Acta Metallurgica Sinica-English Letters最新文献

Joining dissimilar Mg/Cu alloys was still an intractable problem because of the excessive intermetallic compounds (IMCs) and poor mechanical properties using conventional welding methods. In the present study, friction stir welding was employed for the butt joining of dissimilar AZ31B Mg-alloy and T2 pure Cu plates. Defect-free Mg/Cu joints were obtained with Mg-RS and Cu-AS configuration, at a welding speed of 50 mm/min and tool rotating speeds of 325 r/min, 625 r/min and 925 r/min. At the joining interface, both Mg₂Cu and MgCu₂ IMC phases were observed, with a clear, uniform and continuous IMCs layer composed of two sub-layers, layer-A of Mg + Mg₂Cu and layer-B of Mg₂Cu + MgCu₂. The maximum ultimate tensile strength of the Mg/Cu friction stir welding joint reached 130 MPa at 925 r/min due to enhanced mechanical interlocking between Mg and Cu, as well as sufficient metallurgical bonding at the joining interface with an IMCs layer thickness in the range of 1.0–2.0 μm.

The effects of B addition on microstructure and mechanical properties of a γ′-strengthened CoNi-base superalloy are investigated. The addition of B leads to a substantial increase in the volume fraction of both the eutectic structure and borides. The CoNi-base alloy shows a high solubility limit for the element B. Borides become noticeable in the area surrounding the eutectic structure after the B level exceeds 0.46 at.%. It is found that the compression property and stress rupture life of the 4W2Ta alloys exhibit an initial rise followed by a subsequent drop as the B content gradually increases from 0.08 to 0.78 at.%. The 4W2Ta0.46B alloy demonstrates the most excellent high-temperature strength and stress rupture life, revealing that a moderate amount of B in the alloy noticeably enhances its mechanical properties by enhancing the grain boundary cohesion.

The hot deformation behavior of a newly developed Ni–W–Cr superalloy for use in 800 °C molten salt reactors (MSRs) was looked into by isothermal compression tests in the temperature range of 1050–1200 °C with a strain rate of 0.001–1 s⁻¹ under a true strain of 0.693. An Arrhenius-type model for the Ni–W–Cr superalloy was constructed by fitting the corrected flow stress data. In this model, the effect of dispersion of solid solution elements during thermal deformation on microstructure evolution was considered, as well as the effects of friction and adiabatic heating on the temperature and strain rate-dependent variation of flow stresses. The hot deformation activation energy of the Ni–W–Cr superalloy was 323 kJ/mol, which was less than that of the Hastelloy N alloy (currently used in MSRs). According to the rectified flow stress data, processing maps were created. In conjunction with the corresponding deformation microstructures, the flow instability domains of the Ni–W–Cr superalloy were determined to be 1050–1160 °C/0.03–1 s⁻¹ and 1170–1200 °C/0.001–0.09 s⁻¹. In these deformation conditions, a locally inhomogeneous microstructure was caused by flow—i.e., incomplete dynamic recrystallization and hot working parameters should avoid sliding into these domains. The ideal processing hot deformation domain for the Ni–W–Cr superalloy was determined to be 1170–1200 °C/0.6–1 s⁻¹.

Zirconium (Zr) emerges as the most effective grain refiner for magnesium (Mg) alloys incorporating Zr. Typically, Zr is introduced in the form of an Mg–Zr master alloy. However, within Mg–Zr master alloys, Zr predominantly exists in a particle form, which tends to aggregate due to attractive van der Waals forces. The clustered Zr is prone to settling, thereby reducing its refining impact on Mg alloys. In this work, a combined pretreatment process for Mg–Zr master alloys was proposed, encompassing the introduction of a physical field to intervene the agglomeration of particle Zr and the employ of high-temperature dissolution and peritectic reactions to promote the solid solution of Zr. The results demonstrate that the particle Zr within the pretreated Mg–Zr master alloy is effectively dispersed and refined, and greater solute Zr levels can be achieved. The subsequent grain refinement ability was studied on a typical Mg–6Zn–0.6Zr (wt%) alloy. The outcome highlights that an improvement in the grain refinement efficacy (32.4%) of Mg–Zr master alloys was obtained with a holding time of 60 min. The pretreated Mg–Zr master alloy significantly augments the efficiency of grain refinement for Mg alloys through a synergistic strategy involving heterogeneous nucleation and solute-driven growth restriction. The crucial factor in achieving effective grain refinement of Zr in Mg alloys lies in regulating the presence and morphology of Zr in the Mg–Zr master alloy, distinguishing between particle Zr and solute Zr. This study introduces a novel method for developing more efficient Mg–Zr refiners.

The Al₂O₃ laminated preforms with different layers thickness were prepared by freezing casting in present work. Then, the Al₂O_3p/AZ91 magnesium matrix laminated materials were obtained by infiltrating the AZ91 alloy melt into the Al₂O₃ laminated preform based on pressure infiltration process. Subsequently, the influence of freezing temperature on the microstructure, mechanical properties and fracture behavior of magnesium-based laminates was investigated. The results indicated that with the decrease of freezing temperature, the thickness of Al₂O₃ layers decreases gradually, the number of layers increases obviously, and the interlayers spacing decreases. Accompanied with the decrease of interlayers spacing, the size of Mg₁₇Al₁₂ phase precipitated in the AZ91 alloy layers was refined, and the compression strength and strain were both improved obviously. The micro-cracks initiated in Al₂O₃ layers during loading process, while the AZ91 layers could effectively suppress the initiation and propagation of micro-cracks. Furthermore, the changing layers structure influenced by the decrease of freezing temperature had significant inhibiting effect on the initiation and propagation of micro-cracks, which endowed the Al₂O_3p/AZ91 magnesium matrix laminated materials with better strength and toughness. Notably, the best compression properties of Al₂O_3p/AZ91 magnesium matrix laminated materials could be obtained at the freezing temperature of − 50 °C, the compression strength and elastic modulus of which were the 160% and 250% of monolithic AZ91 alloy, respectively.

The Zn0.6Cu wires are fabricated into stents for the potential biodegradable application of nasal wound healing. The degradation behavior of Zn0.6Cu stents in 0.9 wt% NaCl at 36.5 °C is evaluated. It shows that the untreated Zn0.6Cu stent experiences severe crevice corrosion with acceleration and autocatalytic effects within the micro-cracks and ruptures at 4.67 ± 1.15 d, with the average corrosion rate of 0.28 mm y⁻¹. Fortunately, the anodic polarization (AP) + hydrothermal (H) conversion coating, consisting of ZnCO₃, Zn(OH)₂ and ZnO, could inhibit the crevice corrosion significantly by reducing the cathode/anode ratio, extending the rupture time up to 16.50 ± 2.95 d, with the average corrosion rate of 0.14 mm y⁻¹. This research indicates that the biodegradable Zn-based stent has some potential applications in nasal wound recovery area.

Magnesium and its alloys have attracting rising attention as one of biodegradable metallic materials. However, the rapid corrosion and severe localized corrosion still hinder their extensive applications in clinics. In this study, micro-alloying of Ca (≤ 0.1 wt%) into Mg0.5Zn0.2Ge alloy developed in our previous work was explored to further enhance the corrosion resistance and alleviate the localized corrosion of the alloy. The results reveal that the addition of Ca leads to the transformation of the cathodic Mg₂Ge phase in Mg0.5Zn0.2Ca alloy into anodic MgCaGe phase in Ca-containing alloys, thereby changing the galvanic couples in alloys during immersion. The preferential dissolution of MgCaGe phase promotes the participation of Ca and Ge into the formation of corrosion products, resulting in the enrichment of Ca and Ge in the outmost of corrosion product layer, which stabilizes and passivates the corrosion product layer on Mg alloy surface. Additionally, the enrichment of Zn at the corrosion interface seems to further hinder the corrosion of Mg matrix. All of these factors confer a slower and more uniform corrosion on Mg0.5Zn0.2GexCa (x < 0.1 wt%) alloy, which provides favorable candidates for the further processing to gain suitable biodegradable Mg alloys.

In this work, a series of Co-based ternary Co–Er–B bulk metallic glasses (BMGs) with excellent soft magnetic properties and high strength were developed, and the local atomic structure of a typical Co_71.5Er_3.5B₂₅ metallic glass was studied through in situ high-energy synchrotron X-ray diffraction and ab initio molecular dynamics simulations. The results reveal that the BMG samples can be obtained in a composition region of Co_68.5–71.5Er_3.5–4B_25–27.5 by a conventional copper-mold casting method. The Co–Er–B metallic glasses possess stronger atomic bond strengths and denser local atomic packing structure composed of a higher fraction of icosahedral-like clusters but fewer deformed body-centered cubic and crystal-like polyhedrons, and they exhibit slower atomic diffusion behaviors during solidification, as compared to Co–Y–B counterparts. The enhancement in structural stability and the retardation of atomic-ordered diffusion lead to the better glass-forming ability of the Co–Er–B alloys. The smaller magnetic anisotropy energy in the Co–Er–B metallic glasses results in a lower coercivity of less than 1.3 A/m. The Co–Er–B BMGs exhibit high-yield strength of 3560–3969 MPa along with distinct plasticity of around 0.50%.

A refractory high entropy alloy Ti₆₂Nb₁₂Mo₁₂Ta₁₂W₂ was prepared by mechanical alloying and spark plasma sintering. The microstructure and mechanical properties of the Ti₆₂Nb₁₂Mo₁₂Ta₁₂W₂ alloy were analyzed. The experimental results show that the microstructure of the alloy is composed of two BCC phases, an FCC precipitated phase, and the precipitated phase which is a mixture of TiC, TiN and TiO. The alloy exhibits good room temperature compressive properties. The plasticity of the sample sintered at 1550 °C can reach 10.8%, and for the sample sintered at 1600 °C, the yield strength can be up to 2032 MPa, in the meantime the plasticity is 9.4%. The alloy also shows high strength at elevated temperature. The yield strength of the alloy exceeds 420 MPa at 900 °C, and value of which is still above 200 MPa when the test temperature reaches 1000 °C. Finally, the compressive yield strength model at room temperature is constructed. The prediction error of the model ranges from − 7.9% to − 12.4%, expressing fair performance.

La–Mg–Ni-based hydrogen storage alloys have excellent hydrogen storage properties. This work reports the hydrogen storage performance of a series of A₂B₇-type La_0.96Mg_0.04Ni_3.34Al_0.13 alloy and La_0.96-xY_xMg_0.04Ni_3.47–0.6xAl_0.6x (x = 0, 0.22, 0.33, 0.44) alloys, and explores the effect of Y and Al element combined substitution on the microstructure and hydrogen storage performance of A₂B₇-type La–Mg–Ni-based alloys. The alloys are composed of Ce₂Ni₇ phase and LaNi₅ phase. With the increase of x, the cell volume of Ce₂Ni₇ phase decreases, while that of LaNi₅ phase increases, indicating that Y atom mainly enters Ce₂Ni₇ phase and Al atom mainly enters LaNi₅ phase. An appropriate amount of co-substitution increases the hydrogen storage capacity and reduces the hydrogen absorption/desorption plateau pressure hysteresis of the alloy. When x = 0.44, the hydrogen storage capacity of the alloy is 1.449 wt%, and the hysteresis coefficient is 0.302. The cell volume of Ce₂Ni₇ phase and LaNi₅ phase expands to different degrees after 20 absorption/desorption cycles. With the increase of x, the volume expansion rate decreases, and the cycle capacity retention rate also gradually decreases. This is related to the amorphization of Ce₂Ni₇ phase. When x = 0.22, the capacity retention rate of the alloy is 91.4%.