Ni Ti合金具有优异的形状记忆功能和良好的生物体兼容性,近年来对它的应用研究受到工程界和医学界的重视,同时对Ni Ti合金形状记忆效应的微观机制的研究也在逐步深入。介绍了Ni Ti合金的主要特性及影响其形状记忆功能的主要因素,总结了Ni Ti合金的形状记忆效应和超弹性的微观机制研究现状,并指出了需对该合金进一步研究的一些问题。
The microdefects and free electron densities in B2,R and B19’ phases of Ni50.78Ti49.22 alloy were studied by positron lifetime measurements.Comparing the lifetime parameters of the Ni50.78Ti49.22 alloy measured at 295 K and 225 K,it is found that the free electron density of the R phase is lower than that of the B2 phase;the open volume of the defects of the R phase is larger,while the concentration of these defects is lower than that of the B2 phase.The Ni50.78Ti49.22 alloy exhibits B19’ phase at 115 K.In comparison with the R phase,the free electron density of the B19’ phase increases,the open volume of the defects of the B19’ phase reduces,and the concentration of these defects increases.The microdefects and the free electron density play an important role during the multi-step transformations(B2→R→B19’ phase transformations)in Ni50.78Ti49.22 alloy with the decrease of temperature.
