Effect of hot forging on microstructure and mechanical properties of near α titanium alloy/TiB composites produced by casting
Effect of hot forging on microstructure and mechanical properties of near α titanium alloy/TiB composites produced by casting
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DOI：
10.1016/j.jallcom.2017.06.287
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发表时间：
2017-11
影响因子：
6.2
通讯作者：
R. Gaisin;V. Imayev;R. Imayev
中科院分区：
文献类型：
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作者：
R. Gaisin;V. Imayev;R. Imayev
采用铸造工艺，以近α钛合金VT18U （Ti-6.8 al - 4zr -2.5 sn - 1nb -0.7 mo -0.15 si）为基体材料制备了原位Ti/TiB不连续增强复合材料。硼的添加量为1.2 wt.%，对应于6.5体积%的TiB，对于该基体材料是最优的。为了获得高长径比轴向排列的TiB晶须和最耐蠕变的基体组织，采用等温二维热锻，先在β温度范围退火，再在α+β温度范围退火。新型VT18U/TiB复合材料的力学性能是在平行于TiB晶须主导取向的拉伸下建立的。在进行拉伸试验的同时，进行了蠕变试验，并将蠕变曲线与经过相同锻造和热处理的基体合金进行了比较。与基体合金相比，具有排列TiB晶须的复合材料表现出明显更高的强度和抗蠕变性能，但塑性没有明显降低。断裂行为的SEM研究表明，当温度达到600 ~ 700℃时，VT18U/TiB复合材料基体与TiB晶须之间的界面边界仍保持较高的粘附强度。室温和高温下复合材料的主要破坏机制是TiB晶须断裂和基体的延性破坏。
In situ Ti/TiB discontinuously reinforced composites were fabricated using a casting route and near-α titanium alloy VT18U (Ti-6.8Al-4Zr-2.5Sn-1Nb-0.7Mo-0.15Si) as a matrix material. The boron addition in an amount of 1.2 wt.% corresponding to 6.5 vol.% TiB was found to be optimal for this matrix material. To obtain axially aligned TiB whiskers with a high aspect ratio and the most creep resistant matrix microstructure, isothermal 2D hot forging followed by annealing first in the β and then in the α+β temperature range was carried out. The mechanical properties of the novel VT18U/TiB composite material were established in tension parallel to the predominant orientation of the TiB whiskers. Along with tensile tests, creep tests were carried out and the obtained creep curves were compared with those obtained for the matrix alloy subjected to near the same forging and heat treatment. The composite material with aligned TiB whiskers demonstrated appreciably higher strength and creep resistance in comparison with those of the base alloy without significant reduction in ductility. SEM study of the fracture behavior showed that high adhesion strength of interfacial boundaries between the matrix and the TiB whiskers in the VT18U/TiB composites is retained up toT= 600–700 °C. The main failure mechanism of the composites at room and elevated temperatures is fracture of TiB whiskers followed by ductile failure of the matrix.