John Peters

Performance of dicalcium silicate coatings in hot-corrosive environment☆

Abstract Thermally sprayed dicalcium silicate coatings have been developed for increased stability in highly corrosive environments at temperatures up to 900°C. In this study, the performance of dicalcium silicate based coatings was compared to yttria partially stabilized zirconia (Y-PSZ) coatings. The coatings were exposed to a V2O5-15 wt. % Na2SO4 slag at 700 and 900°C. At 700°C, gaseous sulfidation was stimulated by an addition of 0.5 vol.% sulfur dioxide in air. The results demonstrated that dicalcium silicate coatings exhibited superior endurance against hot corrosion induced by the V2O5-Na2SO4 slag. The mechanism of protection was related to stable calcium vanadate compounds, which formed on the surface and prevented the corrosive species from immediate penetration into the coating microstructure. In the presence of an SO2/air atmosphere, a CaSO4 reaction layer formed. Diffusion of SO2 further facilitated sulfidation within the coatings. However, the dicalcium silicate materials withstood combined attack by gaseous SO2 and V2O5-Na2SO4 slag without debonding. In this case, the zirconia coating deteriorated and spalled.

Parameter optimisation of Ti-DLC coatings using statistically based methods

Abstract The influence of process parameters on the mechanical properties of magnetron-sputtered Ti-C:H films was investigated using fractional factorial experimental design. The parameters studied included substrate bias voltage, acetylene flow rate, and argon and nitrogen partial pressures. The results indicated that bias voltages in the range −20 to −60 V had little or no influence on the mechanical properties. The acetylene flow rate, which controlled the titanium content in the Ti-C:H layers, exhibited the most significant effect. An explanation based on the relationship between relative film thickness and critical applied loads is provided for the coating failure mechanisms.

Processing titanium aluminide foils

In an effort to extend the available manufacturing technologies for Ti3Albase aluminides, the potential success of a new hot-rolling process for the production of high-quality foils has been investigated. Processing of Super-α2 aluminide foils approximately 0.15 mm thick takes full advantage of the combined benefits of controlled rolling and a unique pack rolling process. Based on the results of a study of phase transformation kinetics, microstructure and hardness of continuously-cooled and isothermally transformed specimens, the processing parameters are optimized to provide enhanced surface quality and superior ductilities in the as-rolled condition.