Study On Phase Evolution And Properties Of Ti₃SiC₂ And Synthesis Of Other MAX Phases By Different Experimental Parameters

The ternary layered Ti₃SiC₂ cermet is a typical representative of the MAX phase,it has high melting point,high elastic modulus,good high temperature stability,oxidation resistance,corrosion resistance and excellent radiation resistance.These excellent properties make Ti₃SiC₂ an advanced multifunctional material for using in extreme environments,such as high temperature structural materials,thermal conductive components,nuclear reactor cladding materials,electrical contact materials and thermal insulation coatings in the aerospace industry.As the most mature member of the MAX phase,Ti₃SiC₂ has been synthesized by various methods,such as chemical vapor deposition,self-propagating high-temperature reaction synthesis,hot/hot isostatic pressing,spark plasma sintering,and pressureless sintering.However,impurities such as TiC and Ti₅Si₃ are always present in the synthesized sample.In this study,the pressureless sintering method was used to prepare high purity Ti₃SiC₂ considering factors such as cost,energy consumption,purity of prepared samples,and industrial application.In the preparation of high purity Ti₃SiC₂,the impurity phase?such as TiC and Ti₅Si₃?is always difficult to remove from the samples,which affects the performance of Ti₃SiC₂material.Therefore,the synthesis of high purity Ti₃SiC₂ is still a scientific problem to be solved.Experiments have shown that the ratio of raw materials and the regulation of sintering temperature are the key to eliminating the impurity phase and obtaining single-phase materials.In this paper,the raw material powders of Ti,Si,C and Al with coarse particle size are studied.The pressureless sintering method is used,with Al is added as a sintering aid.Through the regulation of temperature and raw material ratio,a high purity Ti₃SiC₂ material was successfully prepared using a new raw material ratio.Combined with XRD,SEM and XPS,the existence state of Al and the specific combustion-supporting mechanism were clarified in detail.The synthesis route of high purity Ti₃SiC₂ was given.In addition,the effects of different amounts of Al on the purity,microstructure and oxidation properties of the synthesized Ti₃SiC₂ materials were also investigated.What's more,the exploration of the relevant properties of synthetic high purity Ti₃SiC₂materials is also a scientific issue in this work.In order to further understand the thermal stability of the Ti₃SiC₂ material,its thermal stability under nitrogen atmosphere was determined,and the pest mechanism was proposed.Doping is one of the important means of material modification.In this work,W-doping is used to improve the oxidation resistance of Ti₃SiC₂.The possible formation path of(Ti_1-x,W_x)₃SiC₂ solid solution is proposed.At the same time,in order to increase the density of the synthetic high purity Ti₃SiC₂ material,high-pressure experiments were also carried out.Furthermore,the application of ceramic materials has been expanded through the exploration of other MAX/B phase pressureless sintering synthesis.