Decomposition of Fe-Ni martensite: Implications for the low-temperature ([<=]500 C) Fe-Ni phase diagram
- Lehigh Univ., Bethlehem, PA (United States). Dept. of Materials Science and Engineering
- Univ. of Massachusetts, Amherst, MA (United States). Dept. of Mechanical Engineering
The low-temperature (<500 C) decomposition of Fe-Ni martensite was studied by aging martensitic Fe-Ni alloys at temperatures between 300 C and 450 C and by measuring the composition of the matrix and precipitate phases using the analytical electron microscope (AEM). For aging treatments between 300 C and 450 C, lath martensite in 15 and 25 wt pct Ni alloys decomposed with [gamma] [face-centered cubic (fcc)] precipitates forming intergranularly, and plate martensite in 30 wt pct Ni alloys decomposed with [gamma](fcc) precipitates forming intragranularly. The habit plane for the intragranular precipitates is [111][sub fcc] parallel to one of the [110][sub bcc] planes in the martensite. The compositions of the [gamma] intergranular and intragranular precipitates lie between 48 and 58 wt pct Ni and generally increase in Ni content with decreasing aging temperature. Diffusion gradients are observed in the matrix [alpha] [body-centered cubic (bcc)] with decreasing Ni contents close to the martensite grain boundaries and matrix/precipitate boundaries. The Ni composition of the matrix [alpha] phase in decomposed martensite is significantly higher than the equilibrium value of 4 to 5 wt pct Ni, suggesting that precipitate growth in Fe-Ni martensite is partially interface reaction controlled at low temperatures (<500 C). The results of the experimental studies modify the [gamma]/[alpha] + [gamma] phase boundary in the present low-temperature Fe-Ni phase diagram and establish the eutectoid reaction in the temperature range between 400 C and 450 C.
- OSTI ID:
- 7244398
- Journal Information:
- Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Journal Name: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States) Vol. 25:8; ISSN 0360-2133; ISSN MTTABN
- Country of Publication:
- United States
- Language:
- English
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