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在2050℃的熔体温度下,在自行研制的定向凝固炉内实现了Nb-Ti-Si-Cr-Hf-Al-B-Y超高温合金的有坩埚整体定向凝固.采用XRD,SEM,EDS等方法分析了凝固速率分别为2.5,5,10,20,50和100μm/s时的整体定向凝固组织、组成相的择优取向及固/液界面形貌,并讨论了其共晶生长机制.结果表明:合金的定向凝固组织主要由沿着试棒轴向排列的横截面为多边形的柱状初生(Nb,X)_5Si_3(X=Ti,Hf,Cr)相与耦合生长的层片状Nbss/(Nb,X)_5Si_3共晶团(Nbss表示铌基固溶体)组成.横截面上共晶胞界明显.当凝固速率由2.5μm/s变化到100μm/s时,定向凝固组织细化,固/液界面经历粗胞状→细胞状→胞枝的演化过程.Nbss/(Nb,X)_5Si_3共晶两相较低的熔化熵及其前沿较大的动力学过冷度是形成规则共晶的主要原因.
The directional solidification of the crucible in Nb-Ti-Si-Cr-Hf-Al-BY superalloy was carried out in a self-developed directional solidification furnace at a melt temperature of 2050 ℃. XRD, SEM, EDS and other methods The global solidification microstructure, the preferred orientation of the composition phase and the morphology of the solid / liquid interface at the solidification rates of 2.5, 5, 10, 20, 50 and 100 μm / s were analyzed and their eutectic growth mechanisms were discussed. : The directional solidification microstructure of the alloy is mainly composed of the Nb (Nb, X) 5Si_3 (X = Ti, Hf, Cr) phase and the coextensive lamellar Nbss / (Nb , X) _5Si_3 eutectic group (Nbss represents niobium-based solid solution) .The eutectic boundary of the cross-section is obvious.When the solidification rate changes from 2.5μm / s to 100μm / s, the directional solidification microstructure is refined and the solid / liquid interface Under the condition of cell-like cell → cell-branch, the lower melting entropy of Nb / (Nb, X) _5Si_3 eutectic and the kinetic undercooling of its frontier are the main reasons for the formation of regular eutectic.