A study of TiNiV ternary shape memory alloys

The TiNiV ternary shape memory alloys, obtained by equal substitution of V for both Ti and Ni, are investigated focusing on their basic transformation behavior, shape memory effect, pseudoelasticity and wear characteristic. Experimental results reveal that the Ti49.25-x/2Ni50.75-x/2Vx (x=0-4 at%) alloys exhibit a B2<->B19' one stage martensitic transformation. The transformation temperatures will drop down about 10 degrees C by adding 1-2 at% V due to the effect of solid-solution strengthening. There appear many (Ti,V)(2)Ni second-phase particles within the matrix of Ti47.75Ni49.25V3 and Ti47.25Ni48.75V4 alloys. The oxygen atoms in the matrix will be easily absorbed by the (Ti,V)(2)Ni second-phase particles to form the (Ti,V)(4)Ni2O oxide. This decreased oxygen content in the matrix will contribute to raise the transformation temperatures for both Ti47.75Ni49.25V3 and Ti47.25Ni48.75V4 alloys. The shape memory effect and pseudoelasticity of Ti49.25Ni50.75 alloys can be improved by the addition of 1-2 at% V due to solid-solution strengthening. The energy storage efficiency (E-2/E-1 + E-2) can also be increased by the addition of V. However, the Ti47.75Ni49.25V3 and Ti47.25Ni48.75V4 alloys exhibit a worse shape memory effect due to the formation of second-phase particles. The wear mechanisms of Ti49.25-x/2Ni50.75-x/2Vx alloys are found to be similar to those of TiNi binary alloys. The Ti49.25Ni50.75, Ti48.75Ni50.25V1, Ti48.25Ni49.75V2 alloys have a better wear resistance than the Ti47.75Ni49.25V3 and Ti47.25Ni48.75V4 alloys, due to their higher hardness and pseudoelastic behaviors of the B2 structure. (C) 1999 Elsevier Science S.A. All rights reserved.