Abstract:The two-stage martensitic transformation B2-B19-B19' in a Ti49Ni41Cu10 alloy has been investigated by means of electrical resistivity, differential scanning calorimetry(DSC), elastic modulus, X-ray diffraction and TEM observation. The cubic B2-orthorhomic B19 transformation has significant transformation heat effect with clear and sharp DSC peaks in a narrow temperature range and is accompanied with a pronounced softening of the elastic modulus; but its resistivity change is minor. The orthorhomic B19 -monoclinic B19' transformation has small heat effect with diffuse DSC peaks over a wide temperature range and an obvious resistivity change.TEM observation reveals the twin substructure of B19' martensite, contrasting to the defect-free B19 martensite.The difference in transformation behaviour of the B2-B19 and the B19-B19' might be related to the different martensite lattice type and substructure. The comparison between ternary and binary alloys have been also discussed.

Key words: TiNiCu shape memory alloy two-stage martensitic transformation