Tanner_2017_Effect.pdf (2 MB)
The effect of single crystal and welded substrates on the development of braze microstructures
journal contributionposted on 2023-03-03, 12:03 authored by EOIN HINCHYEOIN HINCHY, MICHAEL POMEROYMICHAEL POMEROY, DAVID TANNERDAVID TANNER
To emulate combined welding and brazing techniques, frequently used during the rejuvenation of turbine components, TIG and SWET weld overlays have been applied to the surfaces of a single crystal nickel-based alloy and subsequently overlain with braze and subjected to a typical brazing cycle heat treatment. Both welds comprised of columnar dendritic microstructures with an epitaxial  growth orientation near the substrate surface and equiaxed randomly oriented grains at the weld surface. While the TIG weld showed a sharp columnar to equiaxed transition, that for the SWET weld was diffuse and comprised colonies of columnar structures with their  misoriented to the epitaxial columnar directions as a result of shallower temperature gradients. Analysis of the microstructures of the brazed materials showed that the extents of boron penetration were significantly greater for the welds due to enhanced diffusion along grain boundaries between the equiaxed structures compared to y channel limited transport in the single crystal . A striking feature of the diffusion zone microstructures was the development of carbo-boride needles which formed by the reaction of boron, refractory metals and TaC. It is the release of Ta from TaC which stabilises y’ envelope formation around the needles. The post-brazed microstructures of TIG welds used in this study showed considerably fewer detrimental boride precipitates than brazed SWET welds and as a result are expected to show superior mechanical properties.
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PublicationJournal of Alloys and Compounds;690, pp. 856-863
Other Funding informationIRC, Lufthansa Technik Turbine Shannon (LTTS)
RightsThis is the author’s version of a work that was accepted for publication in Journal of Alloys and Compounds. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Alloys and Compounds, 2017, 690, pp. 856-863, http://dx.doi.org/10.1016/j.jallcom.2016.08.148
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