A STUDY ON LATTICE-PARAMETERS OF MARTENSITE IN TI50.5-XNI49.5ZRX SHAPE-MEMORY ALLOYS

Ti50.5-xNi49.5Zrx (x=5 similar to 20 at.%) shape memory alloys exhibit the characteristics of B2 <----> B19' martensitic transformation and their transformation temperatures increase linearly with increasing Zr content. The lattice parameters of B19' martensite in these alloys ar e determined by XRD, SADP of TEM and the Rietveld method. Experimental results show that all of the lattice parameters a and c, monoclinic a ngle beta and unit cell volume V increase, but lattice parameter b dec reases with increasing Zr content in Ti50.5-xNi49.5Zrx alloys. The res ults of the Rietveld method indicate that the martensite of Ti50.5-xNi 49.5Zrx with x less than or equal to 10 at. % has a structure similar to that of Ti50Ni50, but that of Ti50.5-xNi49.5Zrx with x greater than or equal to 15 at.% may change in structure. (C) 1998 Elsevier Scienc e S.A.