NiTi合金形状记忆表面的临界应变

Critical strain on shape surface of NiTi shape memory alloy

利用维氏四棱锥压痕方法,通过温度控制在NiTi合金中获得凸起-平整的双程形状记忆效应表面。通过研磨剥层法,发现随着消除深度的增加所获得的凸起高度和直径减小,在消除160μm深度后,表面凸起现象消失,并从理论上定量分析该深度所对应的临界应变大小。实验表明:双程形状记忆效应是通过对形状记忆合金进行温度-应变循环变形而获得。因此,可能存在一定的临界应变,在低于该应变时,材料不能表现双程形状记忆效应。

Two-way shape memory effect （TWSME） surface in NiTi was obtained using Vickers four-sided pyramidal indentation method, namely, the switchable surface between protrusions and flat state controlled by temperature. By gradual grinding off the deformed layer after indenting, the diameter and height of the protrusions decrease as increasing the removal layer. It is found that no protrusions are observed after 160 μm thick layer was removed. The critical microstrain at this depth is further theoretically calculated. It shows that TWSME can be obtained by means of thermomechanical training in shape memory alloys. Thus, there probably exists a critical microstrain, below which no TWSME will occur.