By using optical microscopy(OM),scanning electron microscopy(SEM),X-ray energy dispersive spectroscopy(EDS),and multi-phase separation technology,a research was conducted on the precipitates along grain boundary of HT700T alloy tubes after thermal exposure.Results show that,the precipitates along grain boundary under etching condition appear as flocculent clusters,which are significantly different from precipitates within grain.The precipitates along grain boundary has already appeared after thermal exposure at 500℃,while the quantity of precipitates increases with an increase of temperature,reaching a peak value at around 750℃,and then gradually decreases until completely dissolving and disappearing at 1 000℃.The precipitates along grain boundary are composed of Cr-rich phase,γ′ phase,and γ matrix phase,and the volume fraction of γ′ phase in grain boundary micro region is higher than that within grain.Through observing different regions in the creep rupture specimen at a high temperature of 700℃,no evidence has been found that the precipitates along grain boundary promote the creep cracking of sample,but the stress has a certain effect on promoting the precipitation along grain boundary.
维普
万方数据