Preparation And Porous Structure Control Of W-based Porous Materials And Porous Graded Materials By Tape-casting

W-based porous material and porous graded material are combined with the characteristics of tungsten and porous materials,namely,high melting point,low heat expansion coefficient,low vapor pressure,high strength of W and low-density,high specific strength and high specific surface area of porous material.They have widely applications in extreme conditions of ultra high temperature and plasma facing components,the field of microelectronics and preparation of high strength and toughness materials.However,the existing preparation methods have been difficult to solve through the problems such as high energy consumption,low efficiency and difficult to realize the controllable pore structure.In this thesis,the preparation method of tape-casting combined with NaCl as space-holder was proposed.Firstly,slips with different space-holder contents were prepared via tape-casting.The results show that when PVB content is 3.0 wt.%and dispersant content is 1.0wt.%,the viscosity stability of W-50vol.%NaCl slurry is good and suitable for tape-casting.Slips with different contents show no obvious defects,good particle dispersion and uniform two-phase distribution.Secondly,the effect of binder burnout and hot-pressing,dissolving NaCl process on the tape-casting billet were studied.The results show that the best binder burnout process is heating to 780^oC under vacuum.The amorphous elementary C deposit on W/NaCl particles.780 ^oC-50MPa-2 h is evaluated as the best hot pressing technology,which can obtain the stable structure of granular packing.After dissolving in the cyclic deionized water for 48h,the composite billet can obtain the porous billet with good pore-making structureW-based porous materials were fabricated by pressureless consolidating.The effects of consolidating temperature,and holding time,space-holder content on the relative density,pore structure,and mechanical property were studied.The results show that W-based porous materials with different porosity from 14.88%to 66.67%can be prepared by changing the content of space-holder at 1600 ^oC-1 h.The pore diameters are 1?m or 3-6?m separately.W₂C which are on the surface of W particles were synthesized by W particles reacting with residue elemental C,ranging from 14.32 wt.%to 34.76 wt.%.The porosity of W-based porous material prepared with 60 vol.%NaCl is 44.32%,and its compressive strength is 311 MPa,which is obviously higher than the value reported.The promotion mainly benefited from the stable pore structure and the ceramic-reinforced phase in the pore strut.The comparison of W-based porous materials prepared by blending shows that the pore structure with controllable porosity and uniform distribution is mainly attributed to the dispersant and binder introduced in tape-casting slurry,and the reason why sintering temperature can be significantly reduced is W₂C ceramic phase formed during sintering process,modifying the W-W sintering to the W-C reactive sintering.W-based porous graded material with porosity distribution of"low-high-low"was designed and successfully prepared by using W-NaCl tapes from 0 vol.%to 80 vol.%NaCl,The results show that the phase contents of graded material are basically in conformity with the homogeneous materials,and the gradient structure changes are in accordance with the experimental design.