To enhance the properties of tungsten diboride, we have synthesized and characterized solid solutions of this material with chromium, molybdenum, rhenium and zirconium. The obtained materials were subsequently deposited as coatings. Various concentrations of these transition metal elements, ranging from 0.0 to 24.0 at.%, on a metals basis, were made. Spark plasma sintering was used to synthesize these refractory compounds from the pure elements. Elemental and phase purity of both samples (sintered compacts and coatings) were examined using energy dispersive X-ray spectroscopy and X-ray diffraction. Microindentation was utilized to measure the Vickers hardness. X-ray diffraction results indicate that the solubility limit is below 8 at.% for Mo, Re and Zr and below 16 at.% for Cr. Above this limit both diborides (W,TM)B₂ are created. Addition of transition metals caused decrease of density and increase of hardness and electrical conductivity of sintered compacts. Deposited coatings W_1−xTM_xB_y (TM = Cr, Mo, Re, Zr; x = 0.2; y = 1.7–2) are homogenous, smooth and hard. The maximal hardness was measured for W-Cr-B films and under the load of 10 g was 50.4 ± 4.7 GPa. Deposited films possess relatively high fracture toughness and for WB₂ coatings alloyed with zirconium it is K_1c = 2.11 MPa m^1/2.

Tungsten borides (WB _x ; x = 2.5 or 4.5) with an increasing substitution of tungsten by zirconium from 0 to 24 at.% were synthesized by spark plasma sintering (SPS) for the first time. The influence of the holding time (2.5–30 min) on the densification behavior, microstructure evolution and development of the properties of W–Zr–B compounds were studied. The samples were characterized using scanning electron microscopy (SEM) for microstructure analysis, X-ray diffraction (XRD) for phase identification, Vickers micro-indentation for microhardness measurements, tribological tests to determine the coefficient of friction and specific wear rate, as well as measurements of electrical conductivity. The XRD results confirm the presence of the WB₄ phase in the microstructure, despite the high sintering temperature (1800 °C) and small overstoichiometric excess of boron (4.5) addition in the sintered samples. This is caused by the high heating rate (400 °C/min), short holding time (2.5 min) and addition of zirconium. The Vickers hardness (HV) values measured at 1 N are 24.8 ± 2.0 and 26.6 ± 1.8 GPa for 24 at.% zirconium in WB_2.5 and for 0 at.% zirconium in WB_4.5, respectively. In addition, the hardest sample (W_0.76Zr_0.24B_2.5) showed electrical conductivity up to 3.961·10⁶ S/m, which is similar to WC–Co cemented carbides. The friction and wear test results reveal the formation of a boron-based film which seems to play the role of a solid lubricant.

In this work, α-WB₂ and (W,Ti)B₂ borides were applied as wear-resistant coatings to commercial WC–Co cutting inserts. Properties of coatings deposited by magnetron sputtering on WC–Co tools were studied. The crystal structure and chemical composition were analyzed. Vickers hardness and surface roughness were determined and wear test in semi-dry conditions was performed. The W–B and W–Ti–B coatings deposited on WC–Co substrate were smooth and very hard. However, titanium alloy W-B films with Vickers hardness of 3630 ± 260 HV_0.02 were characterized by lower adhesion to the substrate, influencing the wear mechanism. Turning tests carried out on 304 stainless steel showed that the W–B film caused less wear compared to uncoated insert. Moreover, when W–B coating was applied, flank wear was reduced by 30% compared to uncoated WC–Co insert. Additionally, coating prevented chipping of the edge during cutting under test conditions. The research shows that W–B film deposited by magnetron sputtering has great potential as a coating for cutting tools for difficult-to-cut materials.

Potentially superhard $$W_{1-x}Zr_{x}B_2$$ W 1 - x Z r x B 2 polymorphs, hP6-P6 $$_{3}$$ 3 /mmc-WB $$_2$$ 2 and hP3-P6/mmm-WB $$_2$$ 2 , were thoroughly analyzed with zirconium doping in the range of x=0-25%, within the framework of the first-principles density functional theory, from both a structural and a mechanical point of view. The obtained results were subsequently compared with the properties of material deposited by the magnetron sputtering method. All predicted structures are mechanically and thermodynamically stable. Theoretical calculations suggest a decrease in hardness $$H_v$$ H v and fracture toughness $$K_{\text {IC}}$$ K IC of the hP6 phase with zirconium doping but no such effect on the hP3 phase. It was observed that an additional defect in the analyzed structure significantly weakens the hP6 phase but strengthens the hP3 phase. The deposited films are characterized by greater hardness but lower fracture toughness. The results of experiments show that not only is solid solution hardening responsible for strengthening the predicted new material but also the change in microstructure, the Hall–Petch effect and vacancies.

In this work, tantalum-doped tungsten boride ceramic coatings were deposited from a single sputtering target with the radio frequency (RF) and high-power impulse magnetron sputtering (HiPIMS) methods. Two-inch torus targets were synthesised from pure elements with the spark plasma sintering (SPS) method with a stoichiometric composition of W_1-xTa_xB_2.5 (x = 0, 0.08, 0.16, 0.24). Films were deposited with RF and HiPIMS power suppliers at process temperatures from RT to 600 °C. The substrate heating and the energy of the ionised material impacting the substrate increase the surface diffusivity of adatoms and are crucial in the deposition process. The results of SEM and XRD investigations clearly show that the addition of tantalum also changes the microstructure of the deposited films. The coatings without tantalum possess a finer microstructure than those with 24% of tantalum. The structure of films is homogeneous along the film thickness and composed mainly of columns with a (0001) preferred orientation. Deposited coatings are composed mainly of P₆/mmm α-WB₂ structures. The analysis of nanoindentation results allowed us to determine that ceramic coatings obtained with the HiPIMS method possess hardness above 41 GPa and a ratio of hardness to reduced Young modulus above 0.1. The thickness of HiPIMS-deposited films is relatively small: only around 60% of the RF magnetron sputtered coatings even when the average power input was two times higher. However, it has been shown that the RF coatings require heating the substrate above 400 °C to obtain a crystalline structure, while the HiPIMS method allows for a reduction of the substrate temperature to 300 °C.

We present the deposition and characterization of tungsten-tantalum diboride (W,Ta)B₂ coatings prepared by the high-power impulse magnetron sputtering technique. We evaluated the influence of pulse duration and substrate bias on the properties of (W,Ta)B₂ films. A high hardness of up to 35 GPa measured by nanoindentation was simultaneously obtained with good elastic properties. Changing the pulse duration greatly affected the B/(W+Ta) atomic ratio, which influenced the properties of the coatings. The deposited films are thermally stable at up to 1000 °C in vacuum and are able to withstand oxidation at 500 °C.