W-Cr-C-N Nanocomposite Thin-Film Coatings via Reactive Magnetron Sputtering

While binary tungsten carbide can form smooth, hard films, these suffer from low fracture toughness. Tungsten nitride films are frequently harder, but are more brittle. Chromium nitride has excellent wear and oxidation resistance, but films often form with low hardness. Composites of these binary compounds offer a possibility to tailor the material for a desired combination of properties. To this end, we have used reactive RF-magnetron sputtering with Cr and WC targets to form quaternary composites, with nitrogen as the reactive gas. The coatings were deposited on Si, Ti, and steel substrates. The nitrogen partial pressure was varied to investigate the relationship between the film properties and the deposition conditions. Energy dispersive spectroscopy showed changes in the chemical composition as a result of the change in nitrogen partial pressure. X-ray diffraction illuminated the structure as either a solid solution with a B1 NaCl structure, or a nanocomposite with the average crystallite size under 11 nm. Optical interferometer revealed low compressive stresses. And nanoindentation established that the films are hard and adherent.U.S. National Science Foundation (DMR-0806521) and the Regional Council of Burgundy, Franc

Growth of WC-Cr-N and WC-Al-N coatings in a RF-magnetron sputtering process

Tungsten carbide-based coatings have been used in a wide variety of industrial applications such as high speed cutting tools, extrusion dies, drills, aerospace industries, and more. A few reports on ternary and quaternary coatings of WC with other elements indicate good prospects for these material systems. The present study focuses on the formation of quaternary WCeCreN and WCeAleN coatings during the simultaneous reactive RF-magnetron sputtering of tungsten carbide and Al or Cr targets in an argon/nitrogen gas mixture. The resulting coatings, with thicknesses of 3.5 mme8.2 mm, were characterized by using several analytical techniques including X-ray diffraction, SEM/EDS, AFM, and X-ray photoelectron spectroscopy. WCeCreN and WCeAleN coatings with high levels of tungsten (i.e. more than 50 at.% of the total metal content) demonstrated dense microstructure. Coatings with lower tungsten content formed columnar grain microstructure, with different surface morphologies depending on the process parameters. It was proposed that crystalline tungsten carbide (with partial N-substitution of C atoms) and chromium (or aluminum) nitride phases coexist in the coatings when the amount of tungsten was greater than 50 at.% of the total metal content; while at lower tungsten content, the dominating crystalline phase is either W-doped CrN1 y or AlN1 y solid solution, with WC1 x and small amounts of free sp2-bonded carbon present as X-ray amorphous phases.U.S. National Science Foundation under the awards DMR-0806521, DRM-0922910 Regional Council of Burgundy, Franc

W-Cr-C-N Nanocomposite Thin-Film Coatings via Reactive Magnetron Sputtering

While binary tungsten carbide can form smooth, hard films, these suffer from low fracture toughness. Tungsten nitride films are frequently harder, but are more brittle. Chromium nitride has excellent wear and oxidation resistance, but films often form with low hardness. Composites of these binary compounds offer a possibility to tailor the material for a desired combination of properties. To this end, we have used reactive RF-magnetron sputtering with Cr and WC targets to form quaternary composites, with nitrogen as the reactive gas. The coatings were deposited on Si, Ti, and steel substrates. The nitrogen partial pressure was varied to investigate the relationship between the film properties and the deposition conditions. Energy dispersive spectroscopy showed changes in the chemical composition as a result of the change in nitrogen partial pressure. X-ray diffraction illuminated the structure as either a solid solution with a B1 NaCl structure, or a nanocomposite with the average crystallite size under 11 nm. Optical interferometer revealed low compressive stresses. And nanoindentation established that the films are hard and adherent.U.S. National Science Foundation (DMR-0806521) and the Regional Council of Burgundy, Franc

Nanocomposite coatings based on quaternary metalnitrogen

Lors de ce projet, des revêtements de CrN-WC ont été étudiés en temps que matériaux hybrides durs et résistants. L'association d'un carbure et d'un nitrure résistants bien à la corrosion et obtenus dans des conditions optimales de dépôt permettra d'avoir des matériaux de protection contre l'usure, la corrosion mais aussi des dépôts servant de couches tampon à du diamant nanocristallin dont l'adhérence est mauvaise. Tout d'abord nous avons déterminé la faisabilité du système de CrN-WC et son utilisation comme couche intermédiaire pour du diamant nanocristallin. En faisant varier les paramètres de dépôt, nous avons optimisé la microstructure, les caractéristiques chimiques, mécaniques et tribologiques de nos couches. Si le système CrN-WC adhère relativement bien sur silicium, ce ne fut pas le cas sur acier. Les propriétés mécaniques de ces dépôts ont été par ailleurs plus faibles que celles que nous attendions. Nous avons ensuite étudié l'influence de la température sur nos dépôts de CrN-WC. En effet, le fait de chauffer lors du dépôt permet d'augmenter l'adhérence des couches et d'améliorer leurs propriétés mécaniques. Les revêtements obtenus à haute température ont bien montré une amélioration marquée de leurs diverses caractéristiques par rapport aux dépôts obtenus sans chauff.For this project, CrN-WC coatings are investigated as a hybrid hard and tough material. The use of a hard-carbide with a corrosion-resistant nitride may produce tailored coatings with the desired combination of properties for use as a stand-alone protective coating, or as a basis for nanocrystalline diamond deposition. The work is divided into three stages. The initial study determined the viability of the CrN-WC system, and its use as an interlayer for nanocrystalline diamond. This successful study was followed by a variation of deposition conditions at low deposition temperature. By varying the deposition parameters, the microstructure, chemical, mechanical, and tribological behavior may be optimized. While the system has relatively good adhesion to silicon substrates, its adhesion to steel was lacking. Additionally, the system showed lower than expected mechanical properties. The final step increased the deposition temperature. The aim here was to increase adhesion and improve the mechanical properties. Prior results with other systems show consistent improvement of mechanical properties at elevated deposition temperatures. The high deposition temperature coatings showed marked improvement in various characteristics over their low deposition temperature cousins.PARIS-Arts et Métiers (751132303) / SudocSudocFranceF

Thermal Stability and Mechanical Properties of Sputtered Chromium-Molybdenum-Nitride (CrMoN) Coatings

Purpose: The purpose of paper is to determinate thermal stability and mechanical properties of sputtered chromium-molybdenum-nitride (CrMoN) coatings. Design/methodology/approach: We have deposited 1.8 m-thick ternary Cr0.5Mo0.5N1.0 films on a CoCrMo alloy using a RF dual magnetron sputtering system, with Cr and Mo targets and N2 as the reactive gas. These films were subjected to various thermal treatments in Ar, air, and microwave plasma. The hardness, Young’s modulus, surface roughness, microstructure, and composition of films were studied by nanoindentation, AFM, x-ray diffraction, and x-ray photoelectron spectroscopy. Findings: The as-prepared CrMoN films consist of an amorphous Cr-rich nitride matrix with Mo-rich nitride crystalline grains, about 15 nm in size. These films are thermally stable up to 600ºC in air. Thermal annealing in the air at 800ºC resulted in an increase in surface roughness and hardness, due to film oxidation, with Cr2O3 as the main crystalline phase. Plasma treatment in a H2/N2 gas mixture, at 800ºC, did not lead to grain growth. Instead, the existing grains were reduced to about 10 nm and a new nanocrystalline phase has been formed. This leads to a decrease in the surface roughness, and an increase in the film hardness. In addition, we have further modified the film properties through a combined thermal treatment process. Thermal annealing in the air at 800ºC, followed by microwave plasma treatment at 800ºC resulted in a film with decreased surface roughness, and improved mechanical properties. Reversing the order of the thermal treatments resulted in a further decrease in surface roughness, but it shows a reduction in the mechanical properties. Research limitations/implications: The present investigation was carried out with only one composition, Cr0.5Mo0.5N1.0, of ternary thin-film system. Originality/value: The combination of thermal and plasma treatments can be used to control the microstructure, surface topography, and mechanical properties of ternary CrMoN films. Such post-deposition treatments can further improve the materials properties for desired application, and to produce new nanocomposite materials with technologically important combination of properties.National Science Foundation under grants DMR-0806521 and OISE-085494

Thermal Stability and Mechanical Properties of Sputtered Chromium-Molybdenum-Nitride (CrMoN) Coatings

Purpose: The purpose of paper is to determinate thermal stability and mechanical properties of sputtered chromium-molybdenum-nitride (CrMoN) coatings. Design/methodology/approach: We have deposited 1.8 m-thick ternary Cr0.5Mo0.5N1.0 films on a CoCrMo alloy using a RF dual magnetron sputtering system, with Cr and Mo targets and N2 as the reactive gas. These films were subjected to various thermal treatments in Ar, air, and microwave plasma. The hardness, Young’s modulus, surface roughness, microstructure, and composition of films were studied by nanoindentation, AFM, x-ray diffraction, and x-ray photoelectron spectroscopy. Findings: The as-prepared CrMoN films consist of an amorphous Cr-rich nitride matrix with Mo-rich nitride crystalline grains, about 15 nm in size. These films are thermally stable up to 600ºC in air. Thermal annealing in the air at 800ºC resulted in an increase in surface roughness and hardness, due to film oxidation, with Cr2O3 as the main crystalline phase. Plasma treatment in a H2/N2 gas mixture, at 800ºC, did not lead to grain growth. Instead, the existing grains were reduced to about 10 nm and a new nanocrystalline phase has been formed. This leads to a decrease in the surface roughness, and an increase in the film hardness. In addition, we have further modified the film properties through a combined thermal treatment process. Thermal annealing in the air at 800ºC, followed by microwave plasma treatment at 800ºC resulted in a film with decreased surface roughness, and improved mechanical properties. Reversing the order of the thermal treatments resulted in a further decrease in surface roughness, but it shows a reduction in the mechanical properties. Research limitations/implications: The present investigation was carried out with only one composition, Cr0.5Mo0.5N1.0, of ternary thin-film system. Originality/value: The combination of thermal and plasma treatments can be used to control the microstructure, surface topography, and mechanical properties of ternary CrMoN films. Such post-deposition treatments can further improve the materials properties for desired application, and to produce new nanocomposite materials with technologically important combination of properties.National Science Foundation under grants DMR-0806521 and OISE-085494

Sputtered tungsten-based ternary and quaternary layers for nanocrystalline diamond deposition

Many of today’s demanding applications require thin-film coatings with high hardness, toughness, and thermal stability. In many cases, coating thickness in the range 2–20 m and low surface roughness are required. Diamond films meet many of the stated requirements, but their crystalline nature leads to a high surface roughness. Nanocrystalline diamond offers a smoother surface, but significant surface modification of the substrate is necessary for successful nanocrystalline diamond deposition and adhesion. A hybrid hard and tough material may be required for either the desired applications, or as a basis for nanocrystalline diamond film growth. One possibility is a composite system based on carbides or nitrides. Many binary carbides and nitrides offer one or more mentioned properties. By combining these binary compounds in a ternary or quaternary nanocrystalline system, we can tailor the material for a desired combination of properties. Here, we describe the results on the structural and mechanical properties of the coating systems composed of tungsten chromium-carbide and/or nitride. These WC-Cr-(N) coatings are deposited using magnetron sputtering. The growth of adherent nanocrystalline diamond films by microwave plasma chemical vapor deposition has been demonstrated on these coatings. The WC-Cr-(N) and WC-Cr-(N)-NCD coatings are characterized with atomic force microscopy and SEM, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and nanoindentation.US National Science Foundation grants (DMR-08606521 and DMR-0922910) and the Regional Council of Burgundy, Franc

Mesenchymal Stem Cell Responses to Bone-Mimetic Electrospun Matrices Composed of Polycaprolactone, Collagen I and Nanoparticulate Hydroxyapatite

The performance of biomaterials designed for bone repair depends, in part, on the ability of the material to support the adhesion and survival of mesenchymal stem cells (MSCs). In this study, a nanofibrous bone-mimicking scaffold was electrospun from a mixture of polycaprolactone (PCL), collagen I, and hydroxyapatite (HA) nanoparticles with a dry weight ratio of 50/30/20 respectively (PCL/col/HA). The cytocompatibility of this tri-component scaffold was compared with three other scaffold formulations: 100% PCL (PCL), 100% collagen I (col), and a bi-component scaffold containing 80% PCL/20% HA (PCL/HA). Scanning electron microscopy, fluorescent live cell imaging, and MTS assays showed that MSCs adhered to the PCL, PCL/HA and PCL/col/HA scaffolds, however more rapid cell spreading and significantly greater cell proliferation was observed for MSCs on the tri-component bone-mimetic scaffolds. In contrast, the col scaffolds did not support cell spreading or survival, possibly due to the low tensile modulus of this material. PCL/col/HA scaffolds adsorbed a substantially greater quantity of the adhesive proteins, fibronectin and vitronectin, than PCL or PCL/HA following in vitro exposure to serum, or placement into rat tibiae, which may have contributed to the favorable cell responses to the tri-component substrates. In addition, cells seeded onto PCL/col/HA scaffolds showed markedly increased levels of phosphorylated FAK, a marker of integrin activation and a signaling molecule known to be important for directing cell survival and osteoblastic differentiation. Collectively these results suggest that electrospun bone-mimetic matrices serve as promising degradable substrates for bone regenerative applications