Mo Partitioning Research Articles

Novel Fe-Mo intermetallic composite synthesized via diffusional-displacive mixed-mode transformation

Transition metal-based intermetallic materials are candidates for high-temperature structural applications. However, they are limited by their low fracture toughness at ambient temperature. Given Fe is a low-cost metal with a low environmental impact, it is necessary to design tough Fe-based intermetallic alloys. We report a novel ferrite-Fe2Mo intermetallic synthesized through arc melting and quenching of Fe0.78Mo0.22 alloy. Diffusional-displacive mixed-mode transformation of the parent ferrite phase resulted in the formation of nanocomposite microstructure. Two distinct microstructure morphologies of the product μ phase were observed: (i) allotriomorphic phase formation at the parent ferrite grain boundaries and (ii) formation of basket-weave Widmanstätten structures at the parent grain interior. Electron probe microanalysis (EPMA) revealed Mo partitioning across ∼800 nm wide Widmanstätten laths, establishing that it is a diffusional-displacive mixed-mode transformation. We performed atom probe tomography (APT) investigations to ascertain the nanoscale Mo solute partitioning. Based on the chemistry of the retained parent ferrite, the Mo partitioning temperature was estimated to be ∼865 °C. Mo partitioned Widmanstätten lath formation is clarified using a shear-assisted diffusional transformation model. APT studies further revealed that the composition of the product μ phase corresponds to stoichiometric Fe2Mo. It is an anomaly since stoichiometric Fe2Mo typically corresponds to λ C14 Laves phase. We explain the mechanism of μ phase formation with Fe2Mo stoichiometry. The nanocomposite exhibits a high hardness (HV2) of 7.54 GPa and excellent toughness (evidenced by resistance to indentation cracking).

Mechanisms underlying enhanced strength-ductility combinations in TRIP/TWIP Ti-12Mo alloy engineered via isothermal omega precipitation

β Ti-alloys can achieve a high strain-hardening rate and tensile ductility by taking advantage of transformation induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects. While nano-precipitation of isothermal ω (ωiso) can have a substantial strengthening effect in these alloys, it usually has a detrimental effect on ductility leading to embrittlement. To overcome the above problem, this work proposes as a novel strategy based on coupling of ωiso formation and mechanical twinning/martensitic transformation to enhance the strength while preserving good ductility in case of the TRIP/TWIP Ti-12Mo alloy. An unprecedented combination of tensile properties, yield stress at 865MPa (80% higher than classic Ti-12Mo) with uniform elongation of 0.35, are recorded after 200°C aging for 60s. Higher yielding stress (990MPa) is achieved when increasing the aging duration to 150s where mechanical twinning is still active. In-situ investigations under traction/heating, and atom probe tomography are performed to clarify the ωiso formation process and the interactions between ω phase and the operating deformation mechanisms, i.e. mechanical {332}<113> twinning, β → α″ martensitic transformation and dislocation glide. The early stages of formation of ωiso precipitates, mediated via Mo partitioning at low aging temperature, and its consequent impact on the deformation mechanisms operative in the β matrix has been characterized. The transformation partition mapping method, based on statistical electron backscatter diffraction characterization developed in our previous work, is employed to individually assess the evolution of the critical resolved shear stresses of each operating deformation mechanism as a function of the ωiso nucleation.

Effect of Cr addition on the γ′ strengthened CoNiCrAlMo compositionally complex alloy

The present study illustrates the effect of varying Cr content in Co51-x Ni30Al10Mo5Nb2Ti2Cr x (x = 2, 5, and 8 at.-%) compositionally complex alloys (CCAs). STEM-EDS analysis suggests a change in Mo partitioning from equal in both the phases (γ and γ′) in CCA-2Cr to the γ phase in CCA-5Cr and CCA-8Cr alloys. This peculiar compositional partitioning with Cr content beyond 2% brings a change in γ′ precipitate morphology from cuboidal to spheroidal in CCAs. The shape change-induced reduction in strain energy rendered a decrease in γ′ coarsening rate by ∼ 1/2, i.e. from 11.5 to 4.6 nm3/s in the CCA-2Cr and CCA-8Cr alloys, respectively. All three alloys show an anomalous increase in 0.2% proof stress (PS) with temperature and achieve peak values at 770°C.

Extremely light molybdenum isotope signature of sediments in the Mariana Trench

Molybdenum (Mo) isotope signature (δ98/95Mo) of marine sediments is a powerful proxy for constraining marine redox conditions and early diagenetic processes. Oxic pelagic sediments have been increasingly acknowledged as an important sink for Mo in its global cycling, however, the mechanisms controlling Mo enrichment and isotope fractionation during early diagenesis in this environment are not fully understood. In this study, four sedimentary cores were sampled by full-ocean-depth lander system in the Mariana Trench, aiming to explore the processes controlling Mo partitioning in the sediments of the deepest ocean in the world. Sediments from four locations exhibit a wide range of authigenic Mo contents (Moauth, relative to continental crust), varying from 1.98 to 43 μg/g. A positive relation between Mo and Mn contents was identified for these sediments, which suggests that Mo are mainly hosted in Fe-Mn (oxyhydr)oxides. In addition, negative correlations between δ98/95Mo values and Mo/Mn ratios are found at each site. The δ98/95Mo values of the sediments vary from −1.71 ± 0.05 to −0.15 ± 0.04‰, revealing similar trends towards lighter values with burial depth from three sites. However, throughout the sediment core TY41 obtained from Mariana Trench, the δ98/95Mo values of sediment remain nearly constant around −0.55‰. Supported by the abundant Fe (oxyhydr)oxides throughout this site, it is likely the sediment is affected by enhanced fluid exchange across sediment-seawater interface, and the δ98/95Mo values of dissolved Mo in pore water resemble seawater signature. Therefore, the Mo isotopic offset between dissolved Mo and sediment is similar to the expected fractionation during the adsorption to Mn oxides (~ + 3.0‰) and hematite (~ + 2.2‰), which suggests that most of the dissolved Mo is scavenged by Mn oxides and/or hematite. The extremely light δ98/95 Mo values of sediments in deeper parts of the cores coincide with enhanced Mo accumulation. This indicates an even lighter isotope signature of dissolved Mo in pore water during the re-precipitation of Fe-Mn (oxyhydr)oxides upon an isotopic equilibrium for Mo adsorption to metal oxides. Both the patterns of both dissolved oxygen and nitrate suggest that the study sites are located within the nitrate reduction zone and Mn reduction occur at deeper depths below the studied interval. Therefore, the source of the isotopically light dissolved Mo in pore water was explained by the preferential release of isotopically lighter Mo from Fe-Mn (oxyhydr)oxides during the enhanced dissolution at deeper depth. In contrast, at the shallower depths of these cores (expect for core TY41), the higher δ98/95 Mo values towards seawater-sediment interface suggest the dissolved Mo is more impacted by the seawater exchange. This study provides a deeper insight into the diagenetic Mo cycling in trench environments, with Fe-Mn (oxyhydr)oxides rich sediments as an important sink for Mo.

Controlling the nucleation of multiple precipitates in precipitation-strengthened steel through Mo partitioning

In this study, atom probe tomography and first-principles calculations were used to investigate the influence of Mo addition on multiple precipitates, including isolated NiAl-based precipitates as well as NiAl-based and Cu-rich co-precipitates, in high-strength ferritic steel. The co-NiAl-based precipitates were experimentally confirmed to be nucleated from the abundance of Cu atoms. The addition of Mo accelerated the nucleation process of Cu-rich precipitates and structural transformation of co-precipitates, led to a considerable increase in the nucleation rate of NiAl-based precipitates, and slightly promoted isolated NiAl-based precipitates. The results were discussed from the perspective of lattice misfits and mixing enthalpy.

Synergistic alloying effects on nanoscale precipitation and mechanical properties of ultrahigh-strength steels strengthened by Ni3Ti, Mo-enriched, and Cr-rich co-precipitates

The synergistic effects of Mo, Ti, and Cr on nanoscale precipitation and mechanical properties of maraging stainless steels were systematically studied using high-resolution scanning transmission electron microscopy, atom probe tomography (APT), thermodynamic and first-principles calculations, and mechanical tests. Our results reveal a notable precipitation pathway involving the co-precipitation of Ni3Ti, Mo-enriched, and Cr-rich precipitates; their formations are not separated, but rather highly interacted. The APT results indicate that Mo partitions to the Ni3Ti precipitate core in the early stage of precipitation, which doubles the number density of Ni3Ti precipitates. Our calculations indicate that the Mo partitioning not only increases the chemical driving force, but also reduces the strain energy for nucleation, thereby accelerating Ni3Ti precipitation. As the precipitation proceeds, Mo atoms are rejected from the Ni3Ti precipitate core to the interface between the Ni3Ti precipitates and matrix, which leads to the heterogeneous nucleation of Mo-enriched precipitates on the outer surface of the Ni3Ti precipitates. This results in a substantial size refinement of Mo-enriched precipitates. In addition, the formation of Ni3Ti precipitates consumes Ni from the matrix, which substantially inhibits the spinodal decomposition and refines the size of Cr-rich precipitates. The cooperative strengthening of Ni3Ti, Mo-enriched, and Cr-rich co-precipitates leads to the development of new steels with a strength of 1.8 GPa; the contributions of these precipitates to the strengthening were quantitatively evaluated in terms of precipitate shearing and Orowan dislocation looping mechanisms.

Preliminary exploration of molybdenum isotope fractionation during coprecipitation of molybdate with abiotic and microbial calcite

Molybdenum isotopes in marine carbonates have been proposed to track the redox conditions of oceans through time. Large variations of Mo concentration and isotopic composition were observed in primary biogenic carbonates and shallow-water carbonate sediments from modern oceans. However, it remains unknown whether the abiotic calcium carbonate precipitation process fractionates Mo isotopes and affects Mo isotopic composition in marine carbonates. To better understand carbonate Mo isotope proxy, we conducted abiotic calcite coprecipitation experiment to determine Mo partition coefficient in calcite and Mo isotope fractionation during molybdate incorporation into calcite. We also investigated Mo isotopic compositions in microbial calcite induced by photosynthetic activity of cyanobacteria and diatoms in the surface water of Fayetteville Green Lake (FGL), New York, USA.Our calcite coprecipitation experiment, for the first time, determined the Mo partition coefficient Kd=MoCacalcite/MoO42−CO32−solution = 1.49 × 10−5 in calcite at pH ~8.3. We observed a relatively small Mo isotope fractionation of 0.15 ± 0.06‰ with light Mo isotopes preferentially incorporated into calcite. The Mo isotope fractionation observed in our experiment most likely results from equilibrium isotope fractionation among different Mo species and preferential incorporation of the isotopically light Mo(VI) species (MoO42−) into calcite. Microbial calcite formed in FGL fractionated Mo isotopes in the same direction as abiotic calcite coprecipitation experiment but with significantly larger isotope fractionations (0.82–2.45‰) and significantly higher Mo concentrations (0.04–0.28 ppm vs. the inferred 0.002 ppm Mo from our abiotic calcite coprecipitation experiment). Molybdenum isotopic composition decreased with Mn/Fe ratios from +1.56 to −0.07‰, suggesting that Fe and Mn oxides dominantly control Mo isotope fractionation in these microbial calcite samples. Additionally, isotopically light Mo associated with organic matter (e.g., live or dead microorganisms like cyanobacteria) might also contribute to the light Mo isotopic composition in microbial calcite.The relatively small Mo isotope fractionation (0.15 ± 0.06‰) and Mo partition coefficient (1.49 × 10−5) in our abiotic calcite coprecipitation experiment indicate that calcite precipitation process has negligible effects on Mo isotopic composition in primary biogenic calcite precipitates. In contrast, Mo associated with organic matter, detrital particles, and Fe and Mn oxides, and carbonate diagenesis strongly affect Mo isotopic compositions in calcium carbonate precipitates in nature. Caution should be taken when applying Mo isotopes in ancient carbonates rocks to track seawater redox conditions.

Refractory alloying additions on the thermal stability and mechanical properties of high-entropy alloys

In this study, alloying effects of Mo and W refractory elements on the microstructural evolution of high-entropy alloys (HEAs) were systematically studied. High-density L12-type precipitates formed during the isothermal treatment at 800 °C. Alloying additions of Mo and W displayed different partitioning behaviors between the matrix and precipitate phases, with Mo partitioning to the matrix phase (KMo = 0.45) and W partitioning to the precipitates (Kw = 1.52) in the 1.5 at.% Mo and 1.5 at.% W alloyed HEA, respectively. A reversal in the partition of W back to the matrix (Kw = 0.95) was identified for the combined Mo and W alloying. It was demonstrated that W not only destabilized the Heusler phase at grain boundaries but also increased the volume fraction of the precipitates. In addition, lattice misfit was significantly reduced after alloying with these refractory additions. The coarsening kinetics was also quantitatively described according to the modified-Lifshitz-Slyozov-Wagner model. The coarsening rate constant for the HEAs was significantly reduced as comparison with that for Ni- and Co-based superalloys, implying an improved thermal stability of HEAs. Moreover, a reduced interfacial energy together with inherently small diffusivity of the refractory elements attributed to the improved thermal stability. Our findings show the remarkable thermal stability for HEAs and the potential for HEAs to be developed as new high-temperature structural materials.

The effect of alloying elements on cementite coarsening during martensite tempering

The effects of anti-segregating elements (Si and Al) and segregating elements (Cr and Mo) on cementite precipitation during tempering of Fe-C-Mn martensites have been quantitatively investigated in terms of both cementite chemistry and particle size evolution. Si and Al additions both accelerate the Mn partitioning kinetics and decelerate the particle growth kinetics. They are trapped in cementite during the initial stage of precipitation but are rejected from cementite after prolonged tempering. By comparison, small Cr and Mo additions do not strongly affect the Mn partitioning kinetics or particle growth kinetics, even though both Cr and Mo partition to cementite. The experimental measurements of cementite coarsening with time-dependent chemistry evolution are compared with a cementite coarsening model recently proposed by Wu et al. that has been generalised to multicomponent steels. The model can describe well the partitioning kinetics of segregating elements Mn/Cr/Mo and cementite particle growth kinetics simultaneously in a range of higher order systems. At 600 °C, the model works very well under local equilibrium (LE) and volume diffusion assumptions. The retardation by Si/Al on cementite coarsening and resulting accelerated Mn partitioning can be understood by the kinetic barrier from the migration of Si/Al spikes in front of growing cementite. At lower temperatures of 500 °C and 400 °C, the model can also reasonably well describe the Mn/Cr/Mo partitioning kinetics (and particle growth kinetics). However, to better describe the particle growth kinetics, the interfacial condition has to be treated with a deviation from LE due to Si/Al solute trapping. The Cr and Mo mobilities in cementite are enhanced by the same factor as for Mn mobility in cementite previously tuned by Wu et al., and the simulated Mn/Cr/Mo partitioning kinetics indicate these substitutional diffusion data are reasonably well estimated, which is further demonstrated in the simulation of Al rejection kinetics.

Elemental partitioning, mechanical and oxidation behaviour of two high-[formula omitted] W-free [formula omitted] polycrystalline Co/Ni superalloys

Cr-containing W-free Co alloys that form L12γ′ strengthening precipitates in an fcc γ matrix are presented to examine the effect of Ta and Nb additions to increase the strength, solvus temperature and gamma prime fraction. The alloys are found to have relatively low density, good oxidation resistance (<0.5 μm scale at 800 °C for 100 h) with coherent Al2O3 and Cr2O3 scales, and reasonable yield strengths, ∼800 MPa. The phase partitioning, measured by atom probe tomography, was found to be similar to W-containing Co/Ni superalloys, with Mo partitioning to the matrix providing solid solution strengthening.

Effects of Mo and Mn microadditions on strengthening and over-aging resistance of nanoprecipitation-strengthened Al-Zr-Sc-Er-Si alloys

Combined microadditions of 0.09 at.% Mo and 0.4 at.% Mn to a dilute Al-0.10Zr-0.01Sc-0.007Er-0.10Si (at.%) alloy lead to increases in strength upon peak-aging, and improved over-aging resistance at 400, 425 and 450 °C for at least 6 months. These improvements are related to four cumulative effects. Firstly, Mn and Mo provide, in the as-cast state, a solid-solution-strengthening contribution of ∼90 MPa. The solid-solution contribution from Mo (∼80 MPa) remains essentially unchanged during aging at 400–450 °C, due to its extremely small diffusivity and precipitation. Secondly, Mn and Mo partition to the cores and shells, respectively, of the nano-size coherent, L12 (Al,Si)3(Zr,Sc,Er) nanoprecipitates, which nucleate in <1 h at 400–450 °C. This is associated with an increase in their number density and a reduction in their growth and coarsening kinetics, thus delaying the loss of strength upon over-aging. Third, Mn and Mo provide precipitation strengthening via submicron α-Al(Mn,Mo)Si precipitates (which form between 1 and 11 days at 400 °C), which counterbalances the loss of Mn solid-solution strengthening. Finally, the α-Al(Mn,Mo)Si precipitates scavenge Si from the matrix, which is then not available to accelerate the coarsening of the L12 precipitates, thereby improving the over-aging resistance of the alloy. Iron additions (0.015 at.%), expected to replace some Mn in the α-phase Al(Fe,Mn,Mo)Si, does not affect the aging behavior.

Arbuscular mycorrhizal inoculation increases molybdenum accumulation but decreases molybdenum toxicity in maize plants grown in polluted soil.

Molybdenum (Mo) is an important micronutrient required by both plants and microorganisms, but may become toxic when presents in excess concentration. However, Mo toxicity in soil-plant systems as influenced by arbuscular mycorrhizal (AM) fungi (AMF) still remains unknown. Here, a pot culture experiment was conducted to study the effects of inoculation with Claroideoglomus etunicatum BEG 168 on the growth and Mo content of maize plants growing in soil supplemented with different levels (0, 1000, 2000, and 4000 mg kg−1) of Mo. Results show that the added Mo had no significant effects on AM colonization rate, which ranged from 77% to 92%. Mo addition decreased plant dry weights and leaf pigment contents, as well as nutrient uptake of P, N, Fe, Mg and Cu in shoots and roots, and in most cases, the highest level (4000 mg kg−1) showed the most inhibitory effects. Overall, AM inoculation enhanced plant growth, mineral nutrient uptake, leaf pigment contents and photosynthetic rate under all Mo addition levels. Mo concentrations in plants without Mo addition ranged from 13.1 to 40.1 mg kg−1 in roots, and from 42.8 to 58.4 mg kg−1 in shoots. Addition of Mo increased Mo concentrations in both shoots and roots of all the plants, but showed no significant dose-dependent effects. In non-inoculated plants receiving Mo addition, Mo concentrations were not lower than 400 mg kg−1 in shoots and higher than 1300 mg kg−1 in roots respectively. AM inoculation further enhanced Mo concentrations in shoots and roots, but decreased shoot/root Mo ratio at 2000 and 4000 mg kg−1 Mo addition levels. In AM inoculation treatments, soil pH exhibited a decreasing trend with increasing Mo addition level. In conclusion, excess Mo caused toxicity in maize plants, while AM fungus C. etunicatum BEG 168 was tolerant to the added Mo, and could alleviate the Mo-induced phytotoxicity by improving plants' mineral nutrition, leaf pigment contents and photosynthetic properties, and by mediating Mo partitioning in plants and soil pH. Our present results suggest a specific protection mechanism exists in AM plants against excess Mo, and their promising potential in ecological restoration and phytoremediation of Mo-polluted sites.

Effect of Cr addition on \u03b3\u2013\u03b3\u2032 cobalt-based Co\u2013Mo\u2013Al\u2013Ta class of superalloys: a combined experimental and computational study

The present article deals with effect of Cr addition (10 at.%) on the partitioning behavior and the consequent effect on mechanical properties for tungsten-free γ–γ′ cobalt-based superalloys with base alloy compositions of Co–30Ni–10Al–5Mo–2Ta (2Ta) and Co–30Ni–10Al–5Mo–2Ta–2Ti (2Ta2Ti). Cr addition leads to a change in the morphology of the strengthening cuboidal-shaped γ′ precipitates to a spherical shape. The site preference of Cr atoms in two alloy systems (with and without Ti) has been experimentally investigated using atom probe tomography with the supportive prediction from first principles DFT-based computations. Cr partitions more to the γ matrix relative to γ′. However, Cr also has a strong effect on the Ta and Mo partitioning coefficient across γ/γ′ interfaces. The value of partition coefficient for Mo (KMo) becomes <1 with Cr addition to the alloys. Results from ab initio calculations show that the Cr atoms prefer to replace Mo atoms in the sublattice sites of the L12 unit cell. The solvus temperature of about 1038 and 1078 °C was measured for 10Cr2Ta and 10Cr2Ta2Ti alloy, respectively, and these Cr-containing alloys have very low densities in the range of ~8.4–8.5 gm/cm−3. The 0.2% compressive proof strength of 10Cr2Ta2Ti alloy yields a value of 720 MPa at 870 °C, substantially better than most Co–Al–W-based alloys and many of the nickel-based superalloys (e.g., MAR-M-247).

Valence and metal/silicate partitioning of Mo: Implications for conditions of Earth accretion and core formation

To better understand and predict the partition coefficient of Mo at the conditions of the deep interior of Earth and other terrestrial planets or bodies, we have undertaken new measurements of the valence and partitioning of Mo. X-ray absorption near edge structure (XANES) K-edge spectra for Mo have been measured in a series of Fe-bearing glasses produced at 1 bar and higher PT conditions. High pressure experiments have been carried out up to 19 GPa in order to better understand the effect of pressure on Mo partitioning. And, finally, a series of experiments at very low fO2 conditions and high Si content metallic liquids has been carried out to constrain the effect of Si on the partitioning of Mo between metallic liquids and silicate melt. The valence measurements demonstrate that Mo undergoes a transition from 4+ to 6+ near IW−1, in general agreement with previous 1 bar studies on FeO-free silicate melts. High pressure experiments demonstrate a modest pressure dependence of D(Mo) metal/silicate and, combined with previous results, show a significant decrease with pressure that must be quantified in any predictive expression. Finally, the effect of dissolved Si in Fe-rich metallic liquid is to decrease D(Mo) significantly, as suggested by previous work in metallurgical systems. The effect of pressure, temperature, oxygen fugacity, metallic liquid composition, and silicate melt composition can be quantified by using multiple linear regression of available experimental data for Mo. Our XANES results show that Mo will be 4+ at conditions of core formation, so only experiments carried out at fO2 of IW−1 and lower were used in the regressions. Application of predictive expressions to Earth accretion shows that D(Mo) decreases to values consistent with an equilibrium scenario for early Earth core–mantle. The Mo content of the primitive upper mantle (PUM) can be attained by metal–silicate equilibrium involving S-, C-, and Si-bearing metallic liquid, and peridotite silicate melt along the peridotite liquidus near 45 GPa and 3600 °C, late in the accretion process. This conclusion is insensitive to late giant impacts unless the degree of equilibration is very low (<5%).

Effect of RE on molybdenum partitioning and resultant mechanical and microstructural behavior of a duplex stainless steel during hot working condition

The effect of rare earth (RE) on Mo partitioning and resultant mechanical and microstructural behavior of a duplex stainless steel during hot working condition was investigated. It was found that RE effect was sensitive to temperature. At the high temperature, the development of dynamic recovery (DRV) in α phase was slowed down while the dynamic recrystallization (DRX) process in γ phase was accelerated by RE, whereby both work hardening rate (at low strain) and dynamic softening rate (at high strain) increased and moreover, the discrepancy on the hardness of the both phase reduced. Whereas at the low temperature, the effect of RE was opposite as compared with those in the high temperature. Mo partitioning analysis by EPMA indicated that RE enhanced the partitioning of Mo in α phase while reduced Mo concentration in γ phase at higher temperature whereby the mismatch between two phases could be improved indicated by the elimination of voids and cracks at α/γ interface, but it was contrary to that at the low temperature. Mo partitioning was believed to be an important cause for the RE effect on the differences of mechanical and microstructural behavior. Also this result provided a reasonable evidence for micro-alloying of RE in DSSs.

Effect of Titanium on the Partition Behavior of Alloying Elements in Single Crystal Superalloys Containing Rhenium

Effect of Ti on the microstructure evolution and element partition in  and  phase after heat treatment were investigated in single crystal superalloy with different contents of Ti addition (0, 0.5, 1.0wt.%) by using scanning electron microscope (SEM) and 3-D atom probe (3DAP). The results show that with the increase of titanium addition, the size of r’phase increase after full heat treatment and the amount of TCP phase increase during long term thermal exposure. Ti makes more r matrix forming elements such Re, W, Cr, Co, Mo partition into r matrix and more Ni element distribute to the r’phase. The electronic structure and binding energy of a number of Ni+X alloy systems were calculated using the discrete variational cluster method based on the local density approximation of the density functional theory

Effect of ruthenium on γ′ precipitation behavior and evolution in single crystal superalloys

The effect of Ru on γ′ precipitation behavior and evolution in single crystal superalloys with different Ru contents were investigated by scanning electron microscopy with energy dispersive spectroscopy, 3D atomic probing, differential scanning calorimetry. The results show that the solvus of the γ′ phase decreases gradually with increasing Ru content in the alloys by casting or by the same solution and aging treatments, the alloy with a larger Ru content yields a smaller γ′ phase. The addition of Ru increases the growth rate and coarsening rate of the γ′ phase. Ru mainly distributes in the γ phase, which causes more Re and Mo partition into the γ′ phase, increasing the absolute value of mismatch and the rafting rate of the γ′ phase.

Sulfidity controls molybdenum isotope fractionation into euxinic sediments: Evidence from the modern Black Sea

Molybdenum (Mo) isotope fractionation has recently been introduced as a new proxy in oceanography and biogeochemistry. It is therefore fundamental to understand the processes controlling Mo partitioning into modern marine environments. This study identifies the availability of dissolved sulfide as the dominant control on overall Mo removal from the water column in euxinic systems. Mo isotopic composition of surface sediments from different localities of the Black Sea demonstrates complete fixation of Mo only below 400 m water depth, above a critical concentration of 11 μmol l −1 aqueous hydrogen sulfide in the bottom water. The Mo isotopic composition of these sediments reflects the homogeneous seawater isotopic composition of 2.3‰. In contrast, significant Mo isotope fractionation into less euxinic sediments is evident at shallower depths in the Black Sea, as well as in temporarily euxinic deeps of the Baltic Sea, consistent with the observed lower maximum sulfide concentrations in the respective water columns. Therefore, Mo isotope signatures in the modern Black Sea constrain the processes responsible for global Mo removal from the ocean by euxinic sediments. Furthermore, models of past ocean anoxia reconstruction have to consider that the seawater Mo isotopic composition is not per se archived in euxinic sediments.

Partitioning of molybdenum to 60 kbar along a warped Fe–FeS liquidus

Mo partitioning between crystalline and liquid metal alloy shows a continuous change with pressure from siderophile to chalcophile behavior at 1100 °C in the interval 0–60 kbar. Pressure is shown to be only a minor direct causative factor in this change. Unusual Fe–S liquid solution behavior causes Fe to dissolve instead of precipitate from solution with increasing pressure to 60 kbar at temperatures up to ∼ 1375 °C. This pathology drives changes in D Mo that overshadow any direct pressure effect on D Mo. The ability to separate the pressure and compositional effects on D Mo arises through the warpage in pressure of the Fe–S liquidus.

A microanalysis study of the bainite reaction at the bay in Fe-C-Mo

A microanalysis study of the eutectoid decomposition of austenite to ferrite and M 2C (bainite) at the bay in Fe-0.24C-4Mo is reported. The carbon remaining in the austenite showed little variation with position at any given reaction time, which ruled out carbon diffusion as a rate-limiting process. Fine-probe EDS at bainite-austenite growth fronts revealed Mo enrichment in the interface and up to 15 nm in the austenite. EDS of extracted M 2C carbides always revealed Mo enrichment, but with a non-equilibrium Fe/Mo ratio at early reaction times. It was concluded that alloy element partition between ferrite and alloy carbides at the reaction front is largely responsible for the slow kinetics in this and related alloys. A thermodynamic analysis showed that ferrite-carbide interfacial energy and non-equilibrium carbide compositions reduce the thermodynamic driving force for diffusive processes (Mo partition) by up to 20%, further slowing the kinetics.