Role of process parameters on microstructure, mechanical properties and erosion performance of HVAF sprayed Cr3C2-NiCr coatings

Abstract

In this study, Cr3C2-NiCr coatings of two different particle sizes (fine: 10–30 and coarse: 15–45 μm) were deposited by variable nozzle lengths (long, medium and short) and profiles (convergent-divergent, over-expanding and straight barrel) using high-velocity air-fuel (HVAF) and oxygen augmented air-fuel (HVAF(O)) spray mode. A comparative analysis of the generated coating specimen was performed through the microstructural features, phases present, properties and erosion performance. Additionally, the deposition efficiency (DE) was evaluated to assess the techno-economic feasibility of HVAF/HVAF(O) sprayed Cr3C2-NiCr coatings. All the deposited coatings were dense, uniform and displayed a homogenous distribution of carbides. The convergent-divergent-based long and medium nozzle sprayed coatings displayed better mechanical properties, whereas coatings deposited by short-length nozzles showed relatively inferior properties. In terms of particle size, fine Cr3C2-NiCr sprayed using HVAF and coarse Cr3C2-NiCr sprayed using HVAF(O) displayed improved coating characteristics and properties. Erosive studies implied coatings with improved intersplat adhesion exhibited ductile eroding behavior like “ploughing” and “micro-cutting” rather than “splat flaking/chipping.” Overall, employing a medium-length, convergent-divergent nozzle deposited Cr3C2-NiCr coatings with an ideal combination of DE, mechanical properties and erosion performance. Besides, short-length nozzles were inappropriate for spraying Cr3C2-NiCr since they displayed compromised coating characteristics and performance.