粉末高温合金等温成形模具升温热负荷分析

Analysis of Thermal Load of Dies for P/M Superalloy Isothermal Forming

通过建立粉末高温合金盘件等温成形模具的有限元分析模型,对Ni-11Co-17W-6Al-8Ta合金模具的升温参数进行了优化。研究结果表明,在升温速率0.1～0.5℃/s内,模具升温过程中表现出的应力峰值较低。升温过程中的阶段保温时间在2～4h,热应力缓失效果最佳,而当该时间大于4h时,热应力下降的后期速度显著降低,保温作用对应力的影响减小。在升温制度0.1℃/s,2h下有限元模拟的温度场和应力场结果显示,模具的外表面以及型面过渡区域出现应力集中现象,且应力-时间曲线显示该区域应力在升温过程中波动幅值较大。然而,1050℃和1100℃下的疲劳试验结果表明,以上区域的热负荷对裂纹扩展的影响较小。

The finite element models of dies used for P/M superalloy disk forming were established, and the heating parameters were optimized based on the thermal-physical property of Ni-11Co-17W-6A1-8Ta alloy. The results show that stress peaks of the dies were lower when they were heated in heating rate range from 0.1℃/s to 0.5℃/s. The effect of holding time on thermal stress decreased when holding time was larger than 4h. This leaded to that the rate of decreasing stress became lower. According stress amplitude-holding time curve, the optimal holding time is between 2-4h. Moreover, at the heating rate of 0. 1℃/s and the holding time of 2h, the outside surfaces and profile transition zones of dies exhibited stress concentration. The values of stress amplitudes were larger in these regions. However, the results of fatigue test at the temperatures of 1050℃ and 1100℃ show that the effect of thermal load on crack propagation in above-mentioned regions was slight.