Ultra – low friction characteristic of titanium diboride (TiB2) thin films at elevated temperature due to excess addition of boron

Abstract

The research goal is to develop a new coating thin film for machining tools. The difficult-to-cut materials have an excellent characteristic and are highly demanded by industry, however there are serious issue on environment load owing to their low processing efficiency. TiB 2 thin film has a potential to decrease friction coefficient at elevated temperature, and we aimed to study decrease of friction coefficient under 0.1 at 600°C. In the previous research, it was found that the friction coefficient of TiB 2 -MoS 2 composite thin film showed 0.01 at 200°C. It is considered that this ultra-low-friction characteristic is caused by tribo-chemical reaction relating with boron. This low friction property was kept even after heat treatment at 400°C. However, the friction coefficient was increased at 500°C , and the boron and sulfur contents at the TiB 2 -MoS 2 composite thin film decreased. A new TiB 2 -MoS 2 composite film enhances boron reaction due to excess addition of boron. As a result, it was found that boron was indispensable for the ultra-low-friction characteristic at elevated temperature because it is maintained after the heat treatment at 500°C. Dry