A new approach to heat-treating NiTi micro-components

A new approach to heat-treat near equi-atomic NiTi samples was studied. Instead of heat-treating samples inside vacuum furnaces, an in-situ electrical power resistance joule heating method was employed. This method eliminated the bothering measurement of the sample temperature and employed the electrical resistance joule heating to heat-treat the samples. An optimum electrical power to heat-treat the samples was determined to be 2 watts. The shape memory phase transformation characteristics show strong dependence on the electrical annealing power. R-phase transformation was also found sensitive to the electrical annealing power. High electrical annealing power would suppress the R-phase transformation process but in turn promotes samples with higher phase transformation temperatures for actuating purposes. Moreover electrically cycling samples at very high power is also detrimental to the R-phase transformations. This new method is proved to have the same heat treatment effect on the NiTi wire equivalent to the traditionally thermal heat treatment method.