Abstract
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. © 1993.
Original language | English |
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Pages (from-to) | 19-26 |
Number of pages | 8 |
Journal | Materials Science and Engineering A |
Volume | 169 |
Issue number | 1-2 |
DOIs | |
Publication status | Published - 15 Sept 1993 |
Keywords
- aging of materials
- bending deformation
- coatings
- cracks
- ductility
- fracture
- materials interfaces
- morphology
- nickel alloys
- strain
- superalloys
- thermal effects
- aluminide coating
- carbide matrix interfaces
- coating transition zone
- crack morphology
- crack path
- ductile brittle transition
- single crystal nickel base superalloy
- aluminum compounds