Preparation, processing and application of corrosion resistant Titanium matrix composites

Known as "modern metal" and "space metal", titanium and titanium alloys have the characteristics of low density, high specific strength, corrosion resistance and excellent high temperature mechanical properties, and have been more and more widely used in aerospace, chemical industry, Marine engineering, biomedicine and other fields. Titanium alloys have also made many breakthroughs in the course of decades of development. Alloying method has significantly improved the performance of Titanium Alloy Forgings, and the service temperature has been increased from 350 ℃ to 600 ℃, but it has not been able to break through the bottleneck of 600 ℃ in the past 30 years. With the rapid development of titanium in aerospace industry, ultra-high-speed aircraft need to work in ultra-high temperature, high stress, strong wear and other extreme conditions, which puts forward more stringent requirements on the strength, stiffness, heat resistance and other properties of titanium-based materials. One of the effective ways to achieve high performance of titanium alloys is to introduce multi-dimension whisker or/particle ceramic reinforcement phase and control its ordered spatial arrangement. The resulting materials are known as Titanium matrix composites (TMCs), Among them, this kind of TMCs with IMI834, Ti1100, BT36, Ti60, Ti600, Ti65 and other near α type high temperature titanium alloy as the matrix is also known as Heat-resistant TMCs (HRTMCs). TiB, TiC, Ti5Si3 and rare earth oxides (such as La2O3) are the most commonly used ceramic reinforcement phases in TMCs, which are usually generated by in-situ autogenesis between titanium matrix and reactants such as B, TiB2, C, B4C, Si and LaB6 during the preparation process. By means of flexible composition design, exquisite distribution, structural optimization and various deformation machining control, TMCs can realize the synergistic coupling between ductile titanium alloys and high stiffness and high strength reinforcement bodies, thus showing higher specific strength, specific stiffness and better heat and wear resistance. The use temperature of HRTMCs is increased by 50 ~ 200 ℃ compared with the traditional titanium alloy, and it is expected to partially replace the traditional superalloy in the use environment of 550 ~ 800 ℃, so as to achieve substantial weight loss. HRTMCs has broad application prospect and development potential in aerospace and other fields, so it has been widely concerned.

With the temperature rising above 600 ℃, the significant weakening of grain boundary strength has become one of the obstacles to further improving the heat resistance of TMCs. Although the single-scale reinforcement can improve the grain boundary strength, it will cause greater brittleness at room temperature. The multi-component and multi-scale reinforcement can effectively strengthen grain boundaries while alleviating plasticity decline. With the more in-depth understanding of fine composite configurations in biological structural materials, more attention has been paid to the effect of "non-uniform" composite configurations on the strengthening and toughening of metal matrix composites. The composite configuration is more conducive to exerting the degree of freedom of the composite design and the synergistic coupling effect between different components, so as to further explore the potential of the heat resistance of TMCs. In addition, the introduction of ceramic reinforcement phase reduces the thermal processing performance of TMCs, so the traditional thermal deformation technology to process TMCs, the yield and product stability are not ideal, can not achieve the preparation of large complex components and mass production. The components formed by near net forming technology such as isothermal forging, precision casting and additive manufacturing do not need to be processed or only need a small amount of processing, which can not only improve the utilization rate of raw materials, but also solve the forming problems of complex components, so that they have broad application prospects and attract attention.

New material design theories such as micro-nano collaborative strengthening and composite configuration design provide new research ideas for further improving the comprehensive properties of HRTMCs. The more and more mature near net forming technology provides a new technical way to effectively solve the difficult problem of HRTMCs component forming. In this paper, the research progress and application examples of HRTMCs are reviewed from the aspects of composite configuration design and preparation, near net forming processing technology and high temperature mechanical properties, and the existing problems, key breakthrough points and future development direction of HRTMCS are proposed.

After years of research, great progress has been made in the design, preparation and processing of TMCs. Through the orderly regulation of the structural parameters such as the size, type and distribution characteristics of the reinforcement phase and the matrix structure, the comprehensive properties of the materials have been improved, and the key problems of TMCs preparation and component forming have been solved, and they have been applied in some key fields. It has produced good social and economic benefits. In order to further improve the comprehensive performance of HRTMCs, promote the development of advanced processing technology for composite materials, and continue to expand the application exploration of materials in aerospace, petroleum, chemical industry, ships and other fields, work can be carried out from the following four directions in the future.

(1) Large-scale TMCs casting ingot or powder metallurgy billet preparation, pipe, rod, plate industrial production. Large scale components need to prepare larger specifications of titanium matrix composite ingot or powder metallurgy billet, how to prepare uniform composition, good consistency, no defects and stable quality of cast ingot and powder metallurgy billet is the key problem that must be solved in the large-scale application of TMCs. On this basis, the production of TMCs tubes, rods and plates is realized by using industrial equipment.

(2) Micro-nano and configuration coupling. Grain boundary strength decreases significantly at high temperature. Strengthening grain boundary is the key to further improve the high temperature performance of HRTMCs in the future. The high temperature performance of HRTMCs can be significantly improved by micro/nano strengthening and configuration strengthening. Therefore, the combination of micro and nano strengthening and configuration strengthening is expected to further improve the high temperature performance of TMCs. By optimizing the type, content, size and spatial distribution of reinforcement in composite materials, the multi-structure distribution of multi-component and multi-scale reinforcement is realized, which becomes a new way to break the bottleneck of heat resistance of TMCs.

(3) Develop advanced near net forming processing technology. Additive manufacturing, precision casting and isothermal superplastic forming are three kinds of near net forming technology, which are important breakthrough to solve the HRTMCs complex component forming. In terms of additive manufacturing, composite powder has a congenital advantage, and the development of a new composite powder short process preparation route to reduce production costs and shorten the process cycle is helpful to promote the development of HRTMCs additive technology. In terms of precision casting, it is necessary to optimize the matrix alloy composition and the type and content of reinforcement, and simulate the TMCs precision casting process to optimize the casting model and process, so as to reduce casting defects, improve fluidity and ensure filling, and improve the mechanical properties of castings. In terms of isothermal superplastic forming, it is necessary to continue in-depth research on HRTMCs superplastic forming process and mechanism, and explore the influence of multiple multi-scale reinforcement and its configuration distribution on the superplastic deformation mechanism, so as to achieve fine regulation of the matrix structure and maintain the configuration distribution of the reinforcement, and further exert its advantages in the stabilization preparation of large-size complex components.

(4)Improve the development of comprehensive performance data and related detection technologies. In addition to good room temperature toughness and excellent high temperature strength, HRTMCs also pays more attention to creep properties, fracture toughness and fatigue properties, which are key indicators that must be considered when TMCs is used in extreme environments such as aerospace. The effects of reinforcement, corresponding configuration distribution and deformation parameters on comprehensive properties should be considered to optimize the design, preparation and processing of composite materials. At the same time, it is necessary to solve the key problems such as the detection of titanium matrix composites and non-destructive testing, which has significant significance for accelerating the application of HRTMCs.