950℃长期热暴露对DD476镍基单晶高温合金组织的影响

Effect of long term thermal exposures at 950℃ on microstructure of DD476 single crystal Ni-base superalloy

通过螺旋选晶法制备了DD476第4代镍基单晶高温合金试棒。经过完全热处理的样品,在950℃下分别保温10、50、100、200、500、1000、2000 h后,通过光学显微镜和扫描电镜对合金的枝晶形貌、微孔及γ′相随时间的演化行为进行观察。结果表明,随着热暴露时间的增加,试样中显微孔洞的数量和大小也随之增加,2000 h后孔洞面积分数(0.62%)约为标准热处理后(0.32%)的2倍;γ′相在热暴露过程中前100 h的变化并不明显,平均尺寸在0.4μm左右,100 h后尺寸呈指数增长最大至1.67μm,但是由于Re元素的加入仅出现轻微的筏排化,整体保持立方状。合金经过950℃,2000 h处理后合金组织稳定,未观察到TCP相析出。

Test bars of a 4th generation nickel based single crystal superalloy DD476 were produced using spiral grain selection method.After solution and subsequent aging heat treatment,the test bars were exposed at 950°C for 10-2000 h.The evolution behaviors of the dendritic morphology,micro-pores and'phase of the alloy with aging time were observed by OM and SEM.The results show that the number and the size of micro-pores in the specimens increase with thermal exposure time,and the pore content(0.62%)after 2000 h is about twice as much as that after standard heat treatment(0.32%).Within the first 100h of thermal exposure,the size of γ'(average size around 0.4μm)only has a very slight change.However,after 10o h of thermal exposure,the pore size dramatically increases to a maximum of 1.67μm.The γ' morphologies with moderate rafts are mainly in cubic shape and no TCP phases are observed after long term thermal exposures at 950℃ for 2000 h.