Cr Alloy Research Articles

Quantitative Characterization of Elemental Segregation in Inconel 718 Superalloy by Micro-Beam X-ray Fluorescence Spectroscopy and Its Correlation Study.

Inconel 718 (IN718) nickel-based superalloy is widely used in aerospace and nuclear applications owing to its excellent comprehensive mechanical properties, oxidation resistance, and hot corrosion resistance. However, the elemental segregation caused by heterogeneous solidification during casting has great influence on the mechanical properties. Therefore, accurately characterizing the segregation behavior is necessary. Traditional quantitative characterization of elemental segregation uses various sampling methods, in which only macroscopic segregation results are obtained. In this study, micro-beam X-ray fluorescence (μ-XRF) is used for the quantitative characterization of element micro-segregation in IN718 superalloy. The concentration distributions of Cr, Fe, Mo, Nb, and Ti in IN718 alloy are determined with optimized testing parameters, and the degree of elemental segregation in different regions of the analytical area is calculated. It is found that the segregation degree of Nb and Ti in the testing area is larger than other alloying elements. The correlation between the microstructure distribution and the segregation degree of Nb and Ti has been studied using scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS). There is severe segregation of Nb and Ti in areas where Nb-containing precipitates are accumulated. The distribution of abnormal signals of Nb with a high fluorescence intensity has a close relationship with the area of precipitates-enriched Nb.

Simultaneous Recycling of Chromium-Containing Waste Slag and Diamond-Wire Silicon Slitting Scrap to Prepare High-Purity CrSi2 and Eutectic Si–Cr Alloy

Simultaneous Recycling of Chromium-Containing Waste Slag and Diamond-Wire Silicon Slitting Scrap to Prepare High-Purity CrSi₂ and Eutectic Si–Cr Alloy

Local structural changes in V–Ti–Cr alloy hydrides with hydrogen absorption/desorption cycling

Vanadium-based solid solution alloys potentially serve as safe, high-capacity hydrogen storage materials. Low-vanadium-concentration alloys have low durability, and their hydrogen absorption and desorption amounts decrease by 20 % after 100 cycles. In this study, we conducted reverse Monte Carlo modeling on X-ray diffraction patterns and neutron pair distribution functions of the hydrogen-absorbed and desorbed samples of a V0.10Ti0.36Cr0.54 alloy to analyze the variations in the local structure. The local structure surrounding the hydrogen atom in the hydrogen-absorbed phase exhibited minimal changes. In contrast, hydrogen occupied both tetrahedral and octahedral sites of the hydrogen-desorbed phase almost equally during the early cycles; however, the amount of hydrogen occupying the tetrahedral sites increased with the number of cycles. It is speculated that hydrogen absorption and desorption cycling induced grain refinement and/or introduced dislocations, which altered both the amount of hydrogen and the sites occupied in the desorbed phase, thereby decreasing the hydrogen storage capacity.

Creep damaged microstructure and mechanical properties of Cr–Mo–V steel subjected to long-term service exposures

Evaluating the degree of creep damage is of high importance for the residual life assessment of high temperature and pressure steam piping systems of power plants. This study aims at assessing creep damaged microstructure and mechanical properties of low alloy Cr–Mo–V steel after long-term service exposures. Variations in mechanical properties have been assessed by means of tensile tests, hardness measurement and instrumented indentation testing (IIT). Optical and scanning electron microscopies were employed for the identification of creep damaged microstructure. The effect of heat treatment on the recovery of microstructure and mechanical properties was also studied. Correlations of IIT and hardness results between surface and bulk values have been obtained. The results of IIT agree well to the results of tensile tests. Moreover, relationships between hardness and tensile properties have been assessed. Eventually, the evaluation of the degree of creep damage by employing IIT and hardness measurement was attempted.

Effect of Cr and Y on the microstructure and mechanical properties of Fe-Cr-Al alloys during corrosion-aging in superheated steam at 500 °C

The α-α’ phase separation of Fe-Cr-Al alloys during long-term service at 475–500 °C may lead to the increase of strength and hardness and the decrease of ductility, which will limit the application of Fe-Cr-Al alloys as accident tolerant fuel (ATF) cladding material. The mechanical behavior and microstructure evolution of Fe-12Cr-5Al, Fe-12Cr-5Al-0.01Y, Fe-20Cr-5Al and Fe-20Cr-5Al-0.02Y (wt%) alloys in 500 °C superheated steam for 2000 h have been investigated by tensile test, Vickers hardness measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), three-dimensional atom probe (3DAP) and thermodynamic calculations. Results show that increasing the Cr content may refine the grain and improve tensile strength of the alloy, while adding trace Y has negligible effect on the grain size and tensile strength of the alloy; the corrosion-aging hardening of 20CrY and 20Cr alloys is attributed to the α-α’ phase separation, which is closely related to the high content of Cr in the alloy. The addition of trace Y promotes the nucleation and growth of α’ phase in alloys with the content of 20%Cr during the corrosion-aging process but has insignificant influence on the mechanical properties of the alloy.

Domain structure ordering and magnetic property enhancement of containerlessly processed quaternary Fe-Mo-Ni-Cr alloy

Quaternary Fe-20 %Mo-12 %Ni-6 %Cr alloy with various composite magnetic structures was fabricated through electromagnetic levitation (EML) coupled with multi-mode quenching techniques. The magnetic domain distributions were characterized and related to the macro/micro-magnetic properties of this containerlessly processed alloy. Under EML condition, nano-scale lamellar (αFe) + Fe2Mo eutectoid structures with completely disordered magnetic domains were formed at small undercoolings. But the eutectoid morphology became anomalous and a ferromagnetic (αFe) single-phase zone with clear stripe domains appeared as undercooling increased, resulting in the obvious improvement of saturation magnetization, coercivity and residual magnetization. The (αFe) + Fe2Mo eutectoid structures were entirely suppressed by multiple quenching processes to secure (αFe) single-phase microstructures with ordered domain distributions including the stripe domains with grain boundary contrast, the maze domains with developed branches and their coexistent mixtures. These magnetic structures displayed much higher saturation magnetization, much lower coercivity and almost unchanged residual magnetization as compared with the highly undercooled alloy at EML state, indicating that the soft magnetic property of this alloy was significantly enhanced after rapid quenching. Moreover, the spin distributions and atomic magnetic moments of two constituent phases were analyzed by first-principle calculations, which were in good accordance with the experimental results.

Oxidation mechanisms of a Cr[sbnd]Si alloyed coating-free press-hardened steel under simulated press hardening conditions

Press-hardened steel (PHS) undergoes severe high-temperature oxidation after press hardening, which significantly degrades surface quality and increases manufacturing cost. This work reports the mechanism by which a coating-free PHS (CF-PHS) with the simultaneous presence of Cr, Si, and Mn alloying elements achieves excellent high-temperature oxidation resistance. It is found that Si and Mn in the CF-PHS promote the formation of a continuous Cr2O3 layer with good protective effect, thereby improving high-temperature oxidation resistance, during the press hardening. Moreover, the continuous amorphous SiO2 layer formed at the oxide scale/matrix interface and the Mn-rich oxides that improve the compactness of the scale further enhance the oxidation resistance of the CF-PHS.

Superior high-temperature strength-ductility of TiB2–Ti2AlN/TiAl composite with core-shell microstructure

Herein, a novel core-shell structured TiAl composite consisting of nanoparticles “shell” and a near fully lamellar “core” was designed using a Ti–48Al–2Nb–2Cr alloy and Boron nitride nanoplates. By tailoring microstructure and nanoparticles strengthening, the TiAl composite exhibited a superior combination of strength and ductility at high temperature, which achieved an ultimate tensile strength of 514.2 MPa and an outstanding fracture strain of 18.8 % at 850 °C.

Laser‐Based Directed Energy Deposition Remanufacturing of Gray Cast Iron using Stainless Steel 316L and Inconel 625 Filler Materials

Directed energy deposition (DED) is identified as an ideal candidate for restoring damaged or worn cast iron components such as agricultural engine blocks, housings, and manifolds. While this laser‐based process offers superior control of the heat input compared to traditional arc‐based repair, gaseous porosity and brittle intermetallic structures reduce the strength and ductility of the fusion zone. Varying combinations of Fe–Ni–Cr alloys have found success in remanufacturing cast iron using laser‐based DED, but little attention has been given to the consequence of filler material composition and form, that is, wire versus powder. This study quantifies structural characteristics in cast iron repairs and offers microstructural and process‐specific insights to support these observations. With appropriate thermal conditions, up to 98.7% of the original tensile strength of gray cast iron may be achieved. These results point toward superior gray cast iron restoration using tunable laser‐based DED.

Efficient acquisition of interdiffusion coefficients matrices and atomic mobilities of fcc Co–Mn–Cr alloys by combining diffusion couple experiments and HitDIC software

Reliable diffusivities and atomic mobilities of fcc Co–Mn–Cr alloys are the important keystones for establishing the accurate diffusion database for CoCrFeMnNi high-entropy alloys and other relevant alloys, but they are still missing in the literature. In this paper, diffusion couple experiments together with High-throughput Determination of Interdiffusion Coefficients (HitDIC) software were employed to efficiently obtain diffusion descriptions of fcc Co–Mn–Cr alloys. Six diffusion couples were prepared and examined to provide the prerequisite composition profiles. Feature selection and regularization techniques in HitDIC software were adopted to extract the corresponding interdiffusion coefficients and atomic mobilities. A reliable set of diffusion descriptions of the fcc Co–Mn–Cr alloys were therefore obtained and verified. Investigations of the underlying composition- and temperature-dependent diffusion behaviors were enabled and demonstrated.

Advances in Diffusion Barrier Coatings for High-Temperature Applications

Diffusion barrier coating (DBC) systems on heat resistant alloys consist of a multi-layer structure: an outer Al-reservoir layer and an inner diffusion barrier layer (DBL). The outer Al-reservoir layer forms a protective Al2O3 scale and DBL acts as a barrier layer against alloy interdiffusion. Three kinds of DBL were developed: Re on Ni-based superalloys; W on stainless steels; and Cr on Ni–Cr alloys. It was found that DBC systems have excellent mechanical properties (creep and fatigue), improving alloy substrate performance, and enhance the anti-exfoliation properties of YSZ in thermal barrier coatings (TBC) in addition to providing excellent oxidation resistance. At temperatures higher than 1300 °C, however, the DBC design based on kinetics (diffusion) is insufficient to form and maintain a protective Al2O3 scale. In this case a self-maintaining coating (SMC) system designed on the basis of thermodynamics (phase stability) is required. The SMC system formed on Nb–Hf (C-103) alloy consists of a multi-layer structure: an outer Re (Al, Si)1.8 and inner NbSi2 layers, plus a transient Nb5Si3 layers formed during oxidation. At temperatures higher than 1300 °C the Al2O3 can be formed by changing the Al/Si ratio in the Re (Al, Si)1.8 in which Si was supplied from the decomposition reaction of NbSi2 to Si + Nb5Si3 during selective oxidation of Al. It is proposed that coating alloys should be designed for considering not only high temperature oxidation, but also alloy substrate mechanical properties and anti-exfoliation of oxide scales, based on both kinetic principles (DBC system) and thermodynamics (SMC system).

Effect of Ti on the microstructure and properties of Cu–Cr alloy

Cu–Cr–Ti alloy was successfully prepared by vacuum melting, solution treatment at 960 °C for 1 h, 80 % cold rolling and aging at 500 °C for 1 h. The effect of Ti content on the microstructure was characterized by Scanning electron microscope (SEM) and Transmission electron microscope (TEM). Their tensile strength, electrical conductivity, thermal stability, wear resistance and arc erosion resistance were also measured. The results showed that Ti can form the Ti0.77S phase with S, which can prevent the occurrence of sulfur embrittlement. And Ti can segregate around the Cr precipitates, hindering their growth. Therefore, the tensile strength, hardness, high temperature softening resistance, wear resistance and arc erosion resistance improved with the increase of Ti content. But the electrical conductivity decreased sharply since Ti was mainly solidly dissolved in the matrix. What's more, the electrical conductivity decreased sharply and other properties did not improve when the content increased from 0.066 wt% to 0.098 wt%, that is, the comprehensive performance was the best when the Ti content was 0.066 wt%. The tensile strength was 551 MPa, electrical conductivity was 78.3%IACS and the friction coefficient was 0.33. This work provides effective ideas for preparing copper alloys with desired properties.

Development of Co–Ni–Al–V–Ta–Cr-based superalloys with high-temperature strength and excellent oxidation resistance

In this study, the effects of V on the microstructure, lattice misfit, solvus temperatures, and oxidation behaviors of the Co–Ni–Al–V–Ta-based superalloys are investigated. The results show that all these alloys exhibit the γ’/γ two-phase structures. More importantly, the γ’ solvus temperature increases, and the oxidation resistance is significantly improved with the reduction of V concentration. Subsequently, the Ti (2 at.%) was added into Co–40Ni–10Al–4Ta–1V–12Cr alloy to further raise the properties of the superalloy. It is found that the Co–40Ni–10Al–4Ta–1V–12Cr–2Ti alloy exhibits a higher solvus temperature reaching 1200 °C of the γ′ phase, a low density of 8.48 g/cm3, a low lattice misfit of only +0.37 %, as well as exceptional oxidation resistance and mechanical properties.

Microstructural and micromechanical characterization of intergranular oxidation in Fe-15Cr alloy

Fe-Cr alloy has great potential as an interconnect material for SOFCs at temperatures up to 800 °C, with Cr providing excellent oxidation resistance through the formation of a protective chromium oxide layer. However, internal brittle oxides formed at grain boundaries (GBs) can lead to severe cracking and cause material failure. Here, we report the formation of internal GBs oxide in an Fe-15 wt%Cr alloy. We carried out microstructural and chemical characterization of the intergranular oxide and performed micromechanical testing and FEM simulation to study the fracture behavior at the GBs. Our findings provide insights for improving the oxidation resistance in the material design.

Formation of Films of Alloys of Cr–Ni, Cr–Ni–Si and Fe–Ni Systems by Sublimation and Evaporation Methods for Electronic Products

The processes of formation of films of alloys of the Cr–Ni, Cr–Ni–Si and Fe–Ni systems with a stab le elemental composition by evaporation methods are considered. It is shown that due to the large difference in the melting temperatures of Ni and Cr, nichrome films are obtained by sublimation. The design of the evaporator is proposed, which makes it possible to stabilize the composition of the films. Calculations of azeotropic compositions of alloys of the Cr–Ni–Si system have been carried out. The position of the isobars of the total pressure of iron and nickel on the state diagram was determined during evaporation in vacuum. The azeotropic composition of the alloy of the Fe–Ni system was calculated and experimentally verified.

Effect Of Surface Treatment on The Shear Bond Strength Between Nickel-Chromium Alloy and Veneering Porcelain

Nickel–chromium (Ni–Cr) alloys, have been used widely, due to their superior physical properties and economic issues in relation to other precious alloys. Many studies have been carried out on porcelain fused to metal restorations to enhance the bonding quality of the porcelain to Ni-Cr alloy, such as mechanical treatment by air abrasion particles or chemical treatment by acid etching to increase the longevity of the restoration. The purpose of this study is to investigate the effect of surface treatments sandblasting with Aluminum Oxide (Al2O3), acid etching with Potassium hydrogen difluoride acid (KHF2) and combination treatment on the shear bond strength between Nickel-chromium alloy substructure and porcelain veneer. Twenty-one cylindrical shaped samples have base of 5 mm in diameter and 1 mm in thickness and a cylinder with 4 mm in diameter and 4 mm in length were prepared from Ni – Cr alloy. The samples were divided into 3 groups (n=7) according to surface treatment: Nickel -chromium treated with sandblasting with 50μm Al2O3 group (c), Nickel – chromium etching with KHF2 group (k), and Nickel – chromium sandblasting with 50μm Al2O3 followed with acid etching with KHF2 group (comb). Then ceramic build up (opaque, dentin, enamel, and glaze Vita VMK Master opaque, dentin, enamel, and glaze Vita VMK Master) and sintering was performed according to manufacturer's instructions and the final dimension of porcelain cylinder (4 X 4X 1) were checked with a metal gauge. All samples were subjected to shear force in a universal testing machine at cross head speed 0.5 mm/min. and recorded in MPa. The fractured samples were checked under (DIGITAL MICROSCOPE) (X50) to evaluate the mode of failure, it was adhesive, cohesive and mixed failure modes. The shear bond strength values were analyzed with one-way ANOVA and LSD. The results showed that the highest mean of shear bond strength values was in Ni – Cr combination surface treatment group (26.11 ± 1.85), while the lowest mean was for Ni- Cr acid etched group (22.02 ± 1.5) and Nic group (20.85 ± 1.5). Within the limitation of the present study, the following conclusion can be drawn: Combination surface treatment produced the highest shear bond strength between Ni – Cr surface and veneering porcelain, followed by etching with KHF2, so combination method would increase longevity of porcelain fused to metal restorations.

Emissivity measurements conducted on intermetallic γ-TiAl-based alloys for aeronautical applications

The directional spectral emissivity of a Ti–48Al–2Nb–2Cr alloy (in at.%), 4822 alloy, and a Ti-43.5Al–4Nb–1Mo-0.1B alloy (in at.%),TNM alloy, used in the aeronautical industry, are measured between 150 and 850 °C. The differences in the emissivity values between both alloys at the lowest temperatures, indicates that the βo phase, only present in TNM, exhibit higher emissivity values. By numerical integration of the measured data, the total directional and hemispherical emissivity have been calculated. At 850 °C the total hemispherical emissivity in vacuum are nearly identical with 0.274 ± 0.006 for the 4822 alloy and 0.273 ± 0.007 for the TNM alloy. The lower emissivity change with temperature measured in TNM alloys is related with the deconvolution of βo phase by diffusion processes. Afterwards, near-normal spectral emissivity measurements are performed in both alloys during isothermal oxidation treatments at 750 °C and 850 °C for 120 h. The emissivity data reveal that the TNM alloy exhibits higher oxidation resistance especially at 750 °C. In parallel, microstructural characterization has been performed before the measurements, after the directional emissivity measurements prior to oxidation and after isothermal oxidations. The formed oxide scale is composed of four layers that coincide with those reported in the literature: an outer layer of TiO2 contiguous with a layer of Al2O3, followed by a TiO2/Al2O3 mixed layer and finally a thin layer of Nb-rich nitride. This mixed layer governs the interferential part of the alloys’ emissivity spectra, which, in combination with the background, determines the overall radiative behavior of the alloys under service conditions.

High-temperature corrosion model of Incoloy 800H alloy connected with Ni-201 in MgCl2–KCl heat transfer fluid

Abstract Long-term dipping corrosion experiments on Incoloy 800H (800H) in molten eutectic MgCl2–KCl salt at 1,073 K with and without connection with Ni-201 alloy were carried out. While connecting with Ni-201 alloy, the corrosion rate of 800H was 4.47 ± 0.26 mg·cm−2·day−1 (10−3.55±0.02 A·cm−2). However, the corrosion rate for the 800H that was not connected to the Ni-201 alloy was 3.00 ± 0.27 mg·cm−2·day−1 (10−3.71±0.04 A·cm−2). Therefore, Ni-201 alloy accelerates the corrosion rate of 800H in the molten MgCl2–KCl salt while connecting to each other. In addition, based on the calculation of Gibbs energy of Ni–Fe–Cr alloy and exchange current density of 800H in MgCl2–KCl salt, a new Tafel model was developed to predict the corrosion rate of 800H alloys. The corrosion rate calculated by the new model is 10−3.74 A·cm−2, which agrees with the experimental data.

Effect of tungsten on structure of chromium-based heat-resistant alloys

The effect of tungsten on the structure and properties of Cr–32Ni–W alloys was studied. Characteristic tungsten concentrations were separated: up to 3%, 3–10%, and more than 10%, which determine the structure of the alloys. The mechanical properties of the alloys are determined. The area of rational application of the alloy Cr–32Ni–W is shown.

Determination of microstructure and mechanical and thermophysical properties of Al–Si–Mg-XCr alloy

The study added different proportions of Cr to the Al–Si–Mg eutectic alloy and applied heat treatment to the quaternary alloy. So, the Al–Si–Mg eutectic alloy's microstructure and morphology were looked at after Cr was added and it was heated. In addition, the hardness, tensile strength, fracture surface analysis, and thermoelectric properties of newly produced Al-12.95 % Si-4.96 % Mg-X%Cr alloys were also determined. In the newly formed alloy, along with the expected Si and Mg2Si phases in the Al matrix phase, a randomly distributed CrSi2 binary intermetallic phase in a white hexagonal structure was observed with the effect of Cr addition. Additionally, a magnesium-rich Al9FeMg3Si5 intermetallic phase was observed, which we think was formed by the effect of Fe impurity atoms. Hardness and tensile strength values, which are the mechanical properties of the alloy, increased significantly after heat treatment. The hardness value of the 0.5 % Cr-added sample increased by approximately 77 % and reached 107.95 ± 6.0 kg/mm2. At the same time, the hardness value of the intermetallic CrSi2 phase in the quaternary Al-12.95 wt%Si-4.96 wt%Mg-1.0%Cr alloy was found to be 794.3 ± 30 kg/mm2. Similarly, the maximum tensile strength value of the 0.5 % Cr-added sample after heat treatment increased by approximately 105 % and reached 160.53 MPa. Melting temperatures (Tm) (K), fusion enthalpy (ΔH) (J/g), and specific heat Cpl (J/gK) were determined for non-heat-treated materials. The 0.5, 1.0, and 1.5 Cr-added samples had Tm of 563.38 °C, 558.44 °C and 572.61 °C, respectively. The ΔH value of samples with 0.5 %, 1.0 % and 1.5 % Cr addition is 605.70 (J/g), 579.92 (J/g) and 552.24 (J/g), respectively. Cpl was 0.724 J/g.K, 0.698 J/g.K and 0.653 J/g.K for 0.5 %, 1.0 %, and 1.5 % Cr-added samples. In both heat-treated and non-heat-treated samples, Cr enhanced electrical resistance.