An effective approach for creating metallurgical self-bonding in plasma-spraying of NiCr-Mo coating by designing shell-core-structured powders

Inter-splat bonding dominates the properties and performance of thermally sprayed metallic coatings. Thus, enhancing the inter-splat bonding is a necessary approach to improve the performances of the metallic coatings. In this study, a new approach is proposed to create metallurgical bonding within plasma-sprayed metal alloy coatings by using shell-core-structured powder particle, which is designed by cladding spherical Ni20Cr powders with refractory Mo as alloying element to raise particle temperature significantly high enough to cause impact melting. NiCr-Mo coating was used as model material which was deposited on stainless steel by gas shrouded plasma spraying. NiCr-Mo splats were deposited on Inconel-738 substrate to study the bonding mechanism. Scanning electron microscope (SEM) was employed to characterize the interface bonding within the coating and between the coating and the substrate. Electron Back-Scattered Diffraction (EBSD) was used to examine the crystallographic relationship between each interface. The results show that the NiCr-Mo coating presents much dense structure with remarkably improved cohesion and adhesion strength in comparison with conventional NiCr coating. Higher bonding strength results from the formation of metallurgical bonding at the interfaces both between substrate and coating, and between lamellae. The strong self-bonding strength among lamellae is attributed to increased Ni-based alloy particle temperature higher than the melting point of Mo achieved by Mo cladding NiCr particle design, which is confirmed theoretically by numerical simulation. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.