Influence of spray angle on the pore and crack microstructure of plasma-sprayed deposits

To understand the influence of processing parameters on the microstructure of plasma-sprayed deposits, small-angle neutron scattering measurements were made of the processing-parameter-dependent specific surface area of the voids in gray alumina deposits, These studies indicate that the voids are in the form of pores between the splats and around inclusions or unmelted particles, and are also in the form of cracks within the splats which may develop during cooling, The porous volume increases as the angle between the spray gun and the substrate (the ''spray angle'') decreases, This study also indicates that the cracks are preferentially oriented, and that the crack orientation also depends on the spray angle, The interlamellar pores, however, are preferentially oriented parallel to the substrate surface, and the orientation of the pore is independent of the spray angle.