Microstructural Investigation and characterization of newly designed HVOLF thermal spray in narrow and complex area

In this work, WC-Co-Cr coating is deposited on the CA6NM steel of Francis runner turbine component using High Velocity Oxy- Fuel thermal spraying gun. Due to unique design of the gun, which allows coating in narrow areas and inside internal diameter (ID) minimum 85 mm. This HVOF thermal spray system provides increase in sustainability of the components without overheating, provides porous free and dense microstructure, with faster means of spraying. As-received powder and as-sprayed coatings were analysed using XRD, SEM to predict the metallic powder reactions, in addition, surface roughness , micro hardness assessment, evaluation of coating porosity, dry abrasion wear measurement, EDS and adhesion strength measurement were conducted to determine the coating characterization. Due to unique design, better properties have been achieved due to less consumption of gases and optimum spray rates, viz. the lowest porosity about 0.61%, less than 0.90%, highest micro hardness of about 1429 VHN , lowest volume wear loss 0.015 grams on the coated area and highest adhesion bond strength 75.01 MPa. Results show that the coating produced by this HVOF spray gun is best in terms of mechanical properties achieved and allows at coating narrow areas of the hydro turbine components like Francis runner.