Deposition of silicon nitride from SiCl4 and NH3 in a low pressure r.f. plasma

Silicon nitride coatings were deposited in a low pressure (1–10 Torr) r.f. plasma from SiCl₄ and NH₃ in the presence of argon onto stainless martensitic steel grounded and floating substrates at 300 °C and 440 °C respectively. The heating of the substrates depends mainly on the position and the induced r.f. power. The coatings were identified as silicon nitride by X-ray investigation and were found to contain chlorine by energy-dispersive analysis of X-rays. The growth rate, the microhardness and the chlorine concentration of the coatings were determined as a function of the total gas pressure, the r.f. power input and the NH₃-to-SiCl₄ ratio. It was observed that the coatings on the floating substrates have higher deposition rates and are of superior quality.     

R.F. reactive sputter deposition of hydrogenated amorphous silicon carbide films

The preparation of hydrogenated amorphous silicon carbide films by r.f. reactive sputtering of a silicon target in Ar-CH₄ gas mixtures with and without an r.f. bias on the substrates was studied. Starting with a pure silicon target and increasing monotonically the CH₄ percentage from 0% to about 10%, films with 1 ⩾ x ⩾ 0 were obtained at decreasing deposition rates. After sputtering for some hours in methane-rich gas mixtures, carbon atoms were incorporated into the silicon target surface, probably as a result of atomic peening, and nearly stoichiometric SiC films were prepared by sputtering of such a target in pure argon. The different mechanisms of film formation, deposition rate, composition, hardness, friction coefficient and stresses in the films as functions of the partial pressure of methane and the value of the r.f. bias were investigated. The IR spectra offilms with different carbon contents were analysed. The greatest hardness was found for nearly stoichiometric SiC films deposited with a bias.     

R.F. plasma deposition of silicon nitride layers

A versatile r.f. plasma deposition system used to deposit high quality Si₃N₄ films at low temperature (200–350°C) is described. By introducing the reactant gases separately and reactively reducing the oxygen content of the system, films which exhibited very little oxygen contamination could be deposited. Rutherford backscaterring studies were used to evaluate the atomic composition of the films. The composition was related to other parameters such as the index of refraction, the etch rate and the deposition rate. The nitride layers described here were used successfully to anneal ion-implanted GaAs with negligible surface degradation.     

Analysis of coating interlayer between silicon nitride cutting tools and titanium carbide and titanium nitride coatings

Silicon nitride (Si₃N₄) cutting tools exhibit excellent thermal stability and wear resistance in the high-speed machining of cast irons, but show poor chemical wear resistance in the machining of steel. Conventional chemical vapour deposition (CVD) coating of Si₃N₄ tools has not been very successful because of thermal expansion mismatch between coatings and the substrate. This problem was overcome by developing a CVD process to tailor the interface for titanium carbide (TiC) and titanium nitride (TiN) coatings. Computer modelling of the CVD process was done to predict which phases would form at the interface, and the results compared with analyses of the interface. Three Si₃N₄ compositions were considered, including pure Si₃N₄, Si₃N₄ with a glass phase binder, and Si₃N₄ + TiC composite with a glass phase binder. Results of machining tests on coated tools show that the formation of an interlayer provides superior wear resistance and tool life in the machining of steel as compared to uncoated and conventionally coated Si₃N₄ tools.     

Deposition of diamond-like carbon on a titanium biomedical alloy

Much of the orthopedic community now believe that the long-term failure of total hip and knee prostheses is directly or indirectly due to the production of wear particles, particularly polyethylene wear particles which are produced at the articulating interface between the metal component and the high molecular weight plastic component. Therefore, a friction and wear reducing coating on the metal component, which is also biocompatible, should reduce the production of the polyethylene wear particles and dramatically extend hip-implant life. Diamond-like carbon (DLC), with its extreme smoothness, hardness, low coefficient of friction, and biocompatibility is an excellent candidate for such an application. One of the key issues that may limit the utility of DLC in this application is the adhesion of this material to common biomedical alloys. We will show that high adhesion strength between sputter-deposited DLC and a silicon-coated titanium biomedical alloy can be easily achieved.     

Boron nitride coatings of steel and graphite produced with a low pressure r.f. plasma

Boron nitride (BN) coatings were deposited onto die steel and graphite substrates with a low pressure r.f. plasma. The coatings were deposited onto substrates at temperatures of 550–620 °C from a gas mixture of argon, NH₃ and BCl₃. X-ray diffraction and scanning electron microscopy were employed to identify and to characterize the coatings. The coatings are mostly amorphous; however, the existence of small amounts of hexagonal BN was identified. The influence on the growth rate of the deposition time and the pressure in the reactor is described.     

Cathodic localization of metal coatings on silicon carbide crystals

Experimental data on the electrical properties of metal contacts fabricated by depositing copper from a porous electrode onto the surface of silicon carbide crystals are reported.     

Parametric study of silicon carbide coatings deposited in a fluidized bed

Silicon carbide coatings have been deposited on microspheres in a fluidized bed by the reaction of methyltrichlorosilane and hydrogen. The principal variables of reactant gas composition and temperature were correlated with the morphology, the microstructure and the density of the coating. The effect of the coating rate on these characteristics was shown to be slight. The optimum gas composition for highly dense coatings was about 5 vol. % or less methyltrichlorosilane in H₂. The amount of grown-in porosity increased as the gas composition increased above 5 vol. % methyltrichlorosilane in H₂. The optimum temperature for highly dense coatings was in the range 1475–1675 °C. Lower temperatures resulted in silicon-rich deposits, while higher temperatures caused unacceptable porosity.     

The tensile behavior of a silicon carbide fiber-reinforced titanium matrix composite

This paper summarizes the results of a study on the effects of composite microstructure and test temperature on tensile deformation and fracture behavior of a symmetric [0/90]_2s titanium alloy metal-matrix composite. Matrix microstructure is controlled by heat treatment, which is used to produce metastable or Widmanstatten + microstructures. The sequence of damage initiation and evolution at both room and elevated temperature (650°C) is identified using ex-situ scanning electron microscopy observations during incremental monotonic loading to failure. The nature, sequence and complexity of damage during uniaxial loading is presented and discussed in light of competing and mutually interactive influences of load level and deformation characteristics of the microstructure.     

Deposition of functional cellulose films on titanium alloy surfaces

Titanium alloy (TiAl6V4) surfaces were treated with ultraviolet (UV) radiation to remove organic “contamination” molecules which remained on the surfaces after conventional cleaning processes. The UV-technique simultaneously revealed reactive surface hydroxyl groups at the metal surface which were monitored by the reaction with perfluorooctanoylchloride and application of Fourier-Transform infrared reflection-absorption spectroscopy and contact angle measurements, respectively. Two different cellulose polymers each made soluble in methanol by functionalized hydroxylalkyl-spacer groups and their mixtures were deposited on UV-treated TiAl6V4 surfaces. Atomic force microscopy measurements could reveal polymer films which covered the metal surfaces completely without defects. Differences were indicated in the surface structure, especially between the pure cellulose phosphate films and cinnamate containing cellulose films.     

Preparation and characterization of carbon and titanium carbide coatings

Carbon and titanium carbide coatings were deposited onto 304 and 316 stainless steel, Monel 400, molybdenum and copper substrates by the d.c. diode sputtering method. The former were prepared using a graphite target in an argon atmosphere whereas the latter were deposited using a titanium target in an argon-methane gas mixture. The coatings were characterized using Auger electron spectroscopy, X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, scanning electron microscopy and X-ray diffraction techniques. The adhesion of the coatings to the substrates and the effect of annealing on their crystallinity were studied.     

Deposition of superconducting niobium coatings on titanium from molten salts

Superconducting niobium coatings have been electrodeposited from molten salts onto titanium substrates with a copper, nickel, or molybdenum protective layer, and their structure and magnetic properties have been studied. The coatings are shown to be suitable as a starting material for the superconducting layer of the rotor of cryogenic gyroscopes.     

R.F. magnetron sputtered tungsten carbide thin films

Thin films of tungsten carbide have been deposited on stainless steel substrates held at 500°C by r.f. reactive magnetron sputtering in two different modes of introducing argon and acetylene gases called normal and high rate mode. A single phase fcc-WC is formed in the normal mode whereas a mixture of A-15-W₃C, hexagonal-WC and graphitic- and diamond-carbon is found in the high rate mode. A microhardness value as high as 3200 kgf/mm² (as compared to the bulk value of 1800 kgf/mm²) is obtained in the film deposited by normal mode.     

Deposition of TiN coatings on shape memory NiTi alloy by plasma immersion ion implantation and deposition

An investigation has been carried out to study the effect of pulse negative bias voltage on the morphology, microstructure, mechanical, adhesive and tribological properties of TiN coatings deposited on NiTi substrate by plasma immersion ion implantation and deposition. The surface morphologies were relatively smooth and uniform with lower root mean square values for the samples deposited at 15 kV and 20 kV negative bias voltages. X-ray diffraction results demonstrated that the pulse negative bias voltage can significantly change the microstructure of TiN coatings. The intensity of TiN(220) peak increased with the increase of negative bias voltage in the range of 5-20 kV. When the negative bias voltage increased to 30 kV, the preferred orientation was TiN(200). Nanoindentation test indicates that hardness and elastic modulus increased with the increase of the negative bias voltage (5 kV, 15 kV and 20 kV), and then dropped sharply at 30 kV. The adhesion between the TiN and NiTi alloy and tribological properties of TiN coated NiTi alloy depend strongly on the bias voltage parameter; the sample deposited at 20 kV possesses good adhesion strength and excellent tribological property.     

On melting of silicon carbide under pressure

The melting of silicon carbide has been studied at pressures 5?C8 GPa and temperatures up to 3300 K. It has been found that SiC melts congruently, and its melting curve has negative slope of ?44 ± 4 K/GPa.