THE SURFACE PERFORMANCE OF SHOT PEENED AND ION-IMPLANTED NITI SHAPE-MEMORY ALLOY

Equiatomic NiTi shape memory alloy in austenitic and martensitic forms has been modified by shot peening with glass media and by N+ ion impl antation. The effect upon microstructure, surface hardness and coeffic ient of friction was measured, along with the effect of the two treatm ents upon the shape memory behaviour. Examination using transmission e lectron microscopy (TEM) showed amorphous regions within the surfaces treated by both peening and ion implantation. In addition, peened and ion implanted samples showed similar increases in surface hardness and reduced surface friction coefficient. Differential scanning calorimet ry showed that both surface treatments had no effect upon the bulk sha pe memory phase transformation behaviour.