Aluminium nitride-molybdenum ceramic matrix composites. Influence of molybdenum addition on electrical, mechanical and thermal properties

Abstract

Aluminium nitride-molybdenum ceramic matrix composites are produced by hot pressing a mixture of two powders without any sintering aids. Sintered samples show homogeneous and dense structure. Electrical resistivity measurements conducted over a series of samples show a rapid decrease in its value once the molybdenum volume fraction in AlN matrix is increased from 0.2 to 0.22. The interface between AlN matrix and Mo particles is found to be devoid of any secondary phases. Mechanical thermal and thermomechanical properties of these composites are then studied in a way to investigate the influence of molybdenum addition on the behaviour of AlN. An important increase in the fracture toughness, bend strength and thermal shock resistance of the composites is observed as a function of Mo concentration. Thermal conductivity measured at room temperature and thermal diffusity measured at temperatures between 400 and 1000 °C also show an improvement when molybdenum concentration in the AlN matrix is increased from 0 to 40%. This improvement in mechanical thermal and thermomechanical behaviour of composites is attributed to a clean adherent AlN-Mo interface deprived of low melting and low thermal conductivity secondary phases as well as better mechanical properties and good thermal conductivity of Mo. Molybdenwn has a thermal expansion coefficient near the AlN one which allows to minimise the residual and thermal stresses at the AlN-Mo interface.