表面完整性对FGH96粉末合金高温低循环疲劳性能的影响研究

Effect of Surface Integrity on Low-cycle Fatigue of FGH96 Powder Metallurgy Superalloy

摘要:

采用陶瓷弹丸和铸钢丸+陶瓷丸为介质对FGH96合金车削表面进行喷丸强化,引入3种表面完整性状态。研究了一次喷丸、二次喷丸和车削状态下表面形貌、残余应力场和高温低循环疲劳寿命。结果表明：二次喷丸强化在消除车削刀痕和表面平均粗糙度增大的同时,引入了底部圆滑的弹坑,二次喷丸后Kurtosis值趋向3,但强度较小的一次喷丸仅能够部分消除刀痕；同时,一次喷丸和二次喷丸后,表面残余压应力由车削的-446MPa,提高到-1000MPa～-1100MPa,二次喷丸后残余压应力场深度由车削的100μm提高到250μm,一次喷丸残余压应力场深度与车削状态相当。在二次喷丸良好的表面完整性作用下,在650℃/ε_t=1.2%的试验条件下,相比于车削状态,二次喷丸后疲劳寿命提高108%；相比之下,一次喷丸提高21%；喷丸后疲劳寿命分散度减小。经过断口宏微观观察和反推分析说明,三种表面完整性状态的疲劳扩展寿命很接近,造成疲劳寿命差别的主要原因是裂纹萌生差别,二次喷丸的裂纹萌生寿命分别是一次喷丸的221%,以及车削状态的216%。利用工艺手段优化表面完整性是提高FGH96合金表面完整性和低循环疲劳寿命的关键。

Abstract:

Ceramic shot and ceramic shot+cast-iron shot were employed to peen the turning surface of FGH96 powder metallurgy superalloy to induce 3 surface integrity statues. Surface topography, residual stress profile and high-temperature low-cycle fatigue performance were investigated of single shot peening (SSP), double shot peening (DSP) and turning statues. The results show that DSP removes turning masks, increases the average roughness Ra, and induce the crater with smooth bottom, which makes the Kurtosis parameter approach 3. Moreover as contrast, SSP with low intensity could only partially eliminate marks. Meanwhile, surface compressive residual stress values are -1000MPa to -1100MPa by SSP and DSP compared with -446MPa by turning, furthermore, the depth of DSP residual stress profile is 250μm, SSP and turning are 100μm. By the effect of perfect DSP surface integrity statue, fatigue cycles increase to 108% compared with turning, and the SSP edges up only 21% in the fatigue condition of 650℃/ε_t=1.2%. The fatigue life dispersion decreases after peening. The results of macro/microscopic observation and analysis show the fatigue propagation lifes are close of three surface integrity statues while the fatigue initiation lifes vary greatly. The initiation life of DSP is 221% of SSP and 216% of turning. It is important and necessary to optimize the shot peening method for surface integrity promotion and high temperature low-cycle fatigue performance improvement.