Abstract
Thermomechanical fatigue (TMF) and isothermal fatigue (IF) experiments were performed on bare Mar-M246 as well as bare and coated Mar-M247 nickel based superalloys at strain ranges from 0.335 to 1 percent. The experiments were conducted in air, through a temperature range of 500 to J038°C at a constant strain rate of 5.0 ⨯ 10-5 s-1. Due to the coarse-grained structure of Mar-M246, TMF lives scattered considerably under low strain range conditions. Electron microscopy studies show that significant surface oxidation and gamma prime, γ’, depleted zones occur for Mar-M246 under these conditions. In the surface grain, where the change in γ’ morphology is most pronounced, γ’ rafted along axes ≈ ±45 deg from the loading axis. The influence of a protective coating on the IF and TMF lives of Mar-M247 was also examined. Results indicate that the coating does not significantly affect the fatigue lives ofMar-M247. The oxidation behavior of bare and coated Mar-M247 was investigated via X-ray microprobe and Auger Spectroscopy. Through these analyses, it is evident that the coating was completely degraded when exposed to the test environment for a long time. In both Mar-M246 and Mar-M247, in-phase thermomechanical fatigue (TMF IP) loading resulted in intergranular cracking. TMF IP loading promoted multiple cracks at the coating/substrate interface of coated Mar-M247. Finally, Eshelby techniques were used to calculate stress distributions in the vicinity of a surface oxide and second-phase particle at the coating/substrate interface.
Original language | English (US) |
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Pages (from-to) | 94-102 |
Number of pages | 9 |
Journal | Journal of Engineering Materials and Technology, Transactions of the ASME |
Volume | 118 |
Issue number | 1 |
DOIs | |
State | Published - Jul 1996 |
ASJC Scopus subject areas
- General Materials Science
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering