Self-lubricating materials are becoming more widespread in fields like metal forming or power generation due to the inability to use conventional lubricants in high-temperature (HT) applications. In an effort to summarise the progress done in this field, a detailed literature review has been carried out, ranging from micron-thickness thin films to hardfacings and bulk materials, and classified by the reported solid lubricants. Moreover, the most-cited deposition techniques have been reviewed for each lubricant class in addition to their advantages and limitations. HT friction and wear data for self-lubricating materials have also been examined in order to identify effective lubrication ranges and general trends in their tribological behaviour, which is expected to be useful for researchers interested in this field. Finally, several apparent research gaps have been described, with suggestions for new experimental work that could lead to the development of new high-temperature self-lubricating materials.

Nickel-based self-lubricating claddings with the addition of Ag and MoS₂ were prepared by means of laser cladding on stainless steel substrates, aiming at their implementation in metal forming applications involving demanding tribological conditions at high temperatures. The novelty of this approach is the addition of MoS₂ with the aim to achieve a uniform silver distribution within the resulting cladding by means of an encapsulation mechanism. This prevents it from floating to the surface during the deposition process and thus being subsequently lost during surface preparation. The role of Ag and MoS₂ concentration on the encapsulation process is discussed in terms of phase composition and resulting microstructures. The tribological behaviour of the resulting laser claddings was evaluated at up to 600 °C under unidirectional sliding. The encapsulation of Ag leads to outstanding tribological properties while keeping the concentration of used Ag low, thus increasing the economic viability of the claddings. An improvement in terms of both friction and wear was observed for the self-lubricating claddings compared to the nickel-based reference alloy, thus making them good candidates for use in high temperature applications such as hot metal forming.

Many high temperature (HT) forming processes require the use of solid lubricants in order to control friction and reduce wear. In an attempt to eliminate the need for solid lubrication in high temperature sliding applications, nickel-based self-lubricating coatings with the addition of Ag and MoS₂ were prepared by means of laser cladding on stainless steel substrates.

The behaviour of the resulting laser claddings was thoroughly evaluated up to 600 °C, including the oxidation behaviour and reciprocating tribotesting using different counter body geometries (ball and flat pin). The self-lubricating coatings showed lower friction than the unmodified reference alloy at all tested temperatures, in addition to a significant microstructural stability after prolonged exposure at high temperatures. The addition of solid lubricants to the claddings was also found to be beneficial in terms of the counter body wear at HT, as no material loss could be measured for the bearing balls after testing at 600 °C against the self-lubricating claddings, despite the significant softening experienced by AISI 52100 bearing steel at HT.

In this work, laser cladding has been employed for the preparation of nickel-based self-lubricating coatings featuring the addition of different combinations of soft metal solid lubricants such as Ag and Cu. Transition metal dichalcogenides (WS₂, MoS₂) were evaluated as precursors for encapsulating and uniformly distributing the soft metals throughout the microstructure. The tribological behaviour of the resulting claddings was evaluated under high temperature reciprocating sliding conditions, including two different counter body geometries that lead to very different ranges of contact pressures during testing. An improved tribological behaviour was observed for the self-lubricating claddings compared to the unmodified nickel-based alloy up to 600 °C, attributed to the presence of silver and the formation of lubricous sulfides during sample preparation due to the thermal degradation of the transition metal dichalcogenides precursors. Additionally, the role of the contact conditions observed when testing the self-lubricating claddings against flat pins instead of spherical counter bodies are discussed in terms of frictional and wear microstructural mechanisms.

In recent years, the use of Al/Si coatings has become widespread in hot stamping in order to protect the work piece from detrimental mechanisms such as scale formation or decarburisation affecting the quality of the finished product. However, the formation of Al-Fe intermetallics due to diffusion at high temperature can lead to unstable friction and damage both the tool and the work piece.

In the present study, self-lubricating coatings with the addition of silver and MoS₂ have been prepared by means of laser cladding deposition, aiming at their use in hot stamping in order to decrease friction and wear. The coatings were evaluated at high temperatures against Al-Si-treated boron steel using two different testing configurations featuring open and closed tribosystems. A significant reduction in friction for the self-lubricating claddings were observed along with decreased material transfer. This could be beneficial for hot stamping applications as it can ensure the stability of the process while preventing surface damage to the work piece. Additionally, closed configuration tribotesting has been found to underestimate friction and wear of the tool/work piece system, thus making it less suited for the lab-scale simulation of hot metal forming compared to open configuration tribometers. This finding has been considered relevant as many references in the available literature still report the use of closed configuration tribometers.