返回次数对一种钴基高温合金组织及冷热疲劳性能的影响

Effect of Revert Recycle Times on Microstructure and Thermal Fatigue Prop erties in Cobalt-Base Superalloy K640S

对铸造钴基高温合金K640S进行10次返回处理,研究了母合金和几种不同返回次数返回料的冷热疲劳性能,并进行了金相观察·结果表明:加热到815℃,然后水冷到25℃,保温5min,冷却5s,循环70次时,7返、10返合金首先出现微裂纹·随着循环次数的增加,返回料比新料疲劳裂纹生长快·循环200次时,无论新料还是返回料裂纹长度都达到2mm·随着返回次数的增加,合金中气体及夹杂物质量分数随之增加,枝晶组织越来越发达·

Microstructure and thermal fatigue mechanical properties of cast cobalt-base su peralloy K640S were investigated during a number of recycles. The results show t hat microcracks appear on the specimens after seven materials recycles and ten r ecycles respectively under the conditions of thermal cycle 70 times at 815?℃ f or 5 minutes then water-cooled down to 25?℃ for 5 seconds. With the increasin g of thermal fatigue cycles,the crack in recycled specimen grows faster than in virgin specimen. When the thermal cycle times reach 200, the crack length of bo th virgin and recycled specimens is as long as 2?mm. The microstructure of the alloy consists of γ-cooled metal matrix and black carbides distributed bet ween dendrite and grain boundary. The skeleton-like carbides are M23C6, and the lamellar-like ones are M7C3. The M23C6 carbides and γ matrix construct lamellar eutectic pattern alternately. With the times of cycle s increasing,it is found that the content of impurity and gas in the alloy are i ncreased,however,there is no obvious change for dendrite structure.