INFLUENCE OF SPRAY ANGLE ON THE PORE AND CRACK MICROSTRUCTURE OF PLASMA-SPRAYED DEPOSITS

To understand the influence of processing parameters on the microstruc ture of plasma-sprayed deposits, small-angle neutron scattering measur ements were made of the processing-parameter-dependent specific surfac e area of the voids in gray alumina deposits, These studies indicate t hat the voids are in the form of pores between the splats and around i nclusions or unmelted particles, and are also in the form of cracks wi thin the splats which may develop during cooling, The porous volume in creases as the angle between the spray gun and the substrate (the ''sp ray angle'') decreases, This study also indicates that the cracks are preferentially oriented, and that the crack orientation also depends o n the spray angle, The interlamellar pores, however, are preferentiall y oriented parallel to the substrate surface, and the orientation of t he pore is independent of the spray angle.