材料期刊网

本文研究了GH133合金的循环应力应变反应和低周疲劳性能,并作了位错结构观察.通过对比拉压对称(R=-1)试验和恒定最大正应变(ε_(max)=C)试验,证明平均拉应力起降低寿命的作用.位错结构观察证明,循环使共格γ质点的相界处产生应力场,最终导致位错的萌生和运动,位错运动又进一步增殖位错.位错运动方式是变化的,由成对切割γ′质点到单位错切割γ′质点和位错绕过γ′质点,滑移带位错结构最终可以出现饱和的梯状结构.晶界和双晶界附近位错密度高,具有位错胞结构,同时可以出现沿晶界或双晶界裂纹.

The cyclic stress-strain response and microstructure were studied on LCF speci-mens of 15Cr-27Ni-1.8Ti-Fe alloy.The strain control LCF tests were performedat 600℃ under two different wave shapes:R=-1 and fixed ε_(max).Comparingthe results of these tests,the detrimental effect of average tensile stress was prov-ed.This was concerned with the influence of tensile stress on the movements ofdislocations and the formation of cracks.The observations of dislocation structure indicated that during the cyclingboth mechanisms caused cyclic hardening and cyclic softening were taking place.Cyclic strain led to generate the stress field at the interface of γ and γ′phasesfirst.As a result of increasing stress field the dislocations were created.The densi-ty of dislocation was further increased by the movement of dislocations themself.The interactions between dislocations and γ′particles degenerated from pair disloca-tion cutting γ′particles to single dislocation cutting γ′particles.It led to formmore faults and ABP's,and the γ′particles became propressively harder to shearand ultimately led to dislocations looping around particles.A typical dislocation structure of persistant slip band,ladder-like structure,wasseen as a saturated dislocation structure in the slip band,and the more ladder-likestructure formed,the more cyclic softening happened.The slip band extends to grain boundaries and twin boundaries.The grain disloca-tion interacted with boundaries,and led to complex boundary dislocation struc-ture.The density of dislocation near grain boundaries and twin boundaries wasmuch higher than others since the boundaries can acted as the barrier and disloca-tion generator.This would cause to form grain boundary cracks and twin boun-dary cracks.