Formation of molybdenum boride cermet coating by the detonation spray process

The effects of the powder particle size and the acetylene/oxygen gas flow r atio during the detonation spray process on the amount of molybdenum phase, porosity, and hardness of the coatings using MoB powder were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), etc. The re sults show that the presence of metallic molybdenum in the coating results from decomposition of MoB powder during thermal spray. The compositions of the coatings are metallic Mo, MoB, and Mo2B, which are different from the p hases of the original powder. The amount of molybdenum phase increases mono tonously with the oxygen/acetylene ratio, but the increasing rate for the f ine powder is faster than that for the coarse powder. The porosity and hard ness of the coating are related to the amount of molybdenum phase. The phas e constitution of the coating is discussed.