Introduction |  Bond Coats |  TBC |  Processes |  Resources | |
[Introduction]  [Aluminides]  [Pt-Aluminides]  [MCrAlY] | Back to phase-transformation home page |
NiAl coatings tends to suffer strongly from interdiffusion with the substrate, which results in formation of γ' at the expense of β.
The idea of introducing a diffusion barrier lead to the invention of the Pt-aluminide coatings, which are obtained by similar methods as conventional aluminide, but after electroplating the blade with Pt. The layer of Pt deposited is typically of 5-10 μm (Schütze, 2000).
Because the plating can increase the life of the blades by up to three times (Sivakumar, 1989), the cost of Pt plating is easily compensated.
Interestingly, it was found that Pt additions not only did not provide a diffusion
barrier, but also enhanced Al diffusion (Chen, 1997). When applied on the second
generation superalloy CMSX4, Pt formed TCP (topologically close-packed) phases
with some elements of the substrate (Re, W, Mo, Cr).
The exact reasons for the beneficial effect of Pt are not fully understood, but
it was found that Pt improves oxide adherence and also contributes to better hot
corrosion resistance.
Pt appears to partially substitute Ni in β-NiAl, and also to form PtAl2 which is believed to act as an Al reservoir. It has also been proposed that Pt acts in a similar manner as Y in MCrAlY coatings. In these coatings, Y combines with S; this greatly increase the coating life as S is otherwise detrimental to the adherence of the oxide layer. There is nevertheless no evidence of a similar effect of Pt in β-NiAl coatings (Evans, 2001).
conditions of use | 2004 Thomas Sourmail. | Feedback greatly appreciated |