Cr Alloy Research Articles

Worn surface topography and mathematical modeling of Ti-6Al-3Mo-2Sn-2Zr-2Nb-1.5Cr alloy

This study aims at investigating worn surface topography and mathematical modeling of annealed Ti-6Al-3Mo-2Sn-2Zr-2Nb-1.5Cr alloy using response surface methodology (RSM). The alloy was subjected to three different regimes in order to study their effect on mechanical properties. First regime was applying cold deformation by compression until 15% drop in height at room temperature. The second regime was performing solution treated on the deformed samples at 920 °C for 15 min then air-cooled (AC) to ambient temperature. Third regime was applying aging on the deformed and solution treated specimen for 4 hr at 590 °C followed by air-cooling. Three different velocities (1, 1.5, and 2 m/s) were adopted to conduct dry sliding wear according to the experimental design technique (EDT). Gwyddion and Matlab softwares were used to detect worn surface photographs analytically and graphically. Maximum hardness of 425 HV20 was obtained for AC+Aging specimen, while minimum hardness of 353 HV20 was reported for the annealed specimen. Applying aging process after solution treatment enhanced considerably the wear property and this enhancement reached 98% as compared to the annealed condition. The relationship between input factors (hardness & velocity) and responses (Abbott Firestone zones) was demonstrated using analysis of variance (ANOVA). The best models for Abbott Firestone zones (high peaks, exploitation, and voids) produced accurate data that could be estimated for saving time and cost. The results showed that the average surface roughness increases with increasing sliding velocity for all conditions except AC+Aging condition where the average surface roughness decreased with increasing sliding velocity. The results revealed that at low velocity and hardness, the material gives the highest exploitation zone (86%). While at high velocity and hardness, the material gives the lowest exploitation zone (70%). In general, the predicted results of mathematical model showed close agreement with experimental results, creating that models could be utilized to predict Abbott Firestone zones satisfactorily.

Cr addition-mediated simultaneous achievement of excellent strength and plasticity in non-equiatomic Nb-Ti-Zr-Ta-base refractory high-entropy alloys

Structural materials with broad application prospects often feature comprehensive strength and plasticity synergy. However, there seems to be an inevitable trade-off between material strength and plasticity associated with post-processing technologies. In this work, an as-cast non-equiatomic NbTiZrTa0.25-based refractory high-entropy alloy (RHEA) with excellent specific strength and plasticity synergy was developed via Cr alloying modification. The yield strength of NbTiZrTa0.25Cr0.2 reached 1054 MPa, with a density of only 7.2981 g/cm3 and plasticity above 60 %. Increasing the amount of Cr in the base alloy did not diminish the plasticity until the single BCC phase was transformed to the BCC + Laves phases at a Cr content up to 0.4, whereas a monotonous improvement in strength was observed. The strength improvement was predominantly related to the solid solution strengthening and consecutive fine-grain strengthening. Embrittlement was attributed to the appearance of the brittle Laves phase. The NbTiZrTa0.25Cr0.2 RHEA with an outstanding specific strength and plasticity is a promising material for use in harsh environments and as a model material to develop new high-temperature alloys.

Ballistic impact response of a heat-treated dual-phase Ti–5.2Mo–4.8Al–2.5Zr–1.7Cr alloy with hierarchical microstructure

In the present study, a dual-phase Ti-5.2Mo-4.8Al-2.5Zr-1.7Cr alloy was hot-rolled at 980 °C with a thickness reduction of 65% and then heat-treated with the strategy of 920 °C/1 h/water quenching +550 °C/6 h/air cooling, and a hierarchical microstructure was prepared, which contained micro-scale equiaxed primary α phase (αp), sub-micro scale rod-like α phase (αr), nano-scale acicular secondary α phase (αs) and β matrix segmented by αs and αr. In addition, the dislocation densities of α phase and β phase were determined as 0.3652 × 1015/m2 and 2.2502 × 1015/m2, respectively. Contributing to αr and αs, the hierarchical microstructure exhibited higher strength (yield strength: 1228 MPa, ultimate tensile strength: 1389 MPa, dynamic compressive strength: 1661 ± 27 MPa). Simultaneously, αp and αr were helpful to the strain transfer, and thus the plasticity was maintained at a considerable level (elongation: 13.4 ± 0.2%, critical fracture strain: 18.9 ± 0.2%). Such hierarchical microstructure overcame the limitation of the strength-ductility trade-off to a certain extent and exhibited a superior combination of strength and ductility. The ballistic impact behavior of the titanium alloy plates with the thickness of 20.3 mm (1#), 19.3 mm (2#) and 18.4 mm (3#) against 7.62 mm armour piercing projectiles illustrated that as the titanium alloy thicknesses decreased from 20.3 mm to 18.4 mm, more ASB-induced cracks were formed near the rear face and connected to form catastrophic cracks in the 2# and the 3# titanium alloy plates, even resulting in the failure for the 3# titanium alloy plate. Ultimately, the 1# and 2# titanium alloy plates exhibited preferable ballistic impact properties.

Synthesis of AuX (X = Ni, Ga, Mo, Zn, and Cr) Alloy Aerogels as High-Performance Electrocatalytic CO2 Reduction Reaction Catalysts.

Electrocatalytic CO2 reduction reaction (eCO2RR) into value-added chemicals is highly desirable to mitigate the global warming effect and energy crisis. Metal aerogels, as featured by a self-supporting structure, large specific surface area, outstanding conductivity, and a hierarchical porous structure, are ideal electrocatalysts in eCO2RR. Herein, we report a simple and general strategy for constructing a series of Au-based alloy aerogels which contain Au with another metal including Ga, Ni, Mo, Zn, and Cr, respectively. For the first time, the electrocatalytic activities of AuGa aerogels, AuNi aerogels, and AuMo aerogels for CO2RR were studied in detail. The resultant Au81Ga19 aerogel achieves a 95.2% Faradaic efficiency (FE) at -1.16 V versus reversible hydrogen (vs RHE) in H-cells. Impressively, a total 99.4% FE for C1 products (CO + HCOOH) with a current density of 100 mA cm-2 at -0.6 V vs RHE and a large current density of 228 mA cm-2 can be achieved at -0.9 V with a 72.3% FE for the C1 product in a flow cell. Electrochemical characterization and theoretical calculations further revealed that the outstanding performance of the Au-based aerogels was derived from the large specific surface area, abundant grain boundaries, low interfacial charge transfer resistance, and synergetic effect. Overall, this study provides a promising alternative to engineer alloy aerogel electrocatalysts for highly efficient CO2 electroreduction.

Effect of laser-induced texture on lubrication retention and tribological properties of 40Cr alloy surfaces

Continuous and proper oil lubrication between the friction pair can reduce wear and increase the service life of mechanical components. The synergistic effects of oil wettability and spreadability on lubrication durability and tribological properties were investigated. The results indicate that the capillary action of textured structures can promote the oil spreadability and reduce the relaxation time of the contact angle, and the final contact angle will be affected by the laser-induced oxidation and hydroxylation. However, the excessive absorption behavior of textures limits the oil wettability and spreadability. In addition, capillary action and hydroxylation formed a textured surface with excellent oil spreadability and a relatively high contact angle. This is a critical factor in maintaining surface lubrication and improving tribological properties.

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.

A microstructural, mechanical and electrochemical/stress corrosion cracking investigation of a Cr-modified Ti–6Al–4V alloy

The microstructural effects of a Cr-modified Ti–6Al–4V (Ti64) alloy on the mechanical, electrochemical and stress corrosion cracking properties were studied. With the aid of thermodynamic calculations and microstructural characterizations, Ti64–3Cr forged alloy was successfully fabricated with no defects by micro-alloying Ti64 with 3 wt% Cr. The microstructure features of the Ti64–3Cr alloy reveal fine alpha laths with a lamellar structure and strong texturing particularly in the basal and prismatic poles. The mechanical results at room temperature show enhanced yield strength and hardness attributed to the refined alpha laths and solid solution strengthening effect caused by Cr addition. Afterward, the electrochemical properties were investigated under different NaCl electrolyte concentrations. The alloy showed good corrosion resistance in the various NaCl concentrations as a result of the formation of Cr2O3 oxide due to the alloying effect of Ti64–3Cr alloy. X-ray photoelectron spectroscopy was used to confirm the presence of the oxides film on the surface of the alloy after the electrochemical studies. Furthermore, the stress corrosion cracking (SCC) properties of the alloy were investigated using a strain rate of 1 × 10−6 s−1 in 3.5 wt% NaCl aqueous solution under different temperatures. The results showed that as the temperature increased during slow strain rate testing, the SCC susceptibility of the alloy decreased. The outstanding SCC strength and enhanced corrosion properties of the novel alloy could serve as a potential use in marine applications.

Design of a Ti–V–Nb–Cr alloy with room temperature hydrogen absorption/desorption reversibility

Computational thermodynamic tools are employed to design Ti–V–Nb–Cr alloys for hydrogen storage. Calculation of phase diagrams (CALPHAD) is employed to find compositions prone to form body centered cubic (BCC) alloys. A thermodynamic model to calculate pressure-composition-temperature (PCT) diagrams is used to select compositions with plateau pressure above 1 bar at room temperature. Three alloys are synthesized via arc melting and present predominantly BCC structures. The alloys show capacity to absorb hydrogen with fast kinetic without any activation treatment. PCT diagrams demonstrate reasonable values of plateau pressures and thermodynamic properties compared to calculated ones. Cycling experiments are measured to evaluate room-temperature reversibility in the Ti11V30Nb28Cr31 alloy. A continuous reduction in capacity is observed due to stabilization of the face centered cubic (FCC) hydride. The resistance to air exposure of the Ti11V30Nb28Cr31 alloy is investigated. The alloy demonstrated to be easily reactivated after air exposure by a heat treatment under dynamic vacuum.

Effects of V concentration on the physical properties of Cr1−x Al x alloy system

Electrical resistivity (ρ), magnetic susceptibility (χ) and thermoelectric power (S) studies reported previously on the (Cr1-x Al x )99V1 alloy system indicate a suppression of antiferromagnetism in the concentration range 0.015 ≤ x ≤ 0.040. The present study incorporates Sommerfeld electronic specific heat coefficient (γ), thermal conductivity (κ), Hall coefficient (R H) and analyses of the previous results in order to have a comprehensive study of the alloy system. γ(x) depicts two peaks close to the same concentrations where dS/dT|T→2K(x) have minima, i.e. at x c1 ≈ 0.015 and x c2 ≈ 0.040. Such peaks and minima, respectively, have been considered as key signatures of quantum criticality (QC) in alloys of Cr. Evidence of band structure modification in the alloy system is shown by a change of slope in the Nordheim-Gorter (N-G) relationship showing a minimum at an extrapolated concentration x = 0.035. The slope is positive for the incommensurate (I) spin-density-wave (SDW) alloys with x < 0.035 and a negative for the commensurate (C) SDW alloys with x > 0.035. A behaviour reminiscent of changes in the band structure is also observed in the Lorenz number, L(x), for the alloy with x = 0. R H(T) results in the range 0 ≤ x ≤ 0.026 have a sharp increase in the charge carrier density, n 2K = [qR H(2k)]−1, at the ISDW to paramagnetic (P) phase transition. The concentrations x = 0.015 and x = 0.040 are therefore considered ISDW to P and P to CSDW quantum critical points, respectively.

Ball Milling and Consolidation Process of Al-Cr Powder Mixture—Microstructural Characterization

The interest in studying the synthesis of an Al–Cr alloy system by non-equilibria processes is due to the formation of metastable or quasicrystalline phases when rapid solidification has been utilized. Similarly, the formation of quasicrystals has been reported to a much lesser extent when the mechanical alloying technique was applied. In the present research, a mixture of powders of Cr and Al (both elements with a purity of 99.99%) with compositions of Al-5 and 7.5 at. % Cr was subjected to a ball milling process. Afterwards, the powder mixture was subjected to a consolidation process, conducted by pressing and sintering processes. The X-ray diffraction analyses revealed that during 20 h of milling there was no formation of metastable or quasicrystalline second phases detected. In addition, the X-ray diffraction peaks revealed that as milling time increased, the nanometric grain size decreased, and once the sintering treatment was applied, the crystallite size decreased following the same tendency. The dislocation density was estimated using the size of nanometric grains; this computation revealed that the dislocation density grew throughout the ball milling process; even after sintering, the multiplication of dislocations prevailed following the same tendency.

Characterization and High-Temperature Oxidation Behavior of Ni–20Cr Deposits Fabricated by Cold Spray-Based Additive Manufacturing

Hot corrosion is a critical problem in a wide range of high-temperature applications. Ni–20Cr alloy is frequently used in such applications owing to its good hot-corrosion resistance. In the current work, thick Ni–20Cr plates in a thickness range of 6–10 mm were fabricated using cold spray-based additive manufacturing (CSAM). High-pressure cold spraying was used with nitrogen as the propellant gas. Pre- (substrate heating, SH) and post-heat treatments (hot isostatic pressing, HIP) were also performed to comprehend the changes in the deposit properties. The deposits were subjected to microstructural and mechanical characterization to explore the potential of cold spraying for CSAM of Ni–20Cr standalone products. The cold-sprayed plates were successfully developed without any oxide formation. HIP treatment was found to be useful to reduce porosity. The cold-sprayed substrate-heated Ni–20Cr deposits exhibited excellent oxidation resistance at a high temperature of 900 °C.

Hybrid machine learning-based prediction model for the bond strength of corroded Cr alloy-reinforced coral aggregate concrete

This study investigated the bond–slip behavior between newly developed Cr alloy steel bars and coral aggregate concrete (CAC) on the basis of experimental and hybrid machine learning. Several variable parameters were examined: (a) corrosion ratio, (b) diameter, (c) CAC strength, (d) anchorage length, and (e) relative protective layer thickness. Results showed that bond strength is positively correlated with relative protective layer thickness and CAC strength, whereas it is negatively correlated with diameter and anchorage length. The bond strength initially rose and subsequently fell as the corrosion ratio increased, with a critical threshold of 1%. The bond–slip curve of Cr–CAC had four stages: microslip, slip, declining, and residual stages. Additionally, the empirical, particle swarm optimization backpropagation (PSO-BP), BP, and support vector machine regression (SVR) models were evaluated using various performance evaluation metrics. The PSO-BP model outperformed the empirical, BP, and SVR models in all evaluation metrics. Compared with the PSO-BP model, the BP and SVR models had a 6.12% and 2.0% reduction in R2, 87.67% and 58.90% increase in root mean square error, 52.27% and 4.54% increase in mean absolute error, 254.72% and 152.83% increase in mean square error, and 76.52% and 52.22% increase in mean absolute percentage error, respectively. The PSO-BP model established in this research can quickly and accurately predict the bond strength of corroded Cr–CAC, providing a rapid assessment method for its application.

Mechanical properties and biocompatibility of various cobalt chromium dental alloys

Cobalt-based metal alloys are often used in dentistry for prosthetic restorations because of their considerable wear and corrosion resistance. For this reason, the effect on the human body of three Co–Cr based alloys, named "Co–Cr", "C" and "L", differing in their concentrations, for subsequent use as dental materials, has been studied and compared. Metallographic observations of the microstructure, electrochemical and three-point bending tests were performed. The metallographic investigations showed similar dendritic microstructure of the Co–Cr and L dental alloys, as well similar porosities and defects. From the corrosion and pitting potential tests, it was found that the samples show surface passivation, reaching closed corrosion potential values from −0.280 V vs SCE to −0.250 V vs SCE. The Pitting Resistance Equivalent Number (PREN) values are above 38 for all the samples, which means that the studied alloys have a high resistance to pitting corrosion. Likewise, when applying the Electrochemical Impedance Spectroscopy technique, a slightly higher corrosion resistance was observed for sample L, since corrosion resistance tends to increase as the applied potential is more positive and as the impedance and phase angle values are higher. Moreover, in the three-point bending test, the alloy C presents the lowest values of the elastic modulus of 134 ± 13 GPa. The analyzed Co–Cr alloys are recommended for the efficient treatment of patients with dental prostheses that have metal frameworks, as shown by all of the obtained results.

Semisolid-Liquid Fabrication of Cu–Cr Pseudobinary Alloy by Laser-Directed Energy Deposition

Copper–Chromium (Cu–Cr) pseudobinary alloys are promising materials for electrical application. Nevertheless, their fabrication remains limited by traditional techniques, which are not suitable for manufacturing homogeneous Cu–Cr alloys with uniformly distributed elements. Recently, semisolid-liquid manufacturing method has emerged as a promising technique route to fabricate Cu–Cr alloys. In this work, the laser-directed energy deposition (L-DED) as one of the laser additive manufacturing (LAM) technology, was successfully introduced for semisolid-liquid fabricating the homogeneous Cu–30 mass%Cr alloys. The obtained Cu–Cr alloys are constituted by fully melted Cu metallurgically combined with semisolid-liquid Cr. The close combination of Cu and Cr is benefit to improve the electrical conductivity of the alloy.

Design and mechanical properties of body-centered cubic AlVCr medium-entropy aluminum alloys

The formation of brittle intermetallic compounds and the poor solubility of other metallic elements in Al alloys render the design of high- and medium-entropy Al alloys (HEAls and MEAls, respectively) challenging. Herein, new AlVCr MEAls were developed based on a reverse approach, which involved starting from an equiatomic V–Cr alloy. Al20VCr, Al33VCr, and Al50VCr were synthesized as MEAls using a vacuum induction-based melting process. The microstructural evolution and mechanical properties of the synthesized MEAls were carefully investigated. Body-centered cubic single-phases formed in Al20VCr and Al33VCr MEAls, in keeping with thermodynamic calculation results as well as multiple phase-prediction parameters. While Al33VCr exhibited brittle fracturing owing to chemical ordering, Al20VCr MEAl exhibited a compressive strain and yield strength of ∼9.4% and ∼1.0 GPa, respectively. Thus, the reverse approach, which is based on the use of an Al-free system initially, should aid the development of a new class of lightweight HEAls and MEAls.

Development of Rotor Core with High Magnetic Flux by Partial Non-Magnetic Improvement of Silicon Steel

Flux leakage in the rotor core bridges is a problem specific to interior permanent magnet motors and has been unsolved till date. It is widely known that if the bridges are partially non-magnetically improved with low magnetic polarization, the leakage flux will be smaller, and the rotor will have a higher magnetic flux. We proposed that the portion of the silicon steel sheets that becomes the bridge after pressing can be non-magnetized and laminated to fabricate the rotor core. Partially non-magnetic material with a polarization of almost zero was obtained by melting and mixing Ni–Cr alloy powder with the silicon steel sheets. This non-magnetic improvement treatment was applied to the bridge in the rotor core sheet, in which the non-magnetic area width was 1.45 mm, and the prototype rotor core was fabricated by laminating 60 rotor core sheets. Upon measurement, the rotor core showed approximately 35% higher magnetic flux than a conventional one, with the actual value nearly identical to that obtained from the magnetic field analysis.

A Study of the Structural and Energy Properties of (210) and (130) Boundaries in Iron and an Fe–Cr Alloy

The structure and energy properties of symmetric tilt boundaries Σ5 (130)[001] and Σ5 (210)[001] in iron and low-concentration Fe–Cr alloys are investigated from first principles and by the molecular statistics method. It is shown that the boundary strongly changes the interplane distances. The sequence of multilayerrelaxation comprises damped oscillations, gradually decreasing into the grains. The energy for the replacement of iron with chromium atoms near the boundaries is lower than in pure iron. Our calculations indicate the tendency to accumulate Cr atoms and vacancies near the grain boundaries.

A Study of the Structural and Energy Properties of (210) and (130) Boundaries in Iron and an Fe–Cr Alloy

A Study of the Structural and Energy Properties of (210) and (130) Boundaries in Iron and an Fe–Cr Alloy

Mechanical Properties of Ti–5Al–5V–5Mo–3Cr Alloy Sintered From Blended Elemental Powders

The field-assisted sintering technique (FAST) was successfully used to sinter, homogenize, and age the Ti–5Al–5V–5Mo–3Cr (Ti-5553) aerospace alloy from blended elemental powders in a single processing run. Sintering at a comparatively high temperature of 1500 °C assured chemical homogeneity of the material. Subsequently, without cooling to the room temperature, the temperature was lowered to 600 °C for 30 min to provide annealing treatment and to produce a desired lamellar α + β microstructure. Using an in-house designed assembly, a fully dense rod of 15 mm in diameter and 70 mm in length was successfully sintered. Microstructural and mechanical properties of the alloy were investigated and compared with the conventionally processed Ti-5553 alloy. A good combination of strength (1183 MPa) and ductility (6 pct) was achieved; these values are fully comparable to the conventional cast, forged, and aged Ti-5553 alloy. It was shown that homogeneous Ti-5553 alloy can be produced by FAST, FAST can instantly provide necessary annealing steps, and the FAST process can be upscaled to produce homogeneous rods.

Interfacial compatibility and thermal cycle stability for glass-sealed oxygen sensors

The oxygen sensors are extensively utilized in vehicles’ exhaust systems to monitor gases composition and control air-to-fuel ratio, thus reducing harmful emission and improving fuel economy. In equilibrium potentiometric sensors, the sealing performance is essential to ensure data accuracy. In this work, the 64SiO2–18TiO2–10Na2O–7K2O–1Al2O3 (wt%) glass was utilized as seals instead of traditional talcum in zirconium dioxide oxygen sensor. The interfacial compatibility with adjacent components (Fe–16Cr, Al2O3 and 8YSZ) and thermal cycle stability of seals were seriously evaluated in various ways. The equilibrium contact angles were lower 60° at high temperature, exhibiting better wettability and tight bonding at the interface. Besides, the leakage rates between glass and Fe–16Cr alloy were less than 0.01 sccm/cm at 650–800 °C and input gas pressures of 6.9–34.5 kPa. The oxygen sensor coupled with glass exhibited better thermal stability that leakage rate maintained around 0.004 sccm/cm under an input gas pressure of 200 kPa during 100 thermal cycles. Additionally, the oxygen sensor with sealed glass can generate continuous response and recovery, which is better than sealed talcum. Owing to these good performance, the glass is a suitable alternative for oxygen sensor sealing.