Increasing Cr Content Research Articles

Effect of Cr addition on the microstructure and mechanical properties of MoNbVTa0.5Crx refractory high-entropy alloys

To increase strength and decrease density of traditional refractory high-entropy alloys (RHEAs), the MoNbVTa0.5Crx RHEAs were synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). The effect of Cr content on microstructure and mechanical properties of the MoNbVTa0.5Crx RHEAs was systematically studied. The results showed the addition of Cr could refine the microstructure, decrease density and increase strength of RHEAs. The microstructure of the sintered alloy was composed of BCC phase and a small amount of oxide phase (Ta2VO6), and Ta2OV6 (200) has a semi-coherent relationship with BCC phase (110), with a lattice mismatch degree of 7.34 %. The compressive yield strength of the MoNbVTa0.5Crx RHEAs initially increased and then decreased with increasing Cr content. The MoNbVTa0.5Cr0.75 RHEAs demonstrated the best mechanical properties, and the compressive yield strength and ultimate compressive strength at room temperature were 3180 MPa and 3596 MPa, respectively, which were far higher than traditional WNbMoTaV RHEAs. And the density of MoNbVTa0.5Cr0.75 RHEAs was 21 % lower than that of sintered WNbMoTaV RHEAs. The strengthening mechanism of sintered MoNbVTa0.5Crx RHEAs involved O/C atoms interstitial solid solution strengthening, grain boundary strengthening, and metal atoms solid solution strengthening, while the contribution of oxide precipitation strengthening was negligible.

Effect of Cr on high-temperature oxidation resistance of Cr–Si–Mn alloyed press-hardened steel during press hardening

It is of great interest to overcome the problem of high-temperature oxidation of press-hardened steels (PHS) in press hardening with a cost-effective Cr alloying strategy. Therefore, since Cr is one of the expensive metals, the effect of Cr (Cr ≤ 3 wt%) content on the oxidation resistance of Cr–Si–Mn alloyed steels was investigated. It was found that Cr–Si–Mn alloyed PHS with a Cr content of about 1.5 wt% or less cannot form a continuous Cr2O3 layer during press hardening. However, when the Cr content reaches around 2.5 wt%, the PHS shows excellent oxidation resistance due to the formation of continuous Cr2O3 and amorphous SiO2 layers, as well as an Mn-rich oxide layer. However, further addition of 0.5 wt% could not significantly improve the oxidation resistance of this PHS. Moreover, the increase in Cr content simultaneously enhances the positive role of Si and Mn in high-temperature oxidation resistance. This work provides new insights into the design of the next generation of PHSs with economical and superior performance.

The effect of chromium on the corrosive performance of novel high manganese steel frogs in a simulated industrial atmosphere

Abstract The corrosion behavior of three novel high manganese steel frogs with different Cr contents in a simulated industrial corrosive atmospheric environment is studied through the corrosion weight gain, x-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and electrochemical testing. The results indicate that the content of Cr in the steel affects the phase composition, density, and electrochemical stability of the rust layer. For instance, as the Cr content increases, the content of the amorphous phase in the rust layer continuously increases while that of γ-FeOOH decreases, leading to enhanced density and electrochemical stability of the rust layer. The study reveals that Cr exists in the rust layer in the form of Cr2O3 and Cr(OH)3, providing nucleation cores to nanoscale colloidal rust particles. Consequently, a higher Cr content leads to more nucleation cores, which improves the density of the rust layer and enhances the corrosion resistance of the novel high manganese steel frogs in industrial corrosive atmospheric environments.

Machine learning assisted study of phase and properties in cobalt-free AlCrxCuFeNi2 high-entropy alloys

The application of machine learning (ML) accelerates the discovery of new materials, the prediction and optimization of properties, and the analysis of the correlation between structure and properties. The design, characterization, and mechanical properties of the novel AlCrxCuFeNi2 cobalt-free high-entropy alloys (HEAs) were investigated in this study. Through the experimental validation combined with the predictive K-nearest neighbor model (KNN) and the extreme gradient boosting model (XGBoost), the influence of Cr content on phase evolution and mechanical behavior were analyzed comprehensively. The results indicate that the optimized KNN and XGBoost models can achieve the 10-fold average cross validation (CV) accuracies of 0.761 and 0.836, respectively. Eight components of AlCrxCuFeNi2 HEAs are selected for experimental verification. The experimental results shows that the microstructures of the eight alloys are composed of FCC + BCC phases, which is agreement with the prediction. With the increase of Cr content, the dendrite morphology becomes finer and the lattice constants increase. The addition of Cr results in the hardness values from 332.4 HV to 447.7 HV and the deviation from the predicted ones is between 5.4 HV and 37.3 HV. It is worth noting that wear resistance is consistent with the change in hardness values, the specific wear rate decreases from 3.152 × 10−4 mm3/Nm to 6.357 × 10−5 mm3/Nm, and when x = 2.0, the wear resistance is the best. This research underscores the efficacy of ML in expediting the discovery and optimization of HEAs, offering valuable insights for promoting materials design and engineering applications.

Effects of ultrasonic impact treatment on the corrosion resistance of laser-cladded CrMnFeCoNi high-entropy alloy coatings

Ultrasonic impact treatment (UIT) was performed on the surface of the laser-clad CrMnFeCoNi high-entropy alloy coatings. The fluences of the UIT on the microstructure, microhardness, nanoindentation metrics and corrosion resistance of the coatings were explored. Furthermore, the enhancing mechanisms of the corrosion resistance of these coatings by the UIT were clarified. The results showed that the UIT markedly enhanced the corrosion resistance of the laser-clad CrMnFeCoNi high-entropy alloy coatings, and the enhancing effect continuously improved with the increasing of the UIT time. The most significant enhancement of corrosion resistance occurred under the action of UIT with a current of 1.6 A for 20 min. Compared to the untreated group, corrosion potential rose by 65.68 %, corrosion current density fell by 74.95 %, and equivalent resistance increased by 340.37 %. Corrosion morphology analysis showed that the primary forms of corrosion before the UIT were stress corrosion and pitting, which vanished after the UIT with a significant improvement in pitting. Analysis of corrosion products revealed an increased Cr content and a decreased FeOOH and O content on the coating surface after the UIT, leading to enhanced corrosion resistance. Additionally, microstructural analysis showed that large columnar crystals in the laser-clad CrMnFeCoNi high-entropy alloy coatings transformed into finer columns, drastically reducing the grain size of the surface. Concurrently, surface microhardness and nanoindentation mechanical properties markedly improved after the UIT, with the effects growing stronger over time. After the UIT with the current of 1.6 A for 20 min, the increasement of surface microhardness reached 109.01 %. A comprehensive analysis of the fluences on the corrosion resistance of laser-clad CrMnFeCoNi high-entropy alloy coatings by the UIT indicated that the refinement of grain size, improvement of the stress state of the coating, increasement of Cr element and its compounds, and decreasement of FeOOH content are the main reasons of enhanced corrosion resistance.

Investigating structural and optoelectronic properties of Cr-substituted ZnSe semiconductors

The optoelectronic and structural characteristics of the Zn1−xCrxSe (0 ≤ x ≤ 1) semiconductor are reported by employing density functional theory (DFT) within the mBJ potential. The findings revealed that the lattice constant decreases with increasing Cr concentration, although the bulk modulus exhibits the opposite trend. ZnSe is a direct bandgap material; however, a change from direct to indirect electronic bandgap has been seen with Cr presence. This transition is caused by structural alterations by Cr and defects forming, which results in novel optical features, including electronic transitions. The electronic bandgap decreases from 2.769 to 0.216 eV, allowing phonons to participate and improving optical absorption. A higher concentration of Cr boosts infrared absorption and these Cr-based ZnSe (ZnCrSe) semiconductors also cover a wider spectrum in the visible range from red to blue light. Important optical parameters such as reflectance, optical conductivity, optical bandgap, extinction coefficient, refractive index, magnetization factor, and energy loss function are discussed, providing a theoretical understanding of the diverse applications of ZnCrSe semiconductors in photonic and optoelectronic devices.

Ligament morphology and elastic modulus of porous structure formed by liquid metal dealloying

We report that the morphology of ligaments also governs the mechanical properties of dealloyed porous materials, in addition to the topology- and size-effects that have been extensively studied previously. Porous Fe–Cr with similar relative density but different Cr content were prepared by liquid metal dealloying. The mechanical efficiency of this material, which is quantified by relative elastic modulus, decreases dramatically with increasing Cr content, although the relative density and network connectivity do not vary significantly. This is linked to the more severe spheroidization of Fe–Cr ligaments at higher Cr, driven by the large excess energy of solid-liquid interfaces and interface energy anisotropy of Fe–Cr under dealloying environment. A shape parameter is introduced to quantitatively account for this ligament-morphology effect. Current study suggests that tailoring interfacial energy, which was largely overlooked in previous studies, is essential to improving the mechanical efficiency of porous or nanoporous materials self-organized in dealloying.

The role of thermal treatment and formulation on modifying the structural nature and optimizing certain physical features of coprecipitated superparamagnetic Co–Mn–Cr spinel ferrite

Examining the composition and heat treatment effects of co-precipitated Co0.7Mn0.3CrxFe2-xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1) ferrite nanoparticles provides valuable insights into the structural, morphological, optical, magnetic, and electrical properties of these materials. X-ray diffraction (XRD) and Rietveld refinement analyses confirm the spinel cubic crystalline phase of the samples, indicating the formation of well-defined crystal structures. Transmission electron microscope micrographs manifest the nanoscale nature of the produced specimens and their narrow particle size distribution with a small standard deviation. This uniformity is often desirable in many applications because it confirms the similarity of the properties and behaviors of the nanoparticles. The Fourier transform infrared spectroscopy study suggests that the substitution of Cr3+ ions at octahedral sites influences molecular stability. Annealing causes a slight expansion in bond length and a subsequent decrease in stability. The presence of Cr3+ ions enhances the strength of the specimens, while annealing weakens them. This indicates a fine balance between composition and processing conditions in determining the strength of the materials. The estimated optical indirect bandgap undergoes a redshift by adding Cr3+ ions. Annealing at elevated temperatures reduces the bandgap due to the quantum confinement effect, indicating the tunability of optical properties through compositional and thermal control. Samples with x ≥ 0.6 exhibit nearly zero coercivity, indicating superparamagnetic behavior, which have promising applications. The preference of Cr3+ ions to occupy octahedral B-sites influences the magnetic behavior of the materials. The dielectric polarization and dielectric loss improved by adding Cr3+ ions, while the alternating current conductivity decreased. From impedance spectroscopy, the real and imaginary parts, Z’ and Z”, were increased by increasing Cr content. Furthermore, the annealing process greatly affects the electrical properties of the specimens. Overall, the study emphasizes the intricate relationship between composition, annealing conditions, and the resulting structural, magnetic, and electrical properties of Co–Mn–Cr ferrite nanoparticles, providing significant observations for the development of tailored materials for diverse applications in electronics, magnetics, and medicine.

Enhanced plastic deformation ability of copper matrix composites through synergistic strengthening of nano-Al2O3 and Cr particles

The commercial application of Al2O3/Cu composites (ODS copper) with high Al2O3 content is consistently restricted by their plastic deformability. In order to synergistically improve the plastic deformability of Al2O3/Cu composites, Al2O3/Cu–Cr composites with different Cr contents are prepared by internal oxidation combined with heat treatment by replacing part of the Al2O3 particles with Cr phases heat treatment. The effects of Cr content on the microstructure and plastic deformability of Al2O3/Cu–Cr composites are investigated. It is found that the nano-Al2O3 (8 nm) and Cr (25 nm) particles are uniformly distributed in the copper matrix, and both reach a semi-congruent interface with copper matrix. Meanwhile, the copper matrix undergoes a transition from a [111]Cu hard orientation to a [100]Cu soft orientation, and the increase in Cr content leads to a more pronounced degree of recrystallization in the Al2O3/Cu–Cr composites. The results of geometric phase analysis (GPA) show that the coordinated deformability between Cr and Cu is better than that between Al2O3 and Cu. The elongation of 2.5Al2O3/Cu-0.3Cr composite increased to 24.48 % from 22.47 % of the Cr-free 2.8Al2O3/Cu composite. The results of tensile strength calculations show that the tensile strength of Al2O3/Cu–Cr composites is mainly dominated by matrix strengthening and Orowan strengthening induced by Al2O3 particles, while grain strengthening, dislocation strengthening, and Orowan strengthening induced by Cr particles play a secondary role. The correlation coefficient (R2) is 0.95 after fitting the experimental and theoretical values of tensile strength of Al2O3/Cu–Cr composites.

Tribochemistry dependence of Ni62Nb33Zr5 bulk metallic glass on the Cr content of steel counterparts

Recent literature showed that Bulk Metallic Glasses can demonstrate repeatable tribological response, and that it might be controlled through a careful selection of the sliding counterpart’s composition. The present study focuses on the effect of Cr content of a steel ball sliding over a Ni62Nb33Zr5 BMG. Three different steels were chosen (C90, 100Cr6, and X105CrMo17) because they demonstrate similar constitutive elements, similar mechanical properties, but different Cr contents. Increasing Cr content resulted in an increase of friction coefficient from 0.13 to 0.85 while maintaining extremely low wear. In depth chemical analysis showed that increasing Cr content favors the loss of the ductile Nb2O5 of protective FeNbO4, and NiNb-oxide to the benefit of NiCrO, CrNbO4, NiFe-oxides, and Cr(VI) oxide.

Quantification of SCC mechanisms in austenitic alloys under PWR primary water conditions

Abstract In order to achieve a full mechanistic understanding of stress corrosion cracking (SCC), the key operating mechanisms need to be identified but also quantified. In this study, we summarize and rationalize key findings from the last 15 years of high-resolution characterization of SCC in our group. A comprehensive characterization of a set of austenitic alloys with different Ni content and constant Cr level, tested under simulated pressurized water reactor (PWR) primary water conditions at various temperatures, has revealed evidence for at least two operating mechanisms: one diffusion-related and the other deformation-related. For their relevance to the nuclear industry, two additional alloys with increased Cr content were also studied (A800 and A690). Key precursors for SCC initiation and propagation are identified and their effect on alloy degradation discussed. A list of key materials’ properties that ensure low SCC susceptibility is proposed.

Cr as a promoter for the In2O3-catalyzed hydrogenation of CO2 to methanol

The utility of Cr as a promoter for In2O3 catalysts in the hydrogenation of CO2 to methanol is investigated. Uniform precursors to binary CrOx-In2O3 and ternary NiO-CrOx-In2O3 catalysts are prepared by flame spray pyrolysis. For the CrOx-In2O3 samples, the highest methanol rate is obtained at a Cr content of 2 mol%, exceeding the methanol rate of In2O3 by 55 %. With increasing Cr content, the CO2 conversion rate does not increase, albeit the methanol selectivity decreases. Characterization of the samples supported by density functional theory calculations provides insight into the role of Cr. At low content, Cr is mainly doped into the lattice of In2O3, which leads to more oxygen vacancy (Ov) sites. The In2O3 surface sites close to Cr-oxide clusters present on the surface are also activated towards Ov formation, offsetting the decrease in Ov due to coverage of the In2O3 surface by Cr-oxide with increasing Cr content. Cr2O3 dispersed on the surface of the In2O3 particles suppresses sintering of In2O3 under reducing conditions, which is especially evident at a Cr content above 2 mol% and higher reaction temperatures. Introducing Ni to the CrOx-In2O3 catalysts results in a higher methanol formation rate compared to CrOx-In2O3. The methanol rate increases with the Ni content with the highest activity obtained at Ni and Cr contents of 22 mol% and 8 mol%, respectively. The optimum Ni(22)-Cr(8)-In2O3 catalyst displays twice the methanol rate of a Ni(22)-In2O3 reference. Ni and Cr play different promoting roles in achieving an increased and more stable rate of methanol formation compared to In2O3: Ni promotes the hydrogenation of formate and methoxy surface intermediates to methanol, while Cr results in more Ov sites and suppresses sintering of In2O3.

Realizing low thermal conductivity in Cr-doped nanostructured higher manganese silicide

Higher manganese silicides have evolved as an efficient thermoelectric material because of their exceptional thermoelectric performance at intermediate temperatures. In this work, we report the ultralow-thermal conductivity with improved thermoelectric properties of Mn1-xCrxSi1.8 (x = 0, 0.025, 0.05 and 0.1) prepared by induction melting followed by ball milling and uni-axial induction hot-pressing. Bragg diffraction patterns confirmed that the as-synthesized compound belongs to the Mn15Si26 phase along with the solid solubility of Cr in the HMS lattice. In addition, the backscattered electron micrographs revealed the precipitation of excess Si in the HMS matrix, originating from Si-rich stoichiometry. Furthermore, an elevation in electrical conductivity with increasing Cr content has been observed because of its acceptor dopant behaviour at the Mn site. On the contrary, the Seebeck coefficient decreased upon an increase in Cr content, and bulk MnSi1.8 has shown the highest Seebeck coefficient of 220 μV/K at 773 K. Impressively, nanostructuring along with the generated point defects as a result of Cr dopant facilitates an intensified phonon scattering at the nanostructured grain boundaries that results in a very low κtotal of 0.99 W/mK at 773 K for ball-milled Mn0.9Cr0.1Si1.8, leading to an elevated zT of 0.46 at 773 K.

First-principles and cluster expansion study of the effect of magnetism on short-range order in Fe–Ni–Cr austenitic stainless steels

Short-range order (SRO), the regular and predictable arrangement of atoms over short distances, alters the mechanical properties of technologically relevant structural materials such as medium/high entropy alloys and austenitic stainless steels. In this study, we present a generalized spin cluster expansion (CE) model and show that magnetism is a primary factor influencing the level of SRO present in austenitic Fe–Ni–Cr alloys. The spin CE consists of a chemical cluster expansion combined with an Ising model for Fe–Ni–Cr austenitic alloys. It explicitly accounts for local magnetic exchange interactions, thereby capturing the effects of finite temperature magnetism on SRO. Model parameters are obtained by fitting to a first-principles data set comprising both chemically and magnetically diverse face-centered cubic configurations. The magnitude of the magnetic exchange interactions are found to be comparable to the chemical interactions. Compared to a conventional implicit magnetism CE built from only magnetic ground state configurations, the spin CE shows improved performance on several experimental benchmarks over a broad spectrum of compositions, particularly at higher temperatures due to the explicit treatment of magnetic disorder. We find that SRO is strongly influenced by alloy Cr content, since Cr atoms prefer to align antiferromagnetically with nearest neighbors but become magnetically frustrated with increasing Cr concentration. Using the spin CE, we predict that increasing the Cr concentration in typical austenitic stainless steels promotes the formation of SRO and increases order–disorder transition temperatures. This study underscores the significance of considering magnetic interactions explicitly when exploring the thermodynamic properties of complex transition metal alloys. It also highlights guidelines for customizing SRO through adjustments of alloy composition.

The Influence of Cr Addition on the Microstructure and Mechanical Properties of Fe-25Mn-10Al-1.2C Lightweight Steel

The influence of Cr addition on the microstructure and tensile properties of Fe-25Mn-10Al-1.2C lightweight steel was investigated. The characteristics of the microstructures and deformation behavior were carried out through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), and room temperature tensile testing. Fe-20Mn-12Al-1.5C steel without Cr exhibited a fully austenitic single phase. With the addition of Cr, the volume fraction of ferrite continuously increased. When the content of Cr exceeded 5 wt%, the precipitation of Cr7C3 carbides was observed. In the steel with 5 wt% Cr, the quantity of κ carbides remarkably decreased, indicating that the addition of 5 wt% Cr significantly inhibited the nucleation of κ-carbides. As the Cr content increases from 0 wt% to 5 wt%, the austenite grain sizes were 8.8 μm and 2.5 μm, respectively, demonstrating that Cr alloying is an effective method of grain refinement. Tensile strength increased slightly while elongation decreased with increasing Cr content. As the Cr content exceeded 5 wt%, the yield strength increased but the elongation drastically decreased. The steel with 2.5 wt% Cr achieved a synergistic improvement in strength and ductility, exhibiting the best tensile performance.

Cr content dependent lattice distortion and solid solution strengthening in additively manufactured CoFeNiCrx complex concentrated alloys – a first principles approach

In the previous study, the authors reported that multicomponent CoFeNiCrx (x = 0, 12, 18, 24 at%) complex concentrated alloys fabricated through laser directed energy deposition experienced a substantial reduction in the saturation magnetization (Ms) and the Curie transition temperature (Tc) with the increase in Cr content. The present investigation additionally explores the effect of Cr concentration on the structural and strengthening behavior in laser directed energy deposition processed CoFeNiCrx alloy system. The novel approach adopted in the present work included the integration of experimental and computational efforts involving laser direct energy deposition (L-DED) based synthesis/fabrication of a series of new CoFeNiCrx alloys through in-situ compositional tuning which is often difficult using conventional techniques and prediction of mechanical properties of these compositionally tuned alloys using a computational methodology based on the density functional theory (DFT). X-ray diffraction and nanoindentation studies revealed that while there was a slight reduction in lattice parameters, the elastic modulus increased by approximately 30 % and the yield strength increased by 25 % with increasing Cr content. The density functional theory framework was employed to interpret the influence of Cr atoms on local lattice distortions and observed yield strength. The calculated local lattice distortion, in terms of first nearest neighbors, significantly increased with Cr concentration, which is attributed to the enlargement of Cr atomic radius in the alloyed multielement environment in comparison to its radius in the elemental form. This distortion at the local level caused solid solution strengthening. The theoretically predicted solid solution strengthening values using the Varvenne model are consistent with experimental results.

Effect of Cr content on microstructure, mechanical, and corrosion properties of CoCrxFeMnNi high-entropy alloys fabricated by selective laser melting

The method of using mixed powder for SLM in-situ alloying to prepare high entropy alloys has been verified to be feasible. In this investigation, the effect of Cr addition on microstructure uniformity, mechanical properties, and corrosion resistance of CoCrxFeMnNi High-entropy alloy (with x = 0.4, 0.7, 1.0, 1.3 at. %) prepared by the SLM in-situ alloying technique has been thoroughly investigated. X-ray diffraction and scanning electron microscopy suggest that all CoCrxFeMnNi HEAs samples are composed of a FCC matrix and little residual Cr particles, and all elements of the FCC matrix are evenly distributed, accompanied by a very small amount of Mn evaporation. Electrochemical corrosion tests have shown that with an increase in Cr content, the corrosion resistance of the alloy is significantly improved. The CoCr1.3FeMnNi HEAs possess the best corrosion resistance against the attack of the Cl ion, with a corrosion rate 0.671 × 10−3 mm / year. Furthermore, the Cr element can significantly improve the microhardness, tensile strength, and plasticity of CoCrxFeMnNi HEAs. The CoCr1.3FeMnNi HEAs possess the best mechanical properties, with microhardness 217.8 HV0.5, tensile strength 691 MPa and elongation rate 18.9%, respectively.

The Influence of CO2 Physical Properties on Casing and Its Prediction Method

In order to reveal the physical properties of CO2 under actual formation conditions, this paper establishes a mathematical model of the temperature field and pressure field in the wellbore under CO2 injection conditions, optimizes the state equation of CO2 physical-property parameters, calculates the change trend of CO2 density, viscosity, and compression factor along the wellbore, and obtains the influence law of CO2 corrosion on the casing and interface. The viscosity showed a downward trend along the well depth; the compression factor showed an upward trend. The surfaces of the three casings were smooth and flat without obvious defects, the cement structure was dense, and there was no obvious pore structure. After corrosion, with the increase of Cr content, the change of interfacial corrosion decreases. The morphology of the Q125 and 3Cr interface is loose after corrosion, while there is no obvious change in the 13Cr interface. With the prolongation of corrosion time, low wellbore internal pressure easily causes casing yield, and high wellbore internal pressure easily causes cement-sheath compression failure. The circumferential stress of the casing increases with the corrosion time extension, and the radial stress of the casing and cement sheath decreases first and then increases with the corrosion time. The compressive strength of the cement sheath does not exceed the compressive strength.

Effects of Cr addition on structure, magnetic properties and corrosion resistance of a Fe85.5B13Cu1.5 nanocrystalline alloy

The melt-spun structure of a Fe85.5B13Cu1.5 alloy was regulated by the addition of corrosion-resistant Cr with a moderate enhancement in amorphous-forming ability, which further refines the nanostructure and improves the soft magnetic properties and corrosion resistance of corresponding nanocrystalline alloys. The results show that high-number-density α-Fe grains in size of below 10 nm are formed in the amorphous matrix of melt-spun Fe85.5-xB13Cu1.5Crx (x = 0–6) alloy ribbons, and the grain size and number density gradually decrease with the increase in Cr content. After annealing, the α-Fe average grain size (Dα-Fe) and coercivity (Hc) of corresponding nanocrystalline alloys reduce significantly with increasing x from 0 to 3, and the reduction becomes less pronounced within x = 3–6, while the saturation magnetic flux densities (Bs) steadily decreases as x increases from 0 to 6. A Fe82.5B13Cu1.5Cr3 nanocrystalline alloy with the Dα-Fe of 14.9 nm possesses excellent comprehensive soft magnetic properties with the Hc and Bs of 13.8 A/m and 1.74 T, respectively. The fine nanostructure and good magnetic softness results from the optimum combination of pre-existing α-Fe competitive growth and Cr-inhibited atom diffusion. The nanocrystalline alloys show improved corrosion resistance in NaCl solution compared to their respective melt-spun precursors, and the addition of Cr further enhances the corrosion resistance. The alloyed Cr also reduces the annealing embrittlement of the nanocrystalline alloys.

Atomic insights into the corrosion behavior of Fe-Cr alloys in supercritical CO2 environment

In this work, the corrosion process of Fe-Cr alloys in flowing CO2 was simulated using molecular dynamics within an extended ReaxFF force field. The effects of Cr content, temperature variations, impurity gases and vacancy defects were discussed. The corrosion process was dominated by oxidation and carburization reactions, with the oxidation rate higher than carburization rate, resulting in the formation of a carbide layer within the central region between two oxide layers. The increase in Cr content tended to decelerate corrosion, while raising temperature aggravated the corrosion of Fe-Cr alloy. The presence of O2 and SO2 impurities was found to thicken the corrosion layer, in contrast to the effects of CO and H2O impurities. A notable finding highlighted the positive influence of 2% vacancy defects in enhancing the corrosion resistance of the Fe-Cr alloy. The Al2O3 coating achieved a good corrosion protection by inhibiting the dissociation of CO2.