Interstitial Carbon Research Articles

Revealing the influence of carbon on shear-coupled grain boundary migrationin α-iron via molecular dynamics simulations

Shear-coupled grain boundary (GB) migration is of importance theoretically on the mechanisms of GB behaviors and application oriented on the development of novel processing methods by plastic deformation. We demonstrate via molecular dynamics simulations that the interstitial species carbon may affect the shear-coupled migration in α-iron strongly. The impact of carbon selectively takes effect depending on the variety of grain boundaries. Specifically, the coupling factor of the Σ9(221) GB is increased in the presence of carbon. While the carbon effect is inactive for the Σ17(223) GB. The influence of carbon is revealed to be connected with the disconnection modes of grain boundaries. The results of the work implicate correlations between the carbon enrichment and the final microstructure after severe plastic deformation.

Interstitial carbon content effect on the microstructure and mechanical properties of additively manufactured NiCoCr medium-entropy alloy

In this study, we manufactured the NiCoCr medium-entropy alloy (MEA) for the first time with controlled interstitial C content of 0.25 at% and 0.75 at% (0.25 C MEA and 0.75 C MEA) using a powder bed fusion-type additive manufacturing (AM) process. Moreover, we investigated the effect of interstitial C content on the microstructure, room temperature tensile properties and deformation behavior of MEA. The initial microstructure shows that both AM-built interstitial C-doped MEAs had a heterogeneous grain structure and epitaxial growth grains along the building direction. The analysis of electron channeling contrast images showed a large amount of nano-sized precipitates (in-situ precipitates) distributed at the sub-structure boundaries formed by a dislocation network, and a large number of stacking faults were simultaneously observed inside the sub-structure. The fraction of in-situ precipitates was higher in 0.75 C MEA than in 0.25 C MEA. A room temperature tensile test measured yield strengths (YS) of 747.5 MPa for 0.25 C MEA and 832.2 MPa for 0.75 C MEA, indicating the highest properties among additively manufactured MEAs reported to date. Considering the strengthening mechanisms, we compared the microstructural characteristics that affected YS, and identified that in-situ precipitates and high-dislocation density were major strengthening factors. On the other hand, deformation twin, which improves strain hardening rate and ductility was observed in both alloys. Based on the above results, we discuss the correlation of microstructure, mechanical properties, and deformation mechanism of AM-built interstitial NiCoCr MEA. • i-MEAs with different carbon contents were fabricated by additive manufacturing. • Mechanical and deformation behavior of AM-built i-MEAs were investigated. • Higher carbon addition lead to the enhanced tensile properties in AM-built i-MEA. • The predicted YS of i-MEAs corresponded well with the experimental data.

Carbon-modified TiO2 nanourchin with Ag nanoparticle decoration for environmental remediation

Multifunctional critical nano-composite material assembling Carbon-modified Ag@TiO2 nanourchin was synthesized to investigate visible light photocatalytic activity. The Carbon-modified Ag@TiO2 nanourchin was prepared by a facile two-step chemical synthesis through solvothermal and chemical reduction. Carbon nanospheres as the substrate play a key role for three dimensional nanourchin structure as well as carbon doping. The morphology, crystal structure, and chemical states were characterized carefully by different analytical procedures via transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD), RAMAN spectroscopy, X-ray photoelectron spectroscopy (XPS) and UV–Vis spectroscopy. It shows that the uniform loaded silver (Ag) on TiO2 surface was metallic Ag0 state. The exist of interstitial carbon and Ag NPs on TiO2 nanostructure collectively enhance the visible light photocatalytic activity. The visible light photocatalytic degradation of methyl orange (MO) studies revealed that Ag@C0.1TiO2 exhibited enhanced photocatalytic efficiency compared with the pure TiO2 nanourchin and commercial TiO2 powder. The improved photocatalytic property can be attributed to lower recombination of the photogenerated e− and h+ pairs in catalyst due to the formation of a Schottky barrier between Ag NPs and TiO2 which improved the surface charge separation greatly and presence of carbon serve as a sensitizer to absorb visible light which inject e- into conduction band (CB) of TiO2.

Effect of interstitial carbon atoms in core-shell Ni3ZnC0.7/Al2O3 catalyst for high-performance dry reforming of methane

Dry reforming of methane (DRM) on Ni-based catalysts provides an economically and environmentally pivotal route to generate synthesis gas. However, coke formation on Ni surface by the growth of carbon atoms is the main reason for catalyst deactivation and reactor blockage. Here, we propose a reaction-induced method to incorporate and store active carbon atoms into nickel octahedral sites in core-shell Ni3ZnC0.7/Al2O3. This strategy can fundamentally avoid C−C bond formation and feasible oxidation of Ni3ZnC0.7 in low-temperature DRM under CO2-rich condition. About 2 nm of thin-layer Al2O3 encapsulated Ni3ZnC0.7 is explored as the carbon reservoir to accommodate sufficient interstitial carbon atoms, and less than 5% Ni3Zn was observed under CH4/CO2 < 1/1 for 100 h. The dynamic balance of carbon atom storage and conversion in robust Ni3ZnC0.7 contributes to the enhanced activity, stability, coke and oxidation resistance, and distinct reaction pathway in low-temperature DRM.

Model for elimination of lifetime-limiting carbon vacancy defects in SiC by thermal treatment

In 4H-SiC semiconductors, carbon vacancies act as traps, which limit the carrier lifetime. During high-temperature treatment of 4H-SiC, the concentration of carbon vacancies can be increased or decreased by several atomistic processes, including the diffusion of carbon vacancies and carbon self-interstitials, and the thermal generation–recombination of defects. In this work, an analytic process model has been developed and calibrated against a collection of measured data. The model describes the concentration of carbon vacancies after thermal processing for a wider range of process conditions than previous works. For inert annealings, bulk recombination, bulk generation, and diffusion of carbon vacancies and carbon interstitials play a critical role. For oxidation processes, carbon interstitials are injected at the oxidizing surface. The injection rate of carbon interstitials at the oxidizing surface and their diffusivity from the surface into the bulk govern the reduction of carbon vacancies via bulk recombination. Basic properties of carbon vacancies and carbon self-interstitials in 4H-SiC, such as the thermal equilibrium concentrations, diffusivities, and bulk recombination rates, are reflected by model parameters and have been determined by model calibration for the temperature range of 1150–1950 °C. High-quality epitaxial films and low-quality substrates are described consistently, when assuming that carbon interstitials can be trapped by defects present only in the substrate.

Study on mechanism of improving wear and corrosion properties of 20CrMnTi ring gear surface by laser carburizing

Laser carburizing is an effective method to improve the surface properties of materials. In order to improve the corrosion resistance and wear resistance of 20CrMnTi ring gear surface, firstly, the material surface was carburized by laser. Secondly, the hardness, wear resistance and corrosion resistance of the surface before and after carburization were tested. Finally, the electronic structure of 20CrMnTi before and after carburization was calculated based on the first principle method of density functional theory. The results show that the surface microstructure after laser carburizing is mainly high carbon martensite and cementite, and the hardness is increased by 109.5%. There are adhesive wear and abrasive wear before and after carburizing. Interstitial carbon increases the density of dislocation and lattice distortion, and significantly improves the wear resistance of the surface. At the same time, the addition of interstitial carbon reduces the corrosion current density, increases the self-corrosion potential, and improves the corrosion resistance of the material. The first principle calculation results show that the interstitial carbon increases the strength of covalent bond and ionic bond, which is the main reason for the improvement of hardness and wear resistance, and the interstitial carbon reduces the density of states at Fermi level and inhibits electron transfer, which is the essential reason for improving corrosion resistance.

Fully gapped superconducting state in interstitial-carbon-doped Zr5Pt3

We report a comprehensive study of the ${\mathrm{Zr}}_{5}{\mathrm{Pt}}_{3}{\mathrm{C}}_{x}$ superconductors, with interstitial carbon between 0 and 0.3. At a macroscopic level, their superconductivity, with ${T}_{c}$ ranging from 4.5 to 6.3 K, was investigated via electrical-resistivity, magnetic-susceptibility, and specific-heat measurements. The upper critical fields ${\ensuremath{\mu}}_{0}{H}_{\mathrm{c}2}\ensuremath{\sim}7$ T were determined mostly from measurements of the electrical resistivity in applied magnetic field. The microscopic electronic properties were investigated by means of muon-spin rotation and relaxation ($\ensuremath{\mu}\mathrm{SR}$) and nuclear magnetic resonance (NMR) techniques. In the normal state, NMR relaxation data indicate an almost ideal metallic behavior, confirmed by band-structure calculations, which suggest a relatively high electronic density of states at the Fermi level, dominated by the Zr $4d$ orbitals. The low-temperature superfluid density, obtained via transverse-field $\ensuremath{\mu}\mathrm{SR}$, suggests a fully gapped superconducting state in ${\mathrm{Zr}}_{5}{\mathrm{Pt}}_{3}$ and ${\mathrm{Zr}}_{5}{\mathrm{Pt}}_{3}{\mathrm{C}}_{0.3}$, with zero-temperature gap ${\mathrm{\ensuremath{\Delta}}}_{0}=1.20$ and 0.60 meV and magnetic penetration depth ${\ensuremath{\lambda}}_{0}$ = 333 and 493 nm, respectively. The exponential dependence of the NMR relaxation rates below ${T}_{c}$ further supports nodeless superconductivity. The absence of spontaneous magnetic fields below the onset of superconductivity, as determined from zero-field $\ensuremath{\mu}\mathrm{SR}$ measurements, confirms the preserved time-reversal symmetry in the superconducting state of ${\mathrm{Zr}}_{5}{\mathrm{Pt}}_{3}{\mathrm{C}}_{x}$. In contrast to a previous study, our $\ensuremath{\mu}\mathrm{SR}$ and NMR results suggest conventional superconductivity in the ${\mathrm{Zr}}_{5}{\mathrm{Pt}}_{3}{\mathrm{C}}_{x}$ family, independent of the C content.

Self-diffusion in carbon-alloyed CoCrFeMnNi high entropy alloys

Tracer diffusion of the substitutional components in interstitial (CoCrFeNiMn)1-xCx high-entropy alloys with nominally x = 0.002, 0.005 and 0.008 (in at. fractions) is measured at elevated temperatures from 1173 to 1373 K. Two different characteristic effects of interstitial carbon addition on substitutional diffusion in these FCC alloys are distinguished. At the highest temperature of 1373 K, alloying by C with relatively low concentrations (x = 0.002) retards diffusion of the substitutional elements with respect to those in the C-free alloy. At lower temperatures and/or higher C concentrations (x ≥ 0.005), an enhancement of the diffusion rates of all substitutional elements is seen. A model is suggested that relates the self-diffusivities in the CoCrFeMnNi–C alloys with the lattice distortion imposed by interstitially dissolved carbon. The experimental results are interpreted in terms of a decrease of the migration barriers for vacancy-mediated diffusion due to the presence of interstitial C atoms.

Atomistic investigation on the impact of substitutional Al and Si atoms on the carbon kinetics in ferrite

The pairwise interactions of substitutional solute atom X = Al, Si with interstitial carbon at stable (octahedral) and saddle-point (tetrahedral) positions in body-centered-cubic iron (α-Fe) are computed using density-functional theory. These pairwise interactions are used in atomistic kinetic Monte Carlo approach to simulate carbon internal friction and tracer diffusion measurements in Fe-Si, Fe-Al, and Fe-Al-Si ferritic alloys without any adjusting parameters. The good agreement between the simulated and experimental Snoek relaxation profiles validates the pair interaction model for kinetic simulations. The predicted effect of Al on slowing down carbon diffusion is consistent with previous studies. We highlight a super-cell size effect on the Si-carbon interactions obtained from first principles. Using a carefully tested database, it is shown that the introduction of Si into ferrite only decreases the carbon diffusivity below a critical temperature.

Simultaneous Twinning and Microband-Induced Plasticity of a Compositionally Complex Alloy with Interstitial Carbon at Cryogenic Temperatures

Intermediate to low stacking fault energy (SFE) high entropy alloys (HEA) have shown an excellent combination of strength and ductility as a result of deformation twinning and martensite transformation. However, even in the absence of these mechanisms HEA can show a good strength-ductility combination, as is the case with non-equiatomic (Fe40.4Ni11.3Mn34.8Al7.5Cr6)C1.1. The room temperature mechanical behavior of this alloy has been associated with Taylor lattice and microband formation. The current research focuses on tensile cryogenic deformation of this alloy and investigates if these features and/or alternate mechanisms like deformation twinning are obtained. Surprisingly, it is not one or the other but both deformation twinning and microband formation that are observed during cryogenic deformation. The activation of both deformation mechanisms is a combination that is not often reported as the former is generally associated with intermediate to low SFE alloys and the latter with intermediate to high SFE alloys. The activation of twinning in (Fe40.4Ni11.3Mn34.8Al7.5Cr6)C1.1 is attributed to the high yield stress-temperature variation, as a result of solid solution strengthening being far greater than in other commonly researched compositionally complex alloys. A ductility retention down to 4 K was observed, while simultaneously showing a significant increase in flow stress. Despite the intermediate to high SFE deformation behavior, (Fe40.4Ni11.3Mn34.8Al7.5Cr6)C1.1 exhibits excellent cryogenic strength-ductility combination.

Carbonatite-melilitite-phosphate immiscible melts from the aragonite stability field entrained from the mantle by a Pliocene basalt

A plagioclase megacryst containing composite crystal-glass inclusions was ejected in a Pliocene basaltic diatreme in the Carpathian back-arc basin (Pannonian Basin). The megacryst grew from phonolitic melt, relics of which are preserved in the crystal-glass inclusions. Most of the pristine melt has undergone substantial compositional resetting by interaction with several batches of a low-viscosity carbonated, P-rich melilitite melt, which infiltrated and largely replaced the original inclusion content. The melilitite melt also caused partial resorption of the host megacryst and crystallisation of new calcic plagioclase forming stringers and palisades. A P-rich calcic carbonatite melt exsolved from the melilitite and later crystallised to aragonite at ~ 800 °C and 1.9 GPa. The phosphate melt fraction exsolved from the carbonatite and solidified as CO32−-rich A-B type apatite. At a very late evolutionary stage, K- and Si-rich fluids caused potassic and silicic alteration of the solidified melilitite glass along cracks and interfaces between calcic carbonate globules and glass at temperatures below 680 °C. The oxygen isotope composition of the plagioclase megacryst (6.2 ‰ V-SMOW; Vienna Standard Mean Ocean Water) and the 87Sr/86Sr isotope ratio of carbonates in the inclusions (0.7034) are consistent with a mantle-derived melt. 87Sr/86Sr isotope ratios (0.7047–0.7051) in interstitial carbonates from associated syenite and carbonatite xenoliths indicate a metasomatised mantle source contaminated with radiogenic crustal material or altered marine carbonate. The O-isotope ratios in the carbonates, 22.7 ± 0.6 ‰ V-SMOW in calcite and 23.6 ± 0.7 ‰ V-SMOW in aragonite, are also consistent with a sedimentary precursor. Contrasting δ13C values in the calcite, -12.7 ± 0.5 ‰ V-PDB (Vienna PeeDee Belemnite), and the aragonite (-4.6 ± 0.5 ‰ V-PDB) indicate low-temperature modification of calcite assisted by delta13C-depleted CO2 and preservation of primary magmatic delta13C values in aragonite. The microstructural and geochemical evidence points towards heterogeneous silicate-carbonate melt fractions generated during the metasomatism and partial melting of a supra-subduction mantle wedge.

Use of Raman Spectroscopy to Qualify Carbon Materials

In the last 30 to 40 years, various new types of carbon materials have been engineered for multiple industrial uses. It is now well-known that the Raman spectrum is sensitive to the structure, even though the spectrum is rather uncomplicated. Because Raman spectroscopy now has a reputation for providing good information, potential users of Raman equipment can request information on the quality of their sample. However, they are often not able to define clearly what they mean by “quality.” If they are growing diamond films, they may or may not want interstitial sp2 carbon to glue polycrystalline diamond together. If they are growing hard diamond-like carbon (DLC) films, they may want to correlate the spectral characteristics with physical characteristics of the film. In this column, I explain how the Raman characteristics can aid in characterization of carbon materials.

Multifunctional interstitial-carbon-doped FeCoNiCu high entropy alloys with excellent electromagnetic-wave absorption performance

Electromagnetic-wave absorbing (EMA) materials that have efficient absorption performances, great mechanical properties and chemical stability are rare and yet essential for communication security and protection. Herein, flaky interstitial-carbon-doped FeCoNiCu high entropy alloys (HEAs) as novel EMA materials were successfully prepared by high-energy ball-milling method. Interstitial-carbon doping as a modulating approach impacted the phase forming, morphology and electromagnetic properties of FeCoNiCu HEAs. Impedance matching was significantly optimized via tuning interstitial carbon contents. The carbon-doped FeCoNiCu HEAs with appropriate carbon contents delivered superior EMA performance compared with other HEAs EMA materials. Strong reflection loss as low as -61.1 dB in the Ku band, broad effective absorption bandwidth of 5.1 GHz was achieved for FeCoNiCuC0.04. Moreover, the carbon-doped FeCoNiCu HEAs exhibited excellent mechanical hardness and chemical stability. This work not only suggests that interstitial-carbon doping is an available approach to tuning electromagnetic properties of HEAs, but also presents carbon-doped FeCoNiCu HEAs as promising EMA materials for civilian and military due to the efficient absorption, broad bandwidth, great durability and stability.

Interstitial concentration effects on incipient plasticity and dislocation behaviors of face-centered cubic FeNiCr multicomponent alloys based on nanoindentation

• The interstitial concentration effects on dislocation behavior and incipient plasticity of a typical equiatomic FeNiCr multicomponent alloy are newly investigated via systematic nano-mechanical experimental study. • The dislocation nucleation of FeNiCr alloy processes in a manner of heterogenous nucleation mode with an activation volume exceeding one single principal atom, by the exchange between primary atoms and vacancies. • Interstitial-atom effects severely suppress the mobility of dislocations in the FeNiCr multicomponent alloys, which hinder the occurrence of pop-ins. • With increasing the concentration of interstitial atoms, both the critical shear stress and activation volume corresponding to the onset of incipient plasticity are enhanced. Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic (FCC) lattice, can significantly affect the dislocation behaviors on deformation. Recently, interstitial doping has been applied to tune the mechanical properties of the emerging multicomponent, often termed high-entropy alloys (HEAs) or medium-entropy alloys (MEAs). However, the fundamental mechanisms of the dislocation nucleation and the onset of plasticity of interstitial multicomponent alloys governed by the concentration of interstitial atoms are still unclear. Therefore, in the present work, an instrumented nanoindentation was employed to investigate the interstitial concentration effects of carbon atoms on single FCC-phase equiatomic FeNiCr MEAs during loading. The results show that the pop-in events that denote the onset of incipient plasticity are triggered by the sudden heterogeneous dislocation nucleation via the primary atoms-vacancy exchange with the instant stress field, regardless of the interstitial concentration. Moreover, the measured activation volumes for dislocation nucleation of the FeNiCr MEAs are determined to be increased with the interstitial concentration, which definitely suggests the participation of interstitial atoms in the nucleation process. Besides, it is also found that the average value measured in statistics of the maximum shear stress corresponding to the first pop-in is enhanced with the interstitial concentration. Such scenario can be attributed to the improved local change transfer and lattice cohesion caused by the interstitial atoms with higher concentrations. Furthermore, the significant drag effect of interstitial carbon atoms hinders the mobile dislocations before exhaustion, which severely suppresses the subsequent occurrence of pop-in events in the carbon-doped specimens. The work gives a microscale view of interstitial effects on the mechanical properties of multicomponent alloys, which can further help to develop new interstitial strengthening strategies for structural materials with remarkable performance.

Stability, Evolution and Diffusion of Intrinsic Point Defects in 4H-SiC

Silicon carbide (SiC) is a wide band-gap semiconductor of great technological importance, showing promise for application areas ranging from quantum computing and communication to power devices. Vital in both the contexts of power devices and quantum technology is the understanding of intrinsic defects that are introduced during various device processing steps, both immediately after their formation and over the course of defect evolution with temperature. Here we monitor the formation and evolution of intrinsic point defects in n-type 4H-SiC after proton irradiation at room temperature and subsequent annealing in the temperature range 300-1000 °C, and discuss the nature and origin of the EH4 and EH5 deep level defects observed by deep level transient spectroscopy around 400-500 K. In particular, the controversy on the nature of the EH5 trap in particular is addressed, where we propose the presence of two overlapping defect peaks: one metastable level that appears after low energy electron irradiation below the silicon displacement limit, and one more stable level that gradually decreases in concentration until an annealing temperature of 1000°C. We argue that the former is likely related to carbon interstitials, while the latter was recently tentatively attributed to the carbon antisite-vacancy pair.

Quantitative evaluation of dislocation density in as-quenched martensite with tetragonality by X-ray line profile analysis in a medium-carbon steel

The crystal structure of as-quenched martensite in steel changes from body-centered cubic to body-centered tetragonal because of the presence of interstitial carbon, and the c/a ratio increases with increasing carbon content. Because the X-ray diffraction peak profiles associated with the c-axis overlap those of the a-axis, the diffraction peak observed in martensite gradually broadens as the solute carbon increases. This may cause an overestimation of the dislocation density in the X-ray line profile analysis (for example, modified Williamson-Hall/Warren-Averbach method). In this study, the effect of the tetragonality of martensite in the X-ray line profile analysis was investigated to evaluate the dislocation density in a medium-carbon martensitic steel. The apparent dislocation density estimated without considering peak broadening due to tetragonality was calculated to be 1.7 × 1016 m−2 in the as-quenched 0.55%C steel. This value is approximately six times higher than that estimated using transmission electron microscopy (TEM), indicating that the dislocation density was overestimated. To eliminate the effect of tetragonality, the specimens were tempered at temperatures below 623 K. The estimation based on the TEM method revealed that the dislocation density only slightly decreased by tempering at 573 K, indicating negligible recovery at this temperature. The dislocation density obtained in the tempered specimen was calculated to be approximately 4.5 × 1015 m−2 using the mWH/WA method. This value was regarded as the true dislocation density of the as-quenched martensite in the 0.55%C steel.

Carbon diffusion in bcc- and bct-Fe: Influence of short-range C–C pair interactions studied from first-principles calculations

Identifying the mechanisms of interstitial diffusion in iron is important to understanding the low-temperature ageing of Fe–C ferritic and martensitic alloys. In spite of the low solubility of carbon in ferrite at equilibrium, carbon-rich areas are often found at segregated grain boundaries and in Cottrell atmospheres around dislocations. Carbon-rich areas also form by spinodal decomposition in martensite. In those cases, carbon atoms experience short-range interactions, susceptible to modify their migration behaviour. We performed first-principles calculations to study the influence of these C–C interactions on the migration of interstitial carbon in body-centered iron. The ab initio energy database was introduced in kinetic Monte Carlo simulations to compute the thermodynamic and kinetic parameters. We found that the migration energies of carbon are largely affected by the presence of a neighbouring carbon atom. We explain the evolution of these energies by the relative stability of the C–C configurations corresponding to stable and transition-state positions. The C–C pair interactions slightly modify the ferrite/martensite transition conditions and significantly change the carbon atomic migration path. The latter leads to an increase of the diffusivity up to 10 times and an important kinetic correlation at low temperature (<300 K) and high carbon contents (>1 at.%).

The effect of interstitial carbon atoms on defect evolution in high entropy alloys under helium irradiation

In this work, a design strategy based on a typical multi-principal element alloy (Fe50Mn30Co10Cr10, at. %) was proposed to tune the irradiation behavior by adding interstitial carbon atoms (Fe49.5Mn30Co10Cr10C0.5, at. %). Advanced scanning transmission electron microscopy was employed to study the evolution of dislocation loops and helium bubbles in alloys after 400 keV He+ ion irradiation at three different temperatures ranging from 350 °C to 450 °C. The results showed that the interstitial carbon atoms inhibited the growth of He bubbles and irradiation hardening. The high-resolution energy dispersive spectroscopy mapping revealed that the segregation at the dislocation loops in Fe49.5Mn30Co10Cr10C0.5 was efficiently lessened compared to that in Fe50Mn30Co10Cr10, which shows an even superior performance than the equiatomic FeMnCoCrNi Cantor alloy. Radiation-induced “W-shaped” elemental oscillation patterns with a width of about 1 nm around dislocation loops, were observed for the first time in high-entropy alloys. Such nanoscale local elemental fluctuations are suggested to modify the lattice friction and thus have an impact on the mechanical properties of the material. First-principles calculations suggest that the interstitial carbon atoms can effectively enhance the site-to-site local lattice distortion and modify vacancy migration energy near carbon atoms. Our systematic experiments demonstrate that adding interstitial carbon atoms into multi-principal element or high-entropy alloy is beneficial for the reduction in irradiation hardening and volumetric swelling, as well as radiation-induced segregation.

Predicting kinetic interface condition for austenite to ferrite transformation by multi-component continuous growth model

A critical issue restricting the application of Hillert-Agren-Liu solute-drag based model to predict interfacial conditions at a migrating ferrite-austenite interface is the lack of value for trans-interface diffusion parameter, i.e., the L parameter. Even an estimation of the parameter's order of magnitude is difficult due to its ambiguous physical interpretation. In this paper we extend a different solute-drag based model, namely the binary continuous growth model originally developed for rapid solidification, toward austenite to ferrite phase transformation to avoid this long-standing issue. The extensions consist of the treatments of multi-alloying components including interstitial carbon element and Gibbs-Thomson effect. The extended multi-component continuous growth model employs a physical parameter with clear physical meanings, i.e., interface diffusive speed in describing trans-interface energy dissipation, and can predict kinetic interface conditions and spontaneous diffusion-controlled to diffusion-less transition without using the ambiguous L parameter. The model is verified by the good agreement of its calculation results with those predicted by Hillert-Agren-Liu model for Fe–C alloys and Fe–C–Mn alloys. Further the model's advantages over Hillert-Agren-Liu model are demonstrated by calculating the kinetic interface condition phase diagrams of Fe–C–Mn–Ni alloys. It is concluded that the extended multi-component continuous growth model is valuable in unifying the efforts in addressing the common question of predicting deviations from local equilibrium at a fast-migrating interface during solidification and solid-state phase transformation.

Iron‐Carbon Alloy Under Shock Compression: Implications for the Carbon Concentration in Earth’s Inner Core

AbstractCarbon has been proposed to be a potential light element in the Earth’s solid inner core. However, its presence and concentration in the core remain limited constrained. In this study, we measured the equation of state of an iron‐carbon alloy with ∼1.5 wt.% (∼6.64 at.%) carbon up to ∼185 GPa and ∼3,750 K via shock compression. The Hugoniot equation of state of the Fe‐1.5wt.%C alloy was determined to be Us (km/s) = 3.94 (0.15) + 1.62 (0.08) Up with an initial density of 7.77 (0.03) g/cm3, where Us and Up are the shock wave velocity and particle velocity, respectively. Hugoniot data combined with the Mie‐Grüneisen equation of state allow us to build the thermal equations of state of the Fe‐C alloy at high pressure‐temperature (P‐T) conditions. Investigations on the pressure‐density relation of Fe‐C alloys by the shock experiments and synchrotron X‐ray diffraction measurements by Pamato et al. (2020), https://doi.org/10.1029/2020jb020159 have indicated that carbon should occupy interstitial sites of iron lattice at high P‐T conditions. The thermal equation of state of the Fe‐1.5wt.%C alloy provided here shows that Fe‐1.5wt.%C is ∼1.65% denser than the inner core under conditions relevant to the inner‐core boundary. This study indicates that iron alloyed with an upper bound of ∼2.2 (0.3) wt.% (∼10.7 [1.6] at.%) carbon may match with the Preliminary Reference Earth Model (PREM) in the Earth’s inner core. Thus, interstitial carbon in iron helps to explain the observed density deficit of the inner core, although other light elements are also expected.