High-temperature oxidation of nickel-based alloys and estimation of the adhesion strength of resulting oxide layers

The kinetics of isothermal oxidation (1100°C) of commercial nickel-based alloys with different content of sulfur (0.22–3.2 wt ppm) is studied. The adhesion strength in a metal/oxide system is estimated as a function of sulfur content and duration of high-temperature exposure. The scratch-test technique is proposed to quantitatively estimate the work of adhesion of resulting oxide films. It is found that the film microstructure is composed of an inner α-Al2O3 layer and an outer NiAl2O4 spinel layer, which are separated by discrete inclusions of TiO2. Residual stresses in the oxide film are experimentally determined by X-ray diffraction. spinel layer, which are separated by discrete inclusions of TiO2. Residual stresses in the oxide film are experimentally determined by X-ray diffractio

Equilibrium distribution of liquid during sintering of assemblies of WC/Co cermets

Assemblies were made by stacking on top of one another two cylinders of WC-Co cermets differing in mean WC particle size (relative size ratio of 3.5) and cobalt concentration (6 or 15 wt pct). These assemblies were bonded by heat treatment at 1400 degrees C under protective atmosphere for a dwell time of 7 hours. After completion of the heat treatment, the distributions of the cobalt concentration and WC grain size as a function of distance from the original interface between the two cermets were analyzed by combining Vickers microhardness measurements and image analysis. At equilibrium, the Co content was always larger on the side containing the smaller WC particle size. The final partition of Co was compared with the predictions of a model developed for expressing the dependence of the solid/solid and solid/liquid interface areas on the system parameters: phase volume fractions, dihedral angle., particle size, and particle coordination. An excellent agreement is found when assuming an average WC coordination of 7