Abstract:
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.