MARTENSITE-TRANSFORMATION OF A TINICU ALLOY

The two-stage martensitic transformation B-2-B-19-B-19' 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 B-2 -orthorhomic B-19 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 B-19-monoclinic B-19' 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 B-19' martensite, contrasting to the defect-free B-19 martensite. The difference in transformation behaviour of the B-2-B-19 and the B-19-B-19' might be related to the different martensite lattice type and substructure. The comparison between ternary and binary alloys have been also discussed.