热诱发ε马氏体量对Co-30Ni合金形状记忆效应的影响

Effect of Amount of Thermal ε Martensite on Shape Memory Effect of Co-30Ni Alloy

为了明确具有ε马氏体转变的Co-Ni基合金形状记忆效应的来源,通过控制不同变形温度,在Co-30Ni合金中获得不同数量的热诱发ε马氏体,在此基础上利用OM和XRD研究了变形时预先存在的热诱发ε马氏体的演化及其对应力诱发ε马氏体转变的影响,并采用弯曲法表征了合金的形状记忆效应。结果表明:合金的形状记忆效应都随热诱发和应力诱发ε马氏体数量的增加而升高,但原位金相未观察到热诱发ε马氏体在应力下的长大合并。Co-Ni基合金的形状记忆效应来源于应力诱发ε马氏体转变,而不是热诱发ε马氏体在应力下的长大合并。低的母相屈服强度是Co-Ni合金形状记忆效应差的原因。预先形成的热诱发ε马氏体能提高母相的屈服强度,因而有利于形状记忆效应的提高。

To know the origin of shape memory effect in Co-Ni alloys showing ε martensitic transformation,different amounts of thermal-induced ε martensite were obtained before deformation through controlling the deforming temperatures.The evolutions of the pre-existing thermal-induced ε martensite and its effect on stress-induced ε martensitic transformation were studied during deformation by OM and XRD,and the shape memory effect was measured by bending method.The results showed that the shape memory effect of Co-Ni alloys resulted from the stress-induced ε martensitic transformation,rather than the coalescence of thermal martensite.The low yield strength accounted for its poor SME.The pre-existing thermal ε martensite can increase the yield strength and thus enhance shape memory effect in Co-Ni alloys.