Cr Alloy Research Articles

Improved microstructure, mechanical properties and electrical conductivity of the Cu–Ni–Sn–Ti–Cr alloy due to Ce micro-addition

In this paper, new Cu–Ni–Sn–Ti–Cr and Cu–Ni–Sn–Ti–Cr–Ce alloys were prepared and studied. After solution treatment and 60% cold rolling, the Cu–Ni–Sn–Ti–Cr alloy with micro-hardness of 221 HV, a tensile strength of 598.1 MPa, elongation of 9.9% and electrical conductivity of 45.2% IACS was obtained after aging at 500 °C for 60 min. Furthermore, the new Cu–Ni–Sn–Ti–Cr–Ce alloy was also obtained using aging at 500 °C for 60 min, having 245 HV micro-hardness, 645.2 MPa tensile strength, elongation 9.4% and 44.6% IACS conductivity. The comprehensive properties of high strength, hardness, and electrical conductivity of the alloy are attributed to the composite effects of solution, deformation, grain boundary, and precipitation strengthening. Among them, precipitation strengthening plays a major role, and the precipitates are mainly nanometer CuNi2Ti, Cr, and NiTi phases. The interface between the nanometer CuNi2Ti phase and Cu matrix is a coherent, which can improve the strength of the alloy without sacrificing plasticity. In addition, texture type transformation and texture strength change of the alloy are closely related to the increase of micro-hardness. The micro-addition of trace rare earth Ce can refine the alloy grains, and promote dynamic recrystallization to produce finer grains, significantly improving the alloy’s micro-hardness.

Atomic diffusion, segregation, and grain boundary migration in nickel-based alloys from molecular dynamics simulations

Grain boundary diffusion and metal mobility in alloys control material performance in many applications and yet remain poorly understood at a mechanistic level. With advances in accessible time and length scales for computational molecular simulations, and recent force field developments, we now possess tools to help unravel those mechanisms. Using large-scale molecular dynamics simulations, here we examined vacancy-mediated diffusion processes in Ni-5Cr alloy with low and high-energy grain boundaries. We show that atomic diffusion inside the grain boundary plane is about four times higher than bulk diffusion, at any temperature, and exhibits a typical Arrhenius behavior with a very small energy barrier (∼0.8 eV for Cr and 0.7 eV for Ni within 1300–1600 K). Additionally, the fastest diffusing species inverts; Cr diffusion was faster than Ni in the bulk but slower in the grain boundaries. This is attributed to the creation of high cohesive energy clusters of Cr at the grain boundary. Grain boundary migration was also observed to be temperature dependent and appears to be two times higher in the 5% Cr alloy than in pure Ni, highlighting the important role of the alloying element on grain boundary motion.

Study on finishing inner wall of Co[sbnd]Cr alloy cardiovascular stent tube via novel atomized CBN/metal spherical magnetic abrasive powders

In this study, in order to solve the problem that the inner wall of the cardiovascular stent is difficult to polish, the magnetic abrasive finishing (MAF) method is used to finish the inner wall of the CoCr alloy tube that is used for the manufacture of the cardiovascular stent. The surface defects such as wrinkles, cracks and pits generated in the production process are removed, and the internal surface roughness is decreased to obtain better surface quality. Firstly, aiming at the problem of poor performance of traditional magnetic abrasive powders (MAPs), “gas-solid two-phase double-stage atomization and rapid solidification” is proposed and a novel atomized CBN/metal spherical MAPs with different sizes are successfully prepared. This MAP is used for MAF of the inner wall of CoCr alloy cardiovascular stent. Secondly, the slotted magnetic pole is designed according to the numerical simulation, and the MAF setup for the inner wall of ultra-fine and ultra-long tubes is developed. Finally, the orthogonal experiment is carried out with surface roughness as the evaluation index. Through the analysis of range theory, the order of the apparent degree of each process parameter on surface roughness is as follows: tube rotational speed > feed speed of magnetic pole > MAPs filling quantity > MAP particle size. According to the result, a model of surface roughness prediction based on whale optimization algorithm (WOA) and least squares support vector machine (LSSVM) is constructed. The interaction between tube rotational speed and other process parameters is analyzed based on the model fitting results, and the process parameters are optimized. The result show that MAF technology can effectively remove the defects of the inner wall of the CoCr alloy cardiovascular stent tube and accurately predict the surface roughness. After MAF under the optimized process parameters, the surface roughness Ra decreases from 0.485 μm to 0.092 μm.

Portable nanosecond laser for handheld laser-induced breakdown spectroscopy instruments

The portable laser is indispensable for handheld laser-induced breakdown spectroscopy (LIBS) instruments. We developed a passive, Q-switched pulsed, Nd:YAG laser system with small size and low cost. The maximum pulse energy of the laser was 10 mJ and the pulse duration was <2 ns. The peak power was >5 MW. The laser exhibited very high stability without any cooling system and its relative standard deviation of the pulse energy was <0.2 % . The laser was also used as a light source of LIBS to measure the concentrations of Cr, Cu, Mn, and Ni in alloys. The experimental results show that the determination coefficient of the calibration curves for these four elements is all better than 0.99. For its shorter pulse duration, the laser can decrease the plasma shield effect to improve the coupling of laser pulse and the target and stability of spectra intensity. The portable laser developed is a good laser source for handheld LIBS instruments.

Mechanical comparison of milled fiber-reinforced resin composite and Co–Cr frameworks with different connector cross-sectional geometries: An in vitro study

This study compared the effect of using milled fiber-reinforced resin composite and Co–Cr (milled wax and lost-wax technique) frameworks for 4-unit implant-supported partial fixed dental prostheses; and also, evaluated the influence of the connector's cross-sectional geometries on the mechanical behavior. Three groups of milled fiber-reinforced resin composite (TRINIA) for 4-unit implant-supported frameworks (n = 10) with three connectors geometries (round, square, or trapezoid), and three groups of Co–Cr alloy frameworks manufactured by milled wax/lost wax and casting technique, were analyzed. The marginal adaptation was measured before cementation using an optical microscope. Then, the samples were cemented, thermomechanical cycled (load of 100 N/2 Hz, 106 cycles; 5, 37, and 55 ᵒC, a total of 926 cycles at each one), and cementation and flexure strength (maximum force) analyzed. Analysis of stress distribution in framework veneered considering resin and ceramic properties for fiber-reinforced and Co–Cr frameworks, respectively, implant, and bone was by finite element analysis under three contact points (100 N) on the central region. ANOVA and Multiple paired test-t with Bonferroni adjustment (α = 0.05) were used for data analysis. Fiber-reinforced frameworks showed better vertical adaptation (mean ranged from 26.24 to 81.48 μm) compared to the Co–Cr frameworks (mean ranged from 64.11 to 98.12 μm), contrary to horizontal adaptation (respectively, means ranged from 281.94 to 305.38 μm; and from 150.70 to 174.82 μm). There were no failures during the thermomechanical test. Cementation strength showed three times higher for Co–Cr compared to fiber-reinforced framework, as well as flexural strength (P < .001). Regarding stress distribution, fiber-reinforced had a pattern of concentration in the implant-abutment complex. There were no significant differences in stress values or changes observed among the different connector geometries or framework materials. Trapezoid connector geometry had a worse performance for marginal adaptation, cementation (fiber-reinforced 132.41 N; Co–Cr 255.68 N) and flexural strength (fiber-reinforced 222.57 N; Co–Cr 614.27 N). Although the fiber-reinforced framework showed lower cementation and flexural strength, considering the stress distribution values and absence of failures in the thermomechanical cycling test, it can be considered for use as a framework for 4-unit implant-supported partial fixed dental prostheses in the posterior mandible. Besides, results suggest that trapezoid connectors mechanical behavior did not perform well compared to round or square geometries.

Friction and dry sliding wear of Al–Fe–Cr quasicrystals with multi-reinforcements by laser powder bed fusion

A specially designed Al–Fe–Cr alloy with a rapid solidification-induced multi-scaled heterogeneous composite structure was manufactured using a laser powder bed fusion (LPBF) process with a high relative density (over 99.7%) and defect-free features. From the aspect of a single molten pool, the LPBF processed sample presents three regions with distinct composite structures: i) inner laser fusion zone (LFZ); ii) molten pool boundary (MPB) and iii) heat-affected zone (HAZ). For instance, spherical Al–Fe–Cr quasicrystals with sizes ranging from 100 to 300 nm inside ultrafine cellular structures are observed in the laser fusion zone. In contrast, the molten pool boundary exhibits a microstructure containing coarse flower-like quasicrystal particles and rectangular θ-Al13(Fe, Cr)2-4 particles. Moreover, the finer reinforcements in the heat-affected zone are spherical, rectangular or structureless and disperse in the α-Al matrix. This heterogeneous structure can be attributed to the graded temperature and solidification rate inside a single molten pool during LPBF processing. The tribological performance of the QC-reinforced aluminum matrix nanocomposites was comparatively investigated on a ball-on-disc reciprocating tribometer (UMT Tribo), in which the coefficient of friction was recorded. The results show that the LPBF-processed sample presents a stable friction coefficient (0.548) from mild to severe loads with a higher wear resistance of 3.704 × 10- 4mm3/(N*m) than the other LPBF-processed Al alloys. The worn surface morphology analysis shows that the wear mechanism presents a duplex wear mechanism of adhesive and oxidation wear.

Hot compression deformation behaviour and microstructure evolution of Ti-3.5Al-3.5V-0.5Fe-0.6Mo-0.5Cr alloy

Ti-3.5Al-3.5V-0.5Fe-0.6Mo-0.5Cr alloy is a new superplastic titanium alloy The alloy was deformed by plane strain compression at 820°C~880°C, 0.16 s−1~8 s−1, which can provide reference for obtaining homogeneous microstructure during the rolling process. The results show that the flow stress of the alloy has a negative correlation with the deformation temperature and a positive correlation with the strain rate. The flow softening behavior of alloy is greatly influenced by deformation temperature. The fraction and the length of α lamellar increase with the decrease of temperature, and the flow-softening phenomenon of the alloy is more obvious. The homogeneity of microstructure and the recrystallization ratio of α lamellae increase with the increase of deformation temperature and the decrease of strain rate. The alloy can obtain homogeneous microstructure at 850°C, 0.16 s−1, and 880°C, 0.16 s−1~1.6 s−1 deformation conditions.

The roles of solidification cooling rate and (Mn,Cr) alloying elements in the modification of β-AlFeSi and hardness evolvements in near-eutectic Al-Si alloys

High recycling rates worldwide underline the economic and environmental value of aluminum scrap. However, several alloying elements in recycled Al negatively affect the final properties of castings, among which Fe has the most permissive effect on the mechanical properties. The extremely restricted solid solubility of Fe in Al leads to the formation of brittle Fe-containing intermetallic compounds (IMCs), and a possible strategy is to use modifiers of harmful IMCs by alloying. The present work aims to investigate the substitutional characteristic of Fe, Mn, Cr in the α-IMC taking the Al-12 %Si alloy as a reference, i.e., by analyzing the directional solidification (DS) of binary (Al-12 %Si), ternary (Al-12 %Si-1 %Fe) and quaternary (Al-12 %Si-1 %Fe-1 %Mn and Al-12 %Si-1 %Fe-0.6 %Cr) alloys. For all DS alloys castings, the macrostructure is shown to be characterized by columnar grains associated with solidification cooling rates (Ṫ) from 0.4 to 42.3 °C/s. The microstructure of the four alloys examined is shown to be typified by an α-Al dendritic matrix with interdendritic regions formed by α-Al, Si and different IMCs, which have been characterized and associated with the local Ṫ. The evolvement of iron-containing IMCs morphologies according to the addition of alloying elements in Al-Si alloys, is as follows: plate-like for Fe, plate-like and Chinese script for Mn, and fishbone and trefoil/blocky for Cr. Experimental power laws equations are determined relating the primary (λ1), secondary (λ2) and tertiary dendritic arm spacings (λ3) to Ṫ, for any experimentally examined DS alloy casting. The microhardness (HV) of the alloys is correlated with λ3 and Hall-Petch type equations are derived relating HV to both λ3 and Ṫ. The Al-12 %Si-1 %Fe-0.6 %Cr alloy achieved the highest HV among all the alloys examined.

Influence of Cr and Ni elements on the electrochemical and early corrosion behavior of FeMnAlC low-density steel

FeMnAlC low-density steel (LDS) is considered to be a promising material due to its good mechanical properties and light weight, its corrosion resistance, however, needs to be improved. In this paper, the effect of Cr and Ni on the electrochemical and early corrosion behavior of a Fe–25Mn–10Al–1.5C LDS in a 3.5% NaCl solution was studied through microstructure characterization, electrochemical tests and immersion tests. The results showed that Cr and Ni alloying reduced the austenite grain size and promoted the formation of the B2 phase. Adding 2% Cr or Ni to the Fe–25Mn–10Al–1.5C LDS clearly inhibited the electrochemical activity and initial micro galvanic effect between the second phases and the austenite. Moreover, the properties of the corrosion product film were optimized, and the local corrosion process beneath the product film was mitigated. Compared with 2% Cr addition, 2% Ni addition improved the corrosion resistance of the FeMnAlC LDS better from the aspects of electrochemistry, corrosion product film and corrosion mode.

Fabrication and mechanical properties of Bi-added Ti–Cr alloys for biomedical applications

The potential of the Bismuth (Bi) addition was evaluated for the development of biocompatible metastable β (bcc) Ti alloys from the viewpoints of mechanical properties and phase stability. The basic alloy was Ti–5 mol% Cr, and 0–9 mol% Bi was added in nominal composition. A Ti–Bi binary alloy was also selected. The alloys were fabricated using a standard laboratory-scale arc melting machine under an Ar atmosphere. The weight loss was significant during melting due to Bi evaporation. The measured Bi content is linearly proportional to the Bi nominal composition with MCBi = 2/3 NCBi, allowing the prediction and control of Bi content of the alloy. Then, the microstructure, workability, and mechanical properties were systematically investigated. The phase constitution of the Ti–5Cr binary alloy was β + α′ (hcp) + ω (hexagonal). The presence of the athermal ω phase resulted in significantly poor cold workability and poor ductility. It was also found that the addition of Bi to the Ti–5Cr alloy stabilized the β phase and suppressed the ω phase formation. The phase stability of Ti–Cr–Bi alloy is discussed using Mo equivalent and electron-to-atom (e/a) ratio. Ti–5Cr–1.6Bi alloy showed improved workability and ductility. However, with further increasing Bi addition, the Ti–5Cr–3.7Bi alloy showed no plastic deformation, and the Ti–5Cr–6.1Bi alloy was broken even during hot-rolling. Thus, it is concluded that ∼2 mol% Bi addition is suitable and that such a small amount of Bi addition is an attractive candidate for the development of β Ti alloys.

Influence of Cr-content on the local atomic structure of Fe–Cr alloy, a study using EXAFS

High Cr ferritic/martensitic steels are considered one of the most promising structural materials for advanced nuclear power plants. Therefore, understanding properties' evolution under operation conditions is of primary importance. Neutron scattering data and more recent ab initio calculations reveal that magnetism controls the transition from the local short-range ordering of the Cr clustering inside the alloy. The transition coincides with the change in the alloy heat of formation, which shifts from a small area with negative values to a region of positive values at around 10% Cr. This work aims to investigate the effect of Cr composition on the local atomic environment of Fe–Cr alloys. This work employed EXAFS to probe the local environment of Fe–Cr alloys as a function of Cr composition. The results show the anomaly (softening) of the nearest neighbor distance around Cr atom in the 10%Cr. Furthermore, the local atomic disorder around Cr absorbing atoms is larger than Fe atoms.

Nb modified Ti-5553 alloy: Effects of heating rate on mechanical properties, corrosion behavior, and crystallographic texture

Ti–5Al–5Mo–5V–3Cr (Ti-5553) is a metastable β-type Ti alloy with excellent hardenability and high mechanical strength designed for aerospace applications. Previous studies have shown that the replacement of V with Nb, resulting in a Ti–12Nb–5Al–5Mo–3Cr (Ti-12553) alloy, can enhance the mechanical strength and hardenability. This study focuses on exploring the effects of V replacement with Nb in this alloy, aiming to evaluate the effects of the aging heating rate during aging heat treatment on the microstructure and its effect on hardness, tensile and compression strengths, corrosion resistance, and crystallographic texture development. The Ti-5553 and Nb-modified Ti-5553 (Ti-12553) alloys aged at 600 °C for 2 h resulted in a microstructure formed by α precipitates in a β matrix, with larger precipitates at a faster heating rate. This effect was more pronounced for the Ti-5553 alloy. The coarsening microstructure affected the mechanical behavior by decreasing the mechanical strength (hardness, ultimate tensile strength, and yield strength) while improving ductility and intergranular fracture mode in combination with a smaller region containing dimples. A decrease in hardness was observed at a faster heating rate, but it was still superior to that of the solution heat-treated samples. The textures formed in both alloys were similar and lacked any strong components. The replacement of V with Nb and the microstructure produced after aging heat treatment did not affect the samples’ corrosion resistance in a 3.5% NaCl solution. A stable passive protective layer with noble corrosion potential and reduced corrosion current density was observed.

Nucleation-Growth Versus Spinodal Decomposition in Fe-Cr Alloys: An Experimental Verification by Atom Probe Tomography and Small Angle Neutron Scattering.

Identifying the operative mode of phase separation [spinodal decomposition (SD) or nucleation-growth (NG)] remains an extremely important area of research. The present work examines this critically in the Fe-Cr system using atom probe tomography (APT) and small angle neutron scattering (SANS), and establishes the framework to distinguish the two different modes of α' phase separation in thermally aged Fe-35 at% Cr and Fe-20 at% Cr alloys. Independent APT analysis determines the mode of phase separation on the basis of (i) the presence/absence of periodic chemical fluctuation through radial distribution function analysis and (ii) interphase interface characteristics (diffuse/sharp). SANS analysis, in contrast, yields virtually indistinguishable correlation peaks for both the modes, which necessitates further investigation of the several different aspects of SANS profiles in the light of APT results. For the first time, key features of SANS profiles have been identified that can unambiguously distinguish SD from NG in the Fe-Cr system: (i) nature of temporal evolution of FWHM of the correlation peak and (ii) appropriate value of γ for fitting with the dynamic scaling model (γ = 6 for SD, Fe-35 at% Cr alloy; γ = 4 for NG, Fe-20 at% Cr alloy).

Solute trapping and solute drag during non-equilibrium solidification of Fe–Cr alloys

During additive manufacturing (AM), velocities of solid–liquid interfaces are on the order of 0.01−1m⋅s−1. Thus, local interfacial equilibrium may not be present. Molecular dynamics (MD) and Monte Carlo methods are employed to extract thermodynamic properties for a Fe–Cr binary alloy and the parameters that characterize the departure from interfacial equilibrium for velocities present during AM. The Gibbs free energies of the BCC, FCC, and liquid phases are determined and used in a partial-solute-drag model that self-consistently describes non-equilibrium solute trapping and solute-drag behavior. The partial-solute-drag model describes well the interfacial velocities as a function of supersaturation in the liquid and the velocity dependence of the partition coefficient. The maximum possible velocities, v0 of the solid/liquid interfaces are determined, with v0 of the stable BCC phase being higher than the metastable FCC phase, but both values are significantly lower than the reported speed of sound. Additionally, the partial-solute-drag model yields a trans-interface diffusivity much different from that of more classical models and very close to that measured in the MD simulations.

Feasibility of a Low-Power, Low-Resolution Laser-Induced Breakdown Spectroscopy Instrument for Analysis of Nickel Alloys: Quantification of the Major Alloying Elements and Classification.

A simple cost-effective laser-induced breakdown spectroscopy (LIBS) instrument was used for quantification of major elements in several nickel alloys and also sorting them. A compact low-power diode-pumped solid-state laser and a miniature low-resolution spectrometer were assembled for the LIBS instrument. Material properties of the nickel alloys depend mainly on the composition of the major elements, Ni, Cr, and Fe, ranging from a few to ∼60 wt%. The emission peaks at 547.7 nm, 520.4 nm, and 438.1 nm for Ni, Cr, and Fe, respectively, were chosen for this analysis. The analytical performance was found to be enough for the quantification of Ni, Cr, and Fe in the nickel alloys. Limits of detection and accuracy were estimated to be a few weight percent (wt%) and measurement precisions were less than 10% in terms of relative standard deviation. The calibration performance of this intensity-based method was compared with that of the "ratio method" which is used in conventional optical emission spectroscopy analyses. The comparison indicates that the intensity-based method is more appropriate with the low-performance LIBS instrument that detects emission peaks of only a few major elements. Also, multivariate modeling of the six different nickel alloy samples based on the emission peak intensities of Ni, Cr, and Fe was performed using k-nearest neighbors (KNN) and linear discriminant analysis (LDA). The KNN and ordinary LDA models showed 95.0% and 98.3% classification correctness for the separate test data set, respectively. To improve classification performance further, the two-step LDA model was trained. In this approach, the two closest sample classes responsible for the decrease in the classification correctness were separately modeled in the second step to exploit their difference effectively. The two-step LDA model showed 100% correctness in classifying the test objects. Our results indicate that such a low-performance LIBS instrument can be effectively utilized for quantitative analysis of the major elements in the nickel alloys and their rapid identification or sorting in combination with an appropriate multivariate modeling algorithm.

Ultra-wideband low-reflectance spinel films with nanostructure prepared by in-situ one-step hydrothermal method

The ultra-wideband low-reflectance materials are ideal core materials for advanced optical instruments, which are difficult to synthesize at present. Herein, in-situ one-step hydrothermal method was firstly introduced to prepare spinel films with nanostructures on low-cost Fe–Cr alloy substrates. The film shows excellent low reflectance in the range of 0.3–2.5 μm and 2.5–13 μm, which are 4.34% and 4.99% respectively, due to the uniform nano-micron structure on surface. The synthesized spinel film can be an ideal candidate ultra-wideband low-reflectance material for improving high-precision for optical instruments.

On the phase transformation pathway during localized grain boundary oxidation in an Fe-10 at% Cr alloy at 200ºC

We have performed short-term, controlled oxidation experiments of sputter deposited Fe-10 at% Cr alloy films at 200ºC. Nanoscale structural characterization by four-dimensional scanning transmission electron microscopy (4d-STEM) and chemical characterization by atom probe tomography (APT) have provided insights on the phase transformation pathway followed during localized, inward-progressing oxidation of grain boundaries at this low temperature. Direct nucleation of a metastable spinel-structured oxide, with suppression of the corundum-structured Cr2O3 has been observed even at the early stages. A ‘partitioning-free oxide nucleation mechanism’ under conditions of extremely restricted kinetics is proposed to explain the non-equilibrium transformation pathway.

Interfacial Engineering Strategies for Efficient Spin–Orbit Torque Devices with Pt Alloys

To make spin–orbit torque magnetic random-access memories (SOT-MRAMs) become competitive enough to replace the contemporary memory architecture, it is of great importance to utilize conductive SOT materials that possess large damping-like spin–orbit torque (DL-SOT) efficiencies and back-end-of-line (BEOL) compatibility. In this work, we report a BEOL-compatible CoFeB/MgO-based heterostructure with the Pt–Cr alloy as the spin current source (SCS) and inserted a Pt/Co/Pt composite layer to achieve texture decoupling and ferromagnetic coupling. A thermally robust perpendicular magnetic anisotropy (PMA) of the hybrid heterostructure can be retained after annealing at 400 °C for 1 h, while maintaining large DL-SOT efficiencies of the annealed Pt–Cr alloys (ξDL ∼ 0.34 for Pt0.70Cr0.30). Additionally, by optimizing the current distribution with a resistive Pt spacer layer, it is possible to simultaneously enhance the current-to-effective field conversion ratio (Hzeff/I) and retain the apparent ξDL (ξDL ∼ 0.37 for Pt0.79Cr0.21). Moreover, the critical switching current density can be reduced from JcPt ∼ 2.0 × 107 A·cm–2 for Pt to JcPt0.70Cr0.30 ∼ 4.9 × 106 A·cm–2 for Pt0.70Cr0.30 without tampering the thermal stability of the annealed heterostructure. These interfacial engineering strategies provide directions to integrate Pt-based SCSs with large ξDL into a BEOL-compatible platform for future SOT-MRAM devices with PMA.

Surface modifications of biodegradable AZ31 alloy after immersion in physiological solution

Internal prosthesis and grafts are currently made of Ti alloys, stainless steels and Co–Cr alloys. In spite of excellent biocompatibility, they show some drawbacks that concern their mechanical properties (e.g. elastic modulus) and the need of secondary surgery for removing the implant. For this reason, a growing attention has been focused on biodegradable materials that can be absorbed into the body after tissue remodelling. In particular, Mg alloys are promising candidates for temporary implants thanks to their high biocompatibility, biodegradability and good mechanical properties that match those of human bone. In this work, the surface modifications of biodegradable AZ31 alloy were analysed after immersion for 15 days in a physiological solution (NaCl 0.09%) by using X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. XPS analysis of the surface of as‐supplied AZ31 alloy showed the presence of MgO, whereas after immersion in the physiological solution, only Mg (OH)2 was detected. The result has been discussed with reference to literature data. From the photoemission spectra and quantitative analysis, a small amount of Ca (about 2 wt%) was also detected.

Elastic Strain Relaxation of Phase Boundary of α' Nanoscale Phase Mediated via the Point Defects Loop under Normal Strain.

Irradiation-induced point defects and applied stress affect the concentration distribution and morphology evolution of the nanophase in Fe-Cr based alloys; the aggregation of point defects and the nanoscale precipitates can intensify the hardness and embrittlement of the alloy. The influence of normal strain on the coevolution of point defects and the Cr-enriched α' nanophase are studied in Fe-35 at.% Cr alloy by utilizing the multi-phase-field simulation. The clustering of point defects and the splitting of nanoscale particles are clearly presented under normal strain. The defects loop formed at the α/α' phase interface relaxes the coherent strain between the α/α' phases, reducing the elongation of the Cr-enriched α' phase under the normal strains. Furthermore, the point defects enhance the concentration clustering of the α' phase, and this is more obvious under the compressive strain at high temperature. The larger normal strain can induce the splitting of an α' nanoparticle with the nonequilibrium concentration in the early precipitation stage. The clustering and migration of point defects provide the diffusion channels of Cr atoms to accelerate the phase separation. The interaction of point defect with the solution atom clusters under normal strain provides an atomic scale view on the microstructure evolution under external stress.