arXiv subjects

Risheng Pei

Publications and source records attributed to Risheng Pei.

5 recordsLinked to original sources

arXiv2025

Solute Co-Segregation Mechanisms at Low-Angle Grain Boundaries in Magnesium: A Combined Atomic-Scale Experimental and Modeling Study

Solute segregation at low-angle grain boundaries (LAGBs) critically affects the microstructure and mechanical properties of magnesium (Mg) alloys. In modern alloys containing multiple substitutional elements, understanding solute-solute interactions at microstructural defects becomes essential for alloy design. This study investigates the co-segregation mechanisms of calcium (Ca), zinc (Zn), and aluminum (Al) at a LAGB in a dilute AZX010 Mg alloy by combining atomic-scale experimental and modeling techniques. Three-dimensional atom probe tomography (3D-APT) revealed significant segregation of Ca, Zn, and Al at the LAGB, with Ca forming linear segregation patterns along dislocation arrays characteristic of the LAGB. Clustering analysis showed increased Ca-Ca pairs at the boundary, indicating synergistic solute interactions. Atomistic simulations and elastic dipole calculations demonstrated that larger Ca atoms prefer tensile regions around dislocations, while smaller Zn and Al atoms favor compressive areas. These simulations also found that Ca-Ca co-segregation near dislocation cores is energetically more favorable than other solute pairings, explaining the enhanced Ca clustering observed experimentally. Thermodynamic modeling incorporating calculated segregation energies and solute-solute interactions accurately predicted solute concentrations at the LAGB, aligning with experimental data. The findings emphasize the importance of solute interactions at dislocation cores in Mg alloys, offering insights for improving mechanical performance through targeted alloying and grain boundary engineering.

cond-mat.mtrl-sci↗

arXiv2023

Orientation relationship of FeNiC and FeNiCSi from variant detection in EBSD data

The determination of orientation relationships in dual or multi-phase materials is very important in the field of interface engineering for the design of materials with tailored properties. In this work, a code is developed for the automated and statistical analysis of the orientation relationship of electron backscatter diffraction data. On the example of Fe-Ni-(Si)-C alloys containing lenticular martensite and retained austenite, the code is applied and it is shown that the orientation relationship (OR) corresponds to the Greninger-Troiano OR and that a statistically reliable investigation of the OR between the retained austenite and the related martensite variants is feasible using the code developed in this study.

cond-mat.mtrl-sci↗

arXiv2023

Atomistic insights into the inhomogeneous nature of solute segregation to grain boundaries in magnesium

In magnesium alloys with multiple substitutional elements, solute segregation at grain boundaries (GBs) has a strong impact on many important material characteristics, such as GB energy and mobility, and therefore, texture. Although it is well established that GB segregation is inhomogeneous, the variation of GB solute composition for random boundaries is still not understood. In the current study, atomic-scale experimental and simulation techniques were used to investigate the compositional inhomogeneity of six different GBs. Three-dimensional atom probe tomography results revealed that GB solute concentration of Nd in Mg varies between 2 to 5 at.%. This variation was not only seen for different GB orientations but also within the GB plane. Correlated atomistic simulations suggest that the inhomogeneous segregation behavior observed experimentally stems from local atomic rearrangements within the GBs and introduce the notion of potential excess free volume in the context of improving the prediction of per-site segregation energies.

cond-mat.mtrl-sci↗

arXiv2023

Strengthening of Mg-Al-Ca alloys with C15 and C36 Laves phases

The Laves phase skeleton in cast Mg-Al-Ca alloys is known to provide considerable strengthening. Laves phases such as CaMg$_2$ (C14), Ca(Al,Mg)$_2$ (C36), and CaAl2 (C15) have high melting points, high hardness at room and elevated temperatures, but unfortunately are inherently brittle. Mg-Al-Ca alloys thus have good creep properties but limited ductility. An understanding of the co-deformation behaviour of $α$-Mg and Laves phases is essential for optimising the strength-ductility balance of these alloys. Here, we study the mechanical behaviour of a Mg-4.65Al-2.82Ca alloy using micropillar compression in the $α$-Mg matrix, at $α$-Mg/C36 and $α$-Mg/C15 interfaces and in the C15 phase in combination with scanning electron microscopy (SE imaging), electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD), and low-kV scanning transmission electron microscopy (STEM). We show that both, C15 and C36, Laves phases provide considerable strengthening to the $α$-Mg matrix by delaying the onset of basal slip and extension twinning, while only the C36 phase appears to allow a certain extent of slip transfer/ plastic co-deformation, in spite of its greater anisotropy compared with the cubic C15 phase. We therefore conclude based on these results that strengthening of the $α$-Mg matrix by the C36 Laves phase is preferable given that it combines easy skeleton formation with some co-deformation and considerable stability at common application temperatures of magnesium alloys.

cond-mat.mtrl-sci↗

arXiv2020

Deformation of micrometer and mm-sized Fe2.4wt.%Si single- and bi-crystals with a high angle grain boundary at room temperature

Plasticity in body-centred cubic (BCC) metals, including dislocation interactions at grain boundaries, is much less understood than in face-centred cubic (FCC) metals. At low temperatures additional resistance to dislocation motion due to the Peierls barrier becomes important, which increases the complexity of plasticity. Iron-silicon steel is an interesting, model BCC material since the evolution of the dislocation structure in specifically-oriented grains and at particular grain boundaries have far-reaching effects not only on the deformation behaviour but also on the magnetic properties, which are important in its final application as electrical steel. In this study, two different orientations of micropillars (1, 2, 4 microns in diameter) and macropillars (2500 microns) and their corresponding bi crystals are analysed after compression experiments with respect to the effect of size on strength and dislocation structures. Using different experimental methods, such as slip trace analysis, plane tilt analysis and cross-sectional EBSD, we show that direct slip transmission occurs, and different slip systems are active in the bi-crystals compared to their single-crystal counterparts. However, in spite of direct transmission and a very high transmission factor, dislocation pile-up at the grain boundary is also observed at early stages of deformation. Moreover, an effect of size scaling with the pillar size in single crystals and the grain size in bi-crystals is found, which is consistent with investigations elsewhere in FCC metals.

cond-mat.mtrl-sci↗