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Journal of Materials Science

, Volume 27, Issue 23, pp 6463–6474 | Cite as

Thermal stability of a platinum aluminide coating on nickel-based superalloys

  • H. M. Tawancy
  • N. Sridhar
  • B. S. Tawabini
  • N. M. Abbas
  • T. N. Rhys-Jones
Papers

Abstract

An investigation was carried out to determine the thermal stability of a platinum aluminide coating on the directionally solidified alloy MAR M 002 and its single-crystal version alloy, SRR 99, at 800, 1000 and 1100°C. The morphology, structure and microchemical composition of the coating were characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. In the as-deposited condition, the coating was found to consist of two layers. Most of the platinum was concentrated in the outer coating layer which consisted of a fine dispersion of PtAl2 in a matrix of β-(Ni, Pt)Al containing other elements in solid solution, such as cobalt and chromium. The inner coating layer was relatively free of platinum and consisted essentially of β-NiAl. Exposure at 800°C was found to have no significant effect on the structure and composition of the coating on each alloy. At temperatures ⩾1000°C, however, PtAl2 became thermodynamically unstable and significant interdiffusion occurred between the coating and alloy substrate. After exposure at 1000°C, the components of the outer coating layer were NiAl and Ni3Al. However, after exposure at 1100°C, the outer coating layer consisted only of Ni3Al. Also, after exposure at both temperatures, the composition of the outer coating layer approached that of the inner layer due to interdiffusion. Although the coating on both alloys exhibited similar structural stability at all temperatures investigated, the coating on alloy MAR M 002 was found to develop a more protective scale. This behaviour was correlated with differences in alloy substrate composition particularly rare-earth elements such as hafnium.

Keywords

Cobalt Thermal Stability NiAl Coating Layer Ni3Al 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Chapman & Hall 1992

Authors and Affiliations

  • H. M. Tawancy
    • 1
  • N. Sridhar
    • 1
  • B. S. Tawabini
    • 1
  • N. M. Abbas
    • 1
  • T. N. Rhys-Jones
    • 2
  1. 1.Materials Characterization Laboratory, Research InstituteKing Fahd University of Petroleum and MineralsDhahranSaudi Arabia
  2. 2.Materials and Mechanical ResearchRolls-Royce plcBristolUK

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