Solubility Limit Of Cr Research Articles

High-throughput pseudo-binary diffusion couple approach for alloy design in cobalt-based superalloys

The paper describes a high-throughput method for alloy design in in Co-based superalloy. The approach is an extension of the diffusion couple method used for the determination of diffusion coefficients. We present the use of such a method in low-density cobalt-based superalloys Co-30Ni-10Al-5Mo-2Ta-2Ti-xCr (x = 0–14 at. %) exploring the effect of Cr content on the microstructural evolution, mechanical, and oxidation properties. The composition profile is developed at relatively high temperature with Co-30Ni-10Al-5Mo-2Ta-2Ti and Co-30Ni-10Al-5Mo-2Ta-2Ti-14Cr as end members in which only the solid solution γ phase grows in the interdiffusion zone. This is subsequently subjected to heat treatment for the evolution of g and γ՛ phases. The composition-dependent microstructure and respective mechanical properties were probed using FE-SEM and nano-indentation respectively. The following composition-dependent properties were successfully probed from the high-throughput diffusion couple: 1) The morphological transition of γ՛ precipitates, 2) The solubility limit of Cr in the alloy for TCP formation, 3) Hardness and average elastic modulus, and 4) The nature and topology of oxidized layers as a function of chromium concentration. Therefore, this method facilitates the optimization of multiple properties in a single experiment, identifying the optimal composition range typically between 5 and 8 at. % of Cr in the present alloy.

Kinetics of Transformation, Border of Metastable Miscibility Gap in Fe–Cr Alloy and Limit of Cr Solubility in Iron at 858 K

The study was aimed at determination of the position of the Fe-rich border of the metastable miscibility gap (MMG) and of the solubility limit of Cr in iron at 858 K. Towards this end, a Fe73.7Cr26.3 alloy was isothermally annealed at 858 K in vacuum up to 8144 hours and Mössbauer spectra were recorded at room temperature after every step of the annealing. Three spectral parameters viz. the average hyperfine field, 〈B〉, the average isomer shift, 〈IS〉, and the probability of the atomic configuration with no Cr atoms in the two-shell vicinity of the probe Fe atoms, P(0,0), gave evidence that the transformation process took place in two stages. All three parameters could have been well described in terms of the Johnson–Mehl–Avrami–Kolmogorov equation, yielding kinetics parameters. The first stage, associated with the phase decomposition, proceeded much faster than the second stage, associated with the alpha-to-sigma phase transformation. The most reliable estimation of the position of the MMG and that of the value of the Cr solubility limit was obtained from the annealing time dependence of 〈B〉, namely 24.5 at. pct Cr for the former and 20.3 at. pct Cr for the latter. A comparison of these figures with the recent phase diagrams pertinent to Fe–Cr system was done.

Insights into grain boundary segregation and solubility limit of Cr in (TiZrNbTaCr)C

• Cr grain boundary segregation is observed in (TiZrNbTaCr 0.125 )C and (TiZrNbTaCr 0.25 )C. • The segregation level can be controlled by adjusting initial Cr content. • Solid solubility dependence of Cr in (TiZrNbTaCr)C on temperature and initial Cr content can be used to optimize Cr addition amount for tailoring microstructure. Dense (TiZrNbTaCr)C with Cr segregation along grain boundaries (GBs) has been first proposed and fabricated by pressureless sintering at 1800-2000°C, utilizing the self-synthesized carbide powders obtained by carbothermal reduction. Cr segregation along GBs is successfully realized as expected via optimizing the initial Cr content. When Cr content is more than 11.12 at.%, Cr addition is excessive and results in Cr-rich second phase formation at triple junctions. To analyze the Cr solubility dependence on temperature and initial Cr content, the Cr content in (TiZrNbTaCr)C grains is investigated by EDS. The solubility limit of Cr in (TiZrNbTaCr)C is about 3.8 at.% at 1900°C. Finally, Vickers hardness of all the samples is measured to assess the mechanical property of (TiZrNbTaCr)C ceramics. The basic understanding of the Cr solubility limit and GB segregation feature in (TiZrNbTaCr)C have been preliminarily clarified, which may pave a potential way to design and tailor microstructure and GB feature of (TiZrNbTaCr)C for the purpose of enhancing its properties in the future.

The role of Cr addition on the processing and mechanical properties of high entropy carbides

Group VI transition metals do not form room temperature stable carbides with a rock salt structure, however, they can be incorporated into a rock salt high entropy carbide lattice. Novel 5-metal high entropy carbides (Cr, Zr, Nb, Hf, Ta)C (HEC5-Cr) were produced using spark plasma sintering and compared with 4-metal carbide (Zr0.25Nb0.25Hf0.25Ta0.25)C (HEC4) and 8-metal carbide containing Cr (HEC8-Cr). The HEC5-Cr ceramics had higher density and smaller grain size (~14 µm) compared with HEC4 (~28 µm). The solubility limit of Cr on the metal site increased from ~2.5 at% for HEC5-Cr to ~6.0 at% for HEC8-Cr, implying that the high entropy effect increased the solubility of Cr. A significant Cr enrichment was observed at the grain boundaries of HEC5-Cr, and it showed a ~14% increase in nanohardness and a similar indentation modulus compared with HEC4. The nanohardness of HEC5-Cr was up to 41.2 GPa due to increased solid solution strengthening.

Thermodynamic assessment of the C[sbnd]Cr[sbnd]Ti system—Supported by DFT calculations

The thermodynamic description of the CCrTi ternary system has been reassessed. The main reason was to adjust the solubility limit of Cr in MC (M = Cr, Ti), but also to take the solubility of Ti in M3C2 and M7C3 into account. Another reason was that the thermodynamic descriptions of all the three constituent binary systems (CCr, CTi and CrTi) had been revised after the previously published description of the CCrTi system. Important metastable end-members and interaction parameters were calculated using Density Functional Theory (DFT). For fcc-CrC and Ti3C2, DFT was used together with a recently published method to calculate the molar Gibbs energy as a function of temperature (Gm(T)). For fcc-CrC also the magnetic contribution and the magnetic transition temperature, i.e. the Curie temperature (TC), were included. DFT was also used to calculate Gibbs energy of formation at 0 K for Ti7C3 and to calculate the molar excess Gibbs energy contribution, and TC, as a function of Ti composition in MC. DFT calculated parameters were compared with experiments or previous assessments. Selected experimental information from literature was then used to optimize parameters that are difficult to calculate with DFT, e.g. interaction parameters for the liquid phase and temperature dependence for interaction parameters in the solid phases. The resulting thermodynamic description, which is based on critically reviewed binary descriptions, reproduces the experimental solidification sequence, found in literature, equally well as the previous description of the CCrTi system. Furthermore, in contrast to the previous description, the new description also reproduces the most recent experimentally determined solubility of Cr in MC and takes the solubility of Ti in M3C2 and M7C3 into account. Finally the new description uses DFT calculated metastable end-members and interaction parameters, which gives more reliable predictions, especially at low temperatures.

Chromium in lead metasilicate glass: Solubility, valence, and local environment via multiple spectroscopy

In this article the doping of chromium in a lead metasilicate glass is explored using Raman, UV–Vis, and Cr K -edge XANES spectroscopy. Our results indicate that the Cr ions are predominantly present as CrO 4 2− complexes, with a minor amounts of Cr(III). The solubility of Cr is limited to ∼1 mol % Cr 2 O 3 . This boundary was inferred from the intensity changes to the CrO 4 2− stretching vibrations and confirmed by the inability to produce a homogeneous glass containing 2 mol % Cr 2 O 3 . The establishment of the solubility limit of Cr in lead glasses is important to design more effective glass compositions depending on the desired application. Finally, this low solubility indicates that Cr 2 O 3 could be used as a potential nucleating agent for lead-silica based glass-ceramics.

Improvement of the Thermal Stability of Zircon by Formation of the Solid Solution of Cr in Zircon

ABSTRACT In this paper, the effects of Cr2O3 additive on the thermal stability and zircon decomposition were investigated. The substitution of Cr at zircon lattice and the formation of solid solution were also discussed. Cr2O3 was added at up to 4 wt.% to zircon. The sintering of samples was carried out at the temperatures of 1450–1650°C for 3 h. The phase composition, physical properties, and microstructural changes for the sintered samples were characterized. Results of Rietveld refinement analysis showed that 1 wt.% of chromia retarded the decomposition of zircon (nearly 40%). Further addition of this additive slightly improved the thermal stability of zircon. Also, up to 2 wt.% of chromia additive decreased the porosity of zircon and suppressed the grain growth. However, 4 wt.% of chromia increased the porosity contents. XRD peaks of zircon shifted to higher angles by the addition of 2 wt.% of Cr2O3 and zircon lattice parameters were decreased, attributed to the formation of a solid solution. Energy dispersive spectroscopy analysis detected the presence of Cr at zircon grains. However, 4 wt.% (4.8 at.%) of Cr2O3 resulted in the formation of a secondary phase concluded that this amount of Cr2O3 is beyond the solubility limit of Cr in zircon.

Microstructure and properties of reactive plasma sprayed nano-TixCr1-xN ceramic coating

TixCr1-xN ceramic coating was prepared by reactive plasma spraying metal composite powders of Ti and Cr. The phase composition, microstructure, and hardness of the TixCr1-xN coating were investigated. The existing forms of Cr atoms in the coating were analyzed. Lattice structure and the elemental composition of the prepared TixCr1-xN coating were analyzed using TEM and EDS. The results revealed that TixCr1-xN coating fabricated on the basis of TiN had an FCC crystal structure with twin grains, the Cr atoms completely entered the TiN lattice when the Cr content was lower than 15 wt.%, and the solubility limit of Cr in TiN of 15 wt.%–20 wt.%. The microstructure of TixCr1-xN was the nanocrystal with a size range of 50–150 nm. The Cr atoms significantly enhanced the electron work function of the coating, improving its mechanical properties.

On the miscibility gap at 800 K in the Fe-Cr alloy system

Issues pertinent to the miscibility gap at 800 K in a Fe73.7Cr26.3 alloy viz. the kinetics of the phase decomposition and borders of the latter were investigated by means of the Mössbauer-effect spectroscopy. The kinetics was revealed to well follow the Johnson-Mehl-Avrami-Kolgomarov equation testifying to a nucleation and growth mechanism underlying the decomposition. A solubility limit of Cr in the Fe matrix was determined to be 17.3(6) at% and that of Fe in the Cr matrix was found as equal to 18.5(9) at%. The results obtained have been compared with various theoretical predictions.

Surface nanocrystallization of Cu-Cr alloy by a high power density continuous laser beam

A nanostructured surface layer of ∼300 μm thickness was fabricated on Cu-30Cr (wt%) hypereutectic alloy by a continuous laser beam with high power density (1.08 × 107 W/cm2). The average grain size of Cr-rich particles was refined to ∼40 nm, and the solid solubility limit of Cr in Cu was extended to 1.96 at. %. Experimental results show that the dispersion of nano-sized Cr-rich spheroids in Cu-rich matrix was attributed to the Brownian motion of Cr-rich spheroids, and the high cooling rate (5.75 × 106 K/s) during liquid phase separation which inhibits the collisions between Cr-rich spheroids.

On exceeding the solubility limit of Cr+3 dopants in SnO2 nanoparticles based dilute magnetic semiconductors

The paper investigates the magnetic behavior of chromium doped SnO2 Dilute Magnetic Semiconductor (DMS) nanoparticles, through structural, spectroscopic, and magnetic studies. A non-equilibrium solution combustion method is adopted to synthesize 0–5 at. % Cr doped SnO2 nanoparticles. The detailed spectroscopic studies on the system using micro-Raman spectroscopy, x-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy along with the structural analysis confirm the presence of Cr in 3+ oxidation state, which substitutes at Sn4+ site in SnO6 octahedra of the rutile structure. This doping is found to enhance the defects in the system, i.e., oxygen vacancies. All the synthesized SnO2 nanoparticles (with or without dopants) are found to exhibit Room Temperature Ferromagnetism (RTFM). This occurrence of RTFM is attributed to the magnetic exchange interaction through F-centers of oxygen vacancies as well as dopant magnetic impurities and explained through the Bound Magnetic Polaron (BMP) model of DMS systems. Nonetheless, as the doping of Cr is further increased beyond 2%, the solubility limit is achieved. This antiferromagnetic exchange interaction from interstitial Cr dopants dominates over the BMP mechanism and, hence, leads to the decrease in the net magnetic moment drastically.

Thermodynamic assessments of the Cr-Si and Al-Cr-Si systems

Abstract Thermodynamic assessments for the Cr-Si and Al-Cr-Si systems were conducted on the basis of the critically evaluated thermodynamic and phase diagram data available in the literature. The Modified Quasi-chemical Model (MQM) was utilized to model the Gibbs energy of the liquid phase and the Compound Energy Formalism (CEF) was used to model the solid phases. Comprehensive comparison between the model-predicted and the experimentally measured phase diagram and thermodynamic property data indicates that the optimized thermodynamic descriptions for the Cr-Si and Al-Cr-Si systems are reliable. Accurate thermodynamic descriptions obtained in the present work in the form of a set of Gibbs energies of all the solid and liquid phases can be used to calculate the phase equilibria and thermodynamic properties in the Al-Cr-Si system at any composition and temperature. As the application of the present thermodynamic study, the solubility limit of Cr in the Al-Si alloy was calculated.

Ferromagnetism in Cr-doped topological insulator TlSbTe2

We have synthesized a new ferromagnetic topological insulator by doping Cr to the ternary topological-insulator material TlSbTe2. Single crystals of Tl1−xCrxSbTe2 were grown by a melting method and it was found that Cr can be incorporated into the TlSbTe2 matrix only within the solubility limit of about 1%. The Curie temperature θC was found to increase with the Cr content but remained relatively low, with the maximum value of about 4 K. The easy axis was identified to be the c-axis and the saturation moment was 2.8 μB (Bohr magneton) at 1.8 K. The in-plane resistivity of all the samples studied showed metallic behavior with p-type carriers. Shubnikov-de Hass oscillations were observed in samples with the Cr-doping level of up to 0.76%. We also tried to induce ferromagnetism in TlBiTe2 by doping Cr, but no ferromagnetism was observed in Cr-doped TlBiTe2 crystals within the solubility limit of Cr which turned out to be also about 1%.

Solid-state synthesis and thermoelectric properties of Cr-doped MnSi1.73

Cr-doped HMSs (higher manganese silicides), MnSi1.73 : Crx (x = 0, 0.005, 0.01, 0.02, 0.03), were prepared by using a solid-state reaction and hot pressing. X-ray diffraction analysis and Rietveld refinement confirmed the synthesis of MnSi1.73. The Cr atoms were confirmed to be soluble in the HMS structure because the lattice constant increased with increasing Cr content (x), and the solid solubility limit of Cr was estimated as x = 0.01. All specimens showed p-type conduction and exhibited degenerate semiconductor characteristics at all temperatures examined (323–823 K). The Seebeck coefficient was decreased and the electrical conductivity was increased by Cr doping. The dimensionless thermoelectric figure of merit ZT was obtained as 0.36 at 823 K for MnSi1.73 : Cr0.005 and MnSi1.73 : Cr0.01 because the power factor was increased and the thermal conductivity was decreased by Cr doping.

Atomistic simulations of the decomposition kinetics in Fe–Cr alloys: Influence of magnetism

Magnetism plays a crucial role in the thermodynamic and kinetic properties of ferritic alloys. In fact, magnetism increases the solubility limit of Cr in Fe, inducing an asymmetrical phase diagram. Moreover, the phase transition from ferromagnetic to paramagnetic (F/P) iron alloys modifies to a large extent the system response to different environmental conditions by modification of the alloy diffusion properties. Indeed, experimental tracer diffusion coefficients deviate from an Arrhenius law during the F/P magnetic transition, leading to a large increase in the paramagnetic regime compared to the extrapolated value from the ferromagnetic domain. Furthermore, as the Curie temperature decreases with the Cr concentration, this evolution of the diffusion properties affects the decomposition kinetics in different ways depending on the alloy composition. An atomic diffusion model, with pair interactions that depend on the local composition and on temperature, has been developed to take into account this magnetic transition effect. The interaction model has been implemented in an atomistic kinetic Monte Carlo algorithm to study the diffusion coefficients and precipitation kinetics of the Fe–Cr alloys. This model has been successfully compared to decomposition kinetic experiments for a wide range of concentrations and temperatures.

Tuning of energy gap, microstructure, optical and structural properties of Cr doped Zn0.96Cu0.04O nanoparticles

Zn0.96−xCu0.04CrxO nanoparticles with different Cr concentrations from 0 to 4% were successfully synthesized by co-precipitation method. The X-ray diffraction pattern showed the crystalline nature with hexagonal wurtzite structure. The diminution in activation energy and the enhanced strain by Cr-doping from 0 to 3% reduced the average crystal size from 27 to 23.8nm while the formation of secondary phase such as spinel ZnCr2O4 enhanced it to 25.6nm after Cr=3% via increasing the activation energy. The solubility limit of Cr in the present system is fixed as 3%. The energy dispersive X-ray spectra confirmed the presence of Cu and Cr in Zn-O. The optical absorption spectra showed the three distinct bands corresponding to UV region (305–324nm) due to electronic transition between the bands; blue region (382–386nm) mainly due to the Zn/Cr interstitials and bluish green (481–482nm) region due oxygen vacancies and interstitials. The noticed poor transmittance throughout the region and the broader absorption bands in Cr=1% doped Zn0.96Cu0.04O confirmed that it had more defects such as oxygen vacancies, Zn interstitials and other defects. The blue shift of energy gap from 3.68eV (Cr=0%) to 3.71eV (Cr=1%) was due to the creations of more defects. The red shift of Eg from 3.71eV (Cr=1%) to 3.6eV (Cr=3%) was explained by sp–d exchange interactions between the band electrons and the localized d-electrons of the Cr3+ ions. Presence of chemical bonding was confirmed by FTIR spectra.

Enhanced Thermoelectric Performance of a Chimney-Ladder (Mn1-xCrx)Siγ (γ∼1.7) Solid Solution

A partially Cr-substituted solid solution of a higher manganese silicide, (Mn1-xCrx)Siγ, has been prepared by an arc-melting method and a subsequent annealing process. The compound consists of two tetragonal subsystems of [Mn1-xCrx] and [Si] with an irrational c-axis ratio, γ= cMn/cSi. According to Vegard's rule, the solubility limit of Cr is determined at x = 0.20. With increasing Cr content x from 0 to 0.20, equivalent to increasing the hole carrier concentration, the a- and cMn-axis lengths linearly increase, while the cSi-axis length gradually decreases. As expected from a valence electron counting rule, the electrical conductivity of (Mn1-xCrx)Siγ increases with increasing x from 334 S·cm-1 (x = 0) to 727 S·cm-1 (x = 0.20) at room temperature. The Cr-substituted samples undergo a microscale domain separation; the sample with a nominal composition of x = 0.20 consists of Cr-rich (x∼0.3) and Mn-rich (x∼0.1) dendritic domains with a typical size of ∼100 µm. Despite the substantial increase in electrical conductivity, the total thermal conductivity decreases with increasing x owing to a marked reduction in lattice contribution. As a consequence, the dimensionless figure-of-merit ZT increases from 0.28 (x = 0) at 800 K to 0.45 (x = 0.20) at 900 K.

Phase stability in proton and heavy ion irradiated ferritic–martensitic alloys

Phase stability of precipitates in ferritic–martensitic alloys T91, HCM12A, HT-9 and a 9Cr model alloy following proton irradiations up to 10 dpa at 400 °C and 500 °C and heavy ion irradiation to 100 dpa at 500 °C were examined using transmission electron microscopy and atom probe tomography. Both the average size and the Cr/Fe ratio of the grain boundary carbides were altered by irradiation in T91. Ni/Si/Mn-rich, Cu-rich and Cr-rich precipitates formed in alloys T91, HCM12A and HT-9 under certain irradiation conditions. Irradiation at 500 °C produced substantially larger Ni/Si/Mn-rich and Cu-rich precipitates but at much lower number density compared to irradiation at 400 °C. Cr-rich precipitates were observed in HCM12A and HT-9 with higher bulk Cr content than the solubility limit of Cr at the irradiation temperature. Heavy ion irradiation produced precipitates of similar size and composition to those induced by proton irradiation at the same temperature but at a lower number density.

Fabrication and characterisation of Cr and Co doped Bi 1.5Zn 0.92Nb 1.5O 6.92 pyrochlores

Cr and Co doped Bi 1.5Zn 0.92Nb 1.5O 6.92 pyrochlore ceramics were produced by solid state mixing of oxides. Cr and Co were doped into the Nb and Nb–Zn sites considering the compositions of Bi 1.5Zn 0.92Nb 1.5− x Cr x O 6.92− x , (Bi 1.5Zn 0.46)(Zn 0.46−3 x/6 Nb 1.5−3 x/5 Cr x )O 6.92− x/2 for Cr doping and Bi 1.5Zn 0.92Nb 1.5−3 x/5 Co x O 6.92, (Bi 1.5Zn 0.46)(Zn 0.46−3 x/6 Nb 1.5−3 x/5 Co x )O 6.92− x/2 for Co doping. The solubility limit of Cr in BZN was higher than that of Co and the solubility limit increased when doping was made both into Nb and Zn sites. The second phases appeared when x > 0.2 for Cr and x > 0.15 for Co doping into the Nb–Zn sites. Simultaneous Cr doping into the Nb- and Zn-sites of BZN pyrochlore gave higher dielectric constant than doping into the Nb-site of pyrochlore. However, Co doping into the Nb- and Zn-sites and only into the Nb-site of BZN gave identical dielectric results in the range of 202–218. The temperature coefficient of dielectric constant decreased with Cr doping and increased with Co doping.

Study of thermal ageing behaviour of Fe-Cr model alloys by magnetic hysteresis loop technique

Fe-Cr alloys with different Cr content (5–20 wt. %) were prepared by arc melting technique. The alloys were solution annealed at 1050 oC/ 2h and air quenched and then tempered at 750 oC/ 1h followed by air cooling. Thermal ageing was carried at 475 oC for various lengths of time up to 1000 hours (hrs) to produce thermal embrittlement. The hardness and coercivity of Fe−20% Cr alloys were increased and the remanence was decreased, being due to the precipitation of Cr-rich a' phase and their subsequent growth. In Fe−15% Cr and Fe−10% Cr alloys, it was found that the coercivity decreased at the initial ageing period and then increased subsequently due to the competing effect of recovery of dislocations and precipitation of Cr rich phase. The change in magnetic properties in Fe−5% Cr alloy was different than other alloys since it was within the solubility limit of Cr in Fe. A linear relationship was found between the coercivity and hardness in Fe−20% Cr alloy, indicating that Magnetic Hysteresis Loop (MHL) technique would be a good tool for the Non-Destructive Evaluatiion (NDE) of embrittlement in Fe-Cr alloys.