冷挤压与热时效对GH4169合金孔结构高温低循环疲劳寿命的影响

Effects of cold expansion and aging on high-temperature low-cycle fatigue of GH4169 alloy with hole structure

对GH4169合金中心孔板材试样进行冷挤压强化,研究了冷挤压和(600℃,500 h)热时效对试样在(600℃,820 MPa,R=0.1,三角波)条件下的低循环疲劳性能的影响。结果表明:冷挤压后中值疲劳寿命估计量由原始状态的7278周次提高到19536周次,提高了约2.5倍,显著提高了高温疲劳寿命,而热时效后原始状态疲劳寿命由7278周次降低到4717周次,降低了35.8%,发生了疲劳弱化。疲劳弱化的原因是热时效使γ″强化相向δ相转变,强化相含量减少,δ相数量增多且发生形态变化。热时效后,原先冷挤压表面残余压应力由−708 MPa降低到−483 MPa。仍然起到强化作用的稳定部分残余压应力场与热时效后强化相减少的弱化作用综合影响,使得冷挤压强化+热时效后疲劳寿命(8188周次)较原始状态寿命(7278周次)提高了12.5%。

The GH4169 alloy center hole plate samples were cold-expanded,and the effects of cold expansion and(600℃,500 h)thermal aging on the low-cycle fatigue performance under the conditions of 600℃,820 MPa,R=0.1,and triangular wave were studied.The results show that the median fatigue life estimation increases from 7278 cycles in the original state to 19536 cycles after cold expansion,representing an increase of about 2.5 times and indicating that the cold expansion process significantly improves the high-temperature fatigue life.While the thermal aging process is subjected,the fatigue life decreases from 7278 cycles to 4,717 cycles.The 35.8%reduction indicates that fatigue weakening has occurred after thermal aging.The reason for fatigue weakening is that thermal aging transforms theγ"strengthening phase toδphase,therefore the content of strengthening phase decreases while the number ofδphases increases and the morphology changes.Additionally after thermal aging,the original cold expansion surface residual compressive stress is reduced from−708 MPa to−483 MPa.The stable part of compressive residual stress profiles that still plays a role of strengthening,and the weakening effect of the reduction of the strengthening phase after thermal aging has a comprehensive effect,making the fatigue life of cold expansion and thermal aging(8188 cycles)increases by 12.5%compared to the original life(7278 cycles).