Effects of Ce-rich RE on microstructure and mechanical properties of as-cast Mg-8Li-3Al-2Zn-0.5Nd alloy with duplex structure

The effects of Ce-rich RE on the microstructure and mechanical properties of as-cast Mg-8Li-3Al-2Zn-0.5Nd-x RE(x = 0, 1, 2, 3 wt%) alloys were investigated. The results indicated that the as-cast Mg-8Li-3Al-2Zn-0.5Nd alloy mainly consisted of α-Mg, β-Li, AlLi, MgLi2 Al and Al2 Nd phases. With the addition of Ce-rich RE in the alloy,Al3 RE and Al2 RE phases generated and gradually grew into net-like or block-like structure. With the addition of RE, Al-RE phases generated by consuming Al element and, thus, less Al element was dissolved in the matrix and less AlLi phase formed. Furthermore, less AlLi phase means that more Li element released to cause the increase ofβ-Li phase and refine the α-Mg phase. Under the influence of these factors, adding more RE led to higher elongation and lower tensile strength and hardness. With the addition of Ce-rich RE, the yield strength and ultimate tensile strength of the as-cast Mg-8Li-3Al-2Zn-0.5Nd alloy gradually decreased from 180 to 152 MPa and from 215 to 193 MPa, respectively, while the elongation was remarkably improved from 21.1% to 40.2%.     

Effect of Nb on the corrosion behavior of continuous bulk metallic glass-coated steel wire composites

(Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5)_100?xNb_x (at%, x=0 and 8) bulk metallic glasses (BMGs) were coated on the surface of Q195 steel wires by a continuous coating process. The potentiodynamic polarization tests of these BMGs were conducted in 3.5wt% NaCl aqueous solution. It is found that the addition of 8at% Nb into Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 alloy results in the improvement of corrosion resistance with the pitting potential of ?52 mV, the open circuit potential of ?446 mV, and the corrosion current density of 9.86×10?6 mA/cm2. This may be attributed to that Nb is beneficial to passivate and stabilize Zr and Ti.     

Corrosion behavior of as-cast Mg–8Li–3Al+xCe alloy in 3.5wt% NaCl solution

Mg–8Li–3Al+xCe alloys (x = 0.5wt%, 1.0wt%, and 1.5wt%) were prepared through a casting route in an electric resistance furnace under a controlled atmosphere. The cast alloys were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The corrosion behavior of the as-cast Mg–8Li–3Al+xCe alloys were studied under salt spray tests in 3.5wt% NaCl solution at 35°C, in accordance with standard ASTM B–117, in conjunction with potentiodynamic polarization (PDP) tests. The results show that the addition of Ce to Mg–8Li–3Al (LA83) alloy results in the formation of Al₂Ce intermetallic phase, refines both the α-Mg phase and the Mg₁₇Al₁₂ intermetallic phase, and then increases the microhardness of the alloys. The results of PDP and salt spray tests reveal that an increase in Ce content to 1.5wt% decreases the corrosion rate. The best corrosion resistance is observed for the LA83 alloy sample with 1.0wt% Ce.     

Effects of yttrium on the formation and magnetic properties of bulk metallic glassy (Fe,Co)-B-Si-Nb alloys

The bulk metallic glassy (BMG) rods of [(Fe_0.5Co_0.5)_0.72B_0.192Si_0.048Nb_0.04]_100-xY_x (x=0-6) and [(Fe_xCo_1-x)_0.72B_0.192Si_0.048Nb_0.04]₉₆Y₄ (x=0.5-0.8) were prepared by copper mold casting. The structure, thermal stability, and magnetic properties of the samples were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and vibrating sample magnetometer (VSM). Adding 1at% to 6at% of yttrium, the bulk glassy alloy rods of [(Fe_0.5Co_0.5)_0.72B_0.192Si_0.048Nb_0.04]_100-xY_x(x=0-6) with the diameter of 3 mm were not formed, and the sample with 4at% of yttrium showed less crystalline phase than others. When the Fe/Co atomic ratio was between 5:5 and 7:3, the bulk glassy alloy rods of [(Fe_1-xCo_x)_0.72B_0.192Si_0.048Nb_0.04]₉₆Y₄ (x=0.5-0.8) with the diameter of 2 mm were fabricated. In the (Fe, Co)-B-Si-Nb-Y BMGs, when the Fe content increased, the thermal stability, the supercooled liquid region, and the glass-forming ability (GFA) decreased, but the saturation magnetization (M_s) increased.     

Microstructure, crystalline phase and electrical properties of Li0.06(Na0.5K0.5)0.94Nb(1−2x/5)Mg x O3 lead-free piezoelectric ceramics

MgO-modified Li_0.06(Na_0.5K_0.5)_0.94NbO₃ (L₆NKN) lead-free piezoelectric ceramics were synthesized by normal sintering at a relatively low temperature of 1000°C. The crystalline phase, microstructure, and electrical properties of the ceramics were investigated with a special emphasis on the influence of MgO content. The addition of MgO effectively improves the sinterability of the L₆NKN ceramics. X-ray diffraction analysis indicates that the morphotropic phase boundary (MPB) separating orthorhombic and tetragonal phases for the ceramics lies in the range of Mg doping content (x) from 0.3at% to 0.7at%. High electrical properties of the piezoelectric constant (d ₃₃=238 pC/N), planar electromechanical coupling coefficient (k _p=41.5%), relative dielectric constant (? _r=905), and remanent polarization (P _r=38.3 μC/cm²) are obtained from the specimen with x=0.5at%, which suggests that the Li_0.06(Na_0.5K_0.5)_0.94Nb_(1?2x/5)Mg _x O₃ (x=0.5at%) ceramic is a promising lead-free piezoelectric material.     

Centimeter-sized Ti-based bulk metallic glass with high specific strength

Based on the quaternary Ti₄₁Zr₂₅Be₂₉Al₅ glassy alloy with a critical diameter of 7 mm reported not long ago, an obvious enhancement of glass-forming ability (GFA) has been realized in this alloy by the addition of Cu element. A series of (Ti₄₁Zr₂₅Be₂₉Al₅)_100?xCu_x (x=0, 2, 5, 7, 9, 11 at%) glassy alloys have been developed and some of them can be cast into one-centimeter diameter fully glassy rods by copper mold suction casting. It has been found that Cu addition could stabilize the liquid phase and suppress the crystallization, resulting in improvement of the GFA of the alloy. The addition of Cu also increases the compressive strength of the alloy and the (Ti₄₁Zr₂₅Be₂₉Al₅)₉₁Cu₉ glassy alloy possesses a specific strength (defined as yield strength/density) of 4.13×10⁵ Nm/kg, which is much higher than most other reported centimeter-sized bulk metallic glasses. The present result suggests that the newly developed (Ti₄₁Zr₂₅Be₂₉Al₅)₉₁Cu₉ glassy alloy is a good candidate for structural applications because of its good glass-forming ability and mechanical properties.     

Phase analysis and thermal conductivity of in situ O′-sialon/β-Si3N4 composites

Typical O??-sialon-based ceramics, with a formula of Si_2?x Al _x O_1+x N_2?x , where x was set as 0.25, were fabricated by in-situ synthesis. Si₃N₄, Al₂O₃, and SiO₂ powders were used as raw materials, and MgO and Y₂O₃ were added as sintering additives. All the samples were sintered at different temperatures under a nitrogen pressure of 0.25?C0.30 MPa, and their microstructure, phase content, and thermal conductivity were evaluated. The effects of O??-sialon and ??-Si₃N₄ on the thermal conductivity were analyzed by numerical calculation in detail. In the case of the similar porosity, the thermal conductivity of O??-sialon-based ceramics decreased with the ratio of O??-sialon/??-Si₃N₄ increasing. When the ratio was 12, the thermal conductivity of O??-sialon ceramics sintered at 1360°C was 1.197 W·m^?1·K^?1.     

Glass-forming ability,microhardness, corrosion resistance,and dealloying treatment of Mg60-xCu40Ndx alloy ribbons

The influence of Nd addition on the glass-forming ability (GFA), microhardness, and corrosion resistance of Mg_60-xCu₄₀Nd_x (x=5, 10, 15, 20, and 25, at%) alloys were investigated by differential scanning calorimetry, Vickers-type hardness tests, and electrochemical methods. The results suggest that the GFA and microhardness of the amorphous alloys increase until the Nd content reaches 20at%. The corrosion potential and corrosion current density obtained from the Tafel curves indicate that the Mg₃₅Cu₄₀Nd₂₅ ternary alloy exhibits the best corrosion resistance among the investigated alloys. Notably, nanoporous copper (NPC) was synthesized through a single-step dealloying of Mg_60-xCu₄₀Nd_x (x=5, 10, 15, 20, and 25) ternary alloys in 0.04 mol·L-1 H₂SO₄ solution under free corrosion conditions. The influence of dealloying process parameters, such as dealloying time and temperature, on the microstructure of the ribbons was also studied using the surface diffusivity theory. The formation mechanism of dealloyed samples with a multilayered structure was also discussed.     

Nd<Subscript>2</Subscript>Fe<Subscript>17</Subscript> nanograins effect on the coercivity of HDDR NdFeB magnets with low boron content

Relationships between the coercivity of hydrogenation disproportionation desorption recombination (HDDR) Nd_12.5Fe_81.5−x Co₆B _x bonded magnets and boron content were investigated. Nd₂Fe₁₇ phase with planar magnetic anisotropy is present in the microstructure when x= 4at%–5.88at%, which does not reduce the coercivity of the bonded magnets. High-resolution transmission electron microscopy (TEM) images show that Nd₂Fe₁₇ phase exists in the form of nanocrystals in the Nd2Fe14B matrix. There is an exchange-coupling interaction between the two phases so that the coercivity of HDDR Nd_12.5Fe_81.5−x Co₆B _x bonded magnets is hardly reduced with a decrease in boron content.     

Influence of Cu content on the mechanical properties and corrosion resistance of Mg-Zn-Ca bulk metallic glasses

(Mg_66.2Zn_28.8Ca₅)_100?xCu_x (at%, x = 0, 1, 3, and 5) bulk metallic glasses (BMGs) of 2 mm in diameter were prepared by the conventional copper mold injection casting method. Besides, the influence of Cu content on the microstructure, thermal stability, mechanical properties, and corrosion behavior of Mg-Zn-Ca BMGs was investigated. It is found that the addition of Cu decreases the glass-forming ability of Mg-Zn-Ca BMGs. Crystalline phases are precipitated at a higher Cu content, larger than 3at%. The compressive fracture strength of Mg-Zn-Ca BMGs is enhanced by the addition of Cu. With the formation of in-situ composites, the compressive strength of the Mg-Zn-Ca alloy with 3at% Cu reaches 979 MPa, which is the highest strength among the Mg-Zn-Ca alloys. Furthermore, the addition of Cu also results in the increase of corrosion potential and the decrease of corrosion current density in Mg-Zn-Ca BMGs, thereby delaying their biodegradability.     

Effect of Co addition on crystallization and magnetic properties of FeSiBPCu alloy

The effects of Co addition on the microstructure,crystallization processes and soft magnetic properties of(Fe1 xCox)83Si4B8P4Cu1(x?0.35,0.5,0.65)alloys were investigated.The experimental results demonstrated that the addition of Co decreased the thermal stability against crystallization of the amorphous phase,and thus improved the heat treatment temperature of this alloy.Fe Co Si BPCu nanocrystalline alloys with a dispersedα0-Fe Co phase were obtained by appropriately annealing the as-quenched ribbons at 763 K for 10 min.Theα0-Fe Co with grains size ranging from 9 to 28 nm was identified in primary crystallization.The coercivity(Hc)markedly increased with increasing x and exhibited a minimum value at x0.35,while the saturation magnetic flux density(Bs)shows a slight decrease.The(Fe0.65Co0.35)83Si4B8P4Cu1nanocrystalline alloy exhibited a high saturation magnetic flux density Bsof 1.68 T,a low coercivity,Hcof 5.4 A/m and a high effective permeability meof 29,000 at 1 k Hz.     

Effect of oxygen on the microstructure and mechanical properties of Ti-23Nb-0.7Ta-2Zr alloy

The influence of oxygen content on the microstructure and mechanical properties of Ti-23Nb-0.7Ta-2Zr (at%) alloy in as-cast and cold-rolled states was investigated systematically in this paper. It is found that the alloy containing oxygen element is only composed of a single β phase, while the alloy without oxygen element consisted of β and α″ phases. Although the grain size becomes larger, the elastic deformation ratio, strength, and hardness of the alloy are all increased with an increase of oxygen content. The as-cast alloy has excellent plastic deformation ability, but the cold-rolled alloy containing oxygen element exhibits brittle characteristics. A conclusion can be drawn that oxygen element can stabilize β phase, inhibit the phase transformation from β to α″, and furthermore help to increase the strength and elastic deformation ability of the alloy.     

Preparation of Al-Cu-Fe-(Sn,Si) quasicrystalline bulks by laser multilayer cladding

(Al₆₅Cul₂₀Fe₁₅)_100-x Sn_x (x=0, 12, 20, 30) and Al₅₇Si₁₀Cu₁₈Fe₁₅ powders were cladded on a medium carbon steel (45# steel) substrate by laser multilayer cladding, respectively. The phases and properties of the produced quasicrystalline bulks were investigated. It was found that the main phases in the Al₆₅Cul₂₀Fe₁₅ sample were crystalline λ-Al₁₃Fe₄ and icosahedral quasicrystal together with a small volume fraction of θ-Al₂Cu phase. The volume fraction of icosahedral phase decreased as the Sn content in the (Al₆₅Cul₂₀Fe₁₅)_100-x Sn_x samples increased owing to the formation of β-CuSn phase. The increase of Sn content improved the brittleness of the quasicrystal samples. The morphology of the solidification microstructure in the Al₅₇Si₁₀Cu₁₈Fe₁₅ sample changed from elongated shape to spherical shape due to the addition of Si. The nanohardness of the laser multilayer cladded quasicrystal samples was equal to that of the as-cast sample prepared by vacuum quenching. In terms of hardness, the laser cladded Al₅₇Si₁₀Cu₁₈Fe₁₅ quasicrystalline alloy has the highest value among all the investigated samples.     

Effect of minor Sc on the microstructure and mechanical properties of AZ91 Magnesium Alloy

The as-cast and heat-treated microstructures and mechanical properties of the AZ91 magnesium alloys with and without minor Sc addition were investigated and compared in this paper. The results indicated that adding0.15–0.45 wt% Sc to the as-cast AZ91 alloy not only could modify and refine the Mg_(17)Al_(12) phase but also suppress the formation of the Mg_(17)Al_(12) phase. At the same time, the grains of the Sc-containing as-cast AZ91 alloys were also effectively refined. As a result, the mechanical properties at room temperature(RT) for the Sccontaining as-cast AZ91 alloys were effectively improved. In addition, adding 0.15–0.45 wt%Sc to the AZ91 alloy promoted the formation of the continuous precipitates(CP) during the aging treatment in spite of that the formation of the discontinuous precipitates(DP) was simultaneously suppressed. Accordingly, the Sc-containing as-aged AZ91 alloys obtained the relatively higher mechanical properties at RT than the as-aged AZ91 alloy.     

Microstructure and electrolysis behavior of self-healing Cu-Ni-Fe composite inert anodes for aluminum electrowinning

The microstructure evolution and electrolysis behavior of (Cu₅₂Ni₃₀Fe₁₈)-xNiFe₂O₄ (x=40wt%, 50wt%, 60wt%, and 70wt%) composite inert anodes for aluminum electrowinning were studied. NiFe₂O₄ was synthesized by solid-state reaction at 950℃. The dense anode blocks were prepared by ball-milling followed by sintering under a N₂ atmosphere. The phase evolution of the anodes after sintering was determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results indicate that a substitution reaction between Fe in the alloy phase and Ni in the oxide phase occurs during the sintering process. The samples were also examined as inert anodes for aluminum electrowinning in the low-temperature KF-NaF-AlF₃ molten electrolyte for 24 h. The cell voltage during electrolysis and the corrosion scale on the anodes were analyzed. The results confirm that the scale has a self-repairing function because of the synergistic reaction between the alloy phase with Fe added and the oxide phase. The estimated wear rate of the (Cu₅₂Ni₃₀Fe₁₈)-50NiFe₂O₄ composite anode is 2.02 cm·a-1.     

Effect of Zr addition on the stability of precipitated Laves phase and mechanical properties of Fe–Cr–Al-based alloys at high temperatures

The effect of a small amount of Zr addition on the temperature-dependent stability of Laves phase particles and mechanical properties of Fe-13.5Cr-4.73Al-2.07Mo-(0.34–0.5)Nb-(0.65–0.98)Ta-(0–0.33)Zr (wt. %) ferritic alloys was investigated in the present study. The designed alloy ingots were hot-rolled, aged at 1073 ?K for 24 ?h, and then re-treated at 1273 ?K, 1323 ?K, 1373 ?K, and 1473 ?K for 1 ?h, respectively. It was found that the Zr addition could not only stabilize the Fe₂M Laves phase (M ?= ?Mo,Nb,Ta,Zr) to a much higher temperature, but also induce the formation of stable Fe₂₃Zr₆ phase. The high-temperature (HT) microstructural stability of the alloys significantly was improved, as evidenced by the fact that a certain amount (0.66–1.19%) of precipitates (Fe₂M, Fe₂₃Zr₆, and core(Fe₂₃Zr₆)-shell(Fe₂M)-structured particles) with an appropriate size (～1.0 ?μm) uniformly distributed in the ferritic matrix even after being re-treated at 1473 ?K. Particularly, the formation of core-shell-structured particles at HTs was studied from the viewpoint of both solid solubility and diffusion coefficient of M in the matrix. All these aged alloys exhibited prominent mechanical properties at both room and elevated temperatures, showing high yield strength with σ_YS ?= ?490–560 ?MPa at room-temperature and σ_YS ?= ?80–85 ?MPa at 1073 ?K. The strengthening effect was further discussed in light of various strengthening mechanisms, and the calculated strength are in good agreement with the experimental results.     

Thermal stability and magnetic properties of Fe–Co–M–Zr–Nb–Ge–B(M=Mo,Cr) bulk metallic glasses

Fe62Co8 xMxZr6Nb4Ge1B19(M=Mo, Cr) bulk metallic glasses were synthesized in the diameter range up to 2 mm by copper mold casting,which exhibit high thermal stability and large glass-forming ability. The super-cooled liquid region diminishes by the dissolution of Mo. The addition of 2 at% Cr leads to the broading of the liquid region remarkably, resulting in the improvement of thermal stability. The crystallization takes place through a single exothermic reaction, accompanying the precipitation of more than three kinds of crystallized phases such as α-Fe,Fe2Zr and ZrB2. The Fe-based alloys show soft ferromagnetic properties. The saturation magnetization(ss) decreases with increasing Mo or Cr content while the saturated magnetostriction increases with raising Mo or Cr content. There is no evident change in the ssand coercive force(Hc)with annealing temperature below the crystallization temperature, which suggests a more relaxed atomic configuration the glasses have. The crystallization causes a substantial enhancement in both ssand Hc. Each soft magnetic property of the glasses containing Cr with higher thermal stability is superior to that of the alloys containing Mo.     

Effects of gadolinium addition on the microstructure and mechanical properties of Mg-9Al alloy

This research aims to study the significance of Gd addition (0wt%-2wt%) on the microstructure and mechanical properties of Mg-9Al alloy. The effect of Gd addition on the microstructure was investigated via X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Mg-9Al alloy contained two phases, α-Mg and β-Mg17Al12. Alloying with Gd led to the emergence of a new rectangular-shaped phase, Al₂Gd. The grain size also decreased marginally upon Gd addition. The ultimate tensile strength and microhardness of Mg-9Al alloy increased by 23% and 19%, respectively, upon 1.5wt% Gd addition. We observed that, although Mg-9Al-2.0Gd alloy exhibited the smallest grain size (181 μm) and the highest dislocation density (5.1×1010 m-2) among the investigated compositions, the Mg-9Al-1.5Gd alloy displayed the best mechanical properties. This anomalous behavior was observed because the Al₂Gd phase was uniformly distributed and present in abundance in Mg-9Al-1.5Gd alloy, whereas it was coarsened and asymmetrically conglomerated in Mg-9Al-2.0Gd.     

Hydrogen storage performance of LaNi3.95Al0.75Co0.3 alloy with different preparation methods

Rare-earth AB₅-type La–Ni–Al hydrogen storage alloys are widely studied due to their extensive application potentials in hydrogen isotope storage, hydrogen isotope isolation and hydrogen compressors, etc. Good hydriding/dehydriding kinetics, easily activation, high reversibility are important factors for their practical application. However, their overall hydrogen storage performance, especially plateau pressure and hydrogen absorption/desorption durability need to be further optimized. In this study, the microstructures and the hydrogen storage properties of as-cast, annealed, and melt-spun LaNi_3.95Al_0.75Co_0.3 alloys were investigated. The experimental results of XRD and SEM showed that all alloys contained a pure CaCu₅ type hexagonal structure LaNi₄Al phase. The cell volume increased in an order of annealed ?> ?melt-spun ?> ?as-cast, resulting in a lower hydrogen absorption/desorption plateau pressure and a more stable hydride phase. The hydrogen storage capacity of three alloys was almost the same. The slope factor of the annealed and melt-spun alloys is smaller than the as-cast alloy, indicating that heat-treatment process can make the alloys more uniform. For the cycle stability of the alloys, the hydrogen absorption rate of the annealed alloy and melt-spun alloy was much faster than that of the as-cast alloy after 500 cycles. The melt-spun alloy showed high pulverization resistance during hydrogen absorption/desorption, and exhibited an excellent cycling retention of 99% after 500 cycles, suggesting that melt-spinning process can enhance the cycle stability and improve the cycle life of the alloy.     

Eutectic reaction and cored dendritic morphology in yttrium doped Zr-based amorphous alloys

The microalloying effect of yttrium on the crystallization behaviors of (Zr_0.525Al_0.10Ti_0.05Cu_0.179Ni_0.146)_100-x Y_x, and (Zr_0.55Al_0.15-Ni_0.10Cu_0.20)_100-x Y_x (x=0, 0.4, and 1, thus the two alloy systems were denoted as Zr52.5, Zr52.5Y0.4, Zr52.5Y1, and Zr55, Zr55Y0.4, Zr55Y1, respectively) was studied. Transmission electron microscopy (TEM) results suggested that the crystalline phases were different in the two Zr-based alloys and with different yttrium contents. ZrNi-phase and Al₃Zr₅ phase precipitations can be well explained by the mechanisms of nucleation and growth. Al₃Zr₅ phase is mainly formed by a peritectic-like reaction, while ZrNi-phase by a eutectic reaction. The contents of elements Y, Al, and Ti may dominate the reaction types. The orientation relationship between Y₂O₃ particles and Al₃Zr₅ phase is also discussed.