Mechanical response of fine grained Ti2AlC under extreme thermo-mechanical loading conditions

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An experimental investigation was conducted to evaluate the compressive constitutive behavior and fracture initiation toughness of fine grained (∼4.2 μm) Ti2AlC in dynamic and quasi-static loading at different temperatures. A Split Hopkinson Pressure Bar (SHPB) apparatus was used in conjunction with an induction coil heating system for dynamic experiments at elevated temperatures, while a universal mechanical testing machine equipped with an extensometer and furnace was used for quasi-static compressive testing. A series of experiments were conducted at different temperatures from 25 °C to 1200 °C and strain rates of 10-4 s-1 and 500 s-1. A single edge notched specimen was used to determine the fracture initiation toughness in dynamic and quasi-static loading from ambient temperature to 900 °C. The SHPB apparatus was modified for this purpose and high speed photography was incorporated to determine fracture initiation time, and the load corresponding to this time was used to calculate the dynamic fracture toughness. The results of this study reveal that the peak compressive failure stress in dynamic conditions decreases with increasing temperature, from 1600 MPa at room temperature to 850 MPa at 1200 °C. In the dynamic testing condition, the failure remains predominately brittle even at temperatures as high as 1200 °C. Under static loading conditions, the peak compressive stresses were always lower than those in dynamic loading conditions, but they also decreased monotonically with increasing temperature. Also under static conditions, a significant drop in peak compressive failure stress and an increase in ductility was observed above the brittle-to-plastic transition temperature of around 900 °C. The fracture experiments reveal that the strength and fracture toughness in dynamic conditions are higher than the corresponding quasi-static values by approximately 35% at room temperature and that they both decrease with increasing temperatures. It was found that high temperature and low strain rate promote plastic behavior of Ti2AlC.

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Materials Science and Engineering A