The effect of parametric variation on the mullite content of plasma sprayed zircon-alumina powder mixture

Mullite was obtained by plasma spraying a mechanical mixture of alumina and zircon sand mixed in 3:2 M ratio. The following parameters were varied during coating deposition: arc current, secondary gas, i.e., hydrogen flow rate, stand-off distance (SOD) and angle of powder injection. These parameters were chosen since they significantly affect powder heating and consequently, mullite formation. Laser surface treatment was undertaken on a couple of selected coatings. The amount of mullite formed in the coating was estimated using Rietveld analysis of the X-ray diffraction patterns of the as-spayed and laser treated coatings. The effects of these parameters on coating hardness and porosity were also taken into account. Finally the mullite yield was correlated with coating porosity and hardness.