The Creep-Oxidation Crack Growth Behavior Of Nickel-Based Alloy

Aiming at the problem of creep-oxidation crack growth of nickel base alloy under high temperature environment,based on the mechanism of environmental oxidation damage,the law of creep-oxidation crack growth in nickel-based alloy was studied by finite element simulation and experiment.The main work and conclusions are as follows:(1)Based on damage mechanics,the ductile depletion model was used to describe creep damage;the oxygen diffusion simulation is realized through the stress accelerated oxygen diffusion model,and the effect of diffusion oxidation on the critical strain is incorporated into the creep damage equation to obtain creep-oxidation crack growth damage model.(2)Based on the mechanism of dynamic embrittlement damage,assuming that oxides are not generated during crack growth,the law of creep-oxidation crack growth was studied.It was found that creep oxidation cracks growth along the grain boundary with additional crack branches;the crack initiation time of different crack growth paths decreases rapidly with the increase of load and oxygen diffusion rate,and the difference of crack initiation time of different paths also decreases rapidly with the increase of load.(3)Based on the mechanism of stress-accelerated grain boundary oxidation damage,assuming that oxides existed at the crack tip and will not break,the oxide expansion model was established using the metal oxidation kinetics,and the effect of crack tip oxide on crack growth was studied.The results show that the oxide at the crack tip will accelerate the crack growth;the larger the oxide size and expansion rate,the shorter the crack initiation time,but the oxide size has less effect on the crack initiation time.(4)Using IN783 alloy,the effects of different loads and temperatures on creep-oxidation crack growth were studied,the crack growth mechanism was analyzed,and compared with the numerical simulation analysis results.It was found that the crack growths along the grain boundary,which was the same as the simulated crack;the crack initiation time decreases with increasing load and temperature;when the load is large,oxide was not observed at the crack tip,the crack growth mechanism is the dynamic embrittlement;when the load is small,there was an obvious oxide layer at the crack tip and crack front,oxide cracking promotes crack growth,and the crack growth is dominated by stress-accelerated grain boundary oxidation damage.In addition,it was found that the crack growth of IN783 alloy has a significant size effect,the thicker the sample,the faster the crack growth rate.