Effects of the fabrication parameters on the phase composition, densification and mechanical properties of alumina-chromium cermets fabricated by combustion synthesis method

As a high temperature structural ceramic، cermets exhibit less brittle than the ceramic-ceramic composites or the monolithic ceramics in presence of the ductile metal second phase. On the other hand، they have higher refractory، higher creep and thermo-mechanical resistance and higher abrasive resistance in comparable of metals. In the present study، Alumina-Chromium cermets with different proportions of Al2O3، Cr2O3 and Al، different ball-milling time and different heat treatment temperatures have been fabricated. In order to evaluate the optimum manufacturing conditions، specimens with different composition of ball-milled starting materials and for different times were subjected to DTA and TGA analysis. Obtained materials were characterized by microstrutural observations (SEM)، phase analyses (XRD)، mechanical properties measurements (toughness and strength- three point bending test) and by hardness testing (Vickers). The results of DTA show that for ball-milling more than two hours، there is a decreasing of intensity and temperature of exothermic peak relating to thermit reaction. Higher proportion of x in starting materials، 3xAl، xCr2O3، (1-x) Al2O3، cause increasing the density and strength until x=0. 5 and increasing toughness of sintered samples until x=0. 7. The hardness however، constantly decreases on increasing of the x value. In addition، the mechanical properties of sample with x=0. 5 is improved by increasing of the sintering temperature to 1550 °C. he difference between thermal expansion coefficient of the metallic and ceramic phase، oxidation of the chromium phase، low wetting of alumina by chromium phase and a coarser structure are the principle responsible for decreasing of properties in higher value of x and high sintering temperature.