The microstructure-property relations were evaluated for a nominally Ti-25Al-17Nb orthorhombic alloy, in terms of the deformation and failure mechanisms of the constituent ordered phases (orthorhombic, alpha-2, and B2). The mechanisms were characterized through observation of slip traces, crack initiation sites, and TEM. Properties of interest were the room temperature elongation, fatigue crack growth (FCG) resistance, and creep resistance.

Amorphous Si0.56G0.44 films were deposited on (001)Si by electron beam evaporation in a vacuum having a base pressure of 10−7 Torr. They were then wet oxidized at 800 and 900 °C in an open tube furnace for various times. Cross (x)-sectional and plan view transmission electron microscope techniques were employed to characterize the samples. At 800 °C, 30 min of wet oxidation produced a continuous polycrystalline Si-Ge layer, whereas 60 min of wet oxidation produced a discontinuous polycrystalline layer. After 100 min of wet oxidation at 800 °C, the Si-Ge layer was almost completely oxidized and no observable evidence of the epitaxial Si-Ge layer was found. Wet oxidation at 900 °C for 10 min produced a bilayer structure; one epitaxial and one polycrystalline layer separated by a contamination layer initially present on the substrate prior to deposition. A mostly epitaxial Si-Ge layer was obtained after 30 min of wet oxidation at 900 °C. These results will be discussed in terms of a previously suggested epitaxial growth model. The failure to obtain an observable epitaxial Si-Ge layer by wet oxidation at 800 °C will be discussed by consideration of changes in the kinetics and the stability of both SiO2 and GeO2 at this temperature.

An amorphous SiO2 substrate was co-implanted with 175 keV Mo+ and 74 keV S+ ions at doses of 4.97 × 1016 and 1.02 × 1017 cm−2, respectively. Energies of the Mo+ and S+ ions were chosen to obtain nearly overlapping depth profiles. Transmission electron microscopy and Rutherford backscattering techniques were used to characterize the ion-implanted materials. The formation of a MoS2 phase was observed in the as-implanted condition. Annealing of the as-implanted material was performed in an oxygen-free atmosphere as well as in air. The MoS2 phase remained stable at 700 °C for 8 h in an oxygen-free atmosphere whereas it starts oxidizing in air at 600 °C for 2 h. Results are discussed in terms of the available data on the oxidation of MoS2 coatings.

The microstructure, friction and wear characteristics of the as-deposited and carbon ion (160 keV, 6.7×1017 ions/cm2) implanted polycrystalline diamond films grown by plasma-enhanced chemical vapor deposition were studied. Cross sectional transmission electron microscopy revealed the amorphous nature of the ion bombarded film. Raman peaks of the ion-implanted film are found to be consistent with the noncrystalline carbon. The pin-on-disk technique was used to determine the friction and wear characteristics of the diamond films in an ultrahigh vacuum (10−7 Pa) at room temperature. Compared to the as-deposited film, considerable reduction in friction and wear of the ion-implanted film was observed.

High-entropy alloys (HEAs) have great potential to be used as high-temperature materials and in coating material applications due to their combination of strength, ductility, thermal stability, wear, and oxidation resistance. In this work, a new HEA alloy based on NiCoCrAlSi composition was designed and deposited into metallic coatings by high-velocity oxy-fuel (HVOF) and air plasma spray (APS) processes, with the aim of developing new HEA bondcoats for thermal barrier coating (TBC) systems. The HEA coatings were analyzed for phases, microstructure and composition using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results showed that the BCC phase is the major phase present in the as-applied HVOF coating that was vacuum diffusion treated at 1080 °C. APS coatings of the same composition HEA alloy showed a two-phase structure consisting of the L12 and BCC/B2 phases. The HEA bondcoats produced by HVOF were tested for oxidation resistance at 1050 °C in air, and for thermal cycling resistance of the TBC comprising of the HVOF-applied HEA bondcoat and standard 8YSZ ceramic topcoat. The results showed internal oxidation in the HEA bondcoat during the high-temperature oxidation exposure, but no significant coating failure after 100 thermal cycles at 1150 °C.