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采用真空自耗电弧熔炼法制备了Nb-Ti-Si基超高温合金的母合金锭,在2050℃的熔体温度下实现了合金的有坩埚整体定向凝固。测定了电弧熔炼态与定向凝固试样的室温条件断裂韧性,采用SEM,EDS等方法分析了凝固速率V分别为10,20和50μm/s的整体定向凝固组织、单边切口梁弯曲试样的断口形貌及裂纹扩展路径,并讨论了其断裂机理。结果表明:合金的整体定向凝固组织主要由沿着试棒轴向挺直排列的横截面为多边形的初生(Nb,X)5Si3(X代表Ti,Hf和Cr元素)棒与耦合生长的层片状Nbss/(Nb,X)5Si3共晶团(Nbss表示铌基固溶体)组成。整体定向凝固显著提高合金的室温条件断裂韧性KQ,且V=50μm/s时的KQ最高,达16.1MPa·m1/2,较电弧熔炼态试样的KQ提高了50.5%。定向凝固试样中Nbss与(Nb,X)5Si3沿垂直于受力方向的定向排列以及粗糙的Nbss产生的裂纹桥接和偏转,增大了裂纹扩展阻力,从而提高了合金的室温条件断裂韧性。
The master alloy ingot of Nb-Ti-Si-based superalloy was prepared by vacuum consumable arc melting method, and the solidification of the crucible was realized at the melt temperature of 2050 ℃. The fracture toughness of the specimens were measured at room temperature under the conditions of arc melting and directional solidification. The solidified microstructures were analyzed by SEM and EDS. The specimens with unidirectional notched beams Fracture morphology and crack propagation path, and discussed the fracture mechanism. The results show that the solidified microstructures of the alloy are mainly consisted of polygonal primary (Nb, X) 5Si3 (X stands for Ti, Hf and Cr elements) rods and coupled growth plies Like Nbss / (Nb, X) 5Si3 eutectic group (Nbss represents a niobium-based solid solution). The overall directional solidification significantly improves the room temperature KQ fracture toughness, and the highest KQ is 16.1MPa · m1 / 2 at V = 50μm / s, which is 50.5% higher than the KQ of the arc melting state sample. The directional bridging and deflection of Nbss and (Nb, X) 5Si3 in the directionally oriented solidification direction and coarse Nbss cracks in the directionally solidified sample increase the crack propagation resistance and improve the room temperature fracture toughness of the alloy.