Effect of Pre-Strain on Mechanical Propertiec of Ni-Ti-Nb Shape Memory Alloy.

Abstract

A shape memory alloy (SMA) is intended to be used as structural elements at elevated temperatures. The mechanical and transformation properties of Ni Ti-Nb SMA were examined at room temperature and 561 K. The chemical composition of Ni-Ti-Nb SMA is 51 wt.% Ni, 38 w.% Ti and 11 wt.% Nb. The tensile strength, the 0.2% proof stress and the vickers hardness are increasing with increasing pre-strain below 14%, but the elongation, the reduction of area and the charpy impact absorption are decreasing with increasing pre-strain below 14%. The SMA is found to have sufficient mechanical strength for structural elements at elevated temperature. Maximum recovery strain due to the shape memory effect was about 5.5%. This value was obtained when 12% pre-strain was added. This means that a pre-strain of 12% is desirable when the Ni-Ti-Nb SMA is used for pipe coupling, etc.