铸造钛合金α层的组织与形成机理

Micrstructure and Formation Mechanism of Alpha-case in Cast Titanium Alloy

摘要:

利用熔模铸造的方法制备了Ti-6Al-4V合金铸造试样，通过金相、电子探针、显微硬度测试等技术研究了铸造钛合金表面α层的组织和形成机理。结果表明，铸造钛合金试样表面均形成了α层，显微组织特征为呈“网篮”状排列的粗大片状α相组织。α层形成机理主要与型壳材料中间隙氧原子和碳原子向合金基体扩散有关。显微硬度测试得到的α层深度略大于金相结果。为完整去除α层，以硬度测试的结果更为可靠。

Abstract:

The ingot of Ti-6Al-4V alloy was prepared by investment casting. Microstructure and formation mechanism of alpha-case in the surface layer of the ingot were investigated by optical microscope (OM), electron probe micro-analyzer (EPMA) and Vickers hardness. The results show that the alpha-case covers the whole surface of the sample, and the microstructure of the alpha-case features in a coarse plate-shaped structure which ranked as-basketweave. The formation mechanism of alpha-case is associated with the diffusion of interstitial oxygen and carbon atoms in the shell material toward matrix alloy. Depth of alpha-case obtained from micro-hardness testing is slightly deeper than that observed by OM. More reliable results come from the micro-hardness testing for removing the alpha-case completely.