Relation of the Adhesion of Plasma Sprayed Coatings to the Process Parameters: Size, Velocity and Heat Content of the Spray Particles

摘要

The heat exchange of a spray particle with the substrate during solidification is specified on the basis of heat conduction theory. For Mo on steel, the heat exchange is related with possible material transport across the contact interface. A theory on the mechanical and thermodynamical collision phenomena which spray particles undergo during the acceleration at the substrate surface is developed. The theory is based on the application of the Murnaghan equation of state and the entropic equations and pressure-volume relations. The theory permits the determination of the relationship between the Hugoniot pressure and the temperature during the impact compression of the spray particle material. The morphology of spread particles was determined experimentally as a function of their velocity and the heat content, while the size range was restricted to a certain sieve fraction. Four different types of spread particles are identified: incompletely deformed pancakes with a loose rim, flat firmly bound pancakes, pancakes with a loose double layered rim and a flower type deposit. The intrinsic strengths of the found morphologies were measured. Diffusion bound pancakes appear to be superior to other geometries.