Compared with conventional grain size (5-10 μm) titanium alloys, ultrafine grained titanium alloys not only have higher strength and good plastic matching, but also have higher wear resistance and better biocompatibility. It is very attractive in many important application fields such as aerospace and biomedicine. However, the preparation and processing of ultra-fine-grained titanium alloys is extremely difficult, and the thermal stability of the microstructure is poor. These two bottleneck problems restrict the development and application of ultra-fine-grained titanium alloys.
The Yang Ke team of the Institute of Metal Research, Chinese Academy of Sciences has long been engaged in the basic and applied research of new medical metal materials. Recently, team members Ren Ling, Wang Hai, etc. adopted the microstructure design idea of "two-phase shell wrapping ultrafine equiaxed crystals" (Fig. 1), and at the same time improved the microstructure and thermal properties of ultrafine grained titanium alloys from both thermodynamics and kinetics. It also uses the combination of conventional heat treatment and thermal processing to realize the large-scale preparation of the above-mentioned microstructure, and solves the two bottleneck problems of difficult preparation and processing of ultra-fine-grained titanium alloys and poor structure stability, and obtains excellent performance and Ultrafine-grained copper-containing titanium alloy with high thermal stability. Recently, related research results were published online in Nature Communications.
Fig. 1
In recent years, the research team has been committed to the integrated research and application of the structure and biological function of copper-containing titanium alloys. On the basis of the previous research work, the team proposed a preparation strategy of "eutectoid element alloying → quenching → hot deformation" (EQD) for the preparation of ultra-fine-grained copper-titanium alloys (Fig. 2). Design ideas for the microstructure of axial crystals. This strategy enables the large-scale fabrication of ultrafine-grained Ti6Al4V5Cu alloys with α-Ti grain sizes in the range of 90–500 nm by conventional thermal processing equipment (Fig. 2).
Fig. 2
At the same time, the β/Ti2Cu dual-phase honeycomb shell structure formed during thermal deformation is used to coat the α grains, which significantly improves the thermal stability of the ultrafine equiaxed grain structure and increases the instability temperature of the material to 973 K ( 0.55Tm) (Figure 3). The room temperature tensile strength of the ultrafine-grained Ti6Al4V5Cu alloy is up to 1.5 GPa, and the elongation exceeds 10%. At 650 °C and a strain rate of 0.01 s-1, the tensile elongation exceeds 1000% (Fig. 1), achieving superplastic deformation.
Fig. 3
In addition, the ultrafine-grained Ti6Al4V-5Cu alloy did not undergo grain coarsening and growth under the thermomechanical coupling condition of high temperature stretching (Fig. 4). This EQD strategy not only realizes the preparation of high performance, high thermal stability ultrafine grain structure of other titanium alloys such as TiCu and TiZrCu, but also has been extended to other alloy systems including iron and steel materials for the preparation of ultrafine grain metal materials. It provides a new approach and is of great significance to the design and research of ultrafine-grained metallic materials.
Fig. 4
The above work was completed by the team of Yang Ke and Ren Ling of the Institute of Metals, the team of Qiu Dong of the Royal Melbourne Institute of Technology, Australia, and the team of Chen Xingqiu of the Shenyang National Research Center for Materials Science of the Institute of Metals. Assistant Researcher Wang Hai of the Institute of Metals is the first author, and Renling Project Researcher of the Institute of Metals and Professor Qiu Dong of RMIT University are the corresponding authors.
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