L.A. Donohue

Microstructure and oxidation-resistance of Ti1-x-y-zAlxCryYzN layers grown by combined steered-arc/unbalanced-magnetron-sputter deposition

Abstract Cation-substituted Ti 1 − x − y −z Al x Cr y Y z N alloys, with y = 0.03 and z = 0.02, have been shown to offer greatly enhanced high-temperature oxidation resistance compared to presently used TiN and Ti 1 − x Al x N films. Layers (3 μm thickness) were deposited by unbalanced magnetron sputter deposition onto austenitic stainless steel and M2 high-speed steel substrates which had been ion etched in situ using a steered Cr-metal-ion cathudic arc discharge at an Ar pressure of 6 × 10 −4 mbar (0.45 mTorr). The metal ion-etching promoted initial local epitaxy on individual substrate grains while the overall film texture evolved through competitive growth to (111) in Ti 0.44 Al 0.53 Cr 0.03 N alloys and (200) in Ti 0.43 Al 0.52 Cr 0.03 Y 0.02 N. Although Ti 0.44 Al 0.53 Cr 0.03 N layers exhibited a columnar microstructure similar to that previously observed in Ti 1 − x Al x N alloys, the addition of 2 mol% YN resulted in significant grain refinement giving rise to a more equiaxed structure. The Knoop microhardness of Ti 0.43 Al 0.52 Cr 0.03 Y 0.02 N alloys was HK 0.025 = 2700 kg mm −2 compared to 2400 kg mm −2 for Ti 0.44 Al 0.53 Cr 0.03 N. The onset of rapid oxidation, as determined from thermo-gravimetric measurements, ranged from ≈ 600 °C for TiN to 870 °C for Ti 0.46 Al 0.54 N to 920 °C for Ti 0.44 Al 0.53 Cr 0.03 N to 950 °C for Ti 0.43 Al 0.52 Cr 0.03 Y 0.02 N.

Thermal stability and oxidation resistance of TiAlN/CrN multilayer coatings

Abstract TiAlN/CrN multilayer films with superlattice characteristics were deposited onto M2 high-speed steel and 304 stainless steel by reactive unbalanced magnetron sputtering involving three TiAl targets and one Cr target. The wavelength of the multilayer structures (ranging from 2.4 nm to 4.8 nm) and Cr content (from 10% to 30%) was controlled by varying the power supplied to the Cr target (P Cr ) from 2 kW to 12 kW. These coatings were then heated in an ambient atmosphere at temperatures ranging from 500 to 1000 °C and for times up to 16 h. Breakdown of the multilayer structure was studied using such techniques as hardness measurements, X-ray diffraction (XRD) and cross-sectional TEM (XTEM). The results show that both the multilayer structure and hardness can be maintained for as long as 16 h at 700 °C. This was found to be independent of the Cr content (multilayer wavelength) of the coatings. Oxidation behaviour involving isochronal thermogravimetric analysis (TGA), XRD and SEM revealed that all coatings exhibited weight gains of as little as 5% of that of TiN under similar conditions at 1000 °C. The resistance to oxidation was found to be dependent on the Cr content, with the greatest effect occurring in the P Cr = 12 kW samples. Two very distinct regimes of oxidation were observed. Up to approximately 900 °C, the rate of oxidation was very low (approximately 0.2 gm 2 in the case of the P Cr = 4 kW samples and 0.1 gm −2 in the case of the P Cr = 12 kW samples). Above this temperature, the oxidation rates increased markedly for all samples, with that of the P Cr = 12 kW being the least severe.

Structural determination of wear debris generated from sliding wear tests on ceramic coatings using Raman microscopy

In order to address the important interest in wear debris and associated wear mechanisms, we have studied a series of physical-vapor deposition ceramic hard coatings (CrN/NbN, CrN, NbN, TiAlN/VN, and TiCN) using a ball-on-disk sliding configuration against corundum. The debris generated were characterized using Raman microscopy to identify compounds, especially oxides, generated during the wear process to gain a better understanding of tribochemical reactions. The high spatial resolution (2 μm), sensitivity to structural changes, and nondestructive nature make this technique ideal for the study of such small amounts of wear debris. This article examines binary, multicomponent, multilayered, and superlattice coatings. Under dry sliding conditions of 5 N normal load and 10 cm/s speed, titanium-based alloy coatings were found to provide TiO2 (rutile) debris. However, the addition of thin layers of VN to the TiAlN system provided a lower friction coefficient, and much less debris through the possible formatio...

Large-scale fabrication of hard superlattice thin films by combined steered arc evaporation and unbalanced magnetron sputtering

Abstract This paper reports on the mechanical and physical properties of a range of TiAIN- and TiN-based polycrystalline superlattice hard coatings fabricated by a combined steered arc evaporation and unbalanced magnetron sputter industrial batch process within a common gas atmosphere. The reactive deposition experiments were carried out in a four-cathode system in which the substrates could be continuously rotated at a nominal target-substrate distance of 250 mm and with variable velocity. The influence of layer composition, deposition technique, substrate rotation and coating rate were investigated by XTEM, XRD, RBS and Knoop indentation testing with regard to the superlattice period and microstructure, and the preferred orientation and hardness of the coatings. All coatings were found to exhibit fine, highly dense lamella microstructure, high hardness and excellent adhesion. Film systems deposited by closed-field unbalanced magnetron sputtering could exhibit preferred 〈111〉 growth, whilst coatings deposited by simultaneous steered arc/unbalanced magnetron sputtering generally showed 〈200〉 orientation. The period of the superlattice could be controlled between 19 and 172 A by alteration of the substrate rotation and deposition rate.

Deposition and characterisation of arc-bond sputter TixZryN coatings from pure metallic and segmented targets☆

Abstract An arc-bond sputtering physical vapour deposition chamber has been used to deposit hard low friction binary and ternary coatings by steered arc evaporation, unbalanced magnetron sputtering and a combination of both techniques. The results of the coating trials using segmented targets manufactured by hot isostatic pressing together with co-sputtering and arc evaporation of pure titanium and zirconium targets are reported. TixZryN coatings with various metal ratios were deposited on high speed steel and stainless steel substrates and characterized using X-ray diffraction, scanning electron microscopy, glow discharge optical emission spectroscopy, Knoop micro hardness, Talysurf roughness and scratch adhesion methods. The results illustrate the relationship between the coating composition and structure with performance in terms of adhesion, hardness and wear properties. The results also serve to show changes in coating properties with deposition technique and the improved performance of TixZryN films over binary systems.

Influence of incorporation of Cr and Y on the wear performance of TiAlN coatings at elevated temperatures

Abstract High temperature, wear-resistant coatings grown by combined steered arc/unbalanced magnetron deposition techniques were tribologically characterized. These coatings are improvements on TiAlN standard processes, including multilayering with CrN and incorporation of yttrium. Commercially available arc-deposited coatings of TiN and TiAlN were taken as reference. Oscillatory sliding tribological tests were performed in the temperature range 400–900°C. This investigation demonstrates that these new coatings significantly outperform the commercial ones. Interestingly, the diffusion barrier effect of the incorporated yttrium becomes particularly important for testing temperatures exceeding 800°C. This property of TiAlCrYN makes this type of film extremely suitable for hard metal cutting operations, such as dry machining of die steel.

Tribological investigation of TiAlCrN and TiAlN/CrN coatings grown by combined steered-arc/unbalanced magnetron deposition

The dry sliding wear of monolayer TiAlCrN and multilayer TiAlN/CrN coatings has been investigated against a BM2 tool steel counterface. The coatings were deposited on a BM2 tool steel substrate by combined steered-arc/unbalanced-magnetron deposition. Increasing either contact load or sliding speed led to a reduction in friction coefficient, typically from 1.1 to 0.2. Increasing load resulted in an increase in wear rate for both TiAlCrN and TiAlN/CrN (e.g. from 7×10-6 mm3/m at 22 N to 4×10-5 mm3/m at 189 N for the TiAlCrN monolayer coating, and from 7×10-6 mm3/m at 22 N to 2.5×10-5 mm3/m at 189 N for TiAlN/CrN multilayer). The wear rate for all coatings was at least an order of magnitude lower than the uncoated BM2 steel. The wear rate of the TiAlCrN coating tended to decrease with an increase in sliding speed (from 7.4×10-5 mm3/m at 0.2 m/s to 1.3×10-5 mm3/m at 1.1m/s) while the wear rate of the TiAlN/CrN was approximately constant as a function of sliding speed (∼1.5×10-5 mm3/m).

Enhanced adhesion through local epitaxy of transition-metal nitride coatings on ferritic steel promoted by metal ion etching in a combined cathodic arc/unbalanced magnetron deposition system

In situ substrate cleaning by ion etching prior to deposition in physical vapor deposition processes is a key step in achieving good film adhesion, which is essential for all coating applications. Irradiation with metal or gas ions alters substrate surface chemistry, topography, and microstructure thus affecting subsequent film growth. This study compares Ti1−xAlxN/ferritic steel (x=0.54) interfaces formed after Cr ion bombardment at negative substrate biases, Us, ranging from 600 to 1200 V during a Cr cathodic arc discharge, stabilized with a 0.06 Pa Ar background pressure. Samples biased with −1200 V in an Ar glow discharge at a pressure of 0.6 Pa were also investigated. Microstructure and microchemistry of the interfaces was studied by scanning transmission electron microscopy with energy dispersive x-ray analysis using cross-sectional samples. Cr ion etching with Us=1200 V resulted in a net removal of over 100 nm of substrate material with the formation, through implantation, of a Cr-enriched near-sur...

Investigation of superlattice coatings deposited by a combined steered arc evaporation and unbalanced magnetron sputtering technique

Abstract In this paper we report on third-generation TiA1N-ZrN superlattice thin films deposited at industrial scale on high speed steel and stainless steel substrates by a combined steered arc evaporation and unbalanced magnetron sputtering technique. The superlattice period and hence the mechanical and physical properties of the film were varied by modification of the rotation velocity and type of rotation (one-fold and three-fold). Characterization of the films was undertaken by a range of bulk and surface analysis techniques including scanning electron microscopy, X-ray diffraction, glow discharge optical emission spectrometry, hardness and adhesion measurement. Results show that a reproducible superlattice structure can be fabricated without a complex atmosphere separation and shuttering mechanism. Control of the planetary rotation velocity and type of rotation has led to variation in the superlattice period from 19 to 132 A. Further analysis has shown that the TiA1N-ZrN superlattice system can exhibit hardness greater than 4000 HK, scratch adhesion values on high speed steel of above 50 N, preferred orientation, average surface roughness less than 0.10 μm and a highly dense microstructure.

Deposition and characterization of TiAlZrN films produced by a combined steered arc and unbalanced magnetron sputtering technique

Abstract Arc-Bond Sputter (ABS™) physical vapour deposition, which utilizes a steered arc metal ion etch substrate pretreatment stage prior to closed field, unbalanced magnetron sputter coating, has been undertaken. This paper presents results on the mechanical and physical properties of a range of TiAlZrN, TiAlN and TiZrN ABS coatings deposited on high speed steel and stainless steel substrates under standard deposition conditions. In addition, this paper also reports on coatings deposited by a new combined steered arc and unbalanced magnetron method to produce superlattice films of variable periodicity in the TiAlN-ZrN and TiAlN-TiN systems, with good adhesion, variable colour, high Knoop microhardness and dense microstructure.