Effects of Withdrawal Rate on the Microstructure of Directionally Solidified GH4720Li Superalloys
Effects of Withdrawal Rate on the Microstructure of Directionally Solidified GH4720Li Superalloys
复制标题
退刀率对定向凝固GH4720Li高温合金显微组织的影响
作者：
Jinglong Qu;Shufeng Yang;Zhengyang Chen;Jingshe Li;Anping Dong;Yu Gu
随着GH4720Li合金铸锭尺寸的增大，其组织难以控制，而拉坯速度是控制和细化GH4720Li合金组织的重要因素。本研究采用Bridgman型定向凝固技术制备了具有不同抽拉速率的GH4720Li高温合金样品。用光学显微镜、Photoshop、Image Pro Plus、场发射扫描电子显微镜和电子探针分析了定向凝固过程中稳定生长区枝晶的形态和平均尺寸、γ‘相的形态和平均尺寸以及各合金元素的微观偏析。提高抽拉速率有助于细化高温合金组织，二次枝晶平均间距从133µm减小到79µm，而枝晶臂和枝晶间区γ‘相的平均尺寸分别从1·02和2·15µm减小到0·69和1·26µm。此外，γ的相分布变得更加均匀。Al、Ti、Cr和Co的微观偏析随拉拔速率的增加而减小，在较高的拉拔速率下，Al、Cr和Co的偏析系数接近1，而Ti的偏析系数在所有的拉拔速率下都保持在2.2以上。
Increasing the ingot size of GH4720Li superalloys makes it difficult to control their microstructure, and the withdrawal rate is an important factor in controlling and refining the microstructure of GH4720Li superalloys. In this study, GH4720Li superalloy samples were prepared via Bridgman-type directional solidification with different withdrawal rates. The morphology and average size of the dendrites in the stable growth zone during directional solidification in each sample, morphology and average size of the γ’ phases, and microsegregation of each alloying element were analyzed using optical microscopy, Photoshop, Image Pro Plus, field emission scanning electron microscopy, and electron probe microanalysis. Increasing the withdrawal rate significantly helped in refining the superalloy microstructure; the average secondary dendrite arm spacing decreased from 133 to 79 µm, whereas the average sizes of the γ’ phases in the dendrite arms and the interdendritic regions decreased from 1.02 and 2.15 µm to 0.69 and 1.26 µm, respectively. Moreover, the γ’ phase distribution became more uniform. The microsegregation of Al, Ti, Cr, and Co decreased with the increase in the withdrawal rate; the segregation coefficients of Al, Cr, and Co approached 1 at higher withdrawal rates, whereas that of Ti remained above 2.2 at all the withdrawal rates.