Influence of Plasma Spray and HVOF Coatings using Advanced Techniques on the Mechanical Properties; A Positron Lifetime Spectroscopy

The surface modification processes such as hard facing, case carburizing, thermal spraying, ion nitriding, tough nitriding, and others, are some of the important techniques being adopted for providing enhanced life for parts and components, in service. Among them, plasma spray and High Velocity Oxy Fuel (HVOF) spray coatings are popular and widely used. In this investigation, plasma & High Velocity Oxy Fuel (HVOF) processes have been employed to prepare chromium oxide and chromium carbide coatings on metal substrates, respectively and evaluated for mechanical and metallurgical properties. Thus the present work mainly focuses on the development and structural integrity evaluation of chromium oxide and chromium carbide coatings in terms of hardness, wear properties and residual stress parameters. Further, a non-destructive test method namely Positron Lifetime Spectroscopy (PLS) has been used to assess the quality and integrity of coatings in terms of its size and defects concentrations. The results show that chromium carbide HVOF coatings showed improvement in the properties namely, abrasion, erosion, slide wear resistance, and hardness in the range 20-25%, 10-45% (all impact angles), 55-75% and 48-50% respectively compared to chromium oxide coatings. The Scanning Electron Microscopic (SEM) pictures reveal the presence of less number of voids and less porosity in chromium carbide coating compared to chromium oxide coating, thus giving good credence to the Positron Lifetime Spectroscopy (PLS) data. Based on the properties investigated in this work, good correlations have emerged. KeywordsHVOF, Plasma Spray, Positron Lifetime Spectroscopy, Erosion, Residual Stress.