Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2607.23995

Nature of Cr Segregation in FCC to BCC quenched Fe-12Cr Alloy, with Post-Quenching Heat Treatment: A Positron Annihilation Study

S. Hari Babu·V. R. Reddy
View original source ↗Read source document ↗Export metadata ↓

Abstract

The Fe-Cr binary alloy is a model system for ferrtitic/martensitic steels. Cr clustering instigated loss of ductility, is one of the influential factors to deteriorate the alloys, and its severity depends on Cr concentration. This study aims at understanding (i) the nature of Cr precipitation in Fe-12Cr alloy using positron lifetime spectroscopy, transmission electron microscopy and Mössbauer spectroscopy studies and (ii) comparing the precipitation concentration and size with respect to Fe-9Cr alloy. The quenched alloys (from the high temperature FCC phase) are found to contain a high density of dislocations along with the sub-grain structure which lead to Cr rich σ-phase precipitation during post-quenching heat treatment at 748 K, while the alloy prepared with no dislocations and the sub-grain structure shows no precipitation, except at grain boundaries, consistent with observations in Fe-9Cr alloys. Selected area diffraction confirmed that the precipitates are tetragonal intermetallic σ-phase, contradicting the majority of the literature on Fe-Cr ferritic alloys which reported it as Cr rich BCC α'-phase. Mossbauer spectroscopy studies showed signatures of Cr depletion from the rest of the matrix, indicating that the precipitates are Cr rich compared to the alloy composition. The kinetics of Cr precipitation is found to be higher in the Fe-12Cr alloy compared to the Fe-9Cr alloy. The average precipitate size is observed to be higher and the number density is lower in the Fe-12Cr alloy compared to the Fe-9Cr alloy. In addition, the experimental positron lifetime in defect-free lattice of Fe-(9, 12)Cr alloys is reported for the first time with substantial evidence.

Explore related subjects

cond-mat.mtrl-sci

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

S. Hari Babu, V. R. Reddy. 2026-07-27. Nature of Cr Segregation in FCC to BCC quenched Fe-12Cr Alloy, with Post-Quenching Heat Treatment: A Positron Annihilation Study. https://arxiv.org/abs/2607.23995

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Symmetry-induced magnetic fullerene

Defect-free, charge-neutral, pure-carbon materials are generally viewed as intrinsically non-magnetic. Here we challenge this view by establishing a fundamental principle of symmetry-induced magnetism in pure-carbon fullerene systems through molecular orbital theory. We show that high-order symmetry of fullerene molecules or their crystalline lattices induces degenerate energy levels and hence, quantised magnetic moments at half filling. This mechanism holds for all high-order symmetries. It suggests a plausible intrinsic origin for the previously debated magnetic fullerene. Additionally, recent experimental advances in the synthesis of monolayer fullerene networks provide a feasible platform to implement our prediction on the deep link between symmetry and magnetism in these systems. Our results create new, broad frontiers of quantum magnetism by introducing molecular or crystalline symmetries in any lattice.

cond-mat.mtrl-sci↗
arXiv2026

Tritium for Nanoscale Hydrogen Analysis by Atom Probe Tomography

Accurate nanoscale detection of hydrogen is essential for understanding hydrogen-related phenomena in materials, yet conventional tracing with deuterium is often complicated by residual background hydrogen. This study evaluates tritium as a highly resolvable isotopic marker for nanoscale hydrogen analysis in metals using atom probe tomography. Titanium was selected for its ability to incorporate hydrogen isotopes, providing a suitable platform for tritium detection. Time of flight secondary ion mass spectrometry and electron backscatter diffraction were performed prior to tritium charging to characterize the initial composition and microstructure. Atom probe tomography in laser mode before and after tritium charging, at three post-charging time intervals, enables tracking of tritium incorporation over time. Thermal desorption analysis confirmed the presence of tritium and complemented the secondary ion mass spectrometry measurements, highlighting the role of the surface oxide layer in modulating tritium release. While tritium, deuterium, and protium differ in their diffusion and trapping behavior, the distinct mass signal associated with tritium provides a practical advantage for resolving hydrogen at very low concentrations. This work serves as a fundamental benchmarking study for leveraging tritium and atom probe tomography as a combined tool for understanding hydrogen in materials, relevant for interpreting local processes such as hydrogen embrittlement.

cond-mat.mtrl-sci↗
arXiv2026

Interfacial melting as a thermodynamic indicator of solid-state synthesizability

Computational materials discovery commonly ranks candidate materials by their thermodynamic stability on the formation energy convex hull, yet many predicted-stable phases resist synthesis. We propose that solid-state synthesizability through interfacial-melt-mediated routes requires an additional thermodynamic condition: the interfacial melt at the target composition must itself remain locally stable against spinodal decomposition. We examine this in the classical Fe--B system, where thermodynamically stable FeB$_4$ has been reported under high-pressure synthesis but not in low-pressure synthesis attempts. Using melt--quench molecular dynamics driven by a fine-tuned machine-learning interatomic potential, we find that, at ambient pressure, the B-rich interfacial melt near the FeB$_4$ composition develops a concave free-energy landscape, signaling a demixing instability that is corroborated by the concentration--concentration structure factor and correlated with low-energy icosahedral and pentagonal-pyramidal boron motifs. In contrast to FeB$_4$, metastable Fe$_3$B and Fe$_{23}$B$_6$ remain synthesizable because their corresponding melts are stable. Applied pressure introduces a convex $PV$ contribution that strongly suppresses this instability, reducing the curvature at the FeB$_4$ composition to within the uncertainty of our fit at 1800~K, consistent with the experimental synthesis boundary. Comparison with CrB$_4$ further shows that weaker melt instability correlates with easier experimental synthesis. Interfacial-melt stability, which atomistic simulations can assess via the low-$k$ concentration--concentration structure factor, is thus proposed as a practical thermodynamic screening descriptor of synthesizability for AI-assisted materials discovery.

cond-mat.mtrl-sci↗