Precipitation-hardening of superalloy 693 and modeling of initial stages of hardening

Journal Article · Sun Apr 15 04:00:00 EDT 2018 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2018.02.007· OSTI ID:22804948

Dey, G. K. ^[1]

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1. Materials Science Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India)

Highlights: • Isothermal Time-Temperature-Precipitation diagram of superalloy 693 established. • At 973–1173 K, increase in hardness up to 1.5 h of ageing followed by drop noticed. • Initial hardening of alloy at 973–1173 K is modeled by Johnson-Mehl-Avrami equation. • XRD, TEM but not SEM-EDS indicate formation of fine γ′ precipitates in aged samples. • Initial stages of hardening is attributed to formation of fine γ′ precipitates. - Abstract: Isothermal time-temperature-hardness behavior for Ni{sub 3}Al type phase in austenitic superalloy 693 was investigated by micro hardness measurements of the aged specimens. Ageing of the alloy between 973 K and 1173 K indicated an initial increase in micro hardness with ageing time attaining a peak at 1.5 h followed by a drop of its value. The early stages of hardening for the alloy was modeled by the expression: ΔH = (Kt){sup n}, where ΔH, t, n and K are increase in hardness, ageing time (h; in hour), time exponent and temperature-dependent rate constant (h{sup −1}) respectively. X-ray diffraction of solution-annealed and aged specimens indicated formation of Ni{sub 3}Al type precipitation-hardening (γ′) phase, while scanning electron microscopy with energy dispersive X-ray spectroscopy could not clearly reveal the formation of γ′ phase. Transmission electron microscopy on peak-aged (1.5 h at 973 K, 1073 K, 1173 K) samples revealed formation of fine, face centered cubic, Ni{sub 3}Al type (γ′) precipitates, while over-aged (3 h at 973 K, 1073 K, 1173 K) specimens indicated coarsening of precipitates. The initial stages of hardening for the alloy (at 973 K, 1073 K, 1173 K) are attributed to formation of fine Ni{sub 3}Al type precipitates.

• OSTI ID: 22804948
• Journal Information: Materials Characterization, Journal Name: Materials Characterization Vol. 138; ISSN 1044-5803; ISSN MACHEX
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AGING
ANNEALING
AUSTENITIC STEELS
COMPUTERIZED SIMULATION
FCC LATTICES
HEAT RESISTING ALLOYS
MICROHARDNESS
PRECIPITATION
PRECIPITATION HARDENING
SCANNING ELECTRON MICROSCOPY
SOLUTIONS
TEMPERATURE DEPENDENCE
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY