R.F. Bunshah

The relationship between the spatially resolved field emission characteristics and the raman spectra of a nanocrystalline diamond cold cathode

Spatially resolved electron field emission measurements from a nanocrystalline diamond film grown by plasma‐enhanced chemical transport deposition have been obtained using a scanning probe apparatus with micrometer resolution. Macroscopic regions with a high emission site density, and turn‐on fields below 3 V/μm, comprised approximately 1/2 of the total sample area. The emitting and the nonemitting regions of the specimen are differentiated distinctly by Raman spectra and subtly by morphologies. Both areas are largely sp3‐bonded, but only the nonemitting regions exhibit a sharp line at 1332 cm−1, a well‐known signature of diamond in larger crystallites.

Electrical and optical properties of In2O3: Sn films prepared by activated reactive evaporation☆

In2O3: Sn films were prepared by an activated reactive evaporation technique developed for this purpose. The films were characterized by transmission electron microscopy, electron diffraction, electrical resistivity and measurements of transmittance as a function of wavelength. The electrical resistivity is found to be strongly dependent on process parameters such as the tin content and the deposition temperature. In contrast, the transmittance is found to be only weakly dependent on various process parameters. Under optimum conditions, films with an electrical resistivity of 7 × 10−5 Ω cm with an integrated (0.4–1.2 μ) transmittance of over 90% were obtained.

Preparation of In2O3 and tin-doped In2O3 films by a novel activated reactive evaporation technique

High quality films of In2O3 and tin-doped In2O3 were prepared by a novel activated reactive evaporation technique developed for use with resistively heated evaporation sources. Transparent conducting coatings of In2O3 have a sheet resistance of 80 Ω/□ with an optical transparency of more than 95% in the 0.4–1.6 μm wavelength range. Thin (0.4 μm) In2O3(Sn) films have a sheet resistance of 25 Ω/□ and an optical transparency as high as 99% at some wavelengths with an average transmission between 0.4 and 1.6 μm of 96%. Thicker films have a sheet resistance as low as 2.2 Ω/□. A comparison of the properties of In2O3(Sn) films with those of transparent conducting films produced by other techniques is made.

Structure and property relationships in microlaminate Ni-Cu and Fe-Cu condensates☆

Abstract Microlaminate metal matrix composites offer considerable potential as high strength high toughness materials with isotropic properties in the plane of the sheet. In this paper we deal with the preparation of Fe-Cu and Ni-Cu microlaminate composites by electron beam evaporation from two sources and alternating deposition onto a rotating substrate. The thickness of the laminae was varied by changing the evaporation rates of the metals and the speed of rotation of the substrate. The deposits were characterized by optical microscopy, scanning electron microscopy and electron microprobe analysis to study the thicknesses of the laminae and interdiffusion of elements between the layers. X-ray diffraction was used to study the composition of the laminates. The microhardness and tensile strength at room and high temperatures of the laminates were studied and correlated with the thicknesses of the laminae and the microstructure. The results showed very marked increases in strength and hardness as the size of the laminae decreased below about 2 μm. Superplastic behavior was observed at a certain thickness of the laminae, strain rate and temperature.

Friction and adhesive wear of titanium carbide and titanium nitride overlay coatings

Abstract The coefficient of friction and self-adhesive wear were studied for hard overlay coatings (4–8 microm thick) of TiC and TiN deposited on 304 stainless steel, titanium and aluminum discs and 440 C stainless steel riders by activated reactive evaporation process. The hard overlay coatings were characterized by X-ray diffraction and indentation hardness techniques. The frictional and adhesive wear behavior were evaluated using a standard pin-on-disc tribotester in dry and lubricated conditions. The coefficient of friction and the wear were very much lower when the test couple consisted of a hard coating rubbing against a hard coating than when one or both of the components were uncoated metals, even in dry (unlubricated) conditions. In some instances of the hard-hard couple, very low coefficients of friction (0.05–0.1) and very low wear, i.e. wear groove depths less than 1 × 10−5 in, were observed for test conditions of a run distance of 500 m under a load of 0.4 kgf in dry conditions. From examination of the wear scar the failure mode of the coating was observed to be microfragmentation resulting from the initiation and propagation of microcracks at the rider-disc interface.

Influence of ion implantation and overlay coatings on various physico-mechanical and wear properties of stainless steel, titanium and aluminium

Abstract This work represents the data on the wear behaviour of 304 stainless steel, commercial grade titanium and commercial grade aluminium without and with different surface treatments, namely ion implantation of boron and nitrogen and overlay coatings of titanium carbide and nitride. The surface treatments were characterized by phase identification, hardness, bend strength, as well as adhesion of overlay coatings. Wear properties were evaluated in adhesive, erosive and abrasive modes of wear. The experimental results showed that surface treatments produced measurable changes in hardness and strength. The results of adhesive wear tests indicated that the wear resistance of all the substrate materials can be considerably improved by overlay coating with superhard materials in dry as well as lubricated test conditions. Ion implantation resulted in improvement of wear properties for only a limited regime of adhesive wear under lubricated conditions and for the abrasive mode of wear. Overlay coatings produced a marked improvement in abrasive wear tests under lubricated conditions on all substrate materials.

SnO2 films prepared by activated reactive evaporation

Abstract Transparent conducting films of SnO2 doped with antimony were prepared on glass substrates by activated reactive evaporation for the first time. The sheet resistance and optical transmittance in the wavelength range 0.4–1.6 μm were studied as functions of various deposition parameters such as the ambient pressure of an 85%Ar15%O2 mixture, the substrate temperature and the antimony doping concentration in the SnSb alloys. The sheet resistance and optical transmittance showed a strong dependence on the above-mentioned deposition parameters. The best results were obtained for a 90at.%Sn10at.%Sb alloy evaporated in 85%Ar15%O2 at a partial pressure of about 5 × 10−4 Torr with a substrate temperature about 350°C. These films, with a sheet resistance of 10 μ/□ had an average transmittance of 95% over the wavelength range 0.4–1.8 μm. The film thickness was about 0.25 μm. Thicker films (about 0.5 μm) had a sheet resistance as low as 1.5 ω/□ with an average transmittance 85% in the wavelength range 0.4–1.6 μm.

Microstructures of TiN and Ti2N deposits prepared by activated reactive evaporation

Abstract Titanium nitride has an important application as a coating on cutting tools to extend their lifetime. In this study various phases in the Ti-N system were deposited by the activated reactive evaporation process. The influence of process variables—evaporation rate, N 2 partial pressure and deposition temperature—on the phases present, their morphology and hardness, was studied using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. As the ratio of the evaporation rate of titanium to the partial pressure of N 2 decreases, the deposit changes from titanium to Ti 2 N to TiN including two-phase mixtures. As the deposition temperature is increased the grain size increases markedly, from about 0.5 μm at 550 °C to 20 μm at 1000 °C, and the grain morphology changes from a faceted to a smooth topography. The hardness of the deposit is influenced primarily by the presence of the Ti 2 N phase which produces the highest hardness levels.

Processes of the activated reactive evaporation type and their tribological applications

Abstract Plasma-assisted deposition processes have created a breakthrough in the deposition of compounds particularly the refractory compounds such as oxides, carbides, nitrides etc. Processes such as sputtering or ion plating inherently contain a plasma in the space between the target and the substrate. Evaporation and chemical vapor deposition processes have to be modified to include a plasma. In all of these reactive deposition processes the plasma plays a vital role in providing the activation energy necessary to carry out the process or to enhance its efficiency. All types of vapor sources can be used in these processes. The original development in 1971 used a thermionic electron beam evaporation source. Subsequently, resistance- heated, arc, induction, plasma electron beam and sputtering sources have all been used. In this paper we shall discuss the processes and the influence of deposition parameters on the microstructure and properties of compounds. Specific examples of the use of these compounds in tribological applications are considered.

Preparation and properties of cubic boron nitride coatings

Cubic boron nitride (CBN) has attracted a great deal of interest in recent years for its unique mechanical and optical properties. Many physical as well as chemical vapor deposition processes have been explored to synthesize CBN coatings. These techniques, however, suffer limitations owing to the requirements of high substrate temperature and/or the necessity of using toxic starting materials. We have developed a new technique where CBN films can be prepared by evaporating boric acid in NH3 plasma. CBN films have been deposited at substrate temperatures as low as 450°C. Structure and optical and electrical characteristics of the films clearly demonstrate the simple cubic phase in the coatings. These results are presented in this paper.