Volume Fraction Of Long Period Stacking Ordered Phase Research Articles

Design of LPSO Phases in Mg-Y-Ni Alloys to Impact Hydrogenation Kinetics

A series of Mg-Y-Ni alloys with different volume fractions of long-period stacking-ordered (LPSO) phase were prepared, by controlling the alloy composition, heat treatment, and single-pass extrusion, to assess the influence of increasing LPSO phase volume fraction on the hydrogen absorption and desorption properties of the extruded alloys. The LPSO phase volume fraction in the alloys increased with increasing solute concentration, from ~24% LPSO in Mg97Y2Ni1 (at.%) to ~60% LPSO in Mg93Y4Ni3 (at.%) up to ~92% LPSO in Mg91Y5Ni4 (at.%). The most refined microstructure was obtained in the alloy with highest volume fraction of LPSO phase. After 100 s at 300 °C, the Mg91Y5Ni4 alloy absorbed 4.6 ± 0.2 wt.% H while the Mg97Y2Ni1 and Mg93Y4Ni3 alloys each absorbed 3.8 ± 0.2 wt.% H. After 10,000 s at 300 °C, all three alloys had absorbed a maximum of 5.3 ± 0.2 wt.% H with no further significant difference in hydrogen absorption kinetics. The Mg91Y5Ni4 alloy desorbed 1.8 ± 0.2 wt.% H after 100 s at 300 °C against a vacuum while the Mg97Y2Ni1 and Mg93Y4Ni3 alloys desorbed 0.8 ± 0.2 wt. H and 0.6 ± 0.2 wt.% H, respectively. After 10,000 s at 300 °C, the Mg91Y5Ni4 and Mg97Y2Ni1 alloys completely desorbed 5.2 ± 0.2 wt.% H and 5.4 ± 0.2 wt.% H, respectively, but the Mg93Y4Ni3 alloy desorbed only 3.7 ± 0.2 wt.% H. Hydrogen absorption and desorption kinetics were fastest in the Mg91Y5Ni4 alloy with the highest LPSO volume fraction, but no consistent trend with LPSO phase volume fraction was observed with the Mg93Y4Ni3 alloy, which showed the slowest absorption and desorption kinetics. The hydrogen pressures corresponding to metal–hydride equilibrium did not vary with LPSO phase volume fraction or alloy composition, indicating that the (de)hydrogenation thermodynamics were not significantly changed in any of the alloys. Hydrogen absorption experiments with thin foils, made of extruded Mg91Y5Ni4 alloy with the highest LPSO phase fraction, demonstrated that the LPSO structures decompose into Mg phase, Mg2Ni phase, lamellar Mg/Mg-Y structures, and YHx particles. This study shows that hydrogen kinetics can be impacted in Mg-Y-Ni alloys by controlling the LPSO phases using common metallurgical techniques.

Effect of long period stacking ordered structure on the biocorrosion resistance and osteogenesis ability of Mg–Zn–Y-Mn alloys

Microstructure, biocorrosion resistance, and osteogenesis performances of as-cast Mg-Zn-Y-Mn alloys with different volume fraction of long period stacking ordered (LPSO) structure are investigated. 18R-LPSO phase can be formed in Mg-1Zn-2Y-0.5Mn (ZWM120), Mg-2Zn-4Y-0.5Mn (ZWM240) and Mg-4Zn-8Y-0.5Mn (ZWM480) alloys, and their volume fraction increases with the elevating Zn and Y content. The micro-galvanic effect between cathodic LPSO and anodic α-Mg dominate the corrosion mechanism of the three alloys, resulting in the accelerating corrosion rate with the increasing volume fraction of LPSO phase in Hank’s solution. With least LPSO phase, ZWM120 exhibits best cytocompatibility and osteogenic differentiation ability in rat bone marrow stem cells, suggesting that few Zn and Y addition is more potential for orthopedic applications.

Rapid corrosion rates and high mechanical properties of as-extruded Mg–Er–Ni alloys by introducing LPSO and γʹ phases

The Mg–Er–Ni alloy with comparable strength and solubility was prepared by controlling the Ni content. The mechanical properties and corrosion mechanism of alloys with long-period stacking ordered (LPSO) phase, as well as those with both LPSO and γʹ phases, were investigated and clarified. This study focused on investigating the underlying reasons for the high mechanical strength and fast corrosion rate of the Mg–13Er–3Ni alloy with LPSO and γʹ phases. The highest corrosion rate of the Mg–13Er–3Ni (wt.%) alloy is not only associated with the high volume fraction of the LPSO phase, which provides a larger zone for the corrosion cathode rather than forming a corrosion barrier, but also linked to the introduction of the γʹ phase that forms new sites for galvanic corrosion and avoids the formation the Er2O3 corrosion product film with corrosion-resistant. Moreover, The high mechanical properties of Mg–13Er–3Ni alloy are mainly attributed to the texture strengthening, dislocation strengthening and the second phase reinforcement that were caused by high volume fraction of LPSO phase and the precipitation of lamellar γʹ phase in Mg matrix. Generally, Compared to the Mg–13Er-1.5Ni (wt.%) alloy, the corrosion rates and mechanical strength of Mg–13Er–3Ni (wt.%) alloy were increased significantly by 302.8% and 50.3%, respectively, by coupling the LPSO and γʹ phases. Its ultimate tensile strength of 445 MPa and corrosion rare of 128.5 mg cm−2 h−1, which provides a new high strength and rapid corrosion Mg alloy materials for fracturing tools application.

Deformation behavior of Mg-Y-Ni alloys containing different volume fraction of LPSO phase during tension and compression through in-situ synchrotron diffraction

The deformation behavior of the as-extruded Mg-Y-Ni alloys with different volume fraction of long period stacking ordered (LPSO) phase during tension and compression was investigated by in-situ synchrotron diffraction. The micro-yielding, macro-yielding, tension-compression asymmetry and strain hardening behavior of the alloys were explored by combining with deformation mechanisms. The micro-yielding is dominated by basal slip of dynamic recrystallized (DRXed) grains in tension, while it is dominated by extension twinning of non-dynamic recrystallized (non-DRXed) grains in compression. At macro-yielding, the non-DRXed grains are still elastic deformed in tension and the basal slip of DRXed grains in compression are activated. Meanwhile, the LPSO phase still retains elastic deformation, but can bear more load, so the higher the volume fraction of hard LPSO phase, the higher the tensile/compressive macro-yield strength of the alloys. Benefiting from the low volume fraction of the non-DRXed grains and the delay effect of LPSO and γ′ phases on extension twinning, the as-extruded alloys exhibit excellent tension-compression symmetry. When the volume fraction of LPSO phase reaches ∼50%, tension-compression asymmetry is reversed, which is due to the fact that the LPSO phase is stronger in compression than in tension. The tensile strain hardening behavior is dominated by dislocation slip, while the dominate mechanism for compressive strain hardening changes from twinning in the α-Mg grains to kinking of the LPSO phase with increasing volume fraction of LPSO phase. The activation of kinking leads to the constant compressive strain hardening rate of ∼2500 MPa, which is significantly higher than the tensile strain hardening rate.

Tailoring the microstructural characteristic and improving the corrosion rate of Mg-Gd-Ni alloy by heat treatment with different volume fraction of LPSO phase

The microstructure and corrosion behaviors of Mg-Gd–Ni alloys with various long period stacking ordered (LPSO) phase volume fraction and heat treatments were investigated. Compared with as-cast alloys, the corrosion rates increased significantly after heat treatment, and increased with increasing volume fraction of LPSO phase, which may be due to the transformation of continuous bulk reticular LPSO phase to discontinuous rod-like and the precipitation of the lamellar 14 H LPSO phase, changing the corrosion propagation paths and providing more galvanic corrosion points for alloy with high LPSO phase volume fraction, resulting in corrosion rate of MgGd3Ni3 alloy increased significantly by 58.1%.

The role of long‐period stacking ordered phase on the discharge and electrochemical behaviors of magnesium anode Mg‐Zn‐Y for the primary Mg‐air battery

This work investigated and discussed the role of long-period stacking ordered (LPSO) phase on discharge performance and electrochemical behaviors of Mg-Zn-Y anode for Mg-air battery in detail. The volume fraction of LPSO phase increases with the increasing Y and Zn content. Compared with Mg-2Zn anode, Mg-Zn-Y anode with low content of LPSO phase has better discharge properties due to high open-circuit potential and low corrosion rate. However, anodes contained a high volume of LPSO phase exhibit poor corrosion resistance and discharge properties. The ZW12 alloy shows the best discharge capacity and anodic efficiency as high as 1612.9 mAh·g and 74.49% at the 40 mA·cm. It also outputs a high peak specific energy 1859.15 mWh·g at 10 mA cm, which is 37.56% higher than Mg-2Zn anode and 249.44% higher than ZW39 anode. The LPSO phase totally changes the decomposition process of Mg matrix, displaying the lamellar peeling surface in LPSO-affect zone. This lamellar peeling mode can help to take away the discharge products from the anodic surface, improving the anode performance.

Effect of Gd addition on microstructure and corrosion behaviors of Mg–Zn–Y alloy

Abstract The Mg97-xZn1Y2Gdx alloys were prepared by as-casting method. Corrosion performance of alloys was evaluated by using potentiodynamic polarization, hydrogen evolution rate and mass loss measurements in 3% sodium chloride solution at room temperature. The results shown that the atomic rate of the long period stacking ordered (LPSO) with the composition of Mg12Zn1Y1. The microstructure of LPSO phases was lamellar structure. When the atomic fraction of Zn is 1% and the atomic ratio of Zn/RE (Y, Gd) is 2:5, the volume fraction of LPSO phase can reach the extreme value. The corrosion resistance of Mg–Zn–Y alloy improves with the increase of the volume fraction of LSPO phase. The Mg96.5Zn1Y2Gd0.5 (MG0.5) alloy had better corrosion resistance than those of other alloys. It meant that 0.5 at. % gadolinium (Gd) was a suitable addition to Mg97Zn2Y alloy about corrosion resistance.

Microstructures, corrosion and mechanical properties of as-cast Mg–Zn–Y–(Gd) alloys

Long period stacking ordered (LPSO) structure phases were prepared by conventional solidification method in Mg94Zn3YxGd3–x (x=3, 2, 1.5, 1, mole fraction) alloys, the microstructures, corrosion and compressive mechanical properties of which were investigated, separately. The results reveal that the microstructures of the as-cast Mg94Zn3YxGd3–x alloys, with n(Zn)/n(Y+Gd)=1:1, consist of α(Mg) phase, Mg3Zn3RE2 (W) phase, Mg12ZnRE (14H-LPSO) phase and a few bright cube-shaped Mg–Y–Gd phases. The formation and the distribution of LPSO-phase in the alloys can be influenced by the content of Gd. The volume fraction of 14H-LPSO phase increases first and then decreases with the increase of the Gd content. For the electrochemical impedance spectroscopy (EIS) measurement, a R(Q(R(QR))) model was used to fit the test results in 3.5% (mass fraction) NaCl solution at room temperature. The corrosion current densities of all samples are about 10−5 A/cm2. When x(Gd)≤1%, Mg–Zn–Y–(Gd) alloy shows good corrosion resistance, which is better than that of the commercial AZ91D magnesium alloy. The corrosion rate increases when the Gd content is higher than 1.5%. At room temperature, the compressive properties of Mg–Zn–Y–(Gd) alloys increase remarkably with the increase of the volume fraction of LPSO phase. In addition, the pinning effect of W-phase and dispersive cube-shaped Mg–Y–Gd phase is beneficial to improving the mechanical properties of as-cast Mg94Zn3YxGd3–x alloy in deformation process.

Effect of long period stacking ordered phase on the microstructure, texture and mechanical properties of extruded Mg–Y–Zn alloy

The effect of long period stacking ordered (LPSO) phase on the microstructure, texture and mechanical properties of extruded Mg–Y–Zn alloys with compositions of Mg98.5Y1Zn0.5, Mg95.5Y3Zn1.5 and Mg92.5Y5Zn2.5 (at%), was systematically investigated. The LPSO phases were aligned along the extrusion direction (ED) in the as-extruded Mg–Y–Zn alloys, and significantly enhanced the dynamic recrystallization (DRX) process during the hot extrusion. With the increase of LPSO phase, the degree of DRX process of Mg alloy was more completed, the growth of the DRXed grains resulted in the grain coarsening, and the following phenomena were also observed that the conventional basal fiber texture was remarkably weakened, a novel texture component of 〈0001〉//ED appeared in the Mg alloys with higher volume fraction of LPSO phase. The microhardness and tensile yield stress (TYS) of Mg–Y–Zn alloy was improved by LPSO phase, but the ductility was degraded. The strengthening effect of LPSO phase was dominant over that from the grain refinement and texture.

Microstructures and mechanical properties of high-strength Mg–Gd–Y–Zn–Zr alloy sheets processed by severe hot rolling

Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr alloy sheets containing long period stacking ordered (LPSO) phase were prepared by hot rolling at 400°C with total reduction of 96%. Microstructure evolution of the sheets during hot rolling was investigated, and its influence on mechanical properties was discussed. Twinning occurred during the early stage of hot rolling, and disappeared after total reduction higher than 89%. Average grain size was gradually refined, microstructure became much more homogeneous and volume fraction of LPSO phase decreased with increasing rolling reduction. Furthermore, the type of LPSO phases far from and near the block shaped phases were identified to be different. Basal texture was obtained during rolling process, but the intensity declined with the further rolling, which is mainly due to the dynamic recrystallization and the addition of RE elements. The as-rolled sheet with 96% reduction shows excellent mechanical properties: yield strength of 318MPa, ultimate tensile strength of 403MPa and elongation to failure of 13.7% at ambient temperature along the rolling direction.