Microstructural stability and mechanical behavior of a Co–20Ni–7Al–7W–4Ti at.% superalloy
| Autor: | David C. Dunand, David N. Seidman, Chunan Li, Ding-Wen Chung |
|---|---|
| Rok vydání: | 2020 |
| Předmět: |
Number density
Materials science Mechanical Engineering Alloy Metals and Alloys 02 engineering and technology engineering.material 010402 general chemistry 021001 nanoscience & nanotechnology Microstructure 01 natural sciences Indentation hardness 0104 chemical sciences Superalloy Creep Mechanics of Materials Volume fraction Materials Chemistry engineering Crystallite Composite material 0210 nano-technology |
| Zdroj: | Journal of Alloys and Compounds. 848:156378 |
| ISSN: | 0925-8388 |
| DOI: | 10.1016/j.jallcom.2020.156378 |
| Popis: | The temporal evolution of the microstructure and microhardness of a polycrystalline L12-strengthened Co-based superalloy (Co–19.6Ni–7.6Al–7.4W–4.1Ti, at.%) was investigated for an aging temperature of 900 °C. The γ(f.c.c.)/γ′(L12) structure remained stable throughout aging to the longest aging time of 2000 h (83 days), with no additional phases present. While the volume fraction of γ′(L12)-precipitates reached an almost constant value of 64% at 16 h, the temporal evolution of the γ′(L12)-precipitates’ mean-radius and their number density (temporal exponent of p = 3.49 ± 0.18 for the equivalent radius, and q = −0.74 ± 0.04 for the volumetric number density) deviated somewhat from the Lifshitz-Slyozov (LS) predictions ( p = 3 and q = −1), suggesting that the alloy had not achieved a true stationary-state at 2000 h. At ambient temperature, a peak Vickers microhardness of 3.80 ± 0.10 GPa was achieved after 240 h of aging. As the testing temperature was increased, an anomalous increase in flow-stress was also observed, with a peak flow-stress value of 705 MPa measured at 750 °C, 30 MPa higher than an archival literature value with about half the Ni concentration (10 at.%). Creep resistance at 850 °C was greater than an archival literature value for a ternary Co–9Al–9W alloy. After 200 h of compressive creep at 850 °C the microstructure evolved as follows: (i) the volume fraction of the γ′(L12)-phase increased from 64% to 79%; and (ii) some grains exhibited rafts of γ′(L12)-precipitates along ⟨100⟩-directions. While the first change is expected to improve creep resistance, the second one is deleterious, as evidenced by a comparison with the creep resistance of a sample without rafts of γ′(L12)-precipitates tested for the same conditions. |
| Databáze: | OpenAIRE |
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