DD494合金叶片返回料的热处理

Heat treatment for recycled material of DD494 alloy turbine blade

研究了3种热处理工艺对DD494合金叶片返回料组织、持久性能及断裂模式的影响。通过金相观察法确定合金的初熔温度,采用扫描电镜(SEM)分析了不同固溶处理温度对合金γ/γ′共晶溶解程度及γ′相形貌的影响,以及不同一级时效处理温度对γ′相尺寸及分布的影响。结果表明,合金的初熔温度在1310~1315℃之间。经1300℃×4 h固溶处理并空冷后,合金中γ/γ′共晶数量较1290℃×4 h固溶处理后有所降低,且γ′相更为细小。较单步固溶处理而言,分段固溶处理工艺能降低合金中的共晶含量。一级时效处理温度由1080℃升高到1140℃,析出的γ′相有所长大,同时在γ基体中观察到大量细小二次γ′相。合金的最佳热处理工艺为分段固溶+高温一级时效+二级时效,即1280℃×1 h+1290℃×2 h+1300℃×6 h,AC+1140℃×3 h,AC+870℃×20 h,AC,该工艺下的合金平均持久寿命达到175.05 h,较经单步固溶+低温一级时效+二级时效处理的试样平均持久寿命提高一倍以上。

Effect of three types heat treatment processes on the microstructure,creep rupture properties and fracture mechanism of recycled material of the DD494 alloy turbine blade was studied.The initial melting temperature of the alloy was determined by metallographic observation.The effect of solution treatment temperature on the dissolution ofγ/γ′eutectic andγ′phase morphology,and the effect of first aging heat treatment temperature on the size,quantity and distribution ofγ′phase were analyzed by using scanning electron microscope(SEM).The results show that the initial melting temperature of the alloy is between 1310℃and 1315℃.After heat treatment at 1300℃for 4 h followed by air cooling,the number ofγ/γ′eutectic and the size ofγ′phase are decreased compared to that of 1290℃for 4 h followed by air cooling.Compared to single step solution,segmented solution treatment can reduce the eutectic content in the alloy.It is found that the higher first aging heat treatment temperature(1140℃compared with 1080℃)causes the growth of primaryγ′phase and a large amount of fine secondary particlesγ′precipitated in theγmatrix.The optimal heat treatment process for the alloy is segmented solution treatment+high temperature first aging+secondary aging,i.e.1280℃×1 h+1290℃×2 h+1300℃×6 h,AC+1140℃×3 h,AC+870℃×20 h,AC.The average creep rupture life of the alloy treated with the optimal process is 175.05 h,which is more than twice that of the specimen treated with“single step solution+low temperature first aging+secondary aging”.