 18R(β'1), 18R+2H, and 2H(β'1) structures in the initial as-quenched state, respectively, were examined. In the specimen with β tensile axis, it was found that proceeds by Luders deformation. That is, narrow band appears at first and then this deformation band propagates along the tensile axis. It was found that in the band region, martensite-martensite transformation, β'1 or γ'1 → α'1(DO22) occurs, by using precession X-ray method. It was also found that γ'1 martensite transformed directly to α'1 martensite without passing the successive γ'1 to β'1 to α'1 transformation like in the Cu-Al-Ni alloys. When the martensite-martensite transformation took place along the whole length of the tensile specimen, single crystal of α'1 martensite was obtained and this α'1 single crystal was stable upon unloading the tensile stress. When the α'1 single crystal specimen which was produced by tensile of the specimen with 2H+18R mixture along [001]β direction, was compressed along [00[MATH]]β (=[00[MATH]]DO22) direction, the reverse transformation α'1 to γ'1 was found to occur without forming β'1 martensite.