W-B-N sputter-deposited thin films for mechanical application

Abstract

The structure, composition and hardness of reactively sputtered W-B-N thin films were investigated by XRD, EPMA, and Vickers ultramicroindentation.The chemical composition of the films was changed from W 80 B 20 to W 42 B 9 N 49 by varying the partial pressure of N 2 . All the as-deposited coatings were amorphous, except the W 60 B 17 N 23 film, which showed crystalline peaks, indexed as bcc a-W, overlapping the amorphous feature. This nanocomposite structure lead to a maximum as-deposited hardness of 36 GPa.The coatings were thermally annealed at 850 and 950 8C in Ar/H 2 atmosphere. All the films crystallised with the formation of the bcc a-W and/or the fcc-W 2 N phases, depending on their B and N contents. A small increase in hardness was registered for 850 8C annealing temperature in comparison to the as-deposited state. However, an inverse trend was detected after post-annealing at 950 8C, which was more evident for the high N content films. This behaviour was attributed to the formation of a soft external layer of boron nitride poorly crystallised. D

Mechanical, tribological and corrosion performance of WBN composite films deposited by reactive magnetron sputtering

“…As the B content is below 31.9 at.%, the (1 1 1) peak shifts to lower angles, indicating an increase in lattice constant. In this work, the nitrogen content is higher than 10 at.%, the boron content is not enough to form W-B binary phases [18,20,21], so the B atoms only exist in the form of interstitial atoms or combine with N atoms to form BN. The increase of lattice constant with the addition of boron is attributed to that the B atoms existed in the form of interstitial atoms.…”

“…According to the FTIR absorption spectrum of films depicted in Fig. 2, as the B content is 31.9 at.%, two absorption peaks of BN which shares similar sp 2 -bonded structure at 800 cm −1 and 1500 cm −1 are observed, indicating forming B N bonds [18]. As the B content increases, the absorption peaks become stronger.…”

“…Louro et al [18] have reported that it was expected that preferential formation of B N bonds would occur, since the affinity of B for N was higher than that of W for N ( H f W2N = −17 kcalmol −1 ; H f BN = −60.8 kcalmol −1 ). However, no crystalline BN diffraction peaks are detected in any of the XRD patterns, which suggests that BN or B may be present in an amorphous form or as interstitial atoms in the W 2 N lattice.…”

“…The grain sizes are determined from the integral peak width in XRD measured data in Â-2Â mode according to Scherrer's equation [23]. The grain size, which has been found to be about 17 nm for pure nitride, drops a little and then decreases sharply due to that the W 2 N phase is forced to re-nucleate on top of segregated BN layers [18].…”

“…Leu L C et al [17] have prepared amorphous WBN thin films at room temperature via reactive magnetron sputtering and found 10 nm WBN thin film deposited at 5% N 2 flow ratio was a potential candidate as a diffusion barrier for copper metallization schemes. C. Louro et al [18] nitrogen flow rate ratio during sputtering had strong influence on the structural characterization, the change of hardness in as-deposited state and after thermal annealing was also studied. All the films crystallised with the formation of the bcc ␣-W and/or the fcc-W 2 N phases, depending on their B and N contents, the presence of an h-BN phase in the coating can be beneficial for dry machining applications.…”