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. E xperimental results reveal that the Ti49.25-x/2Ni50.75-x/2Vx (x=0-4 at%) al loys exhibit a B2<->B19' one stage martensitic transformation. The transfor mation temperatures will drop down about 10 degrees C by adding 1-2 at% V d ue 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 tr ansformation temperatures for both Ti47.75Ni49.25V3 and Ti47.25Ni48.75V4 al loys. 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 strengt hening. 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 a lloys exhibit a worse shape memory effect due to the formation of second-ph ase particles. The wear mechanisms of Ti49.25-x/2Ni50.75-x/2Vx alloys are f ound 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 th e Ti47.75Ni49.25V3 and Ti47.25Ni48.75V4 alloys, due to their higher hardnes s and pseudoelastic behaviors of the B2 structure. (C) 1999 Elsevier Scienc e S.A. All rights reserved.