Zr变质SiCP/ZA27复合材料在部分重熔过程中的组织演变

用扫描电镜(SEM)背散射成像技术对Zr变质SiC_P/ZA27复合材料在部分重熔过程中的组织演变进行了研究,并与未变质复合材料及基体合金作了对比。结果表明:经0.2 wt% Zr变质的SiC_P/ZA27复合材料在460℃加热过程中(0min~30min),其基体组织依次经历了晶臂的快速合并,晶粒的长大,晶界区域的熔化、组织分离,最后经球状化形成触变成形所需的粒径较为均匀、细小、圆整的半固态浆料,在随后的保温过程中(30 min~80 min)未发现明显的粗化现象;未变质复合材料则形成相互连接的不规则组织,即使经长时间的保温(80 min),也未全部球状化;基体合金组织的分离快于变质复合材料,但在保温中的晶粒粗化却较为严重。加热初期晶粒的快速粗化是由共晶组织向晶内的迅速扩散引起的。本文作者从相变角度分析了组织的演变过程。

MICROSTRUCTURAL EVOLUTION OF SiCP/ZA27 COMPOSITE MODIFIED BY Zr DURING PARTIAL REMELTING

The microstructural evolution of SiCP/ZA27 composite modified by Zr during partial remelting was investigated using back-scattered electron imaging technique in scanning electron microscopy (SEM), and also compared with that of the not modified SiCP/ZA27 composite as well as that of the monolithic ZA27 alloy. The results indicated that the matrix microstructure of the composite modified by 0.2 wt% Zr experienced in succession the rapid merging of the secondary dendritic arms and the resulting growth of the primary dendrites, the melting of the interdendritic regions and resulting in the separation of the microstructure, and finally formed the slurry needed by thixoforming with the uniform, small and globular solid particles through the spheroidization during heating at 460℃ (0min~30min). No obvious coalescence of the solid particles was found during the subsequent isothermal holding (30 min~80 min). The primary dendrites of the not modified composite changed into interconnected and irregular grains during the heating stage and did not spheroidize completely even when holding for 80 min. The separation of the microstructure of the monolithic alloy was faster than that of the modified composite during the initial stage, but the particle coalescence was likely more obvious during the subsequent holding period. The rapid coalescence of the primary dendrites during the initial stage of the heating resulted from the diffusion of the interdendritic eutectics towards the dendrites. In addition, the microstructural evolution was also discussed through analyzing the phase transformations which occurred during this process.