Protecting against heavy friction and sticking
Conventional lubrication oils cannot be used to avoid sticking of components. And although thermal spray methods are indicated for producing wear-resistant coatings, tailored coatings including solid lubricants are not commercially available. Turning to tribology offers industrial solutions for such heavy engineering problems. This is a branch of mechanical engineering focused on the science and engineering of interacting surfaces in relative motion. The field includes study and application of the principles of friction, lubrication and wear. The 'High performance self-lubricated multifunctional coating for demanding industrial applications' (Sefuco) project set out to find a way of ensuring the reliable function of critical components' self-lubricating wear-resistance coatings. The EU-funded project focused work on the three technology areas of powder production, thermal spraying and tribology. Advances in these areas also aimed to protect against exposure to hazardous waste as a result of chemical leakage caused by sticking and tribology issues. Project partners sought to enhance manufacturing techniques for novel powder production to render optimal powder structure and new powder compositions for thermal spraying. Thermal spray techniques are coating processes involving the spraying of melted materials onto a surface, with coating quality usually assessed by measuring bond strength, porosity, oxide content and surface roughness. Control of the manufacturing route begins with processing of the coating material. The consortium tailored material compositions according to applications under study and began powder manufacturing and the optimisation of powder processing parameters to achieve suitable quality for the spray powders. When sufficient powder quality level was attained, products were sent for thermal spray tests and team members started optimising spray-coating processes. These included high-velocity oxygen fuel (HVOF), in particular, for spraying powders containing solid lubricant materials. This allowed for adapting them to different application environments. Tribological tests were performed to determine the tribological, wear and corrosion properties of the coatings containing solid lubricants. A major achievement related to powder processing was the successful creation of powder with good flowing properties for thermal spraying. Thermal spraying with developed experimental powders returned good coating quality. Coatings were manufactured where added solid lubricant did not result in decomposition during the spraying process and performed well under abrasive wear tests. Coatings were then sent for extensive tribological testing. Results showed that solid lubricant additions did slightly reduce the wear resistance of coatings. This was expected on the strength of a comprehensive review of the literature. Sefuco members created about 23 new exploitable compositions from their results. Enhanced knowledge regarding the manufacturing of novel powder compositions and tailored compositions can now be applied to certain applications and optimise the reliability of components functionality.
