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A hierarchical microstructure due to chemical ordering in the bcc lattice: Early stages of formation in a ferritic Fe–Al–Cr–Ni–Ti alloy
- Source :
- Acta Materialia. 92:220-232
- Publication Year :
- 2015
- Publisher :
- Elsevier BV, 2015.
-
Abstract
- A hierarchical microstructure is obtained in an alloy with composition Fe–8.1Al–12.2Cr–1.9Mo–18.2Ni–2.0Ti (wt.%) processed by melt-spinning. The evolution of the precipitation pathways is investigated using transmission electron microscopy (TEM) techniques, atom probe tomography (APT) and first-principles thermodynamic calculations. As-solidified ribbons exhibit a random dispersion of B2-ordered precipitates (NiAl-type) in an Fe-based matrix. Subsequent aging at 700 °C yields nucleation and growth of the L21-phase (Ni2TiAl-type) within the primary B2-precipitates, leading to a microstructure exhibiting three types of hierarchy: (i) a structural hierarchy due to chemical ordering, with a chemically disordered matrix of bcc-Fe (A2), the nearest-neighbor (NN) ordered B2-precipitates (NiAl-type) and the next nearest-neighbor (NNN) ordered L21-precipitates (Ni2TiAl-type) within B2, (ii) a dimensional hierarchy with a continuous bcc-Fe matrix, coherently embedded B2-precipitates, with a size range of 60–200 nm and the coherent precipitate substructure, with L21-phase and dimensions of 15–20 nm. (iii) A spatial hierarchy where B2-precipitates are embedded in the bcc-Fe matrix and L21-precipitates nucleate and grow only within B2-precipitates. In addition, it is verified that the interface between B2 and L21 is coherent and adopts a diffuse structural profile. Monte-Carlo simulations reproduce these observations and it is found that interface energies of B2 and L21 reduce from 50 mJ/m2 at 0 K to 11 mJ/m2 at 973 K. Kinetic-Monte-Carlo simulations support the interpretation of the experimental results that the L21 nucleates within the B2 phase.
- Subjects :
- 010302 applied physics
Materials science
Polymers and Plastics
Precipitation (chemistry)
Alloy
Nucleation
Metals and Alloys
02 engineering and technology
Atom probe
engineering.material
021001 nanoscience & nanotechnology
Microstructure
01 natural sciences
law.invention
Electronic, Optical and Magnetic Materials
Crystallography
Precipitation hardening
law
Chemical physics
Lattice (order)
0103 physical sciences
engineering
Ceramics and Composites
Substructure
0210 nano-technology
Subjects
Details
- ISSN :
- 13596454
- Volume :
- 92
- Database :
- OpenAIRE
- Journal :
- Acta Materialia
- Accession number :
- edsair.doi.dedup.....72ce96bf936eb6d523a74bbcb3c4bef3
- Full Text :
- https://doi.org/10.1016/j.actamat.2015.03.043