Preparation Of MAX Phase Ti₃AlC₂ By In-situ Reaction Of Ti-al-c And Its Performance Control

The new layered ceramic material Ti3AlC2 combines the characteristics of metal and ceramics.It not only has the electrical and thermal conductivity and processability as metal,but also has excellent corrosion and high temperature oxidation resistance as ceramics.However,the bonding between the Al atomic layer and the[Ti6C]octahedron in the crystal structure of Ti3AlC2 is weak,resulting in low hardness and strength,which limits the wide application of the material.In this paper,titanium(Ti)powder,aluminum(Al)powder and graphite(C)powder were used as raw materials to prepare high-purity and high-density Ti3AlC2 materials by powder metallurgy,and their properties were studied.On this basis,the effect of Si on the properties of Ti3AlC2 materials was investigated by doping different amounts of Si.Finally,the effects of Si doping on the properties of Ti3AlC2 materials were investigated by analyzing the bending strength,fracture toughness,crack propagation path and fracture morphology.The reaction process of Ti3AlC2 in Ti-Al-C system was analyzed by thermodynamic calculation.By changing the ratio of raw materials(Ti:Al:C=3:1:2,3:1.1:1.8,3:1.2:2),sintering temperature(1200 ℃,1300 ℃ and 1400 ℃)and holding time(10 min,60 min),studied its effect on the synthesis of Ti3AlC2 materials.It was found that the Ti3AlC2 material prepared at Ti:Al:C=3:1.2:2,1300 ℃ and 60 min was the highest purity,reaching 97.23 wt.%.The reaction process of the synthesized Ti3AlC2 material was investigated by analyzing the phase of the product under sintering conditions of 700-1200 ℃ for 10 min.The paper also studied the effect of raw material ratio on the properties of Ti3AlC2 material.the performance of Ti3AlC2 material prepared by Ti:Al:C=3:1:2,Ti:Al:C=3:1.1:1.8,Ti:Al:C=3:1.2:2 were tested.The results show that the ratio of raw materials affects the purity of the product.The higher the purity of Ti3AlC2,the higher the Vickers hardness,flexural strength,fracture toughness and electrical conductivity of the material.The Ti3AlC2 material with the purity of 97.23 wt.%has the best performance,and its Vickers hardness,flexural strength,fracture toughness and electrical conductivity are 5.26 GPa,500 MPa,7.35 MPa·m1/2,3.37×106 s·m-1,respectively.The fracture morphology shows that the material will undergo deformation such as extrusion and kink under load,which is the reason why the bending strength and fracture toughness of Ti3AlC2 are higher than other traditional ceramics.Introduction of Si atoms to solid solution strengthening of Ti3AlC2 With the increase of Si addition,the diffraction peak of Ti3AlC2 material showed a shift to the right,and the Vickers hardness,flexural strength and fracture toughness of the material showed a trend of increasing first and then decreasing.The best performance was obtained when the addition amount of Si was 0.2,and the Vickers hardness,flexural strength and fracture toughness were 5.52 GPa,546 MPa,and 7.51 MPa·m1/2,respectively.When the amount of Si continues to increase,Ti3SiC2 and TiC are formed in the product.During the fracture process of Ti3(Al,Si)C2 material,there are transgranular fracture,interlaminar tear,and crack bridging,bifurcation and deflection.This complex mixed fracture mode can hinder the crack propagation,consume more fracture energy,and improve the flexural strength and fracture toughness of the material.