J. Cawley

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.

Metallurgical study of low-temperature plasma carbon diffusion treatments for stainless steels

Abstract We recently reported a novel low-temperature carbon diffusion technique forsurface hardening of stainless steels. The treatment was shown to provide benefits in terms of abrasive wear resistance. There is also evidence to suggest that by performing diffusion treatments at low temperatures ( i.e. below 400°C), these benefits can be achieved without compromising corrosion resistance. Here a variety of surface analysis and depth profiling techniques have been used to determine the physical and mechanical properties of carbon-rich layers produced on a range of stainless steel substrate materials. X-ray diffraction (XRD) was employed to determine the crystallographic structure, whilst wavelength dispersive X-ray analysis (WDX) and glow discharge optical spectroscopy (GDOS) gave information on the concentration and distribution of the diffused species within the treated layers. A variety of carbide-based structures was detected, including the expected M 23 C 6 and, more surprisingly, M 3 C. Optical and electron microscopy techniques were used to provide information on layer morphology. The surfaces produced by the low-temperature carbon-diffusion process generally exhibit a distinct diffusion layer of between 1 and 20 μm, depending on the material and the treatment conditions. Austenitic stainless steels appear to give the best response to treatment, however other types of stainless steel can be treated, particularly if the microstructure contains above 5% retained austenite. Here we discuss the changes in mechanical and metallurgical properties provided by this technique and its potential value for treatment of both austenitic and other stainless steel substrate materials.

Investigation of substoichiometric titanium nitride grown by unbalanced magnetron sputtering

Abstract TiN x (stoichiometric factor, x =0.1–0.4) films were deposited at a substrate temperature typically of 480°C using an industrial-sized multi-target PVD coating machine. The stoichiometric factor, x , depended on the manner of substrate rotation as well as the reactive gas flow during depositing. In parallel, multiphase compositions of αTi(N), eTi 2 N and δTiN were found with hardness values varying from 1500 to 2300 Hk, and 2100 Hk for e phase Ti 2 N. The XRD spectral showed Bragg reflections associated with mixed phase compositions. The almost pure eTi 2 N phase was found in the film with x close to 0.34 and the XRD diffraction pattern of this film perfectly matched the e phase documented as referred to in the JCPDS file 17-386. SEM and TEM cross-sections exhibited a very fine grain structure for films containing dominant eTi 2 N phase. The microstructure of eTi 2 N film was extremely homogeneous throughout the complete film growth. The surface of eTi 2 N film was surprisingly smooth.

Microstructural characterization of chemically vapor deposited TiN coating

Abstract The objective of the present work is to investigate the morphology, structure and local chemistry of TiN produced by CVD on a 316L stainless steel substrate, chemically etched in situ by using gaseous HCl. The samples were obtained by a reduced pressure CVD process at temperatures of 1173 and 1273 K. The microstructural, chemical characterization and texture of the TiN coatings were performed by using scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), discharge glow spectroscopy (GDEOS) and X-ray diffraction (XRD), respectively. It was determined that the coatings obtained presented a stoichiometric composition and the interface was free of any contaminants. As the concentration of TiCl 4 increased the texture of the coatings presented a stronger component along the 110 planes and a minor component along 111 planes. In general, large grain sizes were obtained due to a reduced pressure in the system, high temperature employed during the deposition process and subsequent annealing. The grain size of the TiN crystallites becomes smaller as the partial pressure of TiCl 4 decreases. The STEM studies have shown the presence of two kinds of grain structures: a region close to the interface with very fine equiaxed grains from which tall steep columnar grains have been nucleated. The structure observed was dense and without pores.

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.

Fundamental studies of the steered arc technique

Abstract Studies were carried out on the physical vapour deposition of titanium nitride wear-resistant coatings by cathodic arc evaporation, incorporating magnetic arc steering. Coatings were laid down under a range of carefully controlled conditions with two process parameters varied, the substrate bias voltage and nitrogen partial pressure. The resulting array of coated samples was subjected to a series of characterization techniques. Test results show the process to be stable over the operating range studied, with several clear trends relating to process parameters. These include a colour shift, a change in microhardness, a change in microstructure and a change in internal stress.

Investigation of elemental distributions in TiAlNZrN multi-layers using analytical transmission electron microscopy

Abstract This microstructural characterisation is described of PVD multilayer coatings. Coatings of TiAlNZrN, approximately 3 μm in thickness were grown on to stainless steel substrates using a combined steered cathodic arc evaporation and unbalanced magnetron sputtering technique. The crystallography and the multilayer periodicities were investigated using X-ray diffraction. Electron-transparent cross-section samples were examined using a conventional transmission electron microscope interfaced with an imaging filter, and with a field emission gun scanning transmission microscope interfaced with an energy dispersive X-ray analyser and a parallel electron energy-loss spectrometer. Quantitative measurements of composition were acquired across individual layers of nominal 13.2 nm spacing using X-ray analysis, but not from layers with periodicity 2.6 nm. However, qualitative elemental distributions from layers of periodicity 2.6 nm were easily resolved using energy-filtered images. The energy-loss spectroscopy also revealed differences in the near-edge fine structure of the nitrogen edge between the two TiAlN and ZrN. It was not possible to clarify the extent of intermixing of the metallic elements between layers.

Design and performance of a hot-isostatically pressed Ti/Zr segmented cathode for electromagnetically steered arc physical vapour deposition

Abstract Hot-isostatic pressing (HIPping) of titanium and zirconium strips has led to the manufacture of a novel Ti/Zr segmented cathode. Metallurgical analysis of the materials prior to and after HIPping has been undertaken by a range of bulk and surface analysis techniques. The cathode performance was evaluated after trials in an electromagnetically steered are physical vapour deposition unit. Control of the are was maintained when crossing perpendicular to the interface, while at very shallow angles only occasional loss of control occurred. Increased erosion was observed at two points on the interface where the are traversed from titanium to zirconium, but crossing from zirconium to titanium occurred without abnormal erosion.