Partitioning Of Si Research Articles

Soil- and Foliar-Applied Silicon and Nitrogen Supply Affect Nutrient Uptake, Allocation, and Stoichiometry in Arabica Coffee Plants

ABSTRACT Silicon (Si) application may affect the plant response to nitrogen (N), possibly by changing the uptake, concentration, and partitioning of nutrients in plant tissues; however, this has not yet been proven in Arabica coffee plants. The effects of Si application methods [no Si, soil-applied soluble Si (168 mg Si L−1), and foliar-applied soluble Si (two application of 2 mg Si plant−1)] and N levels (0 and 80 mg N L−1) on biomass production and partitioning and uptake, partitioning, and stoichiometry of nutrients and Si in young Arabica coffee plants grown under greenhouse conditions were evaluated. Nitrogen fertilization increased the biomass production and uptake of all nutrients; however, reduced the concentrations of K, Ca, Mg, S, Mn, and Si in the leaves, Si in the stems, and K, Mg, and S in the roots of coffee plants as a dilution effect. In the presence of N, soil-applied Si increased the concentrations of Zn in the leaves and Ca and Si in the stems, the uptake of K, S, and Si, and the Si:N ratio. Foliar-applied Si increased the concentrations of N, P, K, and Zn in the leaves and Ca and Si in the stems, as well as the total uptake of K and Si and the Si:N ratio in coffee plants, being more evident in the N fertilization presence. This study unraveled that, especially when it was soil-applied, Si altered the nutrient uptake, allocation, and stoichiometric ratios with N, with a consequent increase in biomass production of young coffee plants fertilized with N.

Strengthening mechanisms in vanadium-microalloyed medium-Mn steels

In this work, the impact of adding vanadium, ranging from 0 to 2 wt%, on the microstructure and mechanical properties of as-cast medium manganese steel was explored. A dual phase microstructure consisting of martensite and retained austenite was observed in the 0 V, 0.05 V and 0.8 V conditions. The 2 V condition contained retained austenite, lath martensite, and δ-ferrite bands. The retained austenite fraction and prior austenite grain size initially increased at lean vanadium concentrations but significantly dropped at the highest vanadium concentration. The element distribution in the constituent phases was investigated in detail. Mn, C and Si partitioning to austenite was observed in the 0 V, 0.05 V and 0.8 V conditions. V and C segregation to the grain boundaries and significant grain refinement were evident in the 2 V condition. The findings also revealed that increasing the vanadium content led to an increase in the hardness of the steel. This assessment was validated by tensile testing, which showed an improvement in yield and tensile strength of the steel with increasing vanadium content, and were supported by reconstruction of the parent austenite grains employing martensitic structures. Finally, the influence of different strengthening mechanisms on the yield strength of as-cast, microalloyed medium-manganese steels was also discussed in terms of simulated stacking fault energy, as well as the quantitative contributions from solid solution, grain boundary, and precipitation strengthening mechanisms.

Austenite stabilization and precipitation of carbides during quenching and partitioning (Q&P) of low-alloyed Si–Mn steels with different carbon content

Three silicon-manganese steels with carbon content of 0.25, 0.33, and 0.44 wt% were subjected to quenching and partitioning (Q&P) treatment to obtain the microstructures consisting of primary martensite (PM) and significant fraction of retained austenite (RA). The microstructural changes during Q&P were systematically characterized by various techniques while tensile and impact tests were performed to investigate the mechanical response of the steel samples. The carbon partitioning between martensite and austenite at 350 °C was accompanied by the formation of carbide-free bainite and resulted in the stabilization of the irregular layers and thin films of RA. Moreover, the precipitation of carbides in PM before partitioning and their subsequent growth affected the carbon partitioning from PM to RA. The volume fraction and width of RA islands in the final microstructure increased with increasing the carbon content. The transformation of significant fraction of RA in 0.44C steel before the strain localization improved uniform elongation, resulting in superior combination of strength and ductility (σ0.2 = 1225 MPa, UTS = 1580 MPa, δ = 16.8 %). On the other hand, the transformation of more stable RA in lower carbon steels occurred mainly in the neck portions of tensile specimens and its contribution to uniform elongation was negligibly small. The prevalence of the dimple pattern on the fracture surfaces of the specimens after tensile and impact tests indicated ductile fracture mode. The effect of carbon content on the precipitation and growth of carbides in PM and its influence on the impact toughness are discussed.

Synergistic Effect of Alloying on the Strength and Ductility of High Carbon Pearlitic Steel

In this work, the effects of the micro-alloying of Mn, Ni, and Si on the microstructure and mechanical properties of high-carbon pearlite steels were investigated. The results indicated that the addition of solely Ni to high-carbon pearlitic steel can enhance the strength through the refinement of interlamellar spacing, but work-hardening in the ferrite of the pearlite colony may be delayed, leading to a reduction in area. The multiple additions of Ni and the increase in Mn and Si contents in high-carbon pearlitic steel were beneficial to obtaining a balance between ultimate tensile strength and reduction in area. Three-dimensional atom probe tomography results showed Si partitioning into ferrite and Mn and Ni elements partitioning into cementite. The addition of Si inhibited the formation of a continuous network of grain-boundary cementite, leading to high strength and high ductility through optimization of the microstructure.

Differentiation of Chemical Components in Basaltic Melts During Eruptions: An Example from Tolbachik–Hawaiian Fissure Zones and Etna Vent

The study on differentiation of chemical components in quenched volcanics from the Etna, Tolbachik and Hawaiian fissure zones was carried out under simulated temperature/pressure (T/P) conditions reflecting real-time conditions in the early stages of magmatic eruptions. The simulation was performed under high-pressure chamber apparatus, and the rocks were then subjected to high T/P conditions resulting in basaltic melts. Various temperature and pressure conditions were adjusted from the apparatus to allow for different rates of magmatic cooling and crystallization. The scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS-microanalysis) was then used to study the quenched glasses with the aim of identifying major element partitioning based on micro-heterogeneity of melts structures. The microscopic study of the experimental melts and their comparisons with natural melts under the electron microscopes indicate the existence of two distinct liquids which fractionated during cooling on the basis of their chemical composition (compositional melts): Fe, Mg liquids concentrated in the poorly polymerized and mobile parts of the melt and K, Na and Al liquids were concentrated in more highly polymerized parts of the melts. Partitioning of Ca and Si appears to be changeable and more dependent on bulk melt composition. Fractionation of non-crystalline melts was evident under post-explosion sharp quenching and high-pressure conditions.

Silicon and iron isotopes in components of enstatite chondrites: Implications for metal–silicate–sulfide fractionation in the solar nebula

AbstractSilicon and iron isotope compositions of different physically separated components of enstatite chondrites (EC) were determined in this study to understand the role of nebular and planetary scale events in fractionating Si and Fe isotopes of the terrestrial planet‐forming region. We found that the metal–sulfide nodules of EC are strongly enriched in light Si isotopes (δ30Si ≥ −5.61 ± 0.12‰, 2SD), whereas the δ30Si values of angular metal grains, magnetic, slightly magnetic, and non‐magnetic fractions become progressively heavier, correlating with their Mg# (Mg/(Mg+Fe)). White mineral phases, composed primarily of SiO2 polymorphs, display the heaviest δ30Si of up to +0.23 ± 0.10‰. The data indicate a key role of metal–silicate partitioning on the Si isotope composition of EC. The overall lighter δ30Si of bulk EC compared to other planetary materials can be explained by the enrichment of light Si isotopes in EC metals along with the loss of isotopically heavier forsterite‐rich silicates from the EC‐forming region. In contrast to the large Si isotope heterogeneity, the average Fe isotope composition (δ56Fe) of EC components was found to vary from −0.30 ± 0.08‰ to +0.20 ± 0.04‰. A positive correlation between δ56Fe and Ni/S in the components suggests that the metals are enriched in heavy Fe isotopes whereas sulfides are the principal hosts of light Fe isotopes in the non‐magnetic fractions of EC. Our combined Si and Fe isotope data in different EC components reflect an inverse correlation between δ30Si and δ56Fe, which illustrates that partitioning of Si and Fe among metal, silicate, and sulfidic phases has significantly fractionated Si and Fe isotopes under reduced conditions. Such isotope partitioning must have occurred before the diverse components were mixed to form the EC parent body. Evaluation of diffusion coefficients of Si and Fe in the metal and non‐metallic phases suggests that the Si isotope compositions of the silicate fractions of EC largely preserve information of their nebular processing. On the other hand, the Fe isotopes might have undergone partial or complete re‐equilibration during parent body metamorphism. The relatively uniform δ56Fe among different types of bulk chondrites and the Earth, despite Fe isotope differences among their components, demonstrates that the chondrite parent bodies were not formed by random mixing of chondritic components from different locations in the disk. Instead, the chondrite components mostly originated in the same nebular reservoir and Si and Fe isotopes were fractionated either due to gas–solid interactions and associated changes in physicochemical environment of the nebular reservoir and/or during parent body processing. The heavier Si isotope composition of the bulk silicate Earth may require accretion of chondritic and/or isotopically heavier EC silicates along with cumulation of refractory forsterite‐rich heavier silicates lost from the EC‐forming region to form the silicate reservoir of the Earth.

Investigation of silicon sublattice substitution within (Al,Si)3Zr intermetallics via DFT simulations

Aluminum alloys commonly contain Si as an impurity or alloying element. The energetic behavior of Si within multiple compounds and solutions is incorporated inside thermochemical packages, such as FactSage. This tool allows determining the Si partitioning within complex multiphasic systems. Recent experimental research suggests that Si can be found within Al3Zr-based intermetallics. Nevertheless, current FactSage databases do not consider the potential substitution of Si within the Al3Zr-D023 solid solution. In this work, Si substitution within the (Al,Si)3Zr-D023 phase was investigated by means of first-principles calculations. Replacement of Al atoms by Si resulted in a negative enthalpy of mixing, indicating that Si substitution is energetically enabled. The density of states (DOS) for both a Si-diluted (Al,Si)3Zr and a non-Si-doped (Al3Zr) simulation cells were analyzed. It is shown that (even in dilution), Si significantly impacts the electronic structure of the Al3Zr-D023 structure. Specifically, the presence of Si localizes electrons in the p orbital of Al, and increases the DOS of the dxy, dxz , and dyz sub-orbitals of Zr at low energies. Thus, yielding a coupled effect that stabilizes the D023 intermetallic. These findings are a benchmark for the future integration of a Si-based end-member within the Al3Zr-D023 solid solution of FactSage databases.

Microstructure-strength correlations in Al-Si-Cu alloys micro-alloyed with Zr

The paper presents the microstructure-strength correlation of copper mould cast thin section of Al-(6–8)Si-Cu (at%). The efficacy of small Zr addition (0.15at%) and three-stage heat treatment on these alloys for achieving superior high-temperature mechanical properties were evaluated. The addition of Zr refines the alloy microstructure, exhibits a feather-like eutectic morphology in the interdendritic spaces and Zr supersaturation in the dendrites. Direct ageing at 450 ℃ yields coherent, spherical, L12 order Al3Zr precipitates of size 9–11 nm in the α-Al matrix. A characteristic composite microstructure of fine θʹ plates (∼58–67 nm in length and ∼4 nm in thickness) on these Al3Zr precipitates could be developed on ageing at 190 ℃ following a brief solution treatment at 500 ℃. The plates are finer in size when compared to that formed in alloys without Zr for similar heat treatment (Al-6Si-Cu:∼234 nm in length and ∼9.3 nm in thickness). Composition analysis has established Zr and Si partitioning in θ′ plates that impart long-term thermal stability and coarsening resistance at 250 °C. The observed complexity of the microstructure with a finer length scale rationalizes the high yield strength of the Zr modified alloys (306–320 MPa at room temperature), which is 1.7 times higher than the corresponding Al-6Si-Cu alloy. At 250 °C, the observed tensile yield strength is ∼140 MPa. A detailed analysis with available models using quantitative microstructural parameters enable rationalization of our observations.

Vapor-liquid distribution and Krichevskii parameters of hydroxides Si(IV), B, Ge(IV), As(III) and Sb(III) in water

The vapor–liquid partitioning of Si(OH)4, B(OH)3, Ge(OH)4, As(OH)3 and Sb(OH)3 in water at temperatures between 567.7 and 633.2 K was studied by sampling the coexisting vapor and liquid phases. For Ge(OH)4 and Sb(OH)3 the measurements in pure water have been made for the first time. Distribution constants for all hydroxides of metalloids, KD, are smaller than unity, i.e., these compounds strongly partition into the liquid phase. Correspondingly, the values of the Krichevskii parameter, AKr, the property that governs the thermodynamic properties of a solute close to the critical point of a solvent, for all these species are negative and equal (in MPa) to −178.6 ± 3.6 for Si(OH)4, −172.4 ± 5.5 for Ge(OH)4, −77.8 ± 1.3 for B(OH)3, −112.6 ± 4.6 for As(OH)3, and −160 ± 12 for Sb(OH)3, correspondingly. For indicated species the recommended values of KD are tabulated at T ≥ 523.15 K.

Mg isotope variations in microphases of unequilibrated enstatite chondrites

AbstractMagnesium, a major mineral‐forming element of the inner solar system, is partitioned between the silicate and the unique sulfidic phases (niningerite, MgS) of enstatite chondrites (ECs) owing to the formation of EC under exceptionally reducing conditions. In this study, we have carried out mineralogical characterization of the distinct Mg‐ and Si‐bearing phases of unequilibrated ECs (EH3). To evaluate the Mg isotope variations in such reduced planetary bodies, we have analyzed the Mg isotope composition of several enstatitic silicate phases, matrices (composed of mixed proportions of silicate and sulfidic phases), and bulk meteorite fractions micro milled from three EH3 chondrites. We found that the stable Mg isotope composition (expressed as δ25Mg) of the microphase separates of EH3 chondrites ranged from −0.216 ± 0.014‰ to −0.094 ± 0.014‰. Despite the dispersion in Mg isotope values, the average δ25Mg of the silicate fractions of the studied EH3 chondrites was similar to its matrix and bulk meteorite fractions. Mass‐dependent Mg isotope fractionation was evinced among the phase separates of EH3 chondrites with the slope of the fractionation line on a δ25Mg versus δ26Mg plot being closer to kinetic fractionation trend. Experimental and theoretical considerations hint that Mg isotope exchange between the silicate and sulfide phases might have generated the observed Mg isotope variations among the microphase separates of EH3 chondrites. Based on our Mg isotope data, in combination with the Si isotope composition obtained in the same aliquot of silicate–matrix fractions of EH3 chondrites and its subsolar Al/Si ratio, we suggest that the high abundance of Si in EC (due to the partitioning of Si among diverse silicates, silica, and metallic phases) and the loss of Mg and refractory components from EC‐forming regions could explain the lower Mg/Si ratio of EC compared to that of ordinary and carbonaceous chondrites.

Silicon accumulation, partitioning and remobilization in spring maize (Zea mays L.) under silicon supply with straw return in Northeast China

Appropriate nutrient management practices are the determinant factors for maintaining good plant growth and development. The combination of inorganic fertilizers and straw may affect soil available micronutrients. The goals of this study were to determine the effects of Si fertilizers under straw return conditions on Si accumulation, partitioning, and remobilization in spring maize (Zea mays L.). A two-year field trial was conducted to investigate Si content accumulation and remobilization in spring maize under straw return conditions in Jilin Province. We evaluated Si accumulation and remobilization using four treatments: JS3 (straw return + 45 kg/hm2 silicon), WS3 (no straw return + 45 kg/hm2 silicon), JS0 (straw return + no silicon) and WS0 (no straw return + no silicon).The experimental results showed that the highest Si accumulation stage in maize occurred between the VT and R2 stages. The JS3 treatment accumulated 20.8% and 32.1% more Si, on average, than did the WS3 and WS0 treatments, respectively, at this stage. Different organs showed the same accumulation trend as the whole maize plant, but the Si remobilization amounts in distinct organs were the highest in the WS0 treatment. The total Si contribution to the grain in the WS0 treatment was 42.2% and 104.6% higher, on average, than those in the WS3 and JS3 treatments, respectively.This outcome showed that silicon fertilizer application could significantly increase silicon accumulation in maize plants and organs. Silicon fertilizer combined with straw returning not only further increased silicon accumulation but also reduced Si remobilization from the vegetative organs.

Partitioning of tramp elements Cu and Si in a Ni-based superalloy and their effect on creep properties

An alloy's processing history, including melting, remelting or the choice of stock material, affects its purity and eventually involves tramp element pickup or retention. In this investigation, variants of a novel Ni-based superalloy were manufactured with different levels of purity. The so-called low purity alloys contained 0.138 wt. % Cu and 0.019 wt. % Si while the Cu and Si levels were below x-ray fluorescence (XRF) detection limits of 0.003 and 0.010 wt. %, respectively, in the high purity ingots. Atom-probe tomography (APT) was carried out and revealed Si partitioning at the following interfaces: grain boundaries, MC carbide/γ, M3B2 boride/γ and M3B2 boride/γ′. Copper was found to primarily segregate to the γ′ precipitates. An average of 2.4 × decrease in creep life and 4.3 × decrease in creep ductility was measured in the low purity alloys, which was attributed to the embrittlement caused by Si segregation to grain boundaries. Furthermore, the positive effect of B on the creep properties was mitigated by the presence of Si. Thermodynamic predictions for the matrix and γ′ precipitate compositions represented the trends observed experimentally although the extent of preferential partitioning lacks accuracy. Monte Carlo simulations were performed to describe the partitioning of Cu and Si atoms to either γ or γ′ phases.

Transformation behavior of precipitates during artificial aging at 170 °C in Al–Mg–Si–Cu alloys with and without Zn addition

The transformation behavior of precipitates in Al–Mg–Si–Cu alloys with and without Zn addition during artificial aging at 170 °C was investigated in this study. For Al–Mg–Si–Cu alloys with and without Zn addition, two types of precipitates, needle-like β″ and lath-like L, are formed with the aging time increasing from 8 to 34 h. The needle-like β″ precipitate exhibits a Mg-to-Si atomic ratio of 1.31 which is in agreement with the theoretical ratio of 1.25 for β″ (Mg5Al2Si4). In addition, the β″ precipitate is supposed to contain Al and Cu. With further partitioning of Mg, Si and Cu and release of Al, the needle-like β″ precipitate can transform to lath-like L phase. The L phase has significantly higher concentrations of Mg, Si and Cu and lower concentration of Al, with a higher Mg-to-Si atomic ratio (1.41) deviated from theoretical ratio of β″. However, the major of Zn has a random distribution in Al matrix and exhibits no significant partitioning into precipitates. Zn remained in matrix can enhance the transformation of β″ precipitates to L precipitates.

Microstructural evolution and nanoindentation of NiCrMoAl alloy coating deposited by arc spraying

Arc spraying is a flexible thermal spray coating that can be used in on-site applications. In this study, a NiCrMoAl alloy was coated onto a mild steel substrate by arc spraying. The cored wire feedstock and the deposited coating were extensively characterized by a combination of X-ray diffraction, scanning electron microscopy, focused ion beam microscopy and transmission electron microscopy. Vickers microhardness and nanoindentation were used to investigate the mechanical properties of individual phases in the coating. The results showed that the NiCrMoAl alloy cored wire feedstock primarily consisted of material in elemental form including Ni, Cr, Mo, Al, Si, and Ti, whilst the arc sprayed coating contained a solute-lean γ-Ni phase, a (Mo, Si)-rich γ-Ni phase, elemental Mo splat as well as Cr2O3, Al2O3, and SiO2 at intersplat regions, together with ≤100 nm spherical Al2O3 particles within the splats. Partitioning of Mo and Si into the γ-Ni phase was observed following the rapid solidification of the splat on deposition. The Vickers hardness analysis showed that the average overall hardness of the coating was about 3.65 ± 0.56 GPa. However, nanoindentation indicated that the highest hardness was in the γ-Ni splat regions, especially those containing a high concentration of solute. The microstructural evolution, as well as the structure and chemistry of the phases that affect mechanical properties in the coating are discussed in detail.

Effects of Heating Rate on Formation of Globular and Acicular Austenite during Reversion from Martensite

The effects of heating rate on the formation of acicular and globular austenite during reversion from martensite in Fe–2Mn–1.5Si–0.3C alloy have been investigated. It was found that a low heating rate enhanced the formation of acicular austenite, while a high heating rate favored the formation of globular austenite. The growth of acicular γ was accompanied by the partitioning of Mn and Si, while the growth of globular γ was partitionless. DICTRA simulation revealed that there was a transition in growth mode from partitioning to partitionless for the globular austenite with an increase in temperature at high heating rate. High heating rates promoted a reversion that occurred at high temperatures, which made the partitionless growth of globular austenite occur more easily. On the other hand, the severer Mn enrichment into austenite at low heating rate caused Mn depletion in the martensite matrix, which decelerated the reversion kinetics in the later stage and suppressed the formation of globular austenite.

Martensite to austenite reversion in a high-Mn steel: Partitioning-dependent two-stage kinetics revealed by atom probe tomography, in-situ magnetic measurements and simulation

Austenite (γ) reversion in a cold-rolled 17.6 wt.% Mn steel was tracked by means of dilatometry and in-situ magnetic measurements during slow continuous annealing. A splitting of the γ-reversion into two stages was observed to be a result of strong elemental partitioning between γ and α′-martensite during the low temperature stage between 390 and 575 °C. Atom probe tomography (APT) results enable the characterization of the Mn-enriched reversed-γ and the Mn-depleted remaining α′-martensite. Because of its lower Mn content, the reversion of the remaining α′-martensite into austenite takes place at a higher temperature range between 600 and 685 °C. APT results agree with partitioning predictions made by thermo-kinetic simulations of the continuous annealing process. The critical composition for γ-nucleation was predicted by thermodynamic calculations (Thermo-Calc) and a good agreement was found with the APT data. Additional thermo-kinetic simulations were conducted to evaluate partitioning-governed γ-growth during isothermal annealing at 500 °C and 600 °C. Si partitioning to γ was predicted by DICTRA and confirmed by APT. Si accumulates near the moving interface during γ-growth and homogenizes over time. We used the chemical composition of the remaining α′-martensite from APT data to calculate its Curie temperature (TCurie) and found good agreement with magnetic measurements. These results indicate that elemental partitioning strongly influences not only γ-reversion but also the TCurie of this steel. The results are important to better understand the thermodynamics and kinetics of austenite reversion for a wide range of Mn containing steels and its effect on magnetic properties.

Characterization of Precipitation Evolution in a Zn-Added Al-Mg-Si-Cu Alloy during Artificial Aging at 170 °C

A Zn-added Al-Mg-Si-Cu alloy during aging at 170 °C up to 34 h exhibits an interesting age-hardening effect. Small clusters, enriched in Mg and Si, are present in the sample after 0.25 h aging. The β′′ phase is dominant with the peak hardness of 135 HV after aging of 8 h. A decrease in hardness of the alloy occurs with the aging time increasing to 34 h, due to the coarsening of β′′ phase. It is also found that the Cu-containing L phase co-exists with the β′′ phase at this aging condition. The quantitative solute concentrations of the matrix show that the formation of clusters is consistent with the slight lower contents of Mg, Si and Cu compared with the alloy chemical composition, and the present of β′′ and L phase is associated with the further partitioning of Mg, Si and Cu from the Al matrix into the precipitates. No Zn-rich clusters and precipitates are observed and the Zn concentration in matrix has no significant change during aging for up to 34 h. This result means that the major of Zn remains in the matrix as aging continues.

Effects of Si on the formation of intermetallic phases in alloying reaction between iron substrate and liquid Zn containing 0.2 wt% Al

The Fe–Zn and Fe–Al-based alloying phases are formed on galvanized/galvannealed steels which are extensively used as automobile bodies. This paper investigated the effects of Si on the formation of intermetallic phases in the alloying reaction between an iron substrate and liquid Zn containing 0.2 wt% Al and partitioning of Si between the phases. The addition of Si to the iron substrate was found to scarcely influence the formation and morphology of the Fe2Al5 intermetallic phase layer but to reduce the amount of the δ1-FeZn7–10 intermetallic phase layer at the substrate/liquid interface and to disperse the phase as grains in the Zn–0.2 wt% Al coating matrix. STEM–EDS analysis demonstrates that Si partitions less into the Fe2Al5 and the δ1 phases than into the iron substrate. Enrichment of Si around an Si-depleted Fe–Zn intermetallic phase product was also observed in the beginning of the alloying reaction. The results obtained allow us to explain the effect of Si on the intermetallic phase formation in terms of a difficulty in nucleating the δ1 phase at the substrate/liquid interface.

Alloying-element interactions with austenite/martensite interface during quenching and partitioning of a model Fe-C-Mn-Si alloy

The alloying elements partitioning from martensite to austenite during quenching and partitioning was analysed by coupling in situ High Energy X-Ray Diffraction experiments and 3D atom probe tomography. A rapid and significant carbon partitioning from martensite to austenite without any partitioning of both Mn and Si was highlighted while the interface was immobile. After a relatively short time at 400 °C, a clear Mn partitioning occurs at the vicinity of the α′/γ interface. The analysis conducted indicates that manganese equilibrates its chemical potential during partitioning and raises the issue of the Constrained Carbon Equilibrium model applicability throughout the partitioning process.

Multiscale Characterization of Microstructure in Near-Surface Regions of a 16MnCr5 Gear Wheel After Cyclic Loading

The dependence of the microstructure on the degree of deformation in near-surface regions of a 16MnCr5 gear wheel after 2.1 × 106 loading cycles has been investigated by x-ray diffraction analysis, transmission electron microscopy, and atom probe tomography. Retained austenite and large martensite plates, along with elongated lamella-like cementite, were present in a less deformed region. Comparatively, the heavily deformed region consisted of a nanocrystalline structure with carbon segregation up to 2 at.% at grain boundaries. Spheroid-shaped cementite, formed at the grain boundaries and triple junctions of the nanosized grains, was enriched with Cr and Mn but depleted with Si. Such partitioning of Cr, Mn, and Si was not observed in the elongated cementite formed in the less deformed zone. This implies that rolling contact loading induced severe plastic deformation as well as a pronounced annealing effect in the active contact region of the toothed gear during cyclic loading.