Research On Sintering Process Of Tungsten-based Materials And Compound Strengthening

Fusion energy will be one of the significant energy sources for human society in the future.The first wall material is the core material for the construction of fusion reactors,which directly confronts the fusion reaction and its environment is quite harsh.Tungsten has been selected as one of the first wall candidate materials on account of its high temperature strength,high melting point,high thermal conductivity,high sputtering threshold,no reaction with ruthenium as well as low corrosion rate.Nevertheless,the brittleness of the room temperature has severely limited its usage in the thermal shock environment.In order to optimize the brittleness of plasma-oriented tungsten materials,this paper mainly studies the sintering process and composite strengthening.In order to obtain the fine-grained tungsten powder sintered material and achieve the purpose of fine grain strengthening,this paper draws on the two-step sintering method of ceramic powder and based on its process curve,conducting a series of investigations on the temperature of different stages in the sintering process,during which the author has found a new process for the sintering of tungsten powder.The process can make a tungsten material with a relative density of more than 99% and a fine grain by using the tungsten powder having an average particle diameter of 3 ?m as a raw material and by utilizing the difference in activation energy between different densification mechanisms in the sintering process,in which the intensity has also been greatly improved.Subsequent studies on the sintering pressure have shown that the material properties augmented with increasing pressure.The analysis of the morphology of the samples at different stages during the sintering process infers that the sintering densification process mainly occurred in the stage of low temperature and insulation.In the study of composite strengthening,the tungsten matrix was studied in the perspective of strengthening by using tantalum layer,tungsten layer and tungsten fiber,respectively.The tantalum layer composites were sintered by a conventional sintering process and a two-step sintering process.The tantalum layer in the two-step sintered samples maintained their intact morphology,but were tightly bonded to the tungsten matrix and could not exhibit interface cracking and prolong crack propagation.However,the sample made by the conventional method is solid-solubilized by the high temperature for a long time,and the tantalum sheet and the tungsten matrix are solid-dissolved to each other,thus the layered composite system cannot be maintained.Sintering of different proportions of tungsten and tungsten fiber composites by two-step sintering method can not achieve excellent strengthening effect,owing to the fact that the toughening phase is embrittled by the carbon diffusion in the SPS sintering mold,and is tightly combined with the matrix.Therefore,the expected strengthening mechanism cannot be achieved.By using a Ta foil to wrap the sample for sintering to reduce the carbon content in the sample,a composite structure using W powder/Ta foil/sheet/Ta foil/tungsten powder can prevent the W/Ta layer from being affected by carbon diffusion.