Abstract:
Compared to dense materials, porous materials are a class of materials with low relative density, high specific strength, high specific surface area, light weight, sound insulation, heat insulation, and good permeability. As part of them, porous metal material has been of considerable interest to the research community in recent years, especially in aerospace. In the design of a spacecraft, in consideration of the extremes of heat (i.e. up to 1200 ºC or even higher) on the exterior surface of spacecraft, outer surface material requires not only features of lightness and acceptable mechanical performance but also needs excellent performance on heat-insulation. For this purpose, based on the low thermal conductivity of Ti (17 W/mK), and usually, lower thermal conductivity achieved by a porous structure, this paper considers the application prospect of a Ti based heat shield for satellite re-entry by fabricating porous Ti with high porosity by adding different foaming agents, such as stearic acid, sodium chloride, PEG, and PMMA. Less mass can also be obtained due to the lower density. To prepare a finished porous product by powder metallurgy technology, we record the decomposition temperature through Thermo Gravimetric Analysis (TGA) with a programming heating curve. According to the TGA analysis, the corresponding sintering process of porous Ti samples is performed. Porosity is adjusted by controlling the amount of foamer, or modifying the sintering profile. Additionally, to decrease the impurities during the debinding and sintering process, mainly obtaining from oxidation and carbonization, more delicate Ti powder has been tried out. As a result, porous Ti samples with high porosity of up to 60% were obtained with metallic lustre. Afterwards, the characteristics of the pores, including pore distribution and pore size, were observed under a microscope. Hardness testing, tensile testing and compression testing were used to evaluate the mechanical performance of as-sintered porous Ti samples. Results suggest the strength drops with increasing porosity. Besides, thermal conductivity was also tested in a thermal conductometer for comparison to illustrate the thermal insulation properties of porous Ti samples (still awaiting results). Keywords: Porous Ti, powder metallurgy, satellite, re-entry, foaming agent, thermal insulation