The research of superplastic titanium alloys has progressed

Superplastic molding technology is expected to solve the molding problem of complex components and has great application prospects. However, at present, most metal superplastic molding temperature is high and the strain rate is extremely slow, which increases the energy consumption and time of superplastic molding, and causes serious oxidation of the surface of the formed material, which restricts the wide application of this technology. 

The research team of Yang Ke and Ren Ling of the Institute of Metal Research, Chinese Academy of Sciences, together with the research team of Qiu Dong of RMIT University, designed and prepared a new titanium alloy with a multiphase nano-network structure on the basis of the high-performance dual-phase core-shell nanostructure Ti6Al4V5Cu alloy developed in the early stage (Figure 1). It uses the nano-β mesh in the matrix to promote the slippage and tilt between micro-nano crystal grains, and uses the nano-Ti2Cu phase nailed along the / β phase boundary to improve the stability of the nano-mesh structure (Figure 2), and comprehensively improve the superplastic deformation ability of the material. This microstructure design reduces the superplastic deformation temperature of the material by about 250 °C compared with Ti6Al4V alloy, and the elongation of more than 900% can be obtained under the conditions of 750 °C and a strain rate of up to 1 s-1, which means that the strain rate of the superplastic deformation of the material is increased by 2~4 orders of magnitude compared with the existing material (Figure 3). After superplastic deformation, the microstructure of the multiphase nano-mesh structure titanium alloy will not be coarseened and grown, which solves the inherent contradiction between the superplastic deformation ability of the material and the thermal stability of the structure (Figure 4), which is of great significance for promoting the development of superplastic molding technology.

Figure 1. Microstructure design, preparation and characterization of multiphase nano-reticular superplastic titanium alloys. (A) Organizational design ideas; (B) material preparation process; (C) EBSD characterization results of initial state tissues; (D) High-resolution TEM observation of initial state tissues.

Figure 2. In situ SEM to observe the superplastic deformation mechanism of materials during high-temperature stretching. (A-D) SEM organizational evolution; (e) strain distribution diagram; (F) Schematic diagram of grain slip and tilt mechanism.

Figure 3. Mechanical properties of multiphase nano-mesh Ti6Al4V5Cu alloy. (A) Tensile properties at room temperature; (B) High temperature tensile properties; (C) High temperature tensile stress-strain curve; (D) Comparative chart of superplastic deformation capacity of different materials.

Figure 4. Microstructure of heterogeneous nano-mesh Ti6Al4V5Cu alloy after superplastic deformation. (A) EBSD analysis after deformation; (B) Changes of grain size, texture strength and Vickers hardness with lnZ parameters after deformation.

The research results, titled Extraordinary superplasticity at low homologous temperature and high strain rate enabled by a multiphase nanocrystalline network, were published online in the International Journal of Plasticity Plasticity). The research work is supported by the National Key Research and Development Program, the Natural Science Foundation of Liaoning Province and the Innovation Fund of the Institute of Metals. (Source: Institute of Metal Research, Chinese Academy of Sciences)

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