Preparation of agglomerated powders for air plasma spraying MoSi2 coating

The agglomerated MoSi2 powders, ideal for air plasma spraying, were prepared by spray drying and subsequent vacuum sintering of ultrafine MoSi2 powders. The apparent density and flowability were measured by an apparent density instrument and a hall flowmeter. The structure of as-prepared powders and coatings was analyzed by X-ray diffraction and scanning electron microscopy. The results indicated that resultant powders were spherical and porous. It was found that heat treatment had decreased the sphericity as well as the porosity of the MoSi2 particles. The agglomerated powders, sintered at 1300 °C for 1 h, showed 57.0% and 46% more flowability and apparent density, respectively, compared to that of the spray dried powders. The as-sintered MoSi2 powders subjected to the plasma flame exhibited a further increase in the density. The as-sprayed coating by using the agglomerated powders with a size of 30–54 μm yielded a network structural MoSi2 composite coating with MoSi2 as the major phase.