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采用冷坩埚定向凝固技术制备了定向柱状晶的Ti-47Al-2Cr-2Nb合金铸锭,在改变抽拉速率的情况下,所获得的铸锭具有不同片层间距的全片层组织.通过拉伸性能实验,测得其室温极限抗拉强度最高达到652 MPa,伸长率最大达到1.5%,而高温极限抗拉强度最高达到490 MPa,伸长率最大达到5.0%.通过高周疲劳性能实验,绘制了抽拉速率分别为1.0和1.2 mm/min时定向凝固合金的应力-循环次数(S-N)曲线以及应力比R为0.1时的疲劳极限值.对比断口形貌分析表明,室温时试样拉伸断裂方式为脆性断裂,而经高周疲劳实验后断裂方式为脆性解理断裂;高温时试样拉伸断裂方式则为大部分脆性断裂与少部分延性断裂并存.对高周疲劳试样断口的分析表明,疲劳裂纹在相界面和B2相附近萌生,据此基于塑性钝化理论分析了其裂纹扩展机制,并绘制了高周疲劳裂纹扩展模式图.
The oriented columnar Ti-47Al-2Cr-2Nb alloy ingot was prepared by cold crucible directional solidification technique, and the obtained ingot had the whole layer structure with different lamellar spacing under the condition of changing the drawing speed. Elongation at room temperature, the ultimate tensile strength at room temperature is up to 652 MPa, the elongation reaches up to 1.5%, while the ultimate tensile strength at high temperature reaches 490 MPa and the elongation reaches up to 5.0% .Through high cycle fatigue test , The stress-cycle times (SN) curves of the directional solidification alloy at the pullout rates of 1.0 and 1.2 mm / min, and the fatigue limit values of the stress ratio R at 0.1 were plotted.Comparison of the fracture surface morphologies showed that at room temperature, The tensile fracture mode is brittle fracture, while the fracture mode is brittle cleavage fracture after high-cycle fatigue test. The tensile fracture mode of the specimen at high temperature is the coexistence of most brittle fracture and a small part of ductile fracture. Fracture analysis shows that the fatigue crack initiation occurs at the phase interface and in the vicinity of the B2 phase. Based on the plastic passivation theory, the crack propagation mechanism is analyzed and the crack growth pattern of the high-cycle fatigue crack is plotted.