The evolution of slipbands into fatigue cracks in surface grains of commercially pure Ni, in wt pct), was studied at ambient temperature. Round-bar specimens with electropolished surfaces were fatigued under displacement-controlled, fully reversed conditions at four strain amplitudes under a nominal strain rate of 1 9 10 À3 s À1 . Low-cycle fatigue tests were periodically interrupted to characterize the slip morphology at various fatigue cycles using scanning electron microscopy. The results showed that the distribution of slip in Ni200 varied considerably in individual surface grains at a given strain amplitude. Some grains were deformed more severely and exhibited more intense slipbands than others, while some surface grains showed the absence of slip lines with no evidence of plastic deformation. The evolutions of slipband width and spacing in deformed surface grains were followed as a function of fatigue cycles in order to assess the slipband morphology at the onset of fatigue crack initiation.

The material constants calculation models for hyperbolic-sine creep model were proposed. The material constants used in hyperbolic-sine creep model for 316 stainless steel were calculated due to the models proposed and experimental data in the temperature range from 873K to 1023K. The relationships between material constants of 316 stainless steel creep model and temperature were obtained by curve fitting. The creep rate predict model of 316 stainless steel with only stress and temperature was also developed, the creep rates predicted were in good agreement with experimental data.

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Stress and strain at the crack tip are main mechanical parameters which estimate the stress corrosion cracking rate in metals, and the creep of metals in high temperature and high pressure environment will lead to the redistribution of stress and strain nearby the crack tip. The effects of creep on stress and strain nearby the crack tip are discussed by using 1T-CT specimen and finite element method in this study. The investigated results indicate that both increasing of temperature and stress intensity factor would induce the equivalent creep strain increases at the crack tip.