Analysis of Fatigue/Creep Crack Propagations Rates and a-N Curves of GH864 Alloy

Abstract:

The crack propagation behavior of GH864 alloy was studied at 650 oC under fatigue/creep interaction with different dwell time; the effects of creep and oxidation and the meaning of transition point were analyzed in da-dN and a-N curves. The results indicate that the crack growth rate under dwell 90 s is higher than that under dwell 5 s. The alloy is mainly trans-granular fracture under dwell 5 s and the fatigue effect is principle. The alloy is mainly inter-granular fracture under dwell 90 s and the creep effect is dominant. The crack propagation rate curves of fatigue/creep interaction at 650 oC could well be described by Saxena model under the condition of this test. The descriptions could estimate the crack growth rates at lower and higher stress intensity factors. In addition, the expressions of different alloys from Saxena could contrast the effects of fatigue and creep as well as their proportion. At last, the transition points of a-Ni/Nf, da/dN-a and da/dN-N curves were obtained and the meaning of these points was analyzed with fracture analysis. The curve analysis method can also be used for the crack propagation rate curves of superalloys and other materials.

Key words:GH864 alloy; crack growth rate curve; a-N curve; fracture analysis; creep; fatigue