Evolution of structure and mechanical properties of hard yet fracture resistant W‐B‐C coatings with varying C/W ratio

Abstract

Preparation of coatings simultaneously exhibiting high hardness and enhanced fracture resistance is a hot topic, as nowadays used ceramic protective coatings show difficulties to cope with increased demands due to their inherent brittleness. Material exhibiting seemingly contradictory combination of mechanical properties-high hardness and moderate ductility enhancing the fracture resistance-was recently predicted by ab initio calculations in the crystalline X2BC system. The presented study is focussed on the study of the influence of the C/W ratio on the microstructure, the content of different chemical bonds and the mechanical properties of W-B-C coatings prepared by magnetron sputtering at moderate temperature. It was shown that change of the deposition conditions to achieve different C/W ratios influences the energy flux and momentum transfer to the coating. The coating with the lowest C/W ratio experienced the highest energy flux and momentum transfer, which resulted in a dense coating microstructure. The microstructure progressively coarsened as the C/W ratio increased, i.e. as

Reactive magnetron sputtering of tungsten target in krypton/trimethylboron atmosphere

“…The Er measured in our films follow the same trends previously described for hardness, see Fig. 8a and 8b, with the highest value of ~ 280 GPa for the film deposited with 10 sccm TMB at 500 o C and a lowest value of ~130 GPa for the film deposited at 900 o C. Similar as for the hardness, our Er ~ 280 GPa value is similar to the Er ~ 300 GPa reported by Debnárová et al [27] but lower than the ~ 450 GPa reported in the studies by Alishahi et al [26]. Furthermore, for W2C and WC1-x films containing 35 at.% C Palmquist et al [14] measured an E-moduli of ~ 450 GPa, i.e.…”

“…3a, centered at 187.9 eV, are of low intensity for films deposited with 1 and 2.5 sccm TMB. This binding energy is identical to the measured B-W binding energy for W2B5 [34] and W-B-C films deposited by Alishahi et al [26], and close to the 188.1 eV reported by Liu et al for W-B-C films [25]. There is no indication of B-B or B-O bonding in the films as no B 1s peaks are visible at 189.4 eV [34] or ~192-193 [34], respectively.…”

“…This is a consequence of the reaction between the Si(100) substrate and the film, resulting in formation of WSi2 at 700 and 800 o C or a Si rich surface at 900 o C as determined from our XRD and XPS measurements and where the reaction also yields an increased surface roughness seen from the loss of the silver-white color and metallic luster. The H varies in the range 23 to 31 GPa for films deposited with different TMB flows and at temperatures ≤ 600 o C; a closer inspection shows the lowest H values for the films deposited at temperatures of 200, 300 and 400 o C, with H = 23, 25, and 24 GPa, respectively.Our H values are comparable or even slightly higher than the reported HV of d-WC with 22 GPa for a 0001-oriented single-crystal[2] as well as to those reported for more carbon and boron rich W-B-C films by Alishahi et al[26] and Debnárová et al[27] with values in the range ~24 to ~29 GPa and ~23 GPa, respectively. In contrast, our H values are lower than the ~37 to ~47 GPa reported by Su et al[24] for d-WC films alloyed with ~4 to ~7 at.…”

Composition, Structure and Mechanical Properties of Industrially Sputtered Ta–B–C Coatings

“…This can be seen in the center diffraction patterns in Figure 8a,b. However, the formation of short-range ordered structures in the X-ray amorphous coating such as those seen in the case of WBC coatings is possible [23,25].…”

“…Later, an ab-initio modeling of similar materials was performed and it was reported that crystalline Ta 2 BC and W 2 BC in particular are also promising candidates for experimental synthesis owing to their calculated elastic properties indicating their simultaneous high stiffness and moderate ductility [13]. Although experimental studies of coating systems like Ti-B-C [14][15][16][17][18][19][20], Ta-B-C [21], Nb-B-C [22], and W-B-C [19,[23][24][25][26][27][28] potentially leading to the formation of the X 2 BC crystalline structure have been published, no formation of the ternary crystalline X 2 BC phase other than Mo 2 BC has ever been reported [11,13].…”