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Superhard nanostructured coatings, prepared by plasma-assisted chemical vapour deposition (PACVD) and physical vapour deposition (PAPVD) techniques, such as vacuum arc evaporation and magnetron sputtering, are receiving increasing attention due to their potential applications for wear protection. In this study nanocomposite (TiAl)B x N y (0.09 ≤ x ≤ 1.35; 1.07 ≤ y≤ 2.30) coatings, consisting of nanocrystalline (Ti,Al)N and amorphous BN, were deposited onto Si (100), AISI 316 stainless steel and AISI M2 tool steel substrates by co-evaporation of Ti and hot isostatically pressed (HIPped) Ti-A1-B-N material from a thermionically enhanced twin crucible electron-beam (EB) evaporation source in an Ar plasma at 450 °C. The coating stoichiometry, relative phase composition, nanostructure and mechanical properties were determined using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), in combination with nanoindentation measurements. Aluminium (∼ 10 at.% in coatings) was found to substitute for titanium in the cubic TiN based structure. (Ti,Al)B 0.14 N 1.12 and (Ti,Al)B 0.45 N 1.37 coatings with average (Ti,Al)N grain sizes of 5-6 nm and either ∼ 70, or ∼ 90, mol% (Ti,Al)N showed hardness and elastic modulus values of ∼ 40 and ∼ 340 GPa, respectively. (Ti,Al)B 0.14 N 1.12 coatings retained their 'as-deposited' mechanical properties for more than 90 months at room temperature in air, comparing results gathered from eight different nanoindentation systems. During vacuum annealing, all coatings examined exhibited structural stability to temperatures in excess of 900 °C, and revealed a moderate, but significant, increase in hardness. For (Ti,Al)B 0.14 N 1.12 coatings the hardness increased from ∼40 to ∼45 GPa.

Copper-based bulk nanocrystalline and amorphous alloys offer attractive mechanical properties such as high hardness and fracture toughness—as well as good corrosion resistance. Such materials can potentially be used as thin film tribological coatings to improve the wear resistance of low strength steels and the light alloys. In this paper novel CrTiCu(B,N) glassy-metal coatings have been successfully deposited on Si-wafer, AISI 316 stainless and AISI M2 tool steel substrates, over a wide range of compositions, by hot-filament enhanced reactive magnetron sputtering. The majority of the coatings produced are X-ray amorphous and exhibit Knoop microhardness values above Hk 25g =2000 Kgf/mm 2 (i.e. ≥ 20 GPa). The coatings provide a significant improvement, by more than two orders of magnitude, in reciprocating sliding wear rate (compared to the stainless steel substrate) when tested against a 10 mm diameter SAE 52100 hardened steel ball counterface at 10 N normal load. In impact tests for 10 5 cycles against a 10 mm diameter WC–6% Co ball, at a maximum load of 1 kN, the coatings exhibit excellent resilience and ductility—with small impact cavities and little or no peripheral or radial cracking around the impact craters.

Metallic nanocomposite coatings offer an enhanced hardness/elastic modulus (H/E) ratio, important for many wear applications. CrCuN coatings have shown promising impact wear properties and CrTiCuBN coatings are now being studied to investigate the effect of boron and titanium additions to this system. The coatings have been deposited by unbalanced reactive magnetron sputtering. The hardness, elastic modulus and nanowear properties of the coatings have been examined. For some compositions, post-coat vacuum annealing for up to 1 h at temperatures between 550 and 600 °C resulted in a significant increase in measured hardness. Characterisation of such films by X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) has been performed to provide information on chemical composition, nanostructure and bonding. The phase composition obtained is considered with reference to the Cr–B–N ternary phase diagram.

This study reports the results of work carried out to improve the corrosion resistance of NdFeB magnets by a direct phosphate treatment of the NdFeB magnet surface. The growth of a phosphate film on a NdFeB based magnet in a solution of 0.15M NaH 2 PO 4 acidified to pH 3.8, was followed by electrochemical impedance spectroscopy (EIS) and open circuit potential variation as a function of time. After removal from the phosphating solution, the magnet surface was analysed by Auger electron spectroscopy (AES) and energy dispersive X-ray analysis (EDX). Phosphate formation on the surface was confirmed and a significant variation in the Fe/Nd ratio in the phosphate between the Fe and Nd rich phases of the magnet was found. The corrosion resistance of the phosphated magnets was evaluated in a normal enclosed atmospheric environment and in Na 2 SO 4 solution and synthetic saliva by EIS measurements. The corrosion resistance was found to be substantially improved by the presence of a phosphate layer.

Coatings with a nanocomposite structure have been identified as offering excellent wear resistant properties. This paper presents results on the CrCu (N) system, in which the immiscibility of Cr (with low N concentration) and Cu offers the potential of a predominantly metallic (and therefore tough) nanocomposite, composed of small Cr (N) grains interdispersed in a (minority) Cu matrix. A range of CrCu (N) compositions have been deposited using a twin-target (Cr and Cu) unbalanced magnetron sputtering system. The stoichiometry and nanostructure have been characterised by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron energy loss spectroscopy (EELS). The hardness and elastic modulus have been determined by nanoindentation. The phase composition of the coatings is generally based on Cr 2 N with the additional presence of Cr and CrN depending on the elemental composition. Cu was found to be incorporated in the Cr based phases. The formation of this metastable structure is attributed to the relatively low deposition temperature employed (∼200 °C). The coating with the best mechanical properties, CrCu 0.07 N 0.48 exhibited a hardness of 20 GPa.

Physical vapour deposition (PVD) Zn alloy coatings are being considered as possible alternatives to conventional hot dip and electrochemically deposited coatings on steel substrates. Variation of the deposition temperature leads to very different microstructures being observed by SEM, primarily due to the low melting point of zinc. In the present study this phenomenon has been investigated in more detail. Zn+5 at.% Al coatings were deposited by magnetron sputtering using a homogeneously alloyed Zn–Al target. As the substrate temperature is increased, the coating morphology changed from a compact to an open sponge/woollen-like microstructure and the coating thickness increased by up to a factor of 10. The Zn–Al coatings displayed a hexagonal structure corresponding to that of Zn. The corrosion properties were investigated by potential–time and salt bath immersion tests. Interestingly, both the barrier and sacrificial protection afforded by the coating were independent of the microstructure.

Near-edge X-ray absorption fine structure (NEXAFS) measurements have been made on carbon nitride films containing as much as 44 at.% of nitrogen. The films have been synthesized by dual ion beam deposition (IBD) bombarding a carbon target with low-energy nitrogen ions at varying nitrogen beam energies and substrate temperatures ranging from the liquid nitrogen temperature up to 400°C. The structural changes induced by the reduction of the temperature have been previously investigated [Hammer et al., J. Vac. Sci. Technol. A 15 (1) (1997) 107; Baker et al., Surf. Coat. Technol. 97 (1997) 544]. The transition from a predominantly sp2/sp3 CN amorphous arrangement to a more polymer-like structure has been confirmed and more deeply examined by X-ray absorption spectroscopy. In particular, for samples deposited at liquid nitrogen temperature, a relevant reduction of sp2 CC fraction has been detected. Moreover, the condensation on the growing film surface of hydrogen containing species (i.e. HCN) has been well identified by the appearance of the CH∗ peak.

TiN–MoSx coatings have been produced using a hybrid reactive arc (TiN) and magnetron sputter (MoSx) deposition process. The process allowed a maximum total Mo and S incorporation of 8 at.%. The coatings displayed a cubic TiN structure with slightly enlarged lattice constants. By suitable process parameter control, coatings of high adhesion on hardmetal and HSS substrates were produced. Hardness values of up to 30 GPa and friction coefficients against steel and Al2O3 of less than 0.2 were obtained for the TiN + 8 mol% MoSx coatings. To determine the suitability of such coatings for use in dry machining, the lifetime of coated drills used in lubrication-free conditions was measured. A comparison of the best performing drills showed the TiN + 8 mol% MoSx coating to increase the lifetime by almost twofold with respect to the TiN coating and up to fivefold with respect to an uncoated drill.

Composite low-friction coatings have been produced by combining a lubricating phase (C) and a hard wear-resistant phase (TiB 2 ), deposited in the form of either multilayer (TiB 2 /C) or homogeneous (TiB 2 -C) films. The multilayer coatings were prepared by sequential magnetron sputtering, and the homogeneous coatings by co-sputtering from TiB 2 and C targets. The coatings were characterised by glancing angle X-ray diffractometry and photoelectron spectroscopy. Friction coefficients were measured using a pin-on-disk tribometer, and hardness was determined by nanoindentation. Co-sputtered coatings were found to consist of two phases: diamond-like carbon (DLC) and a hexagonal TiB 2 -type structure into which carbon is incorporated. In the case of the co-sputtered coatings, overall C concentrations as high as 50 at.% were required to produce a friction-reducing effect. This can be explained by the preferential incorporation of the carbon atoms into the TiB 2 lattice, the lubricating DLC phase only starting to form once saturation is reached. In the case of multilayers, it was found that there was an increase in the overall carbon content required to obtain a friction-reducing effect from about 10 to 50 at.% as the TiB 2 sublayer thickness was decreased from 100 to 1 nm. This was attributed to an increase in the relative proportion of carbon bonded with TiB 2 in the interface regions. It was shown that coatings with a hardness of the order of 20 GPa and displaying friction coefficients against steel as low as 0.1 for temperatures not exceeding 200°C could be obtained by selecting a suitable composition.

Coatings of the overall composition TiNx(MoSy)z have been produced by dc co-sputter deposition from a single unbalanced magnetron target composed of TiN and MoS2 halves. Compositional variation was obtained by placing stainless steel substrates at various positions with respect to the target. X-ray diffraction and photoelectron spectroscopy showed that the coatings were composed of distinct TiNx and MoSy phases in the form of a nanodispersive system. Pin-on-disk tribometry and nanoindentation demonstrated that coatings with a hardness exceeding 20 GPa and friction coefficients of about 0.1 could be produced by selecting suitable composition and deposition parameters. These coatings show potential for improved endurance with respect to current MoS2-based low-friction coatings and may be suitable for use in severe conditions, for example, as cutting tool coatings for dry machining.

Hard, low-friction, TiB 2 -based coatings incorporating C or MoS 2 have been synthesised by magnetron co-sputtering from TiB 2 and C or MoS 2 targets. The coating microstructure was characterised by glancing angle X-ray diffractometry and photoelectron spectroscopy. The friction coefficient was measured using pin-on-disk tribometry and hardness by nanoindentation. Our TiB 2 –C coatings were found to consist of two phases, diamond-like carbon (DLC) and a hexagonal TiB 2 type structure into which carbon is incorporated. A friction-reducing effect was observed only at C concentrations above 66%, where a significant quantity of DLC phase was able to form. For TiB 2 –MoS 2 coatings, a reduced friction was observed, even at low concentrations of MoS 2 . With both types of lubricants, a trade-off between hardness and friction coefficient was found. Coatings exhibiting a relatively high hardness of 20 GPa and friction coefficients as low as 0.05 could be obtained by choosing a suitable composition. Low friction could be obtained for temperatures as high as 400 °C for the TiB 2 –MoS 2 coatings, whilst the TiB 2 –C coatings exhibited a sharp increase in friction coefficient above 150 °C.

Bombarding a carbon target with low-energy nitrogen ions causes the release of neutral carbon atoms (physical sputtering) and volatile carbon nitride compounds (chemical sputtering) with relative yields dependent on the energy of the nitrogen beam. The chemically sputtered species are volatile and can be condensed on the substrate by reducing its temperature. Carbon nitride films have been deposited at varying nitrogen beam energies and substrate temperatures in a dual ion beam deposition chamber. Films were grown both with and without the presence of an additional assisting nitrogen beam. Reduction of the substrate temperature in conjunction with low sputter beam voltages (

The beneficial effect of adding yttrium by ion implantation on the oxidation behaviour of powder metallurgically (PM) produced chromium at 900 °C has been investigated. Comparative studies were made in which yttrium was added as an oxide dispersoid. For further insight into the oxidation process, a two stage oxidation, using oxygen isotope tracers, was performed. The oxide scales formed were analysed by a wide range of analytical techniques, but mostly secondary neutral mass spectroscopy (SNMS). The addition of yttrium changes the oxide scale growth processes. Its presence in the oxide scale, possibly as a segregated phase on the oxide grain boundaries, reduces cation diffusion, causing the oxide growth to be dominated by anion transport. This segregation can cause many, if not all, of the reported beneficial reactive element effects. Ion implantation is shown to be a powerful tool in oxidation studies, and thus for advanced material development.

The interest in TiBN coatings arises from the fact that they generally are composed of several phases. Multiphase systems display many similarities with composite materials and often display higher hardness and toughness values than single-phase materials. TiBN coatings of different composition have beenprepared by sputter deposition from composite Ti BN targets at a substrate temperature of 20 °C. The coatings were characterized by scanning electron microscopy, glancing angle X-ray diffraction and by X-ray photoelectron spectroscopy and Auger electron spectroscopy. The hardness and elasticity were determined by nanoindentation. All films had a dense structrureless morphology. The highest hardness and elasticity were obtained with coatings of composition TiBN0.5. Annealing at 400 °C for up to 6 h produced a 40%–50% hardness and elasticity increase. The origin of this increase could not be attributed to a detectable change in grain size or phase composition. The grain size of the films was of the order of 2 nm. In spite of the high quenching rates associated with sputter deposition, the films were found to contain the phases which are expected to occur under equilibrium conditions according to the phase diagram of the ternary TiBN system.

Ti-B-N coatings of variable composition have been sputter deposited from a heterogeneously composed Ti-BN target, consisting of a boron nitride base plate on which small Ti platelets were regularly arranged. By varying the number of platelets the concentration ratio c Ti / c B of the target and therefore also of the coating could easily be varied. Inhomogeneities in the chemical composition were in the per cent range. Very hard coatings of up to 55 GPa were obtained by sputtering with a substrate bias of - 150V at a substrate temperature of 400°C. The hardness maximum was found at a chemical composition where both the TiB 2 and the TiN phases coexist in equal concentrations. All coatings show very broad diffraction peaks indicating average grain sizes in the nanometre range where the Hall-Petch relation is no more valid. With coatings composed of very small grains an inverse Hall-Petch effect was observed. The tribological performance of the Ti-B-N coatings is promising; however, in general it is worse than that observed with TiN coatings. The main reason seems to be the relatively low cohesive strength of the material.