Fracture behaviour of an aluminide coating on a single crystal nickel base superalloy

Measurement of the coating fracture strain of an aluminide coating on a single crystal nickel base superalloy has been performed both in three-point bending and using variable wall thickness testpieces. As-aged specimens, 28 to 33 μm in thickness, were tested at room temperature, 600, 700 and 750 °C...

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Bibliographic Details
Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 1993-09, Vol.169 (1), p.19-26
Main Authors: Totemeier, T.C., Gale, W.F., King, J.E.
Format: Article
Language:English
Subjects:
Applied sciences
Condensed matter: structure, mechanical and thermal properties
Exact sciences and technology
Mechanical and acoustical properties
adhesion
Metals. Metallurgy
Physics
Solid surfaces and solid-solid interfaces
Surfaces and interfaces
thin films and whiskers (structure and nonelectronic properties)
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Summary:Measurement of the coating fracture strain of an aluminide coating on a single crystal nickel base superalloy has been performed both in three-point bending and using variable wall thickness testpieces. As-aged specimens, 28 to 33 μm in thickness, were tested at room temperature, 600, 700 and 750 °C; specimens pre-exposed for 140 h at 850 and 1100 °C in air and vacuum were tested at room temperature. Fracture strains varied from 0.52 to 0.70% for as-aged specimens tested at temperatures up to 700 °C and specimens exposed at 850 °C and tested at room temperature. The crack path for these conditions was intergranular or transgranular in the main coating, along carbide-matrix interfaces in the coating transition zone, and at an angle of 30–45° to the original crack path in the substrate. The as-aged coating tested at 750 °C was ductile; a ductile-brittle transition occurs between 700 and 750 °C for the strain rate used (1 × 10 −5 s −1). Following 1100 °C pre-exposure, specimens were ductile at room temperature with fractures strains of several percent. In this condition the crack morphology changed to one of subsurface nucleation in β grains and at β-γ′ interfaces.
ISSN:0921-5093
1873-4936
DOI:10.1016/0921-5093(93)90594-5