DD6单晶合金涡轮转子叶片裂纹与内腔等轴晶成因研究

Study on the Crack and the Origin of Inner Cavity Equiaxed Crystal in DD6 Single Crystal Alloy Turbine Rotor Blade

为排除某航空发动机DD6单晶合金涡轮转子叶片振动试验过程中出现异常裂纹的故障,开展了裂纹外观检查、断口宏观和微观形貌分析、表面检查、解剖分析、显微组织检查、成分分析及应力分布计算等工作,对故障叶片失效原因及内腔局部区域的等轴晶成因和机理进行研究。结果表明:DD6单晶合金涡轮转子叶片裂纹性质为高周疲劳,裂纹过早萌生与叶片内腔存在等轴晶有直接关系,且附近存在无枝晶的异常组织也促进了疲劳裂纹的萌生及扩展。同时,等轴晶在叶片使用之前已存在,是由于内腔工艺孔处的高温合金焊料遗留,高温真空焊接时形成易形核质点。建议加强对叶片内腔生产质量的控制,并对叶片内腔工艺孔附近危险部位进行严格检查,避免此类故障再次发生。

In order to eliminate the malfunction of abnormal crack in the vibration test of turbine rotor blade of DD6 single crystalalloy in an aeroengine,crack appearance inspection,macroscopic and microscopic morphology analysis of fracture,surface inspection,anatomical analysis,microstructure examination,component analysis and stress distribution calculation were carried out. The reason of bladefailure and the origin and mechanism of equiaxial crystal in the local area of the inner cavity were studied. The results show that the crackproperty of turbine rotor blade of the DD6 single crystal alloy is high cycle fatigue. The premature initiation of crack is directly related to theexistence of equiaxed crystal in the inner cavity of the blade,and the abnormal structure without dendrites in the vicinity also promotes theinitiation and propagation of fatigue crack. At the same time,the equiaxed crystal already exists before the blade is used,due to the residualsuperalloy solder at the technological hole in the inner cavity and the free-form nucleation particle equiaxed crystal is formed during thehigh-temperature vacuum welding. It is suggested that the quality control of blade inner cavity should be strengthened,and the dangerousposition near the technological hole of blade inner cavity should be strictly checked to avoid the recurrence of this kind of malfunction.