Cr Solid Solution Research Articles

Effect of Mechanical Alloying and Sintering on Phase Transformation, Microstructural Evolution, Mechanical Properties and Density of Zr-Cr Alloy

The purpose of present research was production ofZr-based alloy as the nuclear fuel cladding by mechanical alloying (MA) and sintering process. Firstly, Zr and Cr powders were mechanically alloyed to produce the refractory and hard Zr-10 wt% Cr alloy, and then, the powder mixtures were consolidated by press and following sintering at temperature of 800˚C min. The phase evolution, microstructural changes, microhardness, and density of the Zr-10 wt% Cr alloy were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness measurement, and the Archimedes method. The results showed that the MA increased the solid solubility of the immiscible powders of Cr and Zr; therefore, the Cr atoms were completely dissolved in the Zr lattice after 24 h of the milling time and the nanostructured Zr(Cr) solid solution was obtained with the high microhardness value of about 491 Hv. Also, the results of the density measurement indicated that the resulted density was close to 98% of the theoretical density.

Effect of Cr on the generalized stacking fault energy of impure doped Ni (111) surface: a first-principles study

In the present work, a systematic analysis of the microscopic plastic deformation mechanism and mechanical properties of interstitial impurities (H, O, N, S, and P) and Ni doped, or not doped, with Cr, was conducted based on generalized stacking fault energy curves generated via first-principles calculations. Focus has been put on the effects of Cr on plastic deformation for Ni doped interstitial impurities, upon the GPFE curve, with the aim to investigate the effects of Cr on the deformation mode and mechanical properties for doped Ni systems. It is found that a solid solution of Cr caused the tendency of partial dislocation in Ni. The evaluation of the Rice criterion reveals that Cr tends to decrease the ductility in Ni, and it cannot reverse interstitial H promoting the probability of cleavage fracture in Ni, while increases the ductility of O, P and S doped Ni, particular in O doped Ni, due to increasing the value of ductility D remarkably, so possibly changes the tendency of cleavage fracture. Besides, the solid solution of Cr is beneficial in promoting the dissociation of dislocation into fragments more easily in Ni, and enhances dislocation nucleation, while O, N, and S impurities have a slower rate of partial dislocation emission in Ni when interacting with Cr. Furthermore, Cr promotes the probability of twinning in Ni, and probably switches the deformation mechanism of H doped Ni from dislocation mediated slipping to twinning. Our study provides important insights toward the understanding and control of dislocation dynamics in doped Ni.

Crystal structure, microstructure, and magnetic properties of the Fe2CrSi nanostructured Heusler alloy elaborated by the mechanical alloying method

Abstract The Fe2CrSi nanostructured Heusler alloy was prepared by mechanical alloying followed by heat treatment. The structure, microstructure, and magnetic properties of the samples were studied by the following analysis methods: X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectrometry, transmission electron microscopy, and a vibrating sample magnetometer. The a-Fe (Si, Cr) solid solution with a disordered body centered cubic (bcc) crystal structure was obtained after 24 h of milling. An example of the sample milled for 32 h with a disordered crystal structure a-Fe(Si, Cr) was chosen to investigate the transformation with temperature using differential scanning calorimetry. The effect of annealing temperatures on the structural, microstructural, and magnetic properties of the ordered Fe2CrSi Heusler phase for the sample milled for 32 h was investigated.

High Voltage Mg-Ion Battery Cathode via a Solid Solution Cr–Mn Spinel Oxide

Lattice Mg2+ in a tailored solid solution spinel, MgCrMnO4, is electrochemically utilized at high Mn-redox potentials in a nonaqueous electrolyte. Complementary evidence from experimental and theor...

Double Glow Plasma Surface Metallurgy Technology Fabricated Fe-Al-Cr Coatings with Excellent Corrosion Resistance

Double glow plasma surface metallurgy (DGPSM) technology was applied to obtain a Fe-Al-Cr coating on the surface of Q235 carbon steel. The influence of the sample temperature, gas pressure, the distance between the substrate, and the source electrode on the quality of the obtained Fe-Al-Cr coatings was systematically investigated. The results showed that the parameters for DGPSM have a significant effect on the uniformity, particle size, compactness, and thickness of the coating. Under the optimized parameters (sample temperature: 800 °C, gas pressure: 35 Pa, and electrode distance: 15 mm), the obtained Fe-Al-Cr coating contains Fe2AlCr, Fe3Al(Cr), FeAl(Cr), Fe(Cr) solid solution, Cr23C6, and α-Fe(Al), exhibiting excellent corrosion resistance in a 0.5 mol/L H2SO4 solution, which is even better than that of the 304 stainless steel.

The character of the structure formation of model alloys of the Fe-Cr-(Zr, Zr-B) system synthesized by powder metallurgy

Purpose: The purpose of the work is to synthesize and investigate the character of structure formation, phase composition and properties of model alloys Fe75Cr25, Fe70Cr25Zr5, and Fe69Cr25Zr5B1. Design/methodology/approach: Model alloys are created using traditional powder metallurgy approaches. The sintering process was carried out in an electric arc furnace with a tungsten cathode in a purified argon atmosphere under a pressure of 6·104 Pa on a water cooled copper anode. Annealing of sintered alloys was carried out at a temperature of 800°C for 3 h in an electrocorundum tube. The XRD analysis was performed on diffractometers DRON-3.0M and DRON-4.0M. Microstructure study and phase identification were performed on a REMMA-102-02 scanning electron microscope. The microhardness was measured on a PMT-3M microhardness meter. Findings: When alloying a model alloy of the Fe-Cr system with zirconium in an amount of up to 5%, it is possible to obtain a microstructure of a composite type consisting of a mechanical mixture of a basic Fe2(Cr) solid solution, solid solutions based on Laves phases and dispersive precipitates of these phases of Fe2Zr and FeCrZr compositions. In alloys of such systems or in coatings formed based on such systems, an increase in hardness and wear resistance and creep resistance at a temperature about 800°C will be reached. Research limitations/implications: The obtained results were verified during laser doping with powder mixtures of appropriate composition on stainless steels of ferrite and ferrite-martensitic classes. Practical implications: The character of the structure formation of model alloys and the determined phase transformations in the Fe-Cr, Fe-Cr-Zr, and Fe-Cr-B-Zr systems can be used to improve the chemical composition of alloying plasters during the formation of ferrite and ferrite-martensitic stainless steel coatings. Originality/value: The model alloys were synthesized and their phase composition and microstructure were studied; also, their microhardness was measured. The influence of the chemical composition of the studied materials on the character of structure formation and their properties was analysed.

Structural analysis and densification study of the mechanically alloyed Cr50Ni50 powders

Nanocrystalline Cr50Ni50 material was obtained by high-energy ball milling from pure Cr and Ni powders in a planetary ball-mill P7 under argon atmosphere at ambient temperature. Microstructural, structural, morphological, magnetic, and densification properties were studied by X-ray diffraction, scanning electron microscopy, magnetic measurements, and cold compaction followed by sintering. The Rietveld refinement of the X-ray diffraction pattern reveals after 1 h of milling the formation of the disordered fcc-Ni (Cr) solid solution in addition to pure Cr and Ni. After 25 h of milling, the interdiffusion between Cr and Ni atoms leads to the formation of a mixture of disordered fcc-Ni(Cr) and bcc-Cr(Ni) solid solutions. The average thickness of the grain boundaries of bcc-Cr(Ni) and fcc-Ni(Cr) is of about 3.5 and 2.3 nm, respectively. The morphological observations reveal the fragile aspect of the powder particles which is explained by their fragmentation at different stages of the milling process. The existence of small magnetic particles which are typically single domains is evidenced by Mr/Ms (0.1–0.5) values. The porosity fraction of the cold compacted powders is about 25% then decreases to about 12% after sintering at 1250 °C for 2 h. The Vickers microhardness values of the milled powders for 25 h evolute from 1045 to 1280 Hv while those of the sintered powders vary in the range 716 to 995 Hv.

Inversion of the Sign of the Short-Range Order as a Function of the Composition of Fe–Cr Alloys at Warm Severe Plastic Deformation and Electron Irradiation

This paper presents the results of a Mössbauer spectroscopy investigation of the processes in the binary alloys Fe100−cCrc (c, at. % = 6.0, 9.4, 13.2) and of the short-range (SR) atomic ordering accelerated by applying warm severe plastic deformation via high pressure torsion (HPT). After warm HPT treatment, in the vicinity of the concentration c = 9 at. %, there was revealed to be an inversion of the sign of the SR order, the anomaly of the formation of a Fe–Cr solid solution, which was predicted ab initio and is observed at long-term anneals and exposures to irradiation by electrons. The acceleration of the SR ordering at HPT is due to the continuous generation and a large number density of mobile point defects.

Effect of Lithium Nitrate Doping on the Phase Composition of Alumina–Chromium Catalysts

The effect of a lithium nitrate (LiNO3) modifying additive on the genesis of the phase composition of alumina–chromium catalysts has been studied using the differential dissolution (DD) and X-ray diffraction (XRD) methods. It has been shown that LiNO3 reacts with a pure support (Al2O3) to form lithium aluminate, double oxide Al4Li2O7 with a spinel structure, and mixed hydroxide LiAl2(OH)7(H2O)2. The reaction of an alumina–chromium catalyst with LiNO3 also leads to the formation of lithium aluminate and double oxide Al4Li2O7; however, a mixed hydroxide is not formed. In addition, the reaction of lithium cations with the Cr(VI) catalyst active component leads to the formation of lithium chromate. A comparative analysis of the phase compositions of alumina–chromium catalysts with LiCl and LiNO3 additives has been conducted. It has been found that, depending on the nature of the additive, the phase composition of the catalyst partially changes. In the case of the introduction of lithium chloride, solid solutions of Cr(III) and Li(I) in alumina are formed; the use of lithium nitrate leads to the formation of double oxide Al4Li2O7 and lithium aluminate. The results of studying the activity of 0.5–3% Li + 9.5% Cr + Al2O3 catalyst samples (Li being introduced from LiCl and LiNO3) have shown that the replacement of the LiCl modifying additive by LiNO3 leads to a change in the catalytic properties of the alumina–chromium catalysts. The activity of the sample doped with lithium nitrate is 4–8% higher than the activity of the sample doped with lithium chloride. This finding can be attributed to the fact that, in the case of the LiNO3 additive, the concentration of the formed active phases Li2CrO4 and Cr2O3 is higher. The selectivities of the catalysts modified with lithium salts (chloride and nitrate) differ only slightly owing to the formation of identical active phases.

Effects of Cr Content on Microstructure and Mechanical Properties of WMoNbTiCr High-Entropy Alloys

Refractory high-entropy alloys (HEAs) are promising structure materials in elevated temperature. In the present studies, refractory WMoNbTiCr HEAs with different Cr content were prepared by mechanical alloying followed spark plasma sintering. The effects of chromium content on microstructure and room temperature mechanical properties of WMoNbTiCr HEAs were investigated. The results showed that there are three body-centered cubic (BCC) solid solution phases in the ball-milled powders, including enriching with W, Nb, and Cr solid solution phases, respectively. The bulk WMoNbTiCr alloys were mainly composed of disordered BCC phases and a small amount of Laves phase. As the content of Cr increased from 5 to 20 at.%, the relative content of Laves phase increased correspondingly. With an increase in Cr content, the hardness, fracture toughness, compressive fracture strength, and compressive strain of the WMoNbTiCr HEAs increased, exhibiting the maximum values of 9.73 GPa, 6.68 MPa m1/2, 2116 MPa, and 5.1%, respectively. With an addition of 20 at.% Cr, the WMoNbTiCr HEA exhibited a more refined microstructure. The increasing fracture toughness and compressive strain were mainly attributed to the grain refinement. However, the solid solution strengthening, the second-phase (Laves phase) strengthening, and microstructure refinement resulted in an increase in the hardness and compressive fracture strength.

The Electrodeposition of Amorphous/Nanocrystalline Ni–Cr Alloys from ChCl–EG Deep Eutectic Solvent

The electrodeposition of Ni–Cr alloy was studied in choline chloride-ethylene glycol deep eutectic solvent (ChCl–EG DES) containing NiCl2·6H2O and CrCl3·6H2O. Voltammetric analysis reveals that the presence of Ni(II) ions can promote the deposition of Cr to form Ni–Cr alloy. Electrodeposited Ni–Cr alloy coatings were characterized by EDS, XRD, SEM and HR-TEM. It was found that the deposition potential and metal ion concentration ratio (CNi(II)/CCr(III)) play a central role in controlling the composition and surface morphology of the resultant Ni–Cr alloy coatings. Increasing the deposition potential and higher CNi(II)/CCr(III) ratio is favorable to increase the Cr content of alloy coatings. The structure of Ni–Cr alloys is strongly depended on the Cr content. It changes from a nanocrystalline fcc Ni(Cr) solid solution to amorphous phase (metallic glass) when the Cr content in the alloys increases from 7.3 at% to 14.7 at%. The amorphous Ni–Cr alloy coating (25.2 at% Cr) obtained in DES (CNi(II)/CCr(III) = 1:6) at −0.90 V exhibits the highest resistance, which is superior to pure chromium sheet.

Formation of non-equilibrium ductile solid solutions and textures in NbCr2 bulks produced by mechanical milling and spark plasma sintering

Bulk NbCr2 samples with ultra-fine grains have been fabricated by mechanical milling and subsequent spark plasma sintering. The room-temperature fracture toughness of these bulk samples achieves as high as 11.3 ± 0.5 MPa m1/2, which is remarkably improved compared to the as-cast monolithic NbCr2 Laves phase (1.2 MPa m1/2). The microstructural analysis indicates the presence of abundant non-equilibrium Nb and Cr solid solutions among the grain boundaries. The formation of Nb and Cr solid solutions is attributed to the applied pulsed electric current during spark plasma sintering, which can decrease the critical nucleation undercooling, accelerate the atomic diffusion and enhance the nucleation rate. Based on the microstructural characterization, the enhancement in fracture toughness is ascribed to formation of non-equilibrium Nb and Cr solid solutions toughening and grain boundary toughening mechanisms. Furthermore, strong texture components have been detected in these bulk samples. For the sample sintered with the powder milled for 30 h, the <100> direction of NbCr2 Laves phase is perpendicular to the compressive axis while the Nb and Cr solid solutions show random orientation. When sintered with the powder milled for 60 h and 90 h, the texture component in NbCr2 Laves phase transforms into <110> fiber texture, and the Cr solid solution also show strong <100> and <110> texture components perpendicular to the compressive axis. The evolution of texture component is discussed by considering the crystallization behaviour of the milled powders.

The effect of high-current pulsed electron beam on phase formation and surface properties of chromium/copper system

In this paper, high-current pulsed electron beam (HCPEB) irradiation was used as surface alloying of chromium/copper (Cr/Cu) system to improve the surface hardness and corrosion resistance. After surface alloying, an alloying layer with a spot of craters and plentiful crystal defects (eg. dislocation walls and cells) was prepared on the surface of sample. The existence of crystal defects induced by HCPEB irradiation offered a mass of diffused channels for Cr atoms to facilitate the formation of Cu (Cr) solid solution. Subsequently, partial solid solutions were decomposed to generate GP zone, lobe-shaped particles and spherical particles, which had the characteristic of relationship Nishiyama-Wassermann (N–W) and Kurdjumov-Sachs (K–S) orientation relationship with the Cu matrix. These features account for that surface hardening of Cr alloyed sample was significantly higher than that of W alloyed samples. The corrosion performance of the Cr-alloyed sample exhibited much stable corrosion resistance comparing with that of W-alloyed samples. The enhancement of passivation property was mainly resulted from the formation of more stable passive film, which was associated with the existence of the crystal defects and the alloying particles.

Surface microstructural characteristics and hardness of Cr-coated Zr702 sheet processed by pulsed laser

Microstructural characteristics and hardness of Cr-coated Zr702 sheet after the laser surface treatment (LST) were characterized and investigated by combined use of electron backscatter diffraction, electron channeling contrast imaging, energy dispersive spectrometry and hardness measurement. Results show that after the LST processing at 100 W, three zones with different microstructural characteristics are presented from the surface to the matrix: melted zone (MZ), solid-state phase transformation zone (SSPTZ) and matrix. Surface alloying with Cr occurs in the MZ, leading to the formation of a large number of discontinuous netlike ZrCr2 Laves phases. The SSPTZ is comprised of untransformed bulk α grains with internal substructures and fine martensitic plates. The appearance of such substructures can be attributed to dislocation movements induced by thermal stresses while the martensitic plates result from rapid β→α transformation induced by the pulsed laser. Hardness measurements show that the LST can remarkably increase surface hardness (by ~110%) of the Cr-coated Zr702 sheet, which can be ascribed to strengthening/hardening effects by solid solution of Cr, the formation of dense second phases and significant grain refinement.

Cr-Doped CeO2 Nanorods for CO Oxidation: Insights into Promotional Effect of Cr on Structure and Catalytic Performance

Development of non-noble metal catalysts for oxidation of CO is an important subject for reducing the automotive emissions. Recently, shape-controlled synthesis of CeO2 has increasingly attracted the attention of researchers due to its size- and morphology-dependent unique properties. Following this line of thinking, herein, we successfully report the synthesis of Cr-doped CeO2 (Ce1−xCrxO2−δ; X = 0.05, 0.1, and 0.15) nanorods with various Cr contents by a facile hydrothermal method. Structural, surface, optical, and redox properties of the Cr-doped CeO2 nanorods were investigated by various techniques, namely, ICP-OES, TEM-HRTEM, FE-SEM/EDX/EDS, XRD, BET, Raman, UV–vis DRS, PL, XPS, H2-TPR, and O2-TPD. The catalytic performance was evaluated for CO oxidation. For comparison, the efficiency of Cr2O3 was also studied for CO oxidation under identical conditions. As revealed by various characterization results, the chromium ions were doped into the ceria lattice (formation of Ce–O–Cr solid solution), which enhanced the intrinsic properties such as oxygen vacancy concentration and surface area. It was found that the Cr-doped CeO2 nanorods show superior CO oxidation activity than the pristine counterparts (CeO2 nanorods and Cr2O3). The highest CO oxidation efficiency was achieved with the light-off temperature of T50 = 261 °C, when the Cr doping amount was 10% (Ce0.9Cr0.1O2−δ). A high specific surface area, more number of surface oxygen vacancies, a high concentration of Ce3+, and enhanced oxygen reducibility of Ce0.9Cr0.1O2−δ nanorods were found to be responsible for its superior catalytic performance. Further, the Ce0.9Cr0.1O2−δ nanorods exhibited a steady CO conversion over a period of 55 h investigated. The obtained results are expected to have a significant impact on the use of non-noble metal based Cr-doped CeO2 nanorods in environmental applications. The Cr-doped CeO2 nanorods with Ce0.9Cr0.1O2−δ composition showed enhanced CO oxidation performance at a lower temperature (~ 261 °C) than that of pristine CeO2 nanorods (338 °C) and Cr2O3 (361 °C) catalyst. This behaviour is a result of enhancement of oxygen vacancies, surface Ce3+ species, low-temperature reducibility, and high surface area.

Atomic Redistribution in a Fe-Cr System in the Course of Mechanical Alloying and Subsequent Annealing

Evolution of the structure and atomic distribution in Fe1−xCrx (x = 0.2, 0.3, 0.4 and 0.48) samples in the course of Fe and Cr elemental powder mechanical alloying (MA), as well as during the subsequent isochronous (4 hours) annealing in the 400 °C to 700 °C temperature range, has been studied using 57Fe Mossbauer spectrometry and X-ray diffraction with a focus on the short-range order (SRO). It was established that MA proceeds in one stage for x ≤ 0.3 or three consecutive stages for x > 0.3. The single-stage process is characterized by preferential penetration of Cr into the Fe matrix, while the three-stage process comprises diffusion of Cr into Fe as in the previous case, formation of Cr- and Fe-rich areas, and formation of homogeneous α-Fe(Cr) solid solution. The change in the MA mechanism occurs as Fe is saturated with Cr and is caused by the inversion of the mixing energy sign from negative to positive. For all samples with x ≤ 0.3 annealed at all temperatures and for x > 0.3 annealed at 400 °C, only a small trend toward SRO was observed (SRO parameter 0.3 annealed at temperatures > 400 °C are subjected to thermally induced decomposition, which is accompanied by chromium segregations to the grain boundaries.

INNOVATIVE METHOD FOR PREPARATION OF Fe–Al–Cr INTERMETALLIC FUNCTIONALLY GRADED MATERIAL ON 1045 STEEL WITH UNIQUE TRIBOLOGICAL PROPERTIES

By combining the plasma ion implantation (PII) technology and double glow plasma surface metallurgy (DGPSM), a Fe–Al–Cr intermetallic functionally graded material was deposited on 1045 steel. The obtained Fe–Al–Cr intermetallic functionally graded material was around 11[Formula: see text][Formula: see text]m in thickness and was composed of a Cr-enriched layer (Cr-enriched Fe–Cr compounds), a Fe–Al–Cr-enriched layer (Fe2AlCr and Al8Cr5 compounds), and a Fe-enriched layer (Fe-enriched Fe–Cr solid solution). The interfacial contact between the Fe–Al–Cr intermetallic functionally graded material and the steel substrate is excellent due to the metallurgical bonding. The wear rate of the Fe–Al–Cr intermetallic functionally graded material was only around 25% of that of the 1045 steel substrate. Due to the different compound distributions in the Cr-enriched layer, Fe–Al–Cr-enriched layer, and Fe-enriched layer, the friction coefficients were different and their tribological behaviors were abrasive wear, oxidative wear and adhesive wear, respectively.

Effects of loads on friction–wear properties of HVOF sprayed FeCrBSi coating at elevated temperatures

A FeCrBSi coating was fabricated on H13 hot work mould steel using a high velocity oxygen fuel (HVOF) spraying. The morphologies, chemical compositions and phases of obtained coating were analyzed using a scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and x–ray diffraction (XRD), respectively, and the effects of wear loads on the friction–wear performances of FeCrBSi coating at 500 °C were investigated using a ball–on–disc wear tester. The results show that the FeCrBSi coating with the hardness of 641 HV is composed of α(Fe, Cr) solid solution phase, its bonding strength of 70.35 N is characterized with the scratch test. The average coefficients of friction (COFs) of FeCrBSi coating under the wear loads of 1, 3 and 5 N are 0.78, 0.53, and 0.42, respectively; and the corresponding wear rates are 6.41 × 10−3, 2.90 × 10–3, and 9.26 × 10–3 μm3 · N–1 · m–1, respectively. The wear mechanism of FeCrBSi coating is abrasion wear and oxidation wear, accompanied by abrasion wear under the load of 5 N, showing that the wear degree is deteriorated with the increase of loads.

Investigation of powder fed laser cladding of NiCr-chromium carbides single-tracks on titanium aluminide substrate

In the present study, a Cr3C2NiCr powder mixture was used to fabricate laser claddings on a titanium aluminide (TiAl) substrate. The effect of processing parameters, such as laser power (P), powder feeding rate (F) and scanning speed (S), were studied on the geometrical properties (height, width, dilution and wetting angle) of single-line claddings and their systematic correlation were predicted using the regression analysis method. The results indicated that the clad height showed a linear dependency on the P1.S−1.F0.85 parameter. Similarly, the width, wetting angle and penetration depth depicted a linear dependency on the P1.S−1.F−0.7, P0.8.S−0.7.F1 and P0.75.S0.5.F−1 parameters, respectively, while the dependency on dilution was S0.8.F−0.8. High values of the correlation coefficient were observed for all empirical dependencies. Finally, a processing window was developed for the laser cladding of the Cr3C2NiCr powder mixture on the TiAl substrate. The microstructure analysis of the optimal cladding showed that the microstructure was covered with different chromium carbides (Cr3C2, Cr7C3 and Cr23C6), together with the Ni(Cr) solid solution. The microhardness of the optimal clad was found to be around 820 HV, which was higher than that of the titanium aluminide substrate (320 HV).

Joining of Mn-Cu alloy and 430 stainless steel using Cu-based filler by SIMA-imitated brazing process

A new SIMA-imitated brazing was used to join Mn-Cu damping alloy and 430 stainless steel (SS) with Cu-34Mn-6Ni-10Sn filler metal. The microstructure and mechanical properties of the brazed joint were investigated. The results show that the semi-solid brazing seam was obtained at 790 °C. A (Fe, Mn, Cr) solid solution diffusion layer was formed between 430SS and brazing seam. The Mn-Fe-Cu-Cr compounds were formed in brazing seam due to the dissolution of 430SS. The liquid phase penetrated along the grain boundaries of Mn-Cu alloy. The shear strength of the brazed joint is 230 MPa, the brazed joint exhibits a ductile fracture feature.