Slip Casting And Injection Moulding Of Ti₃AlC₂

The ternary layered compound Ti₃AlC₂ has the combined properties of both ceramics and metals,including high elastic modulus,high-temperature stability,corrosion resistance,oxidation resistance,electrical conductivity,thermal conductivity,machinability and high strength.These properties endow Ti₃AlC₂ broad application prospects.However,nowadays the powder metallurgy technologies suitable to prepare bulk Ti₃AlC₂ in lab are limited to HP,HIP,SHS and SPS,etc.These technologies require pressure-assisted sintering at high temperatures,which need specific equipments and high-energy consumption.What is more,parts with complex geometry or large dimension can not be realized with these processes.Therefore,the keys to speed up its market application are to explore low-pressure moulding technology and to optimize the pressureless sintering of bulk Ti₃AlC₂.In this thesis,we studied the slip casting and injection moulding of Ti₃AlC₂,optimized the parameters of pressureless sintering and finally fabricated the high-performed Ti₃AlC₂ products.Firstly,the preparations of Ti₃AlC₂ powder and Ti₃AlC₂ suspension were studied.High-purity Ti₃AlC₂ powders?⁹9.7wt%?were obtained from 1.8TiC-1Ti-1Al mixtures by sintering at 1450?for 2 h.Arabic gum is found to be more suitable for preparing Ti₃AlC₂ suspension,which is uniform in mixing,stable in dispersion and appropriate in viscosity.Studying on the influence of adding amount of dispersant and pH value on the Ti₃AlC₂ suspension suggests that 1 wt.%Arabic gum as dispersant at pH=10 is the optimum conditions,where the absolute value of zeta potential reaches 57.7 mV and the viscosity stabilizes at 6 mPa·s.And the Ti₃AlC₂ green compact prepared with this suspension shows the most integrate shape.Secondly,the Ti₃AlC₂ green compacts were sintered with or without Al₄C₃ embedding powder at varied temperatures.It is found that Al₄C₃ embedding powders provide an Al-rich environment,retarding the decomposition of Ti₃AlC₂ during pressureless sintering and improving the densification of the sintered products.The Ti₃AlC₂ sample sintered at 1450?for 1.5 h with Al₄C₃ embedding powder has the optimum properties,namely 95.3%relative density,hardness of 4.18 GPa,compressive strength of 796 MPa,thermal conductivity of 29.11 W·m^-1·K^-1 and electrical resistivity of 0.39??·m^-1.Thirdly,the effects of injection moulding processing and sintering parameters on the properties of Ti₃AlC₂ samples were studied.It is found that the wettability between PW and Ti₃AlC₂ is improved by surface modification with SA.The feedstock,a mixture of Ti₃AlC₂:PW:SA:PP=90:8:2.5:2 in mass ratio,is suitable to prepare the integrate green compacts at 70?under 25 MPa.The degreased Ti₃AlC₂ compact sintered at 1450?for 1.5 h shows the optimum properties,namely 96.3%relative density,hardness of 4.03 GPa,compressive strength of 852 MPa,thermal conductivity of 30.66 W·m^-1·K^-1 and electrical resistivity of 0.39??·m^-1.Finally,compared with the Ti₃AlC₂ samples fabricated by conventional powder metallurgy technologies,the present samples prepared by slip casting or injection moulding followed by pressureless sintering have higher purity,slightly lower density and fairly comparable properties.These results suggest that slip casting and injection moulding can provide feasible solutions for mass fabrication of Ti₃AlC₂ products.