Advanced diffusion coatings for improved oxidation and corrosion performance

Research to investigate advanced diffusion coatings for improved oxidation and hot corrosion resistance was conducted. The aim was to build on the performance of the standard aluminide on the nickel-base super alloy IN738LC. The main emphasis of this investigation was to examine the effects of adding small quantities of yttrium to the coating as well as to produce a platinum-modified aluminide diffusion coating which is accepted as the best industrial standard for diffusion aluminides at present. A pack diffusion process was used to produce the coatings in this current study. A standard aluminide coating was modified with a small YCI3 (0.5 Wt.%) addition to the pack, producing an aluminising-yttrising pack. In the platinum-modified altuninide coating process, a sample was coated with several microns of platinum using a sputtering technique prior to the aluminising process. The pack used in this platinum modified aluminide process was a standard aluminising pack. The performance of these modified coatings during oxidation and high temperature corrosion was evaluated. Promising results were obtained, which demonstrated that both platinum and yttrium modified aluminide coatings had beneficial effects on the oxidation performance of the coatings compared to the standard aluminide coating. However, they were found to work in different ways, to improve resistance to oxidation and hot corrosion resistance. The platinum modified aluminide extends the later stage of the coating life by reduces the amount of spall, whist yttrium modified aluminide reducing the amount of spall in the early stage of the coating life and increases the critical oxide thickness before the onset of spallation. From these results, the production of a combined platinum-yttrium modified aluminide coating would be expected to show improved oxidation and hot corrosion resistance throughout the life of the coating. This could be another direction for future work.