Co基耐熱合金HA-188の高温低サイクル疲労破面

概要

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The modes of crack initiation and propagation of low cycle fatigue at high temperature were studied on HA-188 cobalt base alloy by means of scanning electron microscopy. Low cycle fatigue tests were carried out at 700℃ in the strain rate range of 3 x 10^<-5> to 2 x l0^<-2>sec^<-1>. In the high strain rate region, crack initiation occured at twin boundaries, and crack propagation was trans-granular. In the middle strain rate region, crack initiation occured at grain boundaries, and the mode of crack propagation was a mixture of intergranular and transgranular. Striations were observed on all transgranular fracture surfaces at high and middle strain rates. In the low strain rate region, both crack initiation and propagation were entirely intergranular. The strain rate being lower than 6.5 x 10^<-5>sec^<-1>, where crack initiation and propagation were entirely intergranular, the fatigue life was constant at any strain rate, that is, the fatigue behavior was time dependent. The cause of intergranular crack propagation was discussed.
社団法人日本材料学会の論文
1978-01-15