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通过调整铸造工艺参数,研究了K4648合金的组织结构与工艺参数变化之间的关系,进而获得铸造工艺对热疲劳性能的影响规律。对合金经90020℃循环条件下热疲劳试验后的试样表面形貌进行观察分析,研究了晶粒尺寸及晶界结构对合金热疲劳性能的作用机制。研究结果表明:随着浇注温度的升高,合金的晶粒平均尺寸增大,而模壳温度的提高对合金的晶粒尺寸影响不大,采用沙箱+保温棉造型方式可细化合金晶粒。热疲劳主裂纹从V形缺口处萌生,裂纹以穿晶模式扩展。通过调整浇注工艺细化晶粒,并使得晶界结构呈锯齿态,可降低裂纹扩展速率,提升合金的热疲劳性能。
By adjusting the casting process parameters, the relationship between the microstructure and the change of process parameters of K4648 alloy was studied, and the influence of the casting process on the thermal fatigue properties was also obtained. The surface morphology of the sample after thermal fatigue test at 900 ℃ and 20 ℃ was observed and analyzed. The mechanism of the effect of grain size and grain boundary structure on the thermal fatigue properties of the alloy was investigated. The results show that as the pouring temperature increases, the average grain size of the alloy increases, while the increase of the shell temperature has little effect on the grain size of the alloy. The sandbox + insulation cotton can be used to refine the alloy crystal grain. The main thermal fatigue crack initiation from the V-shaped notch, crack propagation in the transgranular mode. By adjusting the casting process to refine the grains and make the grain boundary structure serrated, the crack growth rate can be reduced and the thermal fatigue performance of the alloy can be improved.