Synthesis,microstructure,and properties of high purity Mo_(2)TiAlC_(2) ceramics fabricated by spark plasma sintering

摘要

The synthesis,microstructure,and properties of high purity dense bulk Mo_(2)TiAlC_(2) ceramics were studied.High purity Mo_(2)TiAlC_(2) powder was synthesized at 1873 K starting from Mo,Ti,Al,and graphite powders with a molar ratio of 2:1:1.25:2.The synthesis mechanism of Mo_(2)TiAlC_(2) was explored by analyzing the compositions of samples sintered at different temperatures.It was found that the Mo_(2)TiAlC_(2) phase was formed from the reaction among Mo3Al2C,Mo2C,TiC,and C.Dense Mo_(2)TiAlC_(2) bulk sample was prepared by spark plasma sintering(SPS)at 1673 K under a pressure of 40 MPa.The relative density of the dense sample was 98.3%.The mean grain size was 3.5μm in length and 1.5μm in width.The typical layered structure could be clearly observed.The electrical conductivity of Mo_(2)TiAlC_(2) ceramic measured at the temperature range of 2-300 K decreased from 0.95×10^(6) to 0.77×10^(6)Ω^(-1)·m^(-1).Thermal conductivity measured at the temperature range of 300-1273 K decreased from 8.0 to 6.4 W·(m·K)^(-1).The thermal expansion coefficient(TEC)of Mo_(2)TiAlC_(2) measured at the temperature of 350-1100 K was calculated as 9.0×10^(-6) K^(-1).Additionally,the layered structure and fine grain size benefited for excellent mechanical properties of low intrinsic Vickers hardness of 5.2 GPa,high flexural strength of 407.9 MPa,high fracture toughness of 6.5 MPa·m^(1/2),and high compressive strength of 1079 MPa.Even at the indentation load of 300 N,the residual flexural strength could hold 84% of the value of undamaged one,indicating remarkable damage tolerance.Furthermore,it was confirmed that Mo_(2)TiAlC_(2) ceramic had a good oxidation resistance below 1200 K in the air.