M. Franck

Fretting wear of carbon-ion-implanted physical-vapour-deposited TiN coatings

Abstract Titanium carbonitride top-layers were prepared by selectively implanting 80 ke V C + ions into a physical-vapour-deposited TiN coating 2.8 μm thick. Rutherford-backscattering analysis showed that the implanted carbon depth distribution was the one predicted by the TRIM 87 calculation and that part of the implanted carbon had diffused out from the gaussian-like distribution towards the surface, where an ion-beam-assisted deposition of an ultrathin carbon overlayer had grown. For doses going from 2.8 × 10 16 to 7.8 × 10 16 ions cm -2 the effect of the carbon implantation on the fretting wear behaviour was investigated. Friction and wear measurements demonstrated a well-defined difference between as-plated TiN and carbon-implanted TiN. Related to the carbon implantation, it was observed that a low friction coefficient during break-in corresponds to a lower fretting wear damage.

Microprobe raman-spectroscopy of TiN coatings oxidized by solar beam heat-treatment

Physical vapor deposited TiN coatings oxidized by solar beam heat treatment in air were examined by microprobe Raman spectroscopy. The Raman spectra of TiN treated at 400 °C indicated incipient oxidation by the presence of anatase TiO 2 and additionally showed a broadband feature around the forbidden TiN vibrational mode. Inhomogeneous mixtures of rutile TiO 2 and small amounts of anatase polymorph ( 2±0.02 . The Raman scattered light intensity could be correlated with the rutile layer thickness.

Carbonaceous surface layers deposited on TiN coatings by ion implantation

TiN coatings deposited by physical vapor deposition have been subjected to a postdeposition treatment involving beam line implantation with 80‐keV C+ ions at doses between 1×1017 and 3×1017 ions/cm2. Rutherford backscattering spectrometry measurements showed Gaussian‐like implantation‐depth profiles extending towards the surface which was found to be covered with carbon. The carbonaceous surface layer was characterized by Raman spectroscopy revealing the typical band features of diamondlike carbon. Simulations of the carbon depth profile indicate that the opaque carbon layer was formed from carbon in excess of the implanted dose. Further experiments suggest that the carbon layer resulted from an ion‐beam‐assisted deposition process. Fretting wear tests demonstrated lower friction and improved wear resistance of the TiN covered with the diamondlike carbon layer in comparison with as‐deposited TiN.

Surface modification of TiN hard coatings with concentrated solar energy

Abstract Physical vapour deposited TiN coatings were partially oxidized by a beam induced heat treatment using concentrated solar radiation, in a search for the tailoring of the functionality of hard ceramic coatings. The TiN coatings were heated in ambient air up to 800°C at a mean heating rate of 1.2°C/s and held at this temperature for periods of 10, 60, and 350 s. The solar treated samples were characterized using techniques as Rutherford backscattering spectrometry, grazing incidence X-ray diffraction, and cross-sectional transmission electron microscopy. At the surface of the heat treated TiN coatings, single oxide layers consisting of the rutile polymorph of TiO2 were identified. The oxide microstructure was found to be porous and non-uniform across the layer thickness, in particular near the interface between oxide and nitride. The growth of a dense recrystallized oxide layer at the outer surface was observed after a prolonged solar beam treatment of 350 s.

Potential of photon and particle beams for surface-treatment of thin ceramic coatings

Abstract Laser irradiation and ion implantation have been investigated in order to modify in a two-step process the characteristics of TiN ceramic coatings obtained by physical vapour deposition (PVD) on steel surfaces. Depending on the beam properties and processing variables used, material modifications can be induced either in the coating itself, at the coating/substrate interface, or in the underlying substrate material. Laser irradiation and ion implantation offer possibilities of tailoring the functional surface properties of coated steels with respect to friction and wear resistance by the modification of surface roughness, by the alloying of ceramic coatings with either metallic or metalloid elements, and by inducing substrate hardening.

Comparative investigation by laser profilometry, scanning electron microscopy and atomic force microscopy of wear on solar-beam-irradiated partially oxidized TiN coatings

Abstract TiN coatings produced by physical or chemical vapour deposition have been succesfully introduced in industry, e.g. for cutting and forming of materials. The potential of an additional oxide film on such coatings has been investigated with respect to wear protection. Partial oxidation of TiN coatings was realized by concentrated solar beam irradiation at 800°C for 10 s. Wear testing under controlled conditions was done by reciprocating sliding of coated flat partially oxidized TiN, as-deposited TiN and bulk Al 2 O 3 samples against non-reactive corundum balls. The wear tracks were investigated by laser profilometry, scanning electron microscopy and atomic force microscopy. The essential benefit of atomic force microscopy appears to be the high resolution study of debris and wear damage on the nanometre scale. This technique appears to be complementary to profilometry and scanning electron microscopy. The coefficient of friction showed higher values on partially oxidized TiN in comparison with as-plated TiN; the lowest value was obtained for Al 2 O 3 . Notwithstanding the high coefficient of friction, the wear volume on partially oxidized TiN was considerably smaller in comparison with as-plated TiN owing to a difference in wear mechanism. Small plateaus of compacted wear debris were observed in the wear tracks on the oxidized TiN, while loose wear debris was found in the wear track on TiN.

Micro-Raman spectroscopy for the characterization of wear induced surface modifications on hard coatings

Micro-Raman spectroscopy can be a helpful tool in determining wear induced surface modifications due to its ability to identify compounds and measure internal stress in an area with a diameter as low as 1 pm. Micro-Raman spectroscopy is used here to characterize surface reactions, transfer layers and internal stress relaxation induced by wear processes for four different hard coatings: PVD TiN, solar beam oxidized TiN, CVD diamond and diamond-like carbon coatings. The Raman spectroscopic investigation of partially worn coatings has resulted in very specific information complementary to results that can be obtained with commonly used surface characterization techniques.

Microstructural examination of solar-beam-irradiated TiN hard coatings

Abstract Microstructural examination and characterization of hard coatings may enable engineers to improve coating deposition processes and bring tribologists a step closer to the understanding of tribological mechanisms responsible for the failure of hard coatings. Since a thin oxide film on top of hard coatings could act as a solid lubricant and improve the wear and fretting behaviour of these coatings, the examination of such films is of special interest. The oxide films were produced on physical-vapour-deposited TiN coatings a few micrometres thick by irradiation with concentrated solar energy in ambient atmosphere at 800°C and for holding times between 10 and 350 s. For the analysis and characterization of the oxidized coating microstructure, micro-Raman spectroscopy and atomic force microscopy have been performed on oxidized surfaces. Light optical and scanning electron microscopy were done on polished low angle and fractured coating cross-sections, while transmission electron microscopy has been performed on thin foils showing the coatings either parallel or cross-sectional to the surface. The dark grey oxide films found on TiN have been identified as rutile TiO 2 . These layers appeared with a uniform thickness but contain a non-uniform porosity over the oxide film thickness. Close to the TiN interface generally a higher porosity has been observed in the rutile. No sharp interface between TiN and rutile could be found. The TiN-rutile interface is characterized by oxide formation along the TiN grain boundaries.

Structuring of thin tin Ceramic Coatings with Photon and Particle Beams

Laser irradiation and ion implantation have been investigated in order to modify in a 2-step process the properties of TiN ceramic coatings obtained by physical vapour deposition on steel surfaces. Depending on the beam properties and processing variables used, materials modifications can be induced either in the coating itself, at the coating-substrate interface, or in the underlying substrate material.