Self-Lubricating Properties of Laser Claddings for High Temperature Forming Processes

This thesis summarizes the work done on tribological characterization of multifunctional hardfacing coatings with self-lubricating properties, intended for use in mechanical components operating in high temperature applications for which conventional lubricants are no longer effective. Deposition techniques like laser cladding have a great potential in reworking/repair of high value industrial components in order to extend their lifetime. It is expected that the use of self-lubricating laser claddings could be useful in high temperature applications like metal forming, leading to decreased friction and wear. In this study, the tribological behavior of self-lubricating claddings has been studied against steel and aluminum counter surfaces, using ASI52100 bearing steel in addition to AA6082 and AA2007 aluminum flat pins as the counter bodies. Nickel- and iron-based powders have been chosen for the preparation of claddings. Self-lubricating properties of Ag/MoS2 have been compared to an untreated reference cladding and grade 1.2367 tool steel. For steel counter surfaces, tribological properties in the temperature range between RT and 600⁰C have been investigated and at 300°C for aluminum counter surfaces. Tribological tests were done by a high frequency linear oscillation (SRV) test machine under reciprocating conditions. The wear scar and volume of coatings were measured by using a 3D optical profilometer. SEM/EDS analysis were additionally performed for the characterization of microstructure and wear scar. The results indicated that MoS2 reduced friction and wear of the Fe-based cladding material when tested against steel at room temperature compared to the reference alloy and grade 1.2367 tool steel, and that the addition of silver further decreased wear in addition to early stage friction. It was also observed that the tribolayer, which was formed during the sliding of Ni-based - 5 Ag - 10 MoS2 and against aluminium under lubricated conditions, was protective and provided low and steady friction.