In-situ Preparation And Strengthening Mechanism Of Nb,Ta And W Solid Solved Ti₃SiC₂/Al₂O₃ Composites

Ti₃SiC₂ceramics have low strength and high toughness,while Al₂O₃ceramics exhibit high strength and poor toughness.Their complementary mechanical properties endow Ti₃SiC₂/Al₂O₃composite materials extensive research and application value.Although there have been many studies on Ti₃SiC₂/Al₂O₃composites,several important aspects need to be improved,such as the ratio of two components,control of impurity phase in in-situ synthesis,solid solution strengthening,characterization of interface properties and so on.In order to systematically study Ti₃SiC₂/Al₂O₃composite materials and reasonably analyse from the gatomic level,this paper combines the experiment with the first-principles calculation,starting from the in-situ synthesis of Ti₃SiC₂ceramic,optimized the synthesis process,improved the mechanical properties of composite ceramics by solid solution of M excessive metal elements,and explained its internal mechanism.The details are as follows:First,we analyzed the in-situ synthesis system of Ti₃SiC₂and selected Ti/Si/Al/Ti C as the raw materials.The influence of sintering temperature on in-situ synthesis of Ti₃SiC₂was investigated,which effectively controlled the formation of impurity phase and clarified the sintering process.Combined with XRD,SEM and first-principles calculation,the solid solubility of Si and Al elements in sintering process and the influence of different solid solubility on mechanical properties were studied,and the solid solution substituent mechanism of Si and Al elements in the in-situ synthesis of Ti₃SiC₂was explained.Ti-Al bond ha lower energy than Ti-Si bond,as the temperature increased,Ti-Al bond is particularly susceptible to break,forming Al vacancy in solid solution.Afterward,Si atoms fill the vacancy to generate a stronger Ti-Si bond to maintain the crystal stability.Secondly,we prepared a series of Ti₃SiC₂/Al₂O₃composits using Ti/Si/Al/Ti C/Al₂O₃in-situ synthesis system at 1500℃and 30 MPa for 1.5 h.The composition and microstructure of the composites were characterized by XRD,SEM and TEM,and the mechanical properties of the composites were tested.The results showed that 40 vol%-Ti₃SiC₂/Al₂O₃composite exhibited the optimized mechanical properties,the hardness,strength and toughness were13.8 GPa,566 MPa和5.5 MPa·m^1/2respectively.The surface and interface properties of Ti₃SiC₂/Al₂O₃composites were studied by first principles.The results showed that Ti₃SiC₂（001）∥Al₂O₃（001）interface had the largest adsorption work and the smallest interfacial spacing,indicating the interface strengthening effect of Ti₃SiC₂/Al₂O₃composite.Finally,in order to further improve the mechanical properties of Ti₃SiC₂/Al₂O₃composites,Nb,Ta and W elements were introduced into Ti₃SiC₂/Al₂O₃composites using metal carbide as the starting material.Single-component and multi-component solid solution（Ti,Nb）₃SiC₂/Al₂O₃,（Ti,Ta）₃SiC₂/Al₂O₃,and（Ti,Nb,Ta,W）₃SiC₂/Al₂O₃composites were synthesized,The phase composition,microstructure,distribution of solid solution elements and mechanical properties were analyzed by XRD,SEM,TEM and EBSD.The results show that the upper solution limits of Nb and Ta are between 7.5-10 at%.The solution of Nb has little effect on Ti₃SiC₂/Al₂O₃particles,while the solution of Ta can refine Ti₃SiC₂grains.Multicomponent solid solution（Ti,Nb,Ta,W）₃SiC₂/Al₂O₃composites can be prepared by doping transition metal carbides merely.The mechanical properties of（Ti,Nb,Ta,W）₃SiC₂/Al₂O₃can be enhanced by doping of solid solution elements,with the Vickers hardness,bending strength and fracture toughness reaching 16.6 GPa,659 MPa and7.3 Mpa·m^1/2,respectively.The structural model of solid solution was constructed by first principles calculation.The sites occupied by solid solution elements,the influence of solid solution elements on the elastic properties of Ti₃SiC₂crystal and the interface of Ti₃SiC₂/Al₂O₃composite were analyzed.The results show that Nb,Ta and W elements tend to be soluble in the 2a site of Ti₃SiC₂crystal,and improve the strength of chemical bond inside the crystal and the intergrain boundary strength,which enhances the mechanical properties of Ti₃SiC₂/Al₂O₃composite.