Influence of an Electromagnetic Field in the Rapid Solidification and Adhesion of Ni-based alloys in Thermal Spray

A high electromagnetic field (0.3T-Teslas) has proved to affect the splat formation of Ni-based alloys, including: Ni, NiCr, NiCrAl, NiCrBSiFe powders in flame- and plasma- spraying. An effect of splat selection during deposition due to the interaction of the field has been observed. It is hypothesized that when an electromagnetic field is applied to the substrate, only the particles that reach the surface with sufficient momentum get attached and cannot be repelled by the field. Branches of the splashing are observed to be repelled, as well. As an overall effect, the adhesion strength is enhanced. In this study, adhesion tests and splat characterization is carried out in carefully designed experiments to fulfill the ASTM-C633 standard for adhesion testing with concomitant application of a high electromagnetic field during deposition. The field has been modified to act in two different orientations, perpendicular and parallel to the substrate surface, respectively. The results are discussed considering the splat morphology, the microstructure (by image analysis), and adhesion tests. A multi-physics FEA is conducted to understand the effect of the Lorentz force during the impact and rapid solidification of the particles. Some hypotheses are proposed to explain the improvement in coating adhesion.