DD32单晶组织对电子束浮区熔炼技术定向凝固的响应

Response of Microstructure of DD32 Single Crystal to Electron Beam Floating Zone Melting Directional Solidification

采用电子束浮区熔炼技术对快速凝固法 (HRS)制备的DD32单晶进行了重熔定向凝固处理 ,对在不同扫描速率下处理的DD32单晶重熔定向凝固组织进行了深入观察分析。结果表明 ,固液界面温度梯度是电子束扫描速率的函数 ,当电子束扫描速率为 0 2mm/min时 ,固液界面的温度梯度≥ 1 0 0 0K/cm。DD32合金较高的溶质含量及相对较高的扫描速率导致成分过冷而使单晶难于形成。当电子束扫描速率大于一定数值时 ,重熔后的定向凝固组织内可以观察到细晶和粗晶两种柱状晶区 ;

DD32 single crystal samples, which were prepared by HRS method, were remolten and directionally solidified with electron beam floating zone technology. The microstructures remolten and directionally solidified with difference electron beam scan rate were observed and analyzed deeply. The results show that solid-liquid interface temperature gradient is a function of electron beam scanning rate. When the scanning rate is 0.2 mm/min, solid-liquid interface temperature gradient is greater than or equal 1000 K/cm. High solute contents of DD32 alloy and relatively high scan rates tend to lead to constitutional overcooling and prevent the formation of single crystals. When electron beam scanning rate is greater than certain value, two fine and wide directional columnar crystals regions can be observed in remolten DD32 directional solidification microstructure. Transformation of remelting zone shape and intense convection are the main reasons why distribution of temperature as well as solute fields is asymmetry.