TiAl合金的热暴露表面及其对室温拉伸性能的影响

Hot Exposure Surface of TiAl Alloy and Its Effect on Drawing Properties

对TiAl合金的标准拉伸试样分别进行700℃×100 h和750℃×100 h的热暴露处理,观察表明,机械抛光试样的表面具有规则的抛光痕迹,经700℃×100 h热暴露后试样表面生成絮状氧化物,表面仍可见机械抛光痕迹,而经750℃×100 h热暴露后,试样表面生成较厚的、均匀分布的氧化层,该氧化层的显微硬度显著高于基体的显微硬度。由于合金的层片组织存在取向性,因而在氧化层与基体之间存在富铝的过渡层,有利于阻止基体的进一步氧化。测试结果表明热暴露在一定程度上降低了原抛光试样表面的残余压应力水平。拉伸结果表明,热暴露后试样的室温拉伸塑性普遍明显下降。分析认为,热暴露后合金塑性的下降主要归因于试样表面残余压应力水平的降低而弱化了表面压应力对拉伸中表面裂纹萌生的抑制作用,750℃×100 h热暴露试样承载能力的明显降低与拉伸中氧化层与基体的界面处出现的连续裂纹有关。

The standard tensile specimens of TiAt alloy were treated at 700 ℃× 100 h and 750 ℃ ×100 h respectively. It was found that the polished surface was full of abrasive marks by SiC sand grains, while the post-exposed surface was oxidized. There were a few oxides on the surface of 700 ℃ × 100 h heat treated specimens and the oxide was thin, while that of the 750 ℃ × 100 h heat treated specimens was thicker. The hardness of oxide was higher than that of the matrix. Additionally, there was a middle layer that was rich in Al between the matrix and the oxide layer, which prohibited the continuous oxidation. In comparison with polished specimens the surface residual stress of the post-exposed specimens was compressive, but much lower. Tensile results show that the tensile elongation of the post-exposed specimens is obviously lower. It is due to the reduction of surface compressive stress which weakens the restraining effect of flaw of surface during tensile test. The tensile strength of the 750 ℃ ×100 h heat treated specimens is decreased, which is suspected to be related to the cracks of the interface between oxides and the matrix.