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.
The relationship between the microstructure and casting process was investigated by adjusting the related parameters,to obtain effects of casting process on microstructure and thermal fatigue properties of K4648 alloy.The surface morphology of the alloy after thermal fatigue test at temperature range from 20 ℃ to 900 ℃ was observed,and the influence mechanisms of grain size and boundary structure on thermal fatigue property of the alloy were analyzed.The results show that average grain size increases with the increasing the pouring temperature.However,the shell temperature has no obvious effect on the grain size.So,the grain can be refined by means of modeling procedure combined with sandbox and thermal insulation cotton.The main thermal fatigue crack initiates from the V-shape notch and propogated in a transgranular mode.The grain size can be refined and the serrated grain boundary can be obtained by optimized casting process,which can thus reduce the crack growth rate and improve the thermal fatigue property.
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