Effect of Sputtering Technology on Microstructure and Mechanical Properties of TiN Coatings

The microstructure properties of TiN coating are mainly affected by the deposition conditions, which in turn are affected by the sputtering technology. The proper use of the sputtering technology allows to control the state of ion bombardment during coating growth and tailors the crystal structure, thereby improving the properties of TiN coating. Therefore, TiN coatings were deposited on the M2 high-speed steel by different sputtering technologies (dcMS, HiPMS, and Hybrid) in this work. The effects of different sputtering technologies on the microstructure, mechanical properties, and high temperature wear properties of TiN coatings were investigated. Before coating preparation, the ϕ40 mm×5 mm M2 high speed steel substrate was mechanically polished. The polished substrate was ultrasonically cleaned in ethanol, acetone, and isopropanol sequentially to remove residues on the surface. To improve the adhesion strength between coating and substrate, the M2 high speed steel substrate was etched by applying an intermediate frequency pulse bias (−650 V) with a frequency of 250 kHz, and a 200 nm Ti buffer layer was prepared by dcMS technology. Then, TiN coatings were prepared by different sputtering technologies such as dcMS, HiPIMS, and Hybrid, respectively, in which the average power of Ti targets was always 4.5 kW. During coating deposition, a negative DC bias of −100 V was applied to the substrate. The workpiece holder always maintained the mode of revolution and rotation. The cross-sectional morphology and thickness of the coatings were measured by scanning electron microscopy (SEM, Zeiss Supra 55). The composition of the coatings was analyzed by energy dispersive spectroscopy (EDS). The phase and crystalline structure of the coatings were characterized by X-ray diffraction (XRD, D/Max 2500). The residual stress of the coatings was analyzed by the sin2ψ method. The nanohardness of the coatings was measured by a nanoindenter (Nano-Indentor G200, Agilent). The adhesion of the coatings was evaluated through Rockwell C indentation test and scratch test. The high temperature wear properties of the coatings were tested on a ball-on-disk friction tester (CSM-Instruments, Peseux), and the test temperature was set at 25 ℃, 300 ℃, and 500 ℃, respectively. After the high temperature wear test, the cross-sectional profile of the wear tracks was analyzed by a surface profilometer (Infinite Focus Alicona, Austria), and the wear rates of the coatings were calculated. The TiN coatings prepared by different sputtering technologies all exhibit columnar crystal structures and a preferred orientation at TiN (111). The HiPIMS-TiN coatings have high density, residual stress, and nanohardness. The highest hardness of HiPIMS-TiN coatings reaches 29.7 GPa. The dcMS-TiN coatings show high adhesion with a critical load Lc3 of 100 N. The Hybrid-TiN coatings exhibit the lowest residual stress, high deposition rate, and high adhesion. The adhesion of the Hybrid-TiN coating reaches HF1 level, and the critical load Lc2 is about 82.5 N. The friction coefficient of TiN coatings prepared by different sputtering technologies decreases with increasing temperature. At 500 ℃, the friction coefficient of TiN coatings is about 0.53. However, the wear rate increases with increasing temperature. At different temperatures, the Hybrid-TiN coatings show the lowest wear rate. Sputtering technology plays a more significant role in improving the microstructure and mechanical properties of TiN coatings. Hybrid-TiN coatings exhibit the optimum comprehensive mechanical properties and high temperature wear properties. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.