Effects of Sputtering Technology and Bias Voltage on Structure and Mechanical Properties of TiBx Coatings

For large-scale industrial production, the rotation of the substrate is critical for the uniformity of coating deposition. The work aims to reduce the residual stress of TiBx coatings and improve the mechanical properties of TiBx coatings prepared under rotational substrate conditions. TiBx coatings were synthesized on rotating M2 high-speed steel substrates by different magnetron sputtering techniques (dcMS, HiPMS and Hybrid) under different bias voltages. The effects of sputtering technology and bias voltage on the structure and mechanical properties of TiBx coatings were explored. The M2 high-speed steel substrates were ultrasonically cleaned in ethanol, acetone, and isopropanol for a total of 45 minutes to remove potential residues. Before coating deposition, the substrates were etched by applying a pulse bias voltage. To ensure a good adhesion of TiBx coatings on the M2 steel, a Ti interlayer and a titanium nitride (TiN) interlayer were firstly prepared in a dcMS process by both Ti targets. During the deposition of TiBx coatings, the TiB2 cathodes were operated with an average power of 2 kW in the dcMS, HiPIMS, and Hybrid mode. During the TiBx coating deposition, the substrate temperature was approximately 500 ℃, and the substrates rotated in a two-fold rotation at a speed of 1 r/mim. The dc bias voltage varied and was set to −70, −100, and −130 V. The chemical composition of the TiBx coatings was determined by an electron probe microanalysis (EPMA). The cross-sectional morphology and topography of TiBx coatings were characterized by scanning electron microscopy (SEM). The phase composition and crystal orientation of TiBx coatings were characterized by X-ray diffractometer (XRD). The residual stress of TiBx coatings was evaluated by the sin2ψ method. The hardness and elastic modulus of TiBx coatings were characterized by a nanoindenter G200 equipped with a Berkovich diamond probe in continuous stiffness mode (CSM). In addition, the adhesion behavior of the TiBx coatings was analyzed by the Rockwell C adhesion test. The results indicate that different sputtering modes and substrate bias voltages can significantly affect the structure and mechanical properties of the TiBx coatings. Compared with the TiB2 target, the TiBx coatings exhibit overstoichiometric with the excessive B. All the HiPIMS-TiBx coatings reveal a dense structure and smooth topography. With the increase of the bias voltage, the coatings prepared by other sputtering techniques progressively exhibit a dense structure. Under the condition of substrate rotation, all the TiBx coatings still exhibit the desirable (001) preferred orientation due to the high-temperature heating and ion bombardment. With the bias voltage increasing, the residual stresses of the coatings firstly increase and then decrease, while the hardness and elastic modulus increase monotonously. dcMS- and Hybrid-TiBx coatings exhibit excellent adhesion strength (class HF1-HF2), while HiPIMS-TiBx coatings show the worst adhesion strength (class HF1-HF4). Especially noteworthy is that the Hybrid-mode preparation coatings perfectly combine the advantages of dcMS- and HiPMS-modes, with the highest hardness (40.1±1.3) GPa at −130 V, low residual stress, high deposition rate, and excellent adhesion strength. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.