**2. Materials and Methods**

CrWN coatings having different W contents were synthesized by PEMS [21]. Pure W (99.9%) and Cr (99.6%) were used as sputtering targets. A silicon wafer and cemented carbides (WC-8 wt % Co) were used for the substrate. The samples were mechanically polished using a diamond paste and ultrasonically washed using pure ethanol. High purity nitrogen and argon were utilized for the working atmosphere. The samples were placed on a rotated holder, moving at a rotating speed of 2 rpm. The chamber was evacuated to a base pressure of 5 <sup>×</sup> <sup>10</sup>−<sup>3</sup> Pa and then heated to 300 ◦C. Prior to coating deposition, the samples were cleaned by Ar<sup>+</sup> sputtering to remove any residual pollution and the native oxides. The sputtering parameters were as follows: bias voltage of −120 V, argon flow of 140 sccm, sputtering time 60 min. The CrWN coatings were synthesized in a mixed atmosphere of nitrogen and argon. The chemical composition of the as-deposited coating was varied by adjusting the powers of the Cr and W targets. In this case, the deposition parameters were displayed as follows: bias voltage of –50 V, argon flow 100 sccm, nitrogen flow 100 sccm, and deposition time 100 min. The deposition parameters are listed in Table 1.


**Table 1.** Experimental details of as-deposited coatings.

The compositions of the coatings were determined by an energy dispersive spectrometer (EDS) combined with a scanning electron microscope (SEM, Zeiss IGMA HD, Oberkochen, Germany). Moreover, the crystalline structures of the coatings were investigated by X-ray diffraction (XRD, X' Pert Powder, Malvern Panalytical, Malvern, UK) using a Cu Kα radiation source with parallel beam. The incident angle was of 1◦, while the diffraction angle was scanned from 20◦ to 90◦. Additionally, X-ray photoelectron spectroscopy (XPS, ThermoFisher, K-Alpha+, Waltham, MA, USA) was employed to detect the chemical states of the coatings. The data were collected after 30 s from etching to remove any contaminants adsorbed on the coating surface. A SEM (Zeiss IGMA HD) was employed to characterize the surface morphology of the coatings, while their microstructure was investigated with a transmission electron microscope (TEM, FEI Titan Cubed Themis G2 300, ThermoFisher, Waltham, MA, USA). Moreover, atomic force microscopy (AFM, Oxford MFP-3DInfinity, Abingdon, UK) was employed to evaluate the surface roughness of the coatings: the scanning area of each image was of 10 × 10 μm. The mechanical properties of the coatings were evaluated by using a nm-indentation

system (Hystron TI950, Bruker, Billerica, MA, USA): five indentations were performed on each sample; additionally, the hardness and elastic modulus selected at a depth of corresponding to 1/10 of the coating thickness, as to minimize the negative effect of the substrate. Finally, vacuum annealing was conducted in a heat treatment furnace at a pressure of 0.1 Pa (RTP-500, Beijing Ruiyisi Technology Co.LTD, Beijing, China), the annealing temperature and time were of 650 °C and 300 min, respectively.
