Pulsed DC titanium nitride coatings for improved tribological performance and tool life

Titanium nitride (TiN) has long been used as a hard, wear resistant coating material, but it has never been regarded as a low friction material. Recent results though, suggest that TiN coatings deposited by pulsed magnetron sputtering (PMS) can have significantly enhanced tribological properties, in particular, significantly lower coefficients of friction, in comparison with films deposited by continuous DC processing. This paper, therefore, reports the results to date from a detailed study of the tribological properties of TiN coatings produced by PMS. Coatings were deposited under varying conditions of pulse frequency and substrate bias (DC and pulsed). The structural properties of the coatings were investigated by SEM and XRD, whilst the physical and tribological properties were determined using scratch adhesion testing, thrust washer wear testing, hardness testing and surface profilometry. In addition, batches of 6.35 mm diameter HSS twist drills were also coated by PMS and continuous DC processing. The performance of these drills was assessed in tool life tests, in which holes were repeatedly cut in M200 steel. The results confirm that TiN coatings produced by pulsed processing consistently outperform those produced by continuous processing, in terms of tribological properties and tool life.