Effect of Sputtering Power on the Microstructure and Tribological Properties of TiN/TiAlN Coatings Prepared by DC Magnetron Sputtering

TiN/TiAlN coatings were deposited on 40Cr steel substrates by DC magnetron sputtering to improve the surface tribological performance of the steel. The influence of sputtering power (80, 100, 120, 140, 160 and 180 W) on coating morphology, phase structure, adhesion strength and wear behavior was evaluated using SEM, EDS, XRD, Vickers microhardness testing, scratch testing and ball-on-disk tribological testing. The coatings were dense and relatively smooth, with only a small number of submicron particles. Increasing sputtering power increased the coating thickness, and the EDS results suggested an increase in Al content of up to 160 W, whereas the crystallite size of the TiAlN (200) phase first decreased and then increased. XRD analysis showed that the coatings were dominated by face-centered cubic TiAlN, accompanied by weak TiN and AlN diffraction peaks. Among the tested samples, the coating deposited at 140 W showed the most favorable measured combination of adhesion and tribological properties within the tested series, with a thickness of 1.76 μm, a Vickers microhardness of 906.35 HV0.25, an adhesion strength of 45.6 N, an average friction coefficient of 0.322 and a specific wear rate of 28.37 × 10−7 mm3 N−1 m−1. These measured trends are consistent with the dense morphology, refined crystallites, high microhardness and higher measured adhesion observed at moderate sputtering power. In contrast, excessive sputtering power was associated with particle coarsening and coating defects, accompanied by higher measured friction and wear.