Feng Yangju, Zhang Wencong, Zeng Li, Cui Guorong, Chen Wenzhen
School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai 264209, China.
Materials (Basel). 2017 Apr 18;10(4):424. doi: 10.3390/ma10040424.
In this paper, the microstructure, the room-temperature and high-temperature tensile mechanical properties of monolithic TA15 alloy and TiB whisker-reinforced TA15 titanium matrix composites (TiBw/TA15) fabricated by vacuum hot-pressing sintering were investigated. The microstructure results showed that there were no obvious differences in the microstructure between monolithic TA15 alloy and TiBw/TA15 composites, except whether or not the grain boundaries contained TiBw. After sintering, the matrix microstructure presented a typical Widmanstätten structure and the size of primary grain was consistent with the size of spherical TA15 titanium metallic powders. This result demonstrated that TiBw was not the only factor limiting grain coarsening of the primary grain. Moreover, the grain coarsening of colonies was obvious, and high-angle grain boundaries (HAGBs) were distributed within the primary grain. In addition, TiBw played an important role in the microstructure evolution. In the composites, TiBw were randomly distributed in the matrix and surrounded by a large number of low-angle grain boundaries (LAGBs). Globularization of phase occurred prior, near the TiBw region, because TiBw provided the nucleation site for the equiaxed phase. The room-temperature and high-temperature tensile results showed that TiBw distributed at the primary grain boundaries can strengthen the grain boundary, but reduce the connectivity of the matrix. Therefore, compared to the monolithic TA15 alloy fabricated by the same process, the tensile strength of the composites increased, and the tensile elongation decreased. Moreover, with the addition of TiBw, the fracture mechanism was changed to a mixture of brittle fracture and ductile failure (composites) from ductile failure (monolithic TA15 alloy). The fracture surfaces of TiBw/TA15 composites were the grain boundaries of the primary grain where the majority of TiB whiskers distributed, i.e., the surfaces of the spherical TA15 titanium metallic powders.
本文研究了通过真空热压烧结制备的整体TA15合金以及TiB晶须增强TA15钛基复合材料（TiBw/TA15）的微观结构、室温及高温拉伸力学性能。微观结构结果表明，整体TA15合金与TiBw/TA15复合材料的微观结构没有明显差异，只是晶界是否含有TiBw。烧结后，基体微观结构呈现出典型的魏氏组织，初生晶粒尺寸与球形TA15钛金属粉末的尺寸一致。这一结果表明，TiBw不是限制初生晶粒粗化的唯一因素。此外，柱状晶的粗化明显，大角度晶界（HAGBs）分布在初生晶粒内部。另外，TiBw在微观结构演变中发挥了重要作用。在复合材料中，TiBw随机分布在基体中，并被大量小角度晶界（LAGBs）包围。由于TiBw为等轴β相提供了形核位置，β相的球化在靠近TiBw区域优先发生。室温及高温拉伸结果表明，分布在初生晶粒边界的TiBw可以强化晶界，但会降低基体的连通性。因此，与采用相同工艺制备的整体TA15合金相比，复合材料的抗拉强度提高，而拉伸伸长率降低。此外，随着TiBw的加入，断裂机制从韧性断裂（整体TA15合金）转变为脆性断裂和韧性破坏的混合（复合材料）。TiBw/TA15复合材料的断口是初生晶粒的晶界，大部分TiB晶须分布在该位置，即球形TA15钛金属粉末的表面。
