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Proceedings Paper

Laser Clad Nickel Based Superalloys: Microstructure Evolution And High Temperature Oxidation Studies
Author(s): S. Sircar; C. Ribaudo; J. Mazumder
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Paper Abstract

Application of alloy coatings with superior oxidation resistance at elevated temperatures (1200°C) on superalloy components is of interest at present. There is a general consensus that the addition of rare earths such as hafnium (Hf) to these alloys has a pronounced effect on their performance. An in situ laser cladding technique was used to produce Ni-Al-Cr-Hf alloys on a nickel alloy substrate. Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and Scanning Transmission Electron Microscope (STEM) attached with Energy Dispersive X-ray (EDX) analyzers were employed for microstructural evolution studies of alloys produced during the laser cladding process. The microstructure of these alloys mainly consists of dendrites of Y' of the Ni3Al type with about 11-14 wt% Hf and an interdendritic eutectic phase. Electron microscopy in the dendritic zones reveals ordered domains whose morphology depends on laser cladding process parameters. Variation in these parameters produced only subtle changes in the composition and cell spacing of the dendritic phase. The eutectic constituent consists of a Hf-rich phase and a Hf-lean phase in an alternating lamellar structure. Convergent beam diffraction and x-ray spectroscopy techniques were used to characterize the constituents. A possible phase transformation sequence has been suggested. Differential Thermal Analysis (DTA) work indicates that the Y' dissolution temperature for the claddings is at least as high as the substrate material (Rene 80). Single cycle oxidation tests of eight hours at 1200°C in slowly flowing air reveal that the claddings have a lower weight gain rate than the substrate itself. Microchemistry and microstructure of the oxidized samples are examined using SEM attached with EDX and Auger Electron Spectroscopic (AES) techniques. The improvement in the oxidation resistance is believed to be at least partially due to the mechanical pegging between alumina coated hafnia protrusions and the unoxidized metal matrix.

Paper Details

Date Published: 24 October 1988
PDF: 13 pages
Proc. SPIE 0957, Laser Beam Surface Treating and Coating, (24 October 1988); doi: 10.1117/12.947700
Show Author Affiliations
S. Sircar, University of Illinois at Urbana-Champaign (United States)
C. Ribaudo, University of Illinois at Urbana-Champaign (United States)
J. Mazumder, University of Illinois at Urbana-Champaign (United States)

Published in SPIE Proceedings Vol. 0957:
Laser Beam Surface Treating and Coating
Gerd Sepold, Editor(s)

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