Tribological performance of Ni-based self-lubricating claddings for high temperature forming of lightweight alloys

High operating temperatures in hot forming are associated with detrimental mechanisms like oxidation, thermal softening, loss of strength and galling. To mitigate these challenges high-performance tool materials are used, often combined with lubricants and protective coatings.

The aim of the present research work was to investigate tribological performance and potential of Ni-based self-lubricating claddings for high temperature forming of lightweight alloys. Laser claddings included in this investigation were based on Ni-matrix with the incorporation of 5 wt% silver and 10 wt% MoS₂ as solid lubricant precursors. Tribological evaluation and testing was performed on Load-Scanner to simulate hot forming process and results compared to high performance hot work tool steel. Load-scanner utilizes cross-cylinder contact geometry where normal load is gradually increased during sliding, thus providing information on the coefficient of friction vs. load and determination of critical loads for galling initiation and transfer layer build up. To simulate hot forming process of forging, wire drawing and extrusion, tests were done at room and elevated temperatures (150°C and 300°C) against typical light-weight alloys, including AISI 316L stainless steel, 6xxx series Al alloy and Ti6Al4V Ti alloy and results evaluated in terms of coefficient of friction vs. load (single and multi-cycle mode), critical loads for galling initiation, volume of adhered material and wear track surface analysis. Surface analysis was focused on the formation of self-lubricating surface layers and phases depending on the temperature and work material.