一种铸态亚共析U-Nb合金晶粒细化的热处理工艺研究

A Study on Heat Treatment for Grain Refining in a Certain Sub-Edtectoid as-Cast U-Nb Alloys

通过对某种铸态和预淬火态亚共析U-Nb合金样品的900℃等温淬火实验,利用金相显微镜(OM),透射电镜(TEM)和X射线衍射(XRD)等方法研究了单靠热处理工艺细化该种铸态合金晶粒的可行性。实验结果表明,由a+?1-2两相组成的铸态样品在a+?1-2→?1等温转变过程中没有明显的重结晶行为,?1新相的晶粒特征表现为原?1晶界的平直化迁移,因此淬火后晶粒不能细化;由单一a″相组成的预淬火态样品在a″→?1等温转变过程中则发生完全重结晶,等温0.25h能使晶粒尺寸减小1倍。分析认为,该种铸态合金通过预淬火处理使晶格缺陷增多,以及所生成的单一a″相中存在大量的孪晶结构降低了等温转变时?1新相的形核能导致了a″→?1等温转变发生重结晶。结论认为,采取两次淬火的热处理方法可以细化该种铸态亚共析U-Nb合金晶粒。

The heat treatment process for grain refinement in a certain sub-edtectoid as-cast U-Nb alloys studied and the microstructure of the alloy was determined by metallgraphic, TEM and XRD. The results show that the recrystallization in as-cast sample was not happened, during isothermal transformation of alpha+gamma(1-2)-->gamma(1). But the a' phase in sample formed by pre-quenching can make the recrystallization occur during the phase transformation a'-gamma(1) and result in grain refinement that the grain size was 10 mum at 900degreesC isothermal heating for 0.25 h. This is caused by the increase of defects in crystal and a quantity of twin in a' phase, which is formed by pre-quenching. The grain refinement in the sub-edtoctoid as-cast U-Nb alloy can be realized by means of pre-quenching and final quenching.