Development of New Fe-based Shape Memory Alloy (Fe-Ni-Co-Ti Alloy)

1. 适当淬火的Fe-Ni-Co-Ti合金产生完全孪生的薄板马氏体。通过化学成分的调整和老化条件的改变，薄马氏体的热迟滞现象发生了很大的变化，并且无论热迟滞程度如何，薄板马氏体都具有良好的形状记忆效应。例如，Fe-33Ni-10Co-4Ti合金在973K下时效18ks时，在77k下变形后加热至室温，形成Ms和Af温度均低于室温的热弹性马氏体，并发生完整的形状记忆效应。当Fe-31Ni-10Co-3Ti合金在873K下时效3.6ks时，形成具有较大热滞后的薄板马氏体（Ms 200K, As 350K, Af 500K）。在室温下为完全奥氏体的试样，在接近或低于ms的温度下变形后，加热到a以上时，表现出完全的形状记忆效应，而在室温下变形时几乎没有表现出形状记忆效应。然而，当试样在零度以下冷却到液氮中产生大量马氏体时，即使在室温下进行变形，也会产生几乎完全的形状记忆效应。研究发现，Fe-Ni-Co-Ti合金的形状记忆效应是通过热滞后程度的变化在低温到高温的宽温度范围内发生的。在Fe-Ni-Co-Ti合金中加入B或Al可提高奥氏体时效后的延展性。这是由于抑制了相沿奥氏体晶界的析出。当Fe-33Ni-10Co-4Ti合金的热弹性马氏体在273K ~ 77K之间热循环时，热滞变大，即Ms温度略有下降，Af明显升高。经过几个热循环后，Af温度高于室温，即使加热到室温，仍有一定量的马氏体存在。因此，变形后的形状恢复程度由100%下降到60%左右。少

1. The properly ausaged Fe-Ni-Co-Ti alloys produce a thin plate martensite which is completely twinned. The thermal hysteresis of thin martensite is widely changed by the adjustment of chemical composition and the ausaged condition, and these thin plate martensites cause a perfect shape memory effect irrespective of the extent of the thermal hysteresis. For example, when Fe-33Ni-10Co-4Ti alloy is ausaged at 973K for 18ks, the thermoelastic martensite whose Ms and Af temperature are below room temperature is formed and the complete shape memory effect occurs during heating up to room temperature after deformation at 77 K. In the case of Fe-31Ni-10Co-3Ti alloy ausaged at 873K for 3.6ks, thin plate martensite with a large thermal hysteresis (i.e., Ms 200K, As 350K, Af 500K) is formed. This specimen which is fully austenitic at room temperature shows a complete shapememory effect when specimen is heated up above Af after the deformation at temperatures near or below Ms. The as-ausaged spec … More imen hardly exhibits the shape memory effect when deformed at room temperature. However, when the specimen is once subzero cooled to liquid nitrogen to produce a large amount of martensite, the almost complete shape memory effect occurs even by the deformation at room temperature. It has been found to be characteristic that the shape memory effect in Fe-Ni-Co-Ti alloys occurs over the wide temperature range from low temperature to high temperature by the change in the extent of thermal hysteresis.2. The ductility of austenite after ausaging is improved by the addition of B or Al to Fe-Ni-Co-Ti alloys. This is due to the suppression of precipitation of phase along austenite grain boundaries.3. When the thermoelastic martensite in Fe-33Ni-10Co-4Ti alloy is thermally cycled between 273K and 77K, the thermal hysteresis becomes markedly large, i.e., the Ms temperature is slightly decreased and the Af is markedly increased. After several thermal cycles, the Af temperature is raised above room temperature and the some amount of martensite remains even after the heating up to room temperature. Therefore, the degree of shape recovery is decreased from 100% to about 60% by the transformation. Less