Transition metal diborides; Self-lubrication; Boron oxide; High temperature tribometry; Friction
en
Abstract:
Transition metal borides represent an auspicious family of materials for functional coatings due to their refractory nature, including high melting points, extreme hardness, and outstanding resistance to wear. Additionally, they act as model systems to study in-operando self-lubrication through the formation of friction-reducing boron oxide layers. The prevailing temperature and composition strongly influence the boron oxide formation. In this study TiB2±x thin films have been used to explore the fundamentals of this, so far, not fully understood temperature driven tribo-reaction. Tribological tests indicate that sputter deposited super-stoichiometric TiB2.9 exhibits a significantly lower friction coefficient (∼0.3) compared to sub-stoichiometric TiB1.5 (∼0.4) when tested at 500 °C. This reduction is attributed to the higher oxidation rate of super-stoichiometric TiB2.9 further promoted through the presence of B-rich tissue phases at the column boundaries. Moreover, although the coatings showed slightly higher wear rates at 500 °C than at room temperature, the overall wear remained low – most notably for the oxidation-prone super-stoichiometric TiB2.9, which also displayed the strongest friction-reducing effect. In summary, these results highlight the potential of boron oxide for solid self-lubrication.
en
Research facilities:
Analytical Instrumentation Center Röntgenzentrum Universitäre Service-Einrichtung für Transmissionselektronenmikroskopie
-
Project title:
Unravelling the Solid Self-Lubrication Mechanisms of Boron Oxide on Transition Metal Boride Thin Films: PAT1205324 (FWF - Österr. Wissenschaftsfonds)
-
Project (external):
Swedish Research Council European Union UK Research and Innovation (UKRI) Swiss State Secretariat for Education, Research and Innovation (SERI)