Study On The Heat Treatment And Mechical Properties Of Bulk Ti₃AlC₂ Ceramics

Ti3AlC2,a compound with layered structure, has the characteristics of both metal and ceramic. It is regarded as a new kind of ceramics and being favored by material science researchers. In this paper, we studied effects of heat treatment on microstructure and mechanical properties of Ti3AlC2 ceramics.According to the curve of DSC of 3Ti/1.5Al/1.8C system, there is a decalescence peak at 1060 ℃, and two exothermic peaks at 1020 ℃,1250 ℃ respectively. It shows that some internal transformation is carried out in the Ti-Al-C system in1020-1250℃.However, it was reported that Ti3AlC2 would decompose into TiC when the temperature reached 1360 ℃. Therefore, we set the heat-treatment temperature at the range of 950-1450℃,with an interval of 100℃, do solution and aging 8h heattreatment in vacuum.A new phase Al3 Ti appears after heat treatment at 1050℃,and disappears after heat treatment at 1250℃ in Ti3 Al C2 block material. At the same time, Ti Cx content decreases and Ti3AlC2 content increases, which indicates that Al3 Ti can react with TiCx to form Ti3AlC2.After heat treatment at 1250℃, Ti3AlC2 content reach highest value of 94.2%,increases 6.6 % of its previous content; density gets to 4.01 g/cm3, close to 94.3% of its theoretical density; porosity decrease to 0.9%.It proves that microstructure of Ti3AlC2 block material is improved. after heat treatment. It is crystal clear that 1250 ℃ is the optimal heat treatment temperature for Ti3AlC2 bulk material.Flexural strength fracture toughness and compressive strength of Ti3 Al C2 first increases and then decreases, Vickers-hardness is just the opposite with the increasing of temperature from 1050 ℃ to 1450 ℃. After heat treatment under 1250 ℃, fracture toughness,flexural strength and compressive strength reached the maximum values,which are 3338 MPa,5.9MPa·m1/2and 662 MPa, respectively. Vickers-hardness reduced to the lowest of 2.5 GPa.In addition to its structure, content and grain size of Ti3AlC2,porosity of the sample,content of the second TiCx phase, have an impact on mechanical properties of Ti3 Al C2ceramics. Due to the impurity phase and randomly oriented grains, pores and glass phase form in the grain boundary and glass phase. There are pores and dislocation crystal defects in the crystal. They can reduce strength and toughness of Ti3AlC2. After heat treatment, the impurity phase and pores decreased, grains refined, then the strength and toughness of Ti3AlC2 are enhanced, finally the mechanical properties of Ti3AlC2 ceramic are optimized.