Cr-C Coatings Research Articles

Deposition and focused ion beam milling of anticorrosive CrC coatings on tool steel substrates

For micro replication, the base of a die should be ductile and the surface layer that will undergo processing should have a good machining response to various tool-making processes. At the same time, the resulting working surfaces of the tooling cavities should be hard; having low roughness, low wettability and high erosion resistance. To achieve such diverse properties, nano-crystalline CrC coatings deposited onto 12% Cr tool steel were investigated in this research. To verify the properties of such coatings various metallographic techniques were applied. In particular, the corrosion resistance was studied by means of potentiodynamic anodic polarisation. A scanning transmission electron microscopy analysis of the structure was performed on samples prepared with focused ion beam (FIB) machining. The mechanical properties and grain size distribution were determined and statistically analysed. In addition, X-ray diffraction, scanning electron microscopy and atomic force microscopy were used in studying the surface properties of these coatings. To investigate the response of the CrC coatings to micro- and nano-structuring technologies with high specific energy, a series of rectangular trenches were produced by FIB milling. The effects of the ion beam current, exposure time and ion fluence on the sputtering yield and roughness of the produced micro-structures were especially investigated. Some essential parameter windows for performing FIB milling with relatively high sputtering rates, higher than 1 µm/min, and at the same time achieving the best possible surface integrity were determined during the experiments.

Surface free energy of non-stick coatings deposited using closed field unbalanced magnetron sputter ion plating

Semiconductor IC packaging molding dies require wear resistance, corrosion resistance and non-sticking (with a low surface free energy). The molding releasing capability and performance are directly associated with the surface free energy between the coating and product material. The serious sticking problem reduces productivity and reliability. Depositing TiN, TiMoS, ZrN, CrC, CrN, NiCr, NiCrN, CrTiAlN and CrNiTiAlN coatings using closed field unbalanced magnetron sputter ion plating, and characterizing their surface free energy are the main object in developing a non-stick coating system for semiconductor IC molding tools. The contact angle of water, diiodomethane and ethylene glycol on the coated surfaces were measured at temperature in 20 °C using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the coatings and their components (dispersion and polar) were calculated using the Owens–Wendt geometric mean approach. The surface roughness was investigated by atomic force microscopy (AFM). The adhesion force of these coatings was measured using direct tensile pull-off test apparatus. The experimental results showed that NiCrN, CrN and NiCrTiAlN coatings outperformed TiN, ZrN, NiCr, CiTiAlN, CrC and TiMoS coatings in terms of non-sticking, and thus have the potential as working layers for injection molding industrial equipment, especially in semiconductor IC packaging molding applications.

Combined erosion and corrosion of thermal sprayed WC and CrC coatings

This paper presents investigations of the combined effect of erosion and corrosion on one stainless steel and four different thermal sprayed coatings with carbide particles in a metal matrix. The materials were exposed to flowing synthetic sea water containing sand. Pure erosion, electrochemical corrosion and total material loss were determined at different sand concentrations. The effect of exposure time was also studied. The results show that erosion is the dominating process at high sand concentrations while corrosion is important at lower concentrations. The relative importance depends on the material. The corrosion resistance of the metal matrix has great influence on the total material loss rate. For the coating with lowest corrosion resistance there seems to be a synergistic effect between the mechanical and electrochemical processes.

Properties of MOCVD wear and corrosion resistance coatings

The use of metallorganic precursors for deposition of wear and corrosion resistance coatings has been studied. The coatings were deposited onto steel substrates by MOCVD by the thermal decomposition of bis-aren chromium compounds (BACC) and d.c. plasma-enhanced decomposition of carbonyls of tungsten and/or molybdenum. BACC decompose at 430–470°C in a pressure range of 0.1–3 Torr. The result is Cr-C non-porous shiny coatings with an average rate of deposition of 0.5–1.5 microns min -1. X-ray analysis of the coatings does not reveal a crystalline structure, which suggests that this coating is amorphous. Metallographic examination revealed that after etching the coatings exhibit a “white-black layers” structure. The coating demonstrates high hardness (1800–2000 HVN), good adhesion, and corrosion and wear resistance. PECVD of Mo/W-C coatings was carried out at 320–400°C and pressure 0.01–1 Torr. The substrate was heated up by glow discharge. The coatings produced retain very high hardness and average corrosion resistance.

Deposition process and characterization of chromium-carbon coatings produced by direct sputtering of a magnetron chromium carbide target

Chromium-carbon coatings have been deposited on various substrates by direct sputtering of a chromium carbide, Cr3C2, target in pure argon atmosphere. The composition of coatings determined by Rutherford backscattering spectroscopy and the deposition rate were investigated as functions of the sputtering gas pressure and self-bias voltage applied to substrates. The atom number ratio C/Cr in the coatings was equal to 0.7 regardless of the deposition conditions investigated. Oxygen and argon atoms were the major impurities incorporated in the amorphous coatings. Oxygen-free Cr-C coatings were prepared at low argon pressures or on substrates biased to a voltage in the range −100 to −320 V. The Cr-C coatings deposited on biased substrates contained less than 2 at. % of argon. The morphological features of Cr-C coatings examined by scanning electron microscopy were also dependent on the sputtering gas pressure and bias voltage of substrates. Fully dense structures were observed for coatings deposited at low argon pressures or on biased substrates. The electrical resistivity of Cr-C coatings was extremely dependent on the concentration of oxygen atoms incorporated in the coatings. Oxygen-free Cr-C coatings exhibited electrical resistivity values as low as 120 μΩ cm, i.e., less than twice the bulk resistivity of Cr3C2. The residual stresses in the coatings and microhardness of the deposited material were also investigated as functions of the deposition parameters. Tensile residual stresses were lower than 0.8 GPa, and the maximum microhardness of coatings was about 13000 MPa, i.e., similar to that of the bulk material.

Hard chrome and molybdenum coatings produced by physical vapour deposition

Coatings of solid solutions of carbon or nitrogen in chromium or molybdenum were prepared by cathodic magnetron sputtering. Carbon or nitrogen was introduced either through the gas phase by reactive sputtering or by direct sputtering of sintered composite targets. Chemical and structural analyses of films revealed the formation of supersaturated solid solutions for carbon or nitrogen concentrations of up to several weight per cent. The nitrade and carbide phases predicted from the binary diagrams were not observed. The Cr-C and Mo-C coatings showed hardnesses of up to 2500 HV. The hardnesses of Mo-N and Cr-N reached 3000 HV. The wear and corrosion resistance of these coatings, which showed a dense structure, was superior to that of electrolytic hard chrome.

Hard chrome coatings deposited by physical vapour deposition

Abstract Coatings of pure chromium and of carbon- or nitrogen-doped chromium were prepared by catholic magnetron sputtering. The doping elements are introduced either through the gas phase by reactive sputtering or by direct sputtering of composite targets of chromium and chromium carbide and of chromium and chromium nitride. The Cr-C and Cr-N coatings have hardnesses of up to 3500 HV 50 gf and show fretting wear, fatigue and corrosion properties superior to those of electrolytic hard chrome. X-ray diffraction analysis revealed the presence of supersaturated solid solutions of carbon and nitrogen in chromium for concentration of carbon and nitrogen up to several weight per cent with no detectable nitride and carbide formation as would be predicted from binary Cr-C and Cr-N phase diagrams.