材料期刊网

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。

An in situ observation by SEM was made of the phase transition induced by stain in the specially heat treated 51.6 at.-%Ni-Ti ahoy of which the superelasticity might be reached to such extent of its maximum elastic strain up to 17%. The phase transition is shown as two stages, namely, pre-martensitic and martensitic. The alloy reveals a behaviour for superelasticity, i. e., if the strain exceeds no more than its elastic limit, the whole transition process may be reversible, and the macro-or micro-feature may be back to beginning after unloading at any point of the curve. However, the intergranular cracks and the internal slips may be appeared, as well as the unreversible residual strain may be then remained if it exceeded the limit.