Plasma synthesis of thin films by physical vapour deposition (PVD) enables the creation of materials that drive significant innovations in modern life. High value manufacturing demand for tighter quality control and better resource utilisation can be met by a digital twin capable of modelling the deposition process in real time. Optical emission spectroscopy (OES) was combined with process parameters to monitor all stages of both high power impulse magnetron sputtering and conventional magnetron sputtering processes to provide a robust method of determining process repeatability and a reliable means of process control for quality assurance purposes. Strategies and physics-based models for the in-situ real-time monitoring of coating thickness, composition, crystallographic and morphological development for a CrAlYN/CrN nanoscale multilayer film were developed. Equivalents to the ion-to-neutral ratio and metal-to-nitrogen ratios at the substrates were derived from readily available parameters including the optical emission intensities of Cr I, N 2 (C–B) and Ar I lines in combination with the plasma diffusivity coefficient obtained from the ratio of substrate and cathode current densities. These optically-derived equivalent parameters identified the deposition flux conditions which trigger the switch of dominant crystallographic texture from (111) to (220) observed in XRD pole figures and the development of coating morphology from faceted to dense for a range of magnetron magnetic field configurations. OES-based strategies were developed to monitor the progress of chamber evacuation, substrate cleaning and preventative chamber wall cleaning to support process optimisation and equipment utilisation. The work paves the way to implementation of machine learning protocols for monitoring and control of these and other processing activities, including coatings development and the use of alternative deposition techniques. The work provides essential elements for the creation of a digital twin of the PVD process to both monitor and predict process outcomes such as film thickness, texture and morphology in real time.

We report the production and characterization of nanocomposite thin films consisting of a titanium nitride matrix with embedded molybdenum disulphide fullerene-like nanoparticles. This was achieved by combining a cluster source generating a pulsed supersonic beam of MoS 2 clusters with an industrial cathodic arc reactive evaporation apparatus used for TiN deposition. Cluster-assembled films show the presence of MoS 2 nanocages and nanostructures and the survival of such structures dispersed in the TiN matrix in the co-deposited samples. Nanotribological characterization by atomic force microscopy shows that the presence of MoS 2 nanoparticles even in very low concentration modifies the behaviour of the TiN matrix.

Alumina ceramic heads have been previously shown to reduce polyethylene wear in comparison to cobalt chrome (CoCr) heads in artificial hip joints. However, there are concerns about the brittle nature of ceramics. It is therefore of interest to investigate ceramic-like coatings on metallic heads. The aim of this study was to compare the friction and wear of ultra-high molecular weight polyethylene (UHMWPE) against alumina ceramic, CoCr, and surface-engineered ceramic-like coatings in a friction simulator and a hip joint simulator. All femoral heads tested were 28 mm diameter and included: Biolox™ Forte alumina, CoCr, arc evaporative physical vapour deposition (AEPVD) chromium nitride (CrN) coated CoCr, plasma-assisted chemical vapour deposition (PACVD) amorphous diamond-like carbon (aDLC) coated CoCr, sputter CrN coated CoCr, reactive gas controlled arc (RGCA) AEPVD titanium nitride (TiN) coated CoCr, and Graphit-iC™ coated CoCr. These were articulated against UHMWPE acetabular cups in a friction simulator and a hip joint simulator. Alumina and CoCr gave the lowest wear volumes whereas the sputter coated CrN gave the highest. Alumina also had the lowest friction factor. There was an association between surface parameters and wear. This study indicates that surface topography of surface-engineered femoral heads is more important than friction and wettability in controlling UHMWPE wear.

Simple configuration pin-on-plate tests were conducted in order to compare the wear of ultrahigh-molecular-weight polyethylene (UHMWPE) when sliding against titanium-nitride (TiN)-coated wrought cobalt-chromium (Co-Cr) plates obtained by arc evaporative physical vapour deposition (AEPVD) with that which occurs when sliding against uncoated wrought and cast Co-Cr plates. UHMWPE wear was determined for plates in their undamaged form and following simulated third-body damage to produce scratches similar to those observed on retrieved implants. In their undamaged form, the coatings produced a similar wear rate of UHMWPE to that with the uncoated Co-Cr plates. However, in their damaged form, TiN-coated plates showed significantly lower polyethylene wear than uncoated wrought Co-Cr plates (analysis of variance; α = 0.05). The TiN-coated plates prevented the generation of high scratch lips due to their higher hardness, producing much smaller R p values (0.19 μ) than the scratched uncoated Co-Cr plates (0.92-1.15 μ). This is a probable explanation for the lower wear rate on the scratched TiN-coated plates than on the scratched uncoated wrought plates. The results of this study have illustrated the possibility of using AEPVD TiN coatings in total knee joint replacements in order to reduce polyethylene wear.

The mico-scale abrasion test has become very popular in recent years for the measurement of the abrasive wear of coatings and other materials. A EU-funded project has just been completed that had the aim of developing the test method, and revising the existing CEN ENV for the test into a full standard.Key aspects of the project were concerned with the accuracy of measurements, the repeatability and reproducibility of the test method through an interlaboratory exercise, and the industrial applicability of the measurement method to different types of coatings.The main measurement methods that can be applied are optical measurements and profilometry. Here, it was found that profilometry measurements gave important information on the shape of the crater produced during the test, but optical measurements were found to be adequate in most cases. The reproducibility of the optical measurements was found to be about 2% when the results of different laboratories were compared.Fourteen organisations participated in the interlaboratory exercise. This found reasonable reproducibility and repeatability for the measurement method. The paper concludes by describing the procedure that was recommended at the end of the project, and is likely to be adopted in CEN. ASTM and ISO standards. (c) 2005 Elsevier B.V. All rights reserved.

Metal-on-metal hip arthroplasties have demonstrated low wear rates. However, the ion release and toxicity of the metal wear particles remains a concern. Modifying the surface of metal bearings with thick chromium nitride (CrN) coatings has the potential to further reduce wear and ion release, and improve the biocompatibility of wear particles produced. The aim of this study was to investigate the application of surface engineering technology to modify metal-on-metal (MOM) bearings to reduce wear and improve the functional biocompatibility of metal-on-metal prostheses. CrN-on-CrN bearings had lower wear rates in comparison to metal-on-metal bearings, particularly under adverse loading conditions. CrN-on-CrN bearings produced similar nanometer-sized particles to metal-on-metal bearings, however, CrN wear particles were less cytotoxic when cocultured with macrophage and fibroblast cells.

The wear of existing metal-on-metal (MOM) hip prostheses (1 mm3/million cycles) is much lower than the more widely used polyethylene-on-metal bearings (30–100 mm3/million cycles). However, there remain some potential concerns about the toxicity of metal wear particles and elevated metal ion levels, both locally and systemically in the human body. The aim of this study was to investigate the wear, wear debris and ion release of fully coated surface engineered MOM bearings for hip prostheses. Using a physiological anatomical hip joint simulator, five different bearing systems involving three thick (8–12 μm) coatings, TiN, CrN and CrCN, and one thin (2 μm) coating diamond like carbon (DLC) were evaluated and compared to a clinically used MOM cobalt chrome alloy bearing couple. The overall wear rates of the surface engineered prostheses were at least 18-fold lower than the traditional MOM prostheses after 2 million cycles and 36-fold lower after 5 million cycles. Consequently, the volume of wear debris and the ion levels in the lubricants were substantially lower. These parameters were also much lower than in half coated (femoral heads only) systems that have been reported previously. The extremely low volume of wear debris and concentration of metal ions released by these surface engineered systems, especially with CrN and CrCN coatings, have considerable potential for the clinical application of this technology.

AbstractEin Hauptziel dieser Arbeit war die Adaptierung bzw. Entwicklung eines plasma unterstützten PVD Prozesses zur Herstellung von kostengünstigen TiN Schichten für tribologische Anwendungen bei Prozessdrücken bis zu 10‐1 mbar. Dabei wurde ausgehend von industriell eingesetzten PVD Prozessen, wie Plasma unterstütztes Magnetron Sputtern, Reaktives Ionenplattieren bzw. Arc‐Verdampfung, versucht, durch Prozess‐Adaptierung und Wahl geeigneter Prozessfenster, beständige und qualitativ hochwertige TiN Hartstoffschichten, selbst bei hohen Prozessdrücken, zu erzeugen. Zur qualitativen Beurteilung der verschiedenen Prozesse bei den unterschiedlichen Prozessparametern wurde neben der Schichtcharakterisierung (Schichtdickenverteilung, Morphologie, Härte, tribologische Eigenschaften) auch eine Analyse der Prozessplasmen durchgeführt und versucht die erzielten Schichteigenschaften mit den eingestellten Prozessparametern und den gemessenen Plasmaeigenschaften, wie Ionenart, Ionenstromdichte und Energieverteilung der Ionen, in Korrelation zu bringen. Die unterschiedlichen Prozesse wurden mittels eines Plasmamonitoring Systems (PPM421 von Inficon) und eines Faraday Cup Systems untersucht und die ermittelten Plasmaeigenschaften gegenüber gestellt und diskutiert. Die Untersuchungen wurden im Rahmen eines europäischen BriteEuram Projektes TIPCOAT BE‐3815/Contract BRPR‐CT97‐0397 durchgeführt.

Ein Hauptziel dieser Arbeit war die Adaptierung bzw. Entwicklung eines plasma unterstützten PVD Prozesses zur Herstellung von kostengünstigen TiN Schichten für tribologische Anwendungen bei Prozessdrücken bis zu 10‐1 mbar. Dabei wurde ausgehend von industriell eingesetzten PVD Prozessen, wie Plasma unterstütztes Magnetron Sputtern, Reaktives Ionenplattieren bzw. Arc‐Verdampfung, versucht, durch Prozess‐Adaptierung und Wahl geeigneter Prozessfenster, beständige und qualitativ hochwertige TiN Hartstoffschichten, selbst bei hohen Prozessdrücken, zu erzeugen. Zur qualitativen Beurteilung der verschiedenen Prozesse bei den unterschiedlichen Prozessparametern wurde neben der Schichtcharakterisierung (Schichtdickenverteilung, Morphologie, Härte, tribologische Eigenschaften) auch eine Analyse der Prozessplasmen durchgeführt und versucht die erzielten Schichteigenschaften mit den eingestellten Prozessparametern und den gemessenen Plasmaeigenschaften, wie Ionenart, Ionenstromdichte und Energieverteilung der Ionen, in Korrelation zu bringen. Die unterschiedlichen Prozesse wurden mittels eines Plasmamonitoring Systems (PPM421 von Inficon) und eines Faraday Cup Systems untersucht und die ermittelten Plasmaeigenschaften gegenüber gestellt und diskutiert. Die Untersuchungen wurden im Rahmen eines europäischen BriteEuram Projektes TIPCOAT BE‐3815/Contract BRPR‐CT97‐0397 durchgeführt.

Although the wear of existing metal-on-metal (MOM) hip prostheses (1 mm3/106 cycles) is much lower than the more widely used polyethylene-on-metal bearings, there are concerns about the toxicity of metal wear particles and elevated metal ion levels, both locally and systemically, in the human body. The aim of this study was to investigate the possibility of reducing the volume of wear, the concentration of metal debris and the level of metal ion release through using surfaceengineered femoral heads. Three thick (8-12 μm) coatings (TiN, CrN and CrCN) and one thin (2 μm) coating (diamond-like carbon, DLC), were evaluated on the femoral heads when articulating against high carbon content cobalt-chromium alloy acetabular inserts (HC CoCrMo) and compared with a clinically used MOM cobalt-chromium alloy bearing couple using a physiological anatomical hip joint simulator (Leeds Mark II). This study showed that CrN, CrCN and DLC coatings produced substantially lower wear volumes for both the coated femoral heads and the HC CoCrMo inserts. The TiN coating itself had little wear, but it caused relatively high wear of the HC CoCrMo inserts compared with the other coatings. The majority of the wear debris for all half-coated couples comprised small, 30 nm or less, CoCrMo metal particles. The Co, Cr and Mo ion concentrations released from the bearing couples of CrN-, CrCN- and DLC-coated heads articulating against HC CoCrMo inserts were at least 7 times lower than those released from the clinical MOM prostheses. These surface-engineered femoral heads articulating on HC CoCrMo acetabular inserts produced significantly lower wear volumes and rates, and hence lower volumetric concentrations of wear particles, compared with the clinical MOM prosthesis. The substantially lower ion concentration released by these surface-engineered components provides important evidence to support the clinical application of this technology.

This paper reports on the applications of analytical electron microscopy to the study of cathodic arc deposited CrN coating on a Ti(6% Al, 4% V) substrate. Particular attention is given to analysis of the coating/substrate interface. Electron energy loss spectroscopy is used to show that the Cr sputter cleaning of the Ti(6% Al, 4% V) results in penetration of Cr into the substrate giving a bcc alloy layer whose composition varies from Ti(6% Al, 4% V) at the substrate interface to almost pure Cr at the coating interface. Subsequent deposition of CrN results in an initial deposition of sub-stoichiometric Cr2N followed by sub-stoichiometric CrN with a {022} texture and a columnar structure. The degree of sub-stoichiometry of the nitrides depends on the substrate bias and the substrate orientation relative to the cathode.

In the last decade the demand for hard, low friction and protective coatings with enhanced properties has been growing. In this field the PVD deposition techniques have been found to bring the best results. Two facts however still limit the application: (i) long total process time (pumping down, substrate heating, coating and substrate cooling) and expansive equipment, both resulting in high costs, and (ii) line-of-sight process complicating the coating of 3-D and large parts. In response to the industry demands a Brite-EuRam project was started aiming to cost reduction and widening the field for the use of PVD vacuum coating techniques. The present paper reports on one important part of this project, dealing with enhancing the uniformity of the coating thickness and quality on 3-dimensionally shaped substrates. The experimental depositions were performed using reactive arc evaporation of Ti and TiAl to deposit TiN and TiAlN on steel model substrates and drills.

Reactive cathodic arc evaporation (CAE) is a physical vapour deposition technique employed to produce wear resistant coatings. The adhesion of the coating is improved if the substrate surface is sputter cleaned by running the arc in high vacuum with the substrate held at a rms bias of −1000 V prior to deposition of the coating. In this paper the erosion and deposition of material during the sputter cleaning process is examined using analytical electron microscopy on two different systems. Cr sputter cleaning of Ti results in the formation of a surface layer of thickness ∼20 nm at the surface. This layer is crystalline and has a graded composition with a high fraction of Cr at the vacuum surface and a high fraction of Ti at the substrate interface. There is also some penetration of Cr into the substrate. The material of the substrate is eroded at a rate ∼6 nm per Amp-h of cathode current. Ti sputter cleaning of an existing TiN coating, on the other hand, exhibits negligible erosion of the substrate but results in the deposition of a layer of α-Ti, the thickness of which is strongly dependent on the geometry of the system. The rapid variation of the thickness of the deposited Ti with the angle between the planes of the substrate and the cathode suggests that a plasma sheath does not form under these circumstances. A simple model of the ion trajectories is used to describe this variation of the Ti thickness. The presence of such a Ti layer has implications for the re-coating of tools with TiN. The variation of the thickness of the subsequent TiN layer on the substrate is much smaller.

The use of electron energy loss spectroscopy with parallel detection (PEELS) to study coatings is illustrated by results from TiN/Ti multilayers deposited by reactive arc evaporation. PEELS shows that the distribution of N close to the interface has a 10–90% width of ∼5 nm (determined by fitting an error function to the experimental data points) despite there being a well-defined sharp crystallographic interface. The crystallographic interface between the cubic TiN and α-Ti structures occurs at a N:Ti ratio of ∼0.2. The near edge fine structure (ELNES) on the N K-edge in TiN changes as the fraction of N decreases, this change being most rapid within 2 nm of the crystallographic interface with the Ti. No further change is seen after crossing into the Ti. In a similar manner, there is a change in the thresholds of the Ti L2,3-edges with decreasing N content in the TiN but not in the Ti. These changes reflect the changing electronic structure of the material. The relationship between mechanical and electronic properties is becoming clearer so that, in the future, this type of information will allow greater insight into coating properties. There are also features on the edge whose energies are determined by the lattice parameter. Thus these features offer a method of probing local strain in these highly strained materials. The TiN/Ti system shows a peak of ∼22 GPa in the hardness for a bi-layer spacing of ∼10 nm. At smaller values of the bi-layer spacing, the TiN layers are substantially sub-stoichiometric throughout their widths and this undoubtedly plays a role in the drop in the hardness for such small values of bi-layer thickness. On annealing, a monolithic layer of Ti2N is formed with a hardness of ∼38 GPa. This is similar to the value of ∼37 GPa found in a monolithic coating of TiN deposited under the same conditions. TiN/NbN multilayers deposited by arc evaporation show hardness values in the range of 40–50 GPa with relatively little variation with deposition conditions or bi-layer thickness. This is in contrast to single crystal and polycrystalline TiN/NbN multilayers prepared by magnetron sputtering.

This paper reports on the interface region between a CrN coating and a Ti(6%Al, 4%V) substrate after sputter cleaning with Cr. EELS on a VG HB5 STEM and diffraction showed that Cr sputter cleaning of the Ti(6%Al,4%V) resulted in penetration of Cr into the substrate giving a bcc alloy of Ti and Cr with a graded composition. Subsequent deposition of CrN resulted in an initial layer of Cr2N as the system was changed from sputter cleaning to coating followed by a {022} textured fcc CrN layer.

The production of high quality thin film TEM cross‐sections suitable for microanalysis is often a difficult and time‐consuming task. This is particularly so in cases where there exists a large difference between the sputtering rate of the film and that of the substrate. The problem is further exacerbated when the levels of internal stress in the film are high enough to cause the substrate to distort during the thinning process. This paper describes some modifications to existing techniques which allow a greater degree of mechanical thinning prior to the ion etching stage. Consequently, ion milling times are drastically reduced, typically by a factor of at least 5 and by as much as 25 in some cases.

The solidus of a portion of the Pb-Sn-Te system has been investigated and compared with theoretical models. The agreement between the theoretical models and the experimental results is poor at low temperatures but improves at higher temperatures.