*Article* **Combined Effect of Substrate Temperature and Sputtering Power on Phase Evolution and Mechanical Properties of Ta Hard Coatings**

**Cuicui Liu 1,2, Jian Peng 2, Zhigang Xu 3, Qiang Shen <sup>2</sup> and Chuanbin Wang 1,2,\***


**Abstract:** Ta hard coatings were prepared on PCrNi1MoA steel substrates by direct current magnetron sputtering, and their growth and phase evolution could be controlled by adjusting the substrate temperature (Tsub) and sputtering power (Pspu) at various conditions (Tsub = 200–400 ◦C, Pspu = 100–175 W). The combined effect of Tsub and Pspu on the crystalline phase, surface morphology, and mechanical properties of the coatings was investigated. It was found that higher Pspu was required in order to obtain α-Ta coatings when the coatings are deposited at lower Tsub, and vice versa, because the deposition energy (controlled by Tsub and Pspu simultaneously) within a certain range was necessary. At the optimum Tsub with the corresponding Pspu of 200 ◦C-175 W, 300 ◦C-150 W, and 400 ◦C-100 W, respectively, the single-phased and homogeneous α-Ta coatings were obtained. Moreover, the α-Ta coating deposited at Tsub-Pspu of 400 ◦C-100 W showed a denser surface and a finer grain, and as a result exhibited higher hardness (9 GPa), better toughness, and larger adhesion (18.46 N).

**Keywords:** α-Ta coatings; substrate temperature; sputtering power; combined effect; direct current magnetron sputtering
