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本工作采用一种特殊的热处理工艺,可使51.6 at.-％Ni-Ti合金表现出超弹性行为,其极限弹性应变值为17％。在扫描电镜拉伸样品台上观察了该合金的应变诱发相变:预马氏体转变和马氏体转变。只要应变不超出弹性极限值,在任一点卸载,整个过程将逆向进行,宏观、微观特征完全恢复为原状,表明材料具有超弹性行为。如果应变超出极限值,则会导致晶间裂纹和晶内滑移,带来不可逆的残余应变。
In this work, a special heat treatment process was used to show the super-elastic behavior of 51.6 at .-% Ni-Ti alloy with the ultimate elastic strain of 17%. The strain-induced phase transitions of the alloy were observed on a scanning electron microscope (SEM) tensile specimen stage: pre-martensite transformation and martensitic transformation. As long as the strain does not exceed the elastic limit and is unloaded at any point, the whole process will be reversed and the macroscopic and microscopic features will be completely restored to their original state, indicating that the material has hyperselastic behavior. If the strain exceeds the limit, it will lead to intergranular cracks and intracrystalline slip, resulting in irreversible residual strain.