Study On Synthesis And Properties Of Ti₃SiC₂ Multiphase Ceramics With MoS₂

The laminated ternary compound Ti_SiC₂,which is a new kind of structural ceramics material,receives the widespread attention attributing to its perfect combination of both merits of metals and ceramics.First,Ti₃SiC₂ has a good heat conduction and electric conductivity under the normal temperature,relatively low Vickers hardness,high elasticity coefficient and high shear modulus;second,Ti₃SiC₂ has high bend strength,a good thermo stability and outstanding oxidation resistance; What is more,it is prominent that Ti₃SiC₂ has better self-lubrication performance than graphite and MoS₂.But the bad wear ability because of the easy cleavage character and relatively low hardness limits the project application.Incorporation of second phase into Ti₃SiC₂ is an effective way to overcome these weaknesses.Owing to the sandwich(such as graphite),high hardness(4GPa),high bend strength(3450MPa),low friction coefficient(0.03～0.06),and approximate thermal expansion coefficient(MoS₂ 10.7×10^-6K^-1,Ti₃SiC₂ 9.7×10^-6K^-1),MoS₂ is a good material to improve the wear and tear of Ti₃SiC₂.Many researches indicate that the wear rate of composites added with 2～4wt%MoS₂ is the lowest.MoS₂ herein is chosen to produce MS-TSC composites in order to improve the tribological performance.In this study,Ti₃aSiC₂ powder is synthesized by un-press sintering at 1400℃with composition of 2TiC/1Ti/1Si/0.2Al in molar ratio.And then MS-TSC composites added with the MoS₂ quality content is 2%,4%,6%and 8%could be sintered in the temperature range of 1200～1450℃and under a pressure of 30MPa in argon flow.The phase composition,the microstructures,the physical properties of the MS-TSC materials were investigated,as following respectively:(1)The bulk MS-TSC materials with a relative density of 99%is synthesized by hot-pressing.Analyzing its component through XRD,it indicates that the material principal constituent is Ti₃SiC₂,but also includes few impurities,like Ti₅Si₃,TiC,Mo, (Ti_<sub>0.8Mo_0.2)Si₂ and Ti₄S₂C₂.The decomposition of Ti₃SiC₂ causes by secondary sintering has brought the impurity such as Ti₅Si₃ and TiC,which reduces the purity of MS-TSC material.(2)The results of SEM of sample surface indicated that:The MS-TSC material has a close internal structure and low porosity ratio;the obtained Ti₃SiC₂ grains are well developed and plate-shape.The incorporation of MoS₂ can influence the relative density and Ti₃SiC₂ particle size of MS-TSC material.(3)When the content of MoS₂ is 4%,the Vickers hardness of MS-TSC material is up to 7.83GPa,which the conductivity is 10.05×10⁶S·m^-1simultaneously.Studying on the tribological test of the 2wt%MS-TSC material with GCr15 steel,it finally indicated:the dominant mechanism of attrition has changed with the time going,from the abrasive attrition to the adhesive wear primarily.The friction coefficient is 0.176～0.283,while the friction coefficient is 0.062～0.134 under the oil lubrication condition.And the wear rate under unlubrication condition is less than 2.657×10^-6 mm³Â·N^-1·m^-1while it is less than 1.968×10^-7mm³Â·N^-1·m^-1under oil lubrication condition.It is a low wear rate because the oil adsorbed at the rubbing surface reduces the surface energy greatly,and prevents from the occurrence of adhesive wear.TiC and Ti₅Si₃ decomposed from Ti₃SiC₂ ceramics could enhance the Vickers hardness of MS-TSC material,while the metallographic phase Mo decomposed from MoS₂ can enhance the fracture toughness property of compound material,thus also enhance the ability to resist the micro-fracture wear of MS-TSC material.(4)The oxidized dynamics research indicates:the oxidation process which MS-TSC materials with different content of MoS₂ oxidized at 500℃and 800℃for 30 cycles could divide into three parabola processes.The oxidized activation energy is approximately 120kJ·mol^-1.The principal oxidized product at 500℃is SiO₂, simultaneously including few TiO₂ andα-Al₂O₃.The principal oxidized product at 800℃is TiO₂ and SiO₂,simultaneously includingα-Al₂O₃.Moreover,the more MoS₂ involves the lessα-Al₂O₃ produces.The thickness of oxide layer is 1.5～5.0μm at 500℃and 800℃.Compact oxide layer on the surface of MS-TSC prevents the further oxidation from the inner layer material,thus it enables the MS-TSC material to have a good oxidation resistance performance under low temperature.