Hardfacing steel with nanostructured coatings of Stellite-6 by supersonic laser deposition

The ability to manufacture coatings is critical to engineering design. Many components require the application of additional layers to enhance mechanical properties and protect against hostile environments. Supersonic laser deposition (SLD) is a novel coating method based on cold spray (CS) principles. In this technique, the deposition velocities can be significantly lower than those required for effective bonding in CS applications. The addition of laser heat energy permits a change in the thermodynamic experience of impacting particles, thereby offering a greater opportunity for efficient bonding at lower velocities as compared with the CS process. The work reported in this paper demonstrates the ability of the SLD process to deliver hardfacing materials to engineering surfaces. Stellite-6 has been deposited on low-carbon steel tubes over a range of process parameters to establish the appropriate target power and traverse speeds for the coating formation. The coating properties and parameters were examined to determine the primary characteristics and grain structure size. Their morphology and performance were studied through optical microscopy, scanning electron microscope (SEM), X-ray diffraction, hardness measurements and wear testing. The results have shown that SLD is capable of depositing layers of Stellite-6, with properties that are superior to those of their conventionally manufactured counterparts. Materials processing: stronger metals Supersonic laser deposition (SLD) can be used to provide metal components with ultrahard, high-quality surfaces. Bill O'Neill and co-workers from the University of Cambridge and Zhejiang University of Technology used SLD to coat steel tubes with a C–Co–Cr alloy coating called Stellite 6. Tests showed that the SLD-produced coatings were crack-free, low in porosity and exhibited excellent bond strength. The researchers used a jet of nitrogen gas at a pressure of 30 bar and a temperature of 500 °C to fire 45-µm-sized particles of Stellite-6 powder at speeds of 400–900 m s −1 onto an area of the sample that had been softened by a high-power laser beam. This deposition process provides strong nanocrystalline coatings that outperform those made by the conventional method of laser cladding.