The B2-B19-B19' Transformation in Ti-(45-x)Ni-5Cu-xMn (at%) (x = 0.5-2.0) Alloys

Effect of substitution of Mn for Ni on transformation behavior, shape memory characteristics and superelasticity of Ti45Ni-5Cu alloy has been investigated by means of electrical resistivity measurements, X-ray diffraction, thermal cycling tests under constant load and tensile tests. The one-stage B2-B19' transformation occurred when Mn content was 0.5 at%, above which the two-stage B2-B19-B19' transformation occurred. A temperature range where the B19 martensite exists was expanded with increasing Mn content because decreasing rate of Ms (60 K / % Mn) was larger than that of Ms' (40 K / % Mn). Ti-(45-x) Ni-5Cu-xMn alloys were deformed in plastic manner with a fracture strain of 60 % similar to 32 % depending on Mn content. Clear superelasticity was found in fully annealed Ti-(45-x) Ni-5Cu-xMn alloys with Mn content more than 1.0 at%, which was ascribe to a solid solution hardening by substitution of Mn for Ni.