Direct energy deposition of TiC/Ti6Al4V graded materials and heat resistance improvement during the ablation process

Abstract

A reusable reentry vehicle requires a thermal protection structure with high strength and heat resistance for repeated traveling between the Earth and space. In this study, various transition modes of TiC/Ti6Al4V graded materials were designed and fabricated by direct energy deposition, and then ablation tests were conducted to simulate the service environment. The influence of microstructure morphology on the heat resistance of the graded materials was revealed by analyzing the changes in the internal microstructure, element distribution, and microcrack. Compared with Ti6Al4V titanium alloy, TiC/Ti6Al4V graded materials show almost no mass loss or ablation pits, indicating a significant improvement in heat resistance. The Ti6Al4V titanium alloy exhibited macroscopic cracks up to 700 μm in length on the surface after the ablation test; as a contrast, the surface area of the TiC/Ti6Al4V graded materials exhibited fine microcracks, and there were no significant changes in the internal structure. The improvement in the heat resistance of TiC/Ti6Al4V graded materials is attributed to the combined effects of the interface heat resistance between the TiC and Ti6Al4V and the change of heat conduction path within the matrix.

Keywords

• Functionally graded materials
• Heat resistance
• Directed energy deposition
• Microstructure evolution
• Ti6Al4V titanium alloy