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Inferior absolute strength and dissolution properties are the main bottlenecks for the widespread application of dissolvable magnesium alloys in complex working environments for unconventional oil and gas resources. Here, a novel functional peak-aged Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.4Ni (wt.%) alloy for fracturing tools is reported, and it possesses an ultimate tensile strength of 457.6 MPa, ultimate compressive strength of 620.7 MPa and dissolution rate of ∼43.7 mg·cm−2·h−1 in 3 wt.% KCl solutions at 93 °C. The excellent strength of the aged-alloy is primarily attributed to the combination of grain refinement, long-period stacking ordered (LPSO) strengthening, and precipitation strengthening induced by stacking fault and β' phase, among which the precipitation strengthening is dominant. Further investigations confirm that the corrosion is triggered from the micro-galvanic coupling between the Mg matrix and the cathodic lamellar and block LPSO phases. Strip-shaped corrosion pits along with LPSO phases are subsequently formed, significantly accelerating corrosion. The β' precipitates can effectively improve the strength without compromising the dissolution rate because of their nanoscale size. This study provides an excellent material selection for dissolvable fracturing tools and presents a strategy by which a synergistic combination of strength and dissolution rate is achieved via peak-aging treatment. [ABSTRACT FROM AUTHOR]

Magnesium alloys, a novel functional material for the fabrication of fracturing tools, are being paid more and more attentions recently due to their relatively high mechanical properties and fast dissolubility ability after fracturing. In this study, the novel extruded Mg–10Gd–3Y–0.3Zr–xNi alloys will be reported and their microstructure, mechanical and corrosion behaviors will be also studied. The results show that Ni contents influence phase precipitation behaviors. With adding 0.2 wt% Ni, a large amount of Zr 7 Ni 10 phases will be precipitated insides α-Mg matrix, directly leading to degradation of strength and large corrosion rate. With further increasing Ni contents, the precipitation phases can be changed from Mg 5 RE to 18R-LPSO structure, resulting in higher mechanical properties and faster corrosion rate. Moreover, adding Ni element also change the texture orientation by influencing the precipitation behavior of the alloys. The alloys invented in this paper have attained the highest compressive and tensile properties among all the reported dissoluble magnesium alloys. This work is beneficial in understanding the role of Ni in the magnesium alloys and provides more materials alternatives for the fabrication of dissoluble fracturing tools. [ABSTRACT FROM AUTHOR]

The influence of precipitation on the recrystallization nucleation and mechanical properties of Al-Mg-Si-Cu-Zn alloys was investigated by means of tensile tests, SEM, TEM, XRD and EBSD. The results reveal that there are distinct contributions from the various precipitates that form during annealing and that these critically influence the evolution of microstructure and its associated texture, as well as mechanical behaviour. In contrast to alloy sheets A, B, and C annealed at a lower temperature or for a shorter time, the T4P alloy sheet D with an annealing at 450°C for 3 h not only possesses almost identical strength and elongation, but also a higher average r (0.659) and n (0.313) values, and also a lower Δr (0.091) value. After solution treatment, the four alloy sheets are comprised of equiaxed grains with somewhat different grain sizes and different textures, but texture volume fraction and grain size in alloy sheet D both are decreased due to the effect of precipitate-assisted nucleation during solution treatment. The corresponding nucleation and growth mechanisms of recrystallization grains were established and the relationship between textures and r value in the four alloy sheets was also analyzed on the basis of a Visco-plastic self-consistent (VPSC) model. [ABSTRACT FROM AUTHOR]

Abstract: Two kinds of Mg-rich and low neodymium Mg–Zn–Nd alloys including icosahedral quasicrystal phase (I-phase) were prepared under conventional casting conditions. The microstructures and phases of Mg–Zn–Nd quasicrystal alloys were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The results indicate that the I-phase in Mg–Zn–Nd quasicrystal alloy is a simple icosahedral quasicrystal with quasi-lattice of aR =0.525nm. It has been proved that the as-cast Mg70.8Zn28Nd1.2 quasicrystal alloy mainly consisted of I-phase and Mg7Zn3 matrix phase. While the as-cast Mg70.5Zn28.5Nd1 alloy mainly consisted of I-phase, Mg7Zn3 matrix phase, dendrite α-Mg phase and a new rod-like hexagonal phase. [Copyright &y& Elsevier]

At Korea Atomic Energy Research Institute (KAERI), we investigated the corrosion behavior of a series of Fe–Cr–Ni alloys with different chromium contents in molten LiCl and molten LiCl–25wt%Li2O mixture at temperatures ranging from 923 to 1123 K. In molten LiCl, dense protective scale of LiCrO2 grows outwardly while corrosion is accelerated by addition of Li2O to LiCl. The basic fluxing of Cr2O3 by Li2O would be the cause of accelerated corrosion. Because of low oxygen solubility and very high Li2O activity in the molten LiCl–Li2O mixture, Cr is preferentially corroded while Ni remains stable and thus, corrosion rate of the alloys in molten LiCl–Li2O mixture increases with an increase in Cr content. [Copyright &y& Elsevier]

WNbMoTa refractory high entropy alloy (RHEA) with single BCC phase has high strength, high hardness and excellent high-temperature mechanical properties. However, the limited plasticity greatly affects its engineering applications. In this work, WNbMoTaZr x (x = 0.1, 0.3, 0.5, 1.0) RHEAs were prepared by vacuum arc melting. The microstructure, hardness, compressive properties and fracture behavior were characterized. The results have shown that WNbMoTaZr x RHEAs have a single BCC1 solid solution phase at low Zr content, and a second BCC2 phase appeared in the RHEAs with a higher Zr content. With the increase of Zr content, the microstructure of WNbMoTaZr x RHEAs changed to a typical dendrite structure, and simultaneously increase of strength, hardness and compressive plasticity was observed. The improvement of the mechanical properties was mainly attributed to the solid solution strengthening of Zr elements, the formation of more interdendritic regions, and the refinement of dendrite structures. The deformation mechanisms of the RHEAs with increased compressive plasticity were examined using step-by-step observations and discussed related to the evolution of microstructures. The results have shown that under applied loadings, deformation bands were initiated within the dendrite regions, while the propagation of deformation bands was impeded by interdendritic regions, resulting in significantly increased compressive plasticity. The fracture mode also changed from the intergranular fracture in WNbMoTa RHEA to the transgranular fracture in WNbMoTaZr 1.0 RHEA. The present work not only gives more insight into the strengthening and deformation mechanisms of the WNbMoTaZr x (x = 0.1, 0.3, 0.5, 1.0) RHEAs, but also explores the application potential of WNbMoTa-based RHEAs. ● Effect of Zr on the phase formation of the WNbMoTaZrx RHEAs was examined. ● Effect of Zr on the microstructure of the WNbMoTaZrx RHEAs was examined. ● Both strength and compressive plasticity were significantly improved. ● The deformation mechanisms were examined using step-by-step observations. [ABSTRACT FROM AUTHOR]

Developing alloys capable of withstanding high temperatures is crucial for modern engineering applications. Introducing multi-component alloys (MPEAs) has provided new strategies for designing high-temperature alloys. We have successfully prepared a series of AlCr x FeNi lightweight MPEAs in this study. The oxidation behavior of AlC x FeNi lightweight at 800 °C was investigated systematically through a combination of experimental methods and first-principles calculations. The microstructure characterization before oxidation reveals that the lightweight AlCr x FeNi MPEAs consist of BCC and B2 phases. In contrast, the AlCrFeNi alloy exhibited a microstructure characterized by typical eutectic features. Oxidation tests indicate that all three alloys exhibited oxidation kinetics following a parabolic law, with oxidation rates decreasing as the Cr content increased. Post-oxidation microstructural characterization revealed an oxide layer composed primarily of Al 2 O 3 and Cr 2 O 3 on the alloy surfaces. First-principles calculations provided insights into the microscopic mechanisms underlying the oxidation process. The results demonstrate that the adsorption energy of the O atom at the top position of the Cr atom is significantly lower than that of the Al atom at the top position. Electronic structure analysis shows that the Cr-O covalent bonding is stronger than the Al-O covalent bonding, which accounts for the oxidation resistance improvement as the Cr element content increases. This study advances MPEAs for high-temperature environments by elucidating these microscopic mechanisms. • The low-cost and lightweight anti-oxidation eutectic AlCrFeNi multi-component alloy has been successfully prepared. • The oxidation behavior of the AlCr x FeNi alloy at 800 °C has been systematically studied by first-principles calculation and experimental characterization. • First-principles calculations indicate that the increased oxidation resistance is due to the stronger bonding of the O-Cr bond as the content of chromium increases. [ABSTRACT FROM AUTHOR]

Abstract: Mg–Zn–Nd master alloy containing icosahedral quasicrystal phase with an interesting macro-shape has been prepared under conventional casting conditions. The microstructures and phases of Mg–Zn–Nd ternary alloy have been investigated by using SEM, EDS and TEM. The results show that the spherical phase in Mg–Zn–Nd master alloy is a simple icosahedral quasicrystal with stoichiometric composition of Mg40Zn55Nd5 and quasi-lattice a R =0.525 nm. In this research, when the content of Nd is 1.20 at.% and atom ratio value of Mg/Zn at the range of 2.4–2.7, the as-cast solidification microstructure mainly consists of primary I-phase and Mg7Zn3 single-phase matrix. [Copyright &y& Elsevier]

An innovative spray-deposition technique has been applied to produce in situ TiC/Al and TiC/Al–20Si–5Fe–3Cu–1Mg composites. This technique provides a new route to solve the problems of losses and agglomeration of the reinforcement particles when they are injected into the spray cone of molten droplets during spray forming process. Experimental results have shown that the presence of needle-like Al3Ti and Al–Si–Fe compounds, which are detrimental not only to the fracture toughness, but also to the stability of the microstructure, can be eliminated completely from the final product by using a proper Ti:C molar ratio of 1:1.3 in the Ti–C–Al preforms and adding 5 wt% TiC particles to Al–20Si–5Fe–3Cu–1Mg alloy. Moreover, another major problem of coarsening of silicon particles usually encountered in the hypereutectic Al–Si alloys has also been solved by the technique. The silicon particles in the spray-deposited 5 wt% TiC/Al–20Si–5Fe–3Cu–1Mg composite were much refined (∼2 μm) compared to those (∼5 μm) obtained in the matrix alloy without TiC addition. The formation and elimination mechanisms of Al3Ti phase in TiC/Al composites can be explained based on thermodynamic theory. The modification of the microstructures in the spray-deposited Al–20Si–5Fe–3Cu–1Mg alloy can be interpreted in the light of the knowledge of atomic diffusion. The experimental results also showed that the ultimate tensile strength of the TiC/Al composites was improved over that of the unreinforced Al matrix. [Copyright &y& Elsevier]

• La-Al-Cu alloys were employed for grain boundary diffusion for the first time. • Coercivity and thermal stability of NdFeB magnet are enhanced by La-Al-Cu diffusion. • Optimized microstructure after grain boundary diffusion is observed and confirmed. • Diffusion behavior and diffusion coefficients of La, Al and Cu are investigated. Different from many previous reports, La-Al-Cu alloys with different Al/Cu ratios containing only high abundant rare earth element La were employed for grain boundary diffusion treatment for sintered NdFeB permanent magnets. It is found that Al and Cu contents should be optimized to achieve coercivity enhancement. The coercivity of the magnet was enhanced from 1000 to 1006, 1077 and 1156 kA/m after La 70 Al 10 Cu 20 , La 70 Al 15 Cu 15 and La 70 Al 20 Cu 10 alloys diffusion, at 800 °C for 1 h followed by 500 °C for 3 h. The coercivity stability was also improved, indicated by the enhanced temperature coefficient of β from −0.63 to −0.61, −0.61 and −0.60%/K. Microstructure investigation indicates that the formation of continuous grain boundary phase after diffusion reduces the magnetic exchange interaction and contributes to the enhanced coercivity. After diffusion, the La 2 O 3 phase was observed in both the triple junction and strip grain boundary. La, Al and Cu elements showed different distributions in the magnets. The diffusion coefficients obtained from Fick's second law indicate that La diffuses faster than Al and Cu at 800 °C, which explains the various effects of the diffusion sources and different coercivity enhancements by the alloys with different Al/Cu ratios. Although the process should be further optimized, the current results demonstrate that the grain boundary diffusion using low cost La-Al-Cu alloys can improve the microstructure and enhance the coercivity of NdFeB magnets. [ABSTRACT FROM AUTHOR]

This study reports that Zn addition greatly enhances the bake-hardening response of an Al–Mg–Si–Cu alloy. The pre-aged alloy exhibits a high strength increment of 135 MPa after paint baking. Differential scanning calorimetry, atom probe tomography and high-resolution transmission electron microscopy reveal that Zn addition and pre-aging have significant effects on the solute nanostructure formation. Zn atoms partition into solute clusters/GP zones, and reduce the activation energy of β” precipitation in the alloy. [ABSTRACT FROM AUTHOR]

[Display omitted] • The η'-Mg(Zn,Cu) 2 precipitates with sizes less than 10 nm are out of electrochemical function at the initial pitting stage. • Grown η particle undergoes de-alloying and leaves a cathodic Cu/Zn-rich remnant promoting corrosion of the nearby alloy. • Localized Mg enrichment in the surface oxide film is observed on η' surface, even the thickness of η' is less than 2 nm. • A remarkable Mg-rich zone is found in the surface film above the larger η particle and the surrounding aluminum matrix. • The flawed structure in the Mg-rich oxide should be responsible for the insufficient protection of the material underneath. Precipitate-induced discontinuity of the surface oxide film is a significant reason for the increasing pitting susceptibility of age-hardening aluminum alloys but lacking of direct characterization. In the present work, the oxide film heterogeneity induced by Mg(Zn,Cu) 2 particles with different sizes in an Al-Zn-Mg-Cu alloy and the consequent corrosion behaviors were studied. Quasi in-situ transmission electron microscopy (TEM) observations indicated that the η'-Mg(Zn,Cu) 2 precipitates with sizes less than 10 nm were electrochemically inert, while the grown η particles underwent de-alloying and then promoted pitting events of the nearby alloy matrix. By means of cross-sectioning, it was revealed that the surface film on the solid solution and peak-aged alloys were structurally uniform although oxidation of the η' resulted in local Mg enrichment in the surface film. For the grown η particle, the Mg-rich zone was remarkable and covered not only the particle but also the surrounding alloy matrix. The flawed structure in the Mg-rich area should be responsible for the immediately de-alloying of the precipitate and then the corrosion attack of the peripheric alloy. [ABSTRACT FROM AUTHOR]

Abstract: High-intensity pulsed ion beam (HIPIB) treatment is a promising technology of surface modification. In this paper, the creep property of 316L stainless steel irradiated by HIPIB at incident energy fluence per shot of 1.1–3.4J/cm2 with 1–10 shots at 700°C have been studied. It is found that the creep property of the treated specimens after 10 shots fluctuates greatly with increasing energy density per shot. HIPIB irradiation at energy density of 1.1J/cm2 and 2.3J/cm2 prolong the creep rupture life and reduce the steady creep rate with respect to the original specimen. In contrast, HIPIB irradiation at 3.4J/cm2 proves to be detrimental, causing a shorter rupture life and a faster steady creep rate. Otherwise, at a fixed irradiation intensity of 2.3J/cm2 per shot, the number of shots has little effect on the creep property of the treated specimens. The specimens irradiated with 1, 5 and 10 shots all have better creep property compared to the control one and the difference between them is not big. The surface morphology and phase structure in the near surface region of the specimens before and after irradiation were analyzed by using scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. It is shown that the HIPIB irradiation can smooth the surface of the specimens, which can restrain the production of the surface crack. And the presence of a preferred orientation implies the treatment creates an intense compression wave and high dislocation density in the surface layer of the irradiated specimens, which hinders the dislocations movement. [Copyright &y& Elsevier]

Abstract: High-intensity pulsed ion beam (HIPIB) treatment is a new technology for surface modification of materials. In this paper, the surface of 316L stainless steel was irradiated by high-intensity pulsed ion beams at ion current density of 100, 200 and 300A/cm2 with 1, 5 and 10 shots. The surface morphology and the phase structure in the near surface region of original and treated samples were analyzed with scanning electron microscope (SEM) and X-ray diffraction (XRD). Electron probe microanalysis (EPMA) was used to study the distribution of elements on the irradiated surfaces. It is found that the HIPIB irradiation can smooth the surface of the targets, and a preferred orientation presents in the surface layer of the treated samples. Otherwise, selective ablation of impurities occurs during the interaction between HIPIB and the targets. The influence of HIPIB irradiation on the electrochemical corrosion resistance of 316L stainless steel in 0.5mol/L H2SO4 was investigated. The polarization curves show that under the cooperation of the smooth surface and the grain refinement with the selective ablation of impurities, the corrosion resistance of the irradiated samples was improved significantly. [Copyright &y& Elsevier]