Thermodynamic Assessments and mechanically activated synthesis of ultrafine Cr2AlC MAX phase powders

This work attempts to produce ultrafine powders and studies the effect of mechanical activation on reaction kinetics and thermodynamics of Cr2AlC formation, which are essential to design the processing parameters. Cr2AlC formation was found to be exothermic in nature, which occurred as soon as Al started melting. Milling energies (1.6 kJ/g and 3.2 kJ/g after milling for 15 h and 30 h respectively) were found to enhance the reactivity of chromium carbide powders with Al, and lowered the activation energy of reaction significantly. The enthalpy of reaction was found to be changed from -53 kJ/mol to -66 kJ/mol and the change in Gibbs free energy of reaction was decreased from -107 kJ/mol to -139 kJ/mol, when milling duration was increased from 15 h to 30 h. Thus the mechanical activation provides more favorable condition for the conversion and nearly pure Cr2AlC powder with ultrafine (<400 nm) size were produced at relatively lower temperature (at 800 degrees C). (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.