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对Al-40%Cu(质量分数)过共晶合金在2、10和100μm/s速率下进行定向凝固实验,观察了不同速率下的组织形态,并分析造成组织形态差异是由于各相之间的竞争生长所致;采用X射线衍射技术对过共晶合金中Al_2Cu相进行宏观极图测试并计算其取向分布函数(ODF),同时采用EBSD技术对定向凝固样品进行微观取向测试。结果表明:当定向凝固速率为2μm/s时合金组织为全共晶组织(Al/Al_2Cu),其中的Al_2Cu相取向集中在(001)方向;随着凝固速率增加到10μm/s时,Al_2Cu相优先共晶相生长形成初生Al_2Cu相枝晶组织,具有小平面相生长特征,其取向主要集中在(001)方向;当凝固速率达到100μm/s时,Al_2Cu相枝晶为非小平面特征的复杂枝晶形貌,其取向集中在(100),(110)和(001)等方向;且Al_2Cu相枝晶沿着平行于定向凝固热流方向生长。XRD宏观取向结果表明,取向更为集中的定向凝固组织在相对较低的抽拉速率下可以得到很好地控制。
Directional solidification experiments were carried out on Al-40% Cu (mass fraction) hypereutectic alloys at 2, 10 and 100μm / s rates. The morphological changes at different rates were observed and the differences in microstructure were analyzed. The macro-polar diagram of Al 2 Cu phase in hypereutectic alloy was measured by X-ray diffraction and its orientation distribution function (ODF) was calculated. Meanwhile, the microstructural orientation of the samples was investigated by EBSD. The results show that when the solidification rate is 2μm / s, the microstructure is fully eutectic (Al / Al 2 Cu), and the Al 2 Cu phase orientation is concentrated in the direction of (001). With the solidification rate increasing to 10 μm / s, The primary eutectic phase grows to form primary Al 2 Cu phase dendrites, which have the characteristics of small plane facies growth and their orientations mainly in the (001) direction. When the solidification rate reaches 100 μm / s, the Al 2 Cu phase dendrite is a complex branch with non-faceted features (100), (110) and (001) directions. The dendritic Al 2 Cu phase grows parallel to the direction of the solidification heat flux. The results of XRD macro-orientation show that directional solidification with more concentrated orientation can be well controlled at relatively low drawing rates.