采用透射、X射线及显微硬度分析等方法，研究了TC21合金中淬火马氏体在长时间低温时效过程中的组织演变及马氏体分解机制。研究表明，淬火态TC21合金在400～450℃进行长时间等温处理后，易获得弥散分布的颗粒状d相，显著提高合金性能，而a相颗粒的形核与马氏体中层错的分布密切相关。正交马氏体在低温时效过程中的具体分解方式为n→a＋a目→a＋β亚隐→a＋β进一步提高时效温度或时效时间仅相颗粒将粗化为片层状，降低合金强度。
Microstructure evolution and martensite decomposition mechanism of quenched TC21 alloy during long term ageing process at low temperatures were studied by TEM,XRD and microhardness analysis techniques. Result shows that the alloys exhibit good properties after long term isothermal treatment at 400-450℃ due to aphase particles uniformly distribute in the parent phase. Furthermore, TEM observation indicates that the nucleation of （xphase particle is related with the distribution of stacking faults in the quenched TC21 alloy. The transformation sequence of martensite decomposition for TC21 alloy is （x→a ＋ arich→a ＋βmetastable→a＋β.a→β.. Further increasing the ageing temperature and time, a particles will coarsen to lamellar structure and strength of the alloy will decrease. The low temperature ageing porccss mentioned in this paper creates a new way to improve mechanical properties of TC21 alloy.
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