Dresden 2009 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 32: Topical Session High Temperature Materials III

MM 32.1: Topical Talk

Wednesday, March 25, 2009, 16:45–17:15, IFW A

The formation and growth of Secondary Reaction Zones in coated 4th generation Ni-base Blade Alloys — •Catherine Rae and Aya Suzuki — Department of Materials Science and Metallurgy, Cambridge, CB2 3QZ, UK

Secondary Reaction Zone (SRZ) formed under aluminized and Pt-aluminised coating have become an increasing problem in advanced single crystal superalloys. The distinctive morphology grows by a discontinuous precipitation reaction similar in many ways to recrystallisation, and destroys the distinctive fine γγ' microstructure. In thin sections of HP turbine blades this can reduce the load-bearing cross section of a blade by as much as 10%. The morphologies and growth kinetics of the Secondary reaction zones formed between the Plat-Aluminised coating and 4th generation Ni-base superalloy substrates have been investigated. Three alloys were studied with systematically varying Ru content in the range of 2-5 wt%. At the lowest Ru content sporadic formation of SRZ was observed, whilst the higher Ru-containing alloys formed a continuous SRZ within the first hour of exposure at 1100°C. These alloys also showed more rapid SRZ growth, regardless of the original surface finish. EBSD analysis revealed that the higher Ru-containing alloys nucleate many more grains of the SRZ and this leads to a deeper penetration depth into the substrate. Orientation relationships between the coating and the SRZ reveal possible nucleation routes for the SRZ grains. These have been investigated using Focussed Ion Beam sectioning and the extraction of sections for TEM analysis.