Microstructural Design of Self-lubricating Metals for Forming Processes and Aerospace Applications Using Laser Metal Deposition

Abstract

Self-lubricating materials are a broad class of compounds featuring the incorporation of one or more solid lubricants, leading to decreased friction and wear during sliding contact. In our contribution, we devote our effortton the development of self-lubricating metallic alloys for laser deposition processes. Laser deposition processes, such as laser metal deposition or direct energy deposition, are additive manufacturing techniques that offer a great flexibility and efficiency compared to traditional subtractive manufacturing processes. However, the extreme thermal conditions experienced during deposition in addition to rapid cooling pose great challenges for alloy design. This contribution illustrates these challenges by means of self-lubricating iron and nickel-base alloys incorporating lubricious soft metals and metal sulfides. Their microstructure and phase composition are characterized using X‑ray diffraction in addition to scanning and transmission electron microscopy, showing the importance of having the soft metal as single phase without forming intermetallic compounds or being in solid solution. Afterwards, their friction and wear performance are evaluated by using high temperature tribological tests in air and vacuum. The results reveal that the self-lubricating laser deposited alloys are able to control friction from room temperature to 600 °C in ambient air and at least until 300 °C in vacuum.