长期热暴露对不同表面状态的Ti-44Al-5Nb-1W-1B合金疲劳性能的影响

Effects of long-term thermal exposure on fatigue behavior of Ti-44Al-5Nb-1W-1B alloy with varied surface conditions

通过喷丸和电解抛光的方法处理Ti-44Al-5Nb-1W-1B(摩尔分数,%)合金,研究其在长期热暴露(10000 h,700℃)前后疲劳性能的变化。结果表明:在热暴露前,电解抛光处理比喷丸处理更能改善该合金的疲劳性能。经过长期热暴露后,两种表面处理样品的疲劳性能均出现不同程度的衰减,但电解抛光处理相对于喷丸处理能够更好地保持合金的疲劳性能。长期热暴露会导致合金表面发生氧化,合金内部发生"释氧脆化"和"B2+ω有序相生成脆化",这3种变化均对合金的疲劳性能产生不利影响。表面氧化使得喷丸工艺所引入的表层残余压应力在长期热暴露时明显降低,这导致疲劳性能大幅度衰减。相对而言,电解抛光工艺使合金获得光滑平整无缺陷的表面,无明显应力集中,因此合金有较高的抵抗热暴露性能衰退的能力。

The Ti-44Al-5Nb-1W-1B（mole fraction, %） alloy was treated by two surface treatment processes of shot peening and electropolishing, the changes of the fatigue behavior of the alloy exposed at 700 ℃ in air for 10000 h was studied. The results show that the fatigue strength of electropolishing specimens is higher than that of shot peening specimens before exposure. The fatigue strengths of the alloys with both surface conditions reduce after long-term thermal exposure, but the electropolishing specimens can maintain the fatigue properties of the alloy better than the shot-peening specimens. Long-term thermal exposure can cause oxidation on the surface and ＂B2＋ω-formation induced embrittlement＂ and ＂oxygen-release induced embrittlement＂ inside of the alloy. All the three types of changes are detrimental to the fatigue performance of the alloy. The residual compressive stresses introduced by shot peening are released during long-term thermal exposure owing to the oxidation, which leads to a significant deterioration of the fatigue properties. The electropolishing specimens have very smooth surface without defects and stress concentration, therefore, the electropolishing specimens are more capable of resisting the deterioration of the fatigue properties than shot peening specimens during long-term thermal exposure.