铸造镍基高温合金M963的高温低周疲劳行为

LOW CYCLE FATIGUE BEHAVIOR OF A CAST NICKEL BASE SUPERALLOY M963 AT ELEVATED TEMPERATURE

对铸造镍基高温合金M963在900℃下的低周疲劳行为进行了研究,实验采取轴向总应变控制,应变速率分别为4×10^(-3)s^(-1)和1×10^(-4)s^(-1)．结果表明:在相同的总应变幅下,合金在低应变速率下具有较低的寿命,这归因于与时间相关的机制如氧化的损伤作用．疲劳断面以及纵向剖面的SEM分析表明,疲劳裂纹通常萌生于试样表面或亚表面的碳化物或铸造缺陷处．而当应变速率较低时,某些裂纹会在试样表面的枝晶间区域萌生．两种应变速率下疲劳裂纹开裂均呈穿晶形式．

Low cycle fatigue tests for cast nickel base superalloy M963 have been conducted at 900 ℃ in air under fully reversed total strain control cycling at strain rates of 4×10^-3 s^-1 and 1×10^-4 s^-1. The experimental results showed that at the same strain amplitude, fatigue life at low strain rate was shorter than that at high strain rate, which is attributed to time dependent damage mechanism such as oxidation. SEM observation revealed that the cracks initiated at the surface-connected carbides and/or casting micropores at subsurface. When the strain rate was lower, some of the cracks tended to initiate at interdendritic regions and then propagate along interdendritic regions. In all tests, the cracking mode was transgranular.