K40S钴基高温合金的高温低周疲劳行为 Ⅱ.疲劳断口分析

LOW CYCLE FATIGUE BEHAVIOR OF K40S COBALT- BASE SUPERALLOY AT ELEVATED TEMPERATURE II. Fatigue Fractography

研究了K40S钴基高温合金在700℃和900℃温度条件下由应变控制的高温低周疲劳行为,对疲劳断口形貌进行观察,结果表明:在高温低周疲劳加载条件下,K40S合金疲劳裂纹萌生机制为表面滑移带开裂与表面碳化物相界面开裂的综合作用;疲劳裂纹萌生与扩展方式为穿晶型,瞬断区呈现枝晶断裂特征;碳化物可作为障碍,阻碍疲劳裂纹的扩展,且为主要的二次裂纹策源地;K40S合金高温低周疲劳断裂为机械疲劳与高温环境氧化共同作用的结果.

High temperature low cycle fatigue fracture behavior of K40S cobalt-base superalloy at 700℃ and 900℃ in ambient atmosphere has been investigated under fully reversed total strain-controlled mode. The results show that the fatigue crack initiation is frequently associated with the slip bands and the carbides at the specimen surfaces. The fatigue cracks initiate and propagate both in a transgranular manner for all the total strain amplitudes under consideration. Both the transgranular crack initiation and propagation are accelerated by high temperature oxidation. The well-distributed carbide particles are the second crack initiation sites. The second crack initiation relaxes the stress concentration at the crack tip, reducing the driving force of crack propagation. High temperature low cycle fatigue failure of K40S alloy results from the interaction of the mechanical fatigue and environmental oxidation.