Novel chemical process for preparing h-BN solid lubricant coatings on titanium-based substrates for high temperature tribological applications

Hexagonal boron nitride (h-BN) coatings prepared from a polyborazylene (PBN) polymeric precursor were deposited on titanium-based substrates and annealed via infra-red irradiation in a rapid thermal annealing (RTA) furnace. Crystallized h-BN coatings were obtained by adding Li3N as a catalyst at a relatively low annealing synthesized temperature (~ 1200 °C). The resulting coatings had a thickness of 15 μm and were evenly coated and homogenous. The coating/substrate adhesion was evaluated by the micro-scratch test, with the value of best critical load occurring at approximately 12 N against a Rockwell C diamond point. This adhesion increased with the growth of the additive ratio of Li3N. The friction coefficient measurements were carried-out by tribological testing at 360 °C using a cylinder/disk configuration. Stainless steel 15-5PH cylinders were used as counter bodies to the titanium disk. The friction coefficient was reduced from 0.72 for the Ti/stainless tribosystem to 0.35 for the Ti/h-BN/stainless tribosystem.