Superelastic (Cr,Al)N coatings for high end spindle bearings

Due to the increase in performance of machine parts, the surfaces of l00Cr6 ball bearings are highly stressed. High rotational speeds and machining forces arising from up-to-date production processes increase Hertzian pressures and – as a consequence – the wear of the bearings. In this matter, new composite materials are investigated to extend the bearing capability. In preliminary investigations, cylinder roller bearings were successfully coated to reduce wear and friction within the mixed lubrication. As a follow up, these coatings are now investigated for elastohydrodynamical (EHD) lubrication in spindle bearings. In this paper, (Cr,Al)N coating is presented, which was deposited at low temperatures (< 160 °C) to avoid annealing of the bearings. In the first part of the paper, the coating and its design were investigated with respect to mechanical, elastic and tribological properties. In the second part, these coatings were then evaluated in a spindle bearing test unit with respect to the temperature rise dependent on rotational speeds.