定向凝固镍基高温合金CM247LC热处理工艺优化及持久性能研究

Heat Treatment Optimization and Stress Repture Properties of Directionally Solidified Ni-based Superalloy CM247LC

目的研究定向凝固镍基高温合金CM247LC的最优热处理工艺制度,通过优化热处理工艺提高合金的力学性能。方法分别用JMatPro热力学分析软件和金相法判断CM247LC合金的初熔温度点,并确定合金的热处理窗口温度;利用光学显微镜(OM)和能谱分析仪(EDS)观察合金经不同固溶处理后的微观组织和元素偏析情况;利用扫描电子显微镜(SEM)观察合金经不同时效处理及持久断裂后的微观组织形貌。结果CM247LC合金的初熔温度为1260℃,热处理窗口温度为1215-1255℃。根据热处理窗口温度,设计了6种固溶处理工艺,对比发现,经1228℃/2 h+1240℃/2 h+1255℃/2 h、AC固溶工艺处理后,合金的组织均匀化程度最高,元素偏析得到了显著改善,γ/γ′共晶的体积分数从铸态时的18.9%降至5.04%,确定此工艺为合金优化固溶处理工艺参数。合金经优化固溶处理后再经1080℃/4 h、AC高温时效处理和870℃/22 h、AC中温时效处理,析出的γ′相尺寸(337.3 nm)、体积分数(67.81%)适宜且立方度最高,确定此工艺为最优热处理工艺。经最优热处理工艺处理的合金在980℃/205 MPa下的持久寿命为162 h,相比于铸态和固溶态处理的合金持久寿命分别提高了87 h和45 h。结论通过优化固溶处理和时效处理,确定合金最优热处理工艺参数为:1228℃/2 h+1240℃/2 h+1255℃/2 h、AC(固溶处理)+1080℃/4 h、AC+870℃/22 h、AC(时效处理),经最优热处理工艺处理的合金持久寿命显著提高。

The work aims to study the optimal heat treatment process of directionally solidified nickel base superalloy CM247LC,and improve the mechanical properties of the alloy by optimizing the heat treatment process.The initial melting temperature point of CM247LC alloy was determined by JMatPro thermodynamic analysis software and the metallographic method,and the heat treatment temperature window of the alloy was determined.An optical microscope(OM)and an energy dispersive spectrometer(EDS)were used to observe the microstructure and element segregation of the alloys after different so-lution treatments.A scanning electron microscope(SEM)was used to observe the microstructure of the alloy after different ag-ing treatment and the microstructure after long fracture.The initial melting temperature of CM247LC alloy was 1260℃,and the heat treatment window temperature was 1215-1255℃.According to the heat treatment window te mperature,six solution treatments were designed.It was found that after AC solution treatment at 1228℃ for 2 h+1240℃ for 2 h+1255℃ for 2 h,the microstructure homogenization of the alloy was the highest,and the element segregation was significantly improved.The content of γ/γ'eutectic decreased from 18.9%to 5.04%(volume fraction)in the cast state,which indicated that this process was an optimal solution processing parameter for alloy.After the optimized solution treatment,the alloy underwent AC high tem-perature aging treatment at 1080℃ for 4 h,and AC medium temperature aging treatment at 870℃ for 22 h.The precipitation of γ'phase size(337.3 nm)and volume fraction(67.81%)were suitable and the cubed degree was the highest,which determined that this process was the optimal heat treatment process.The stress-repture life of the alloy after the optimal heat treatment was 162 h at 980℃/205 MPa,which was 87 h and 45 h respectively higher than that of the alloy after the cast and solution treatment.Based on the optimization of solution treatment and aging treatment,the optimal heat treatment process parameters of the alloy are determined as follows:1228℃/2h+1240℃/2h+1255℃/2h,AC(solution treatment)+1080℃/4h,AC+870℃/22h,AC(aging treatment),the stress-repture life of the alloy treated by the optimal heat treatment process is significantly improved.