Phase Equilibria of the Ternary Al-Cu-Zn Alloys on Al-Zn Rich Side

Phase equilibria of the Al-Cu-Zn system on Al-Zn rich side was experimentally determined with 16 alloys annealed at 360 °C. The annealed alloys were examined by means of x-ray diffraction, electron probe microanalysis and differential scanning calorimetry. Five single-phase regions and seven two-phase regions as well as three three-phase regions, i.e. α-(Al)?+?θ-Al₂Cu?+?τ′-Al₄Cu₃Zn, α-(Al)?+?τ′-Al₄Cu₃Zn?+?ε-CuZn₄ and α-(Al)?+?ε-CuZn₄?+?(Zn), were determined. The partial isothermal section of the Al-Cu-Zn system on Al-Zn rich side at 360 °C was constructed based on the obtained experimental data in this work. It was observed that the solid solution phase α-(Al) would easily decompose into ε-CuZn₄, (Zn) and α′-(Al) at the ambient temperature in the early stages. The ternary phase τ′-Al₄Cu₃Zn would form and ε-CuZn₄ would disappear gradually along with the extension of aging time.     

On the Reaction Mechanism of MCrAlY Alloys with Oxide–Sulfate Deposits at 1100 °C

The corrosion of γ-(Ni,Co) + β-(Ni,Co)Al NiCoCrAlY alloys exposed to CaO-rich, Na₂SO₄-containing deposits in air and CO₂–H₂O–O₂ at 1100 °C was studied with a focus on the mechanisms governing the accelerated attack of γ-rich compositions. Internal oxidation of Al resulted from the breakdown of an initially formed Al₂O₃ scale, due to its reaction with the deposit. Compared to deposit-free conditions, this scale exhibited: (i) a delayed Al₂O₃ structure transition from metastable θ to stable α; (ii) finer grains; (iii) a reduced adherence to the metal, to the extent that a gap developed at the metal/oxide interface; and (iv) significant permeability to S, as well as N during air exposures. The occurrence of sulfidation in S-free gases reflected the establishment of an elevated S activity under the molten Na₂SO₄, due to the locally reduced \(p_{{{\text{O}}_{ 2} }}\). The factors affecting the Al₂O₃-scale microstructure were examined, as well as the associated consequences on Al consumption and on the transition to internal oxidation. The roles of alloy and gas compositions in the identified mechanisms were also discussed.     

Properties of the Ti<Subscript>40</Subscript>Zr<Subscript>10</Subscript>Cu<Subscript>36</Subscript>Pd<Subscript>14</Subscript> BMG Modified by Sn and Nb Additions

The results of investigation of the influence of additions of 2 and 3 at.% of Sn and simultaneously of Sn and 3 at.% Nb on microstructure and properties of the bulk metallic glasses of composition (Ti₄₀Cu_36?x Zr₁₀Pd₁₄Sn _x )_100?y Nb _y are reported. It was found that the additions of Sn increased the temperatures of glass transition (T _g), primary crystallization (T _x ), melting, and liquidus as well as supercooled liquid range (ΔT) and glass forming ability (GFA). The nanohardness and elastic modulus decreased in alloys with 2 and 3 at.% Sn additions, revealing similar values. The 3 at.% Nb addition to the Sn-containing amorphous phase decreased as well all the T _g, T _x , T _L, and T _m temperatures as ΔT and GFA; however, relatively larger values of this parameters in alloys containing larger Sn content were preserved. In difference to the previously published results, in the case of the amorphous alloys containing small Nb and Sn additions, a noticeable amount of the quenched-in crystalline phases was not confirmed, at least of the micrometric sizes. In the case of the alloys containing Sn or both Sn and Nb, two slightly different amorphous phase compositions were detected, suggesting separation in the liquid phase. Phase composition of the alloys determined after amorphous phase crystallization was similar for all compositions. The phases Cu₈Zr_3, CuTiZr, and Pd₃Zr were mainly identified in the proportions dependent on the alloy compositions.     

Phases and microstructures of high Zn-containing Al–Zn–Mg–Cu alloys

Phases and microstructures of three high Zncontaining Al–Zn–Mg–Cu alloys were investigated by means of thermodynamic calculation method, optica microscopy(OM), scanning electron microscopy(SEM)energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), and differential scanning calorimetry(DSC) analysis. The results indicate that similar dendritic network morphologies are found in these three Al–Zn–Mg–Cu alloys. The as-cast 7056 aluminum alloy consists of aluminum solid solution, coarse Al/Mg(Cu, Zn, Al)_2 eutectic phases, and fine intermetallic compounds g(MgZn_2). Both of as-cast 7095 and 7136 aluminum alloys involve a(Al)eutectic Al/Mg(Cu, Zn, Al)_2, intermetallic g(MgZn_2), and h(Al_2Cu). During homogenization at 450 °C, fine g(MgZn_2) can dissolve into matrix absolutely. After homogenization at 450 °C for 24 h, Mg(Cu, Zn, Al)_2 phase in 7136 alloy transforms into S(Al_2Cu Mg) while no change is found in 7056 and 7095 alloys. The thermodynamic calculation can be used to predict the phases in high Zncontaining Al–Zn–Mg–Cu alloys.     

Fabrication and Characterization of Plasma-Sprayed Carbon-Fiber-Reinforced Aluminum Composites

Carbon fiber (C_f)/Al specimens were fabricated by plasma-spraying aluminum powder on unidirectional carbon fiber bundles (CFBs) layer by layer, followed by a densification heat treatment process. The microstructure and chemical composition of the C_f/Al composites were examined by scanning electron microscopy and energy-dispersive spectrometry. The CFBs were completely enveloped by aluminum matrix, and the peripheral regions of the CFBs were wetted by aluminum. In the wetted region, no significant Al₄C₃ reaction layer was found at the interface between the carbon fibers and aluminum matrix. The mechanical properties of the C_f/Al specimens were evaluated. When the carbon fiber volume fraction (CFVF) was 9.2%, the ultimate tensile strength (UTS) of the C_f/Al composites reached 138.3 MPa with elongation of 4.7%, 2.2 times the UTS of the Al matrix (i.e., 63 MPa). This strength ratio (between the UTS of C_f/Al and the Al matrix) is higher than for most C_f/Al composites fabricated by the commonly used method of liquid-based processing at the same CFVF level.     

Isothermal Section of the Al-Mn-Dy System at 500 °C

Phase relationships in the Al-Mn-Dy ternary system at 500 °C have been investigated by X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, and electron probe microanalysis. From the experimental results it was concluded that the isothermal section consists of 16 single-phase regions, 26 two-phase regions and 12 three-phase regions. Two extensive solid solutions, (Al _x Mn_1?x )₁₂Dy and (Al_1?x Mn _x )₂Dy, were observed. The solid solution (Al _x Mn_1?x )₁₂Dy forms by Al replacing Mn in Mn₁₂Dy, while the continuous solid solution (Al_1?x Mn _x )₂Dy forms by Mn and Al mutually substituting in Al₂Dy and Mn₂Dy, respectively. The maximum solid solubility of Al in Mn₁₂Dy is 79.3 at.%.     

Microstructures,Martensitic Transformation,and Mechanical Behavior of Rapidly Solidified Ti-Ni-Hf and Ti-Ni-Si Shape Memory Alloys

In this work, the microstructure and mechanical properties of rapidly solidified Ti_50?x/2Ni_50?x/2Hf _x (x = 0, 2, 4, 6, 8, 10, and 12 at.%) and Ti_50?y/2Ni_50?y/2Si _y (y = 1, 2, 3, 5, 7, and 10 at.%) shape memory alloys (SMAs) were investigated. The sequence of the phase formation and transformations in dependence on the chemical composition is established. Rapidly solidified Ti-Ni-Hf or Ti-Ni-Si SMAs are found to show relatively high yield strength and large ductility for specific Hf or Si concentrations, which is due to the gradual disappearance of the phase transformation from austenite to twinned martensite and the predominance of the phase transformation from twinned martensite to detwinned martensite during deformation as well as to the refinement of dendrites and the precipitation of brittle intermetallic compounds.     

Preparation and high-frequency soft magnetic property of FeCo-based thin films

A series of FeCo-based thin films were prepared by magnetron sputtering without applying an induced magnetic field.The microstructure,electrical properties,magnetic properties and thermal stability of FeCo,FeCoSiN monolayer thin film and[FeCoSiN/SiN_x]_n multilayer thin film were investigated systematically.When FeCo thin film was doped with Si and N,the resistivity and soft magnetic properties of the obtained FeCoSiN thin film can be improved effectively.The coercivity(H_c),resistivity(ρ) and ferromagnetic resonance frequency(f_r) can be further optimized for the[FeCoSiN/SiN_x]_n multilayer thin film.When the thickness of FeCoSiN layer and SiN_x layer is maintained at 7 and 2 nm,the H_c,p and f_r for[FeCoSiN/SiN_x]_n multilayer thin film are 225 A·m~(-1)392 μΩ·cm~(-1) and 4.29 GHz,respectively.In addition,the low coercivity of easy axis(H_(ce) ≈ 506 A·m~(-1)) of[FeCoSiN/SiN_x]_n multilayer thin film can be maintained after annealing at 300 ℃ in air for 2 h.     

Effect of Al and Mg Contents on Wettability and Reactivity of Molten Zn–Al–Mg Alloys on Steel Sheets Covered with MnO and SiO<Subscript>2</Subscript> Layers

The reactive wetting behaviors of molten Zn–Al–Mg alloys on MnO- and amorphous (a-) SiO₂-covered steel sheets were investigated by the sessile drop method, as a function of the Al and Mg contents in the alloys. The sessile drop tests were carried out at 460 °C and the variation in the contact angles (θ_c) of alloys containing 0.2–2.5 wt% Al and 0–3.0 wt% Mg was monitored for 20 s. For all the alloys, the MnO-covered steel substrate exhibited reactive wetting whereas the a-SiO₂-covered steel exhibited nonreactive, nonwetting (θ_c?>?90°) behavior. The MnO layer was rapidly removed by Al and Mg contained in the alloys. The wetting of the MnO-covered steel sheet significantly improved upon increasing the Mg content but decreased upon increasing the Al content, indicating that the surface tension of the alloy droplet is the main factor controlling its wettability. Although the reactions of Al and Mg in molten alloys with the a-SiO₂ layer were found to be sluggish, the wettability of Zn–Al–Mg alloys on the a-SiO₂ layer improved upon increasing the Al and Mg contents. These results suggest that the wetting of advanced high-strength steel sheets, the surface oxide layer of which consists of a mixture of MnO and SiO₂, with Zn–Al–Mg alloys could be most effectively improved by increasing the Mg content of the alloys.     

Microstructure and Room-Temperature Mechanical Properties of FeCrMoVTi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> High-Entropy Alloys

FeCrMoVTi _x (x values represent the molar ratio, where x = 0, 0.5, 1.0, 1.5, and 2.0) high-entropy alloys were prepared by a vacuum arc melting method. The effects of Ti element on the microstructure and room-temperature mechanical properties of the as-cast FeCrMoVTi _x alloys were investigated. The results show that the prepared alloys exhibited typical dendritic microstructure and the size of the microstructure became fine with increasing Ti content. The FeCrMoV alloy exhibited a single body-centered cubic structure (BCC1) and the alloys prepared with Ti element exhibited BCC1 + BCC2 mixed structure. The new BCC2 phase is considered as (Fe, Ti)-rich phase and was distributed in the dendrite region. With the increase of Ti content, the volume fraction of the BCC2 phase increased and its shape changed from a long strip to a network. For the FeCrMoV alloy, the fracture strength, plastic strain, and hardness reached as high as 2231 MPa, 28.2%, and 720 HV, respectively. The maximum hardness of 887 HV was obtained in the FeCrMoVTi alloy. However, the fracture strength, yield stress, and plastic strain of the alloys decreased continuously as Ti content increased. In the room-temperature compressive test, the alloys showed typical brittle fracture characteristics.     

Temperature-Dependent Flow Behavior and Microstructural Evolution During Compression of As-Cast Mg-7.7Al-0.4Zn

The microstructure and mechanical properties improve substantially by hot working. This aspect in as-cast Mg-7.7Al-0.4Zn (AZ80) alloy is investigated by compression tests over temperature range of 30-439°C and at strain rates of 5 × 10^?2, 10^?2, 5 × 10^?4 and 10^?4 s^?1. The stress exponent (n) and activation energy (Q) were evaluated and analyzed for high-temperature deformation along with the microstructures. Upon deformation to a true strain of 0.80, which corresponds to the pseudo-steady-state condition, n and Q were found to be 5 and 151 kJ/mol, respectively. This suggests the dislocation climb-controlled mechanism for deformation. Prior to attaining the pseudo-steady-state condition, the stress-strain curves of AZ80 Mg alloy exhibit flow hardening followed by flow softening depending on the test temperature and strain rate. The microstructures obtained upon deformation revealed dissolution of Mg₁₇Al₁₂ particles with concurrent grain growth of α-matrix. The parameters like strain rate sensitivity and activation energy were analyzed for describing the microstructure evolution also as a function of strain rate and temperature. This exhibited similar trend as seen for deformation per se. Thus, the mechanisms for deformation and microstructure evolution are suggested to be interdependent.     

Microstructure and Mechanical Properties of Mg-8Li-(0, 1, 2)Ca-(0, 2)Gd Alloys

A series of new Mg-8Li-xCa-yGd (x = 0, 1, 2; y = 0, 2; wt.%) alloys were prepared, and the microstructure and mechanical properties were investigated. The mechanical properties were characterized by tensile, compression and bending tests at room temperature. The results show that Mg-8Li-1Ca alloy is composed of alpha(Mg), beta(Li) and CaMg₂ phases. In addition to the same phases in Mg-8Li-1Ca, there also exists CaLi₂ phase in Mg-8Li-2Ca. In addition to the same phases in Mg-8Li-2Ca, GdMg₅ phase is also formed in Mg-8Li-1Ca-2Gd alloy due to the addition of Gd. Both Ca and Gd have refining effect in the alloys, and the refining effect of Ca is better than that of Gd. The additions of Ca and Gd can improve the tensile strength and yield strength, but decrease the elongation and the bending strength. Comparing the mechanical properties of the investigated alloys, Mg-8Li-1Ca-2Gd possesses the best mechanical properties.     

Effect of Si and Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Additions on the Oxidation Behavior of Ni–<Emphasis Type="Italic">x</Emphasis>Al (<Emphasis Type="Italic">x</Emphasis> = 5 or 10 wt%) Alloys at 1150 °C

The effect of Si and Y₂O₃ additions on the oxidation behavior of Ni–xAl (x = 5 or 10 wt%) alloys at 1150 °C was studied. The addition of Y₂O₃ accelerates oxidation rate of alloys, especially growth rate of NiO, but improves adherence of the scale to the substrate. The addition of Si facilitates the selective oxidation of Al, suppresses the formation of NiO and therefore reduces the critical Al content to form continuous layer of alumina scale. Higher Al content decreases the oxidation rate of alloys in binary Ni–Al alloys and increases the oxidation rate of alloys in ternary Ni–Al–Si alloys. The effect of third-element Si is more significant and beneficial than that of Al content in ternary Ni–Al–Si alloys.     

Characterization of Microstructure and Wear Resistance of PEO Coatings Containing Various Microparticles on Ti6Al4V Alloy

Titania-based composite coatings were prepared by plasma electrolytic oxidation (PEO) treatment of Ti6Al4V alloy in electrolyte with α-Al₂O₃, Cr₂O₃ or h-BN microparticles in suspension. The microstructure, composition of PEO composite coatings were analyzed by SEM, EDS and XRD. The wear resistance of composite ceramic coatings was studied by ball-on-disk wear test at ambient temperature and 300 °C. The results showed that the addition of microparticles accelerated the growth rate of PEO coating and changed the microstructure and composition of PEO coating. PEO coating was porous and mainly composed of rutile-TiO₂, anatase-TiO₂ and Al₂TiO₅. PEO/α-Al₂O₃ (Cr₂O₃ or h-BN) composite coating only had small micropores and appeared some α-Al₂O₃ (Cr₂O₃ or h-BN) phase. Besides, the addition of α-Al₂O₃ (Cr₂O₃ or h-BN) microparticles greatly improved the wear resistance of PEO coating. At ambient temperature, abrasive wear dominated the wear behavior of PEO coating, but abrasive wear and adhesive peel simultaneously happened at 300 °C. Whether at ambient temperature or 300 °C, PEO composite coating had better wear resistance than PEO coating. Besides, PEO/h-BN composite coating outperformed other composite coatings regardless of the temperature.     

Investigation of Fe content in Cu–Al–Ni Shape Memory Alloys

Polycrystalline Cu–Al–Ni–Fe-based shape memory alloys with different chemical composition were produced in an arc-melting furnace under an argon atmosphere. Homogenized and aged specimens were prepared for multiple analyses. The temperatures of reversible martensitic transformations, namely A_s, A_f, M_s, M_f, A_max and ΔH enthalpy values were determined by a DSC device. The phase transition analysis from the room temperature to 850°C was undertaken by DTA. To characterize the lattice structure, an XRD analysis was conducted, the results of which were confirmed by microstructure images obtained from optical microscope observations.     

Influence of High Pulsed Magnetic Field on the Dislocations and Mechanical Properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al Composites

At T6 state, Al–Zn–Mg–Cu aluminum matrix composites reinforced with Al₂O₃ particles generated in situ were subjected to high pulsed magnetic fields at different magnetic induction intensities (B = 2, 3 and 4 T). The results show that the dislocation densities in the treated samples increased with increasing B, and the magnetoplastic effect was determined to be the primary cause. The effect of the magnetic field is believed to alter the spin state of free electrons between dislocations and obstacles from the singlet state (associated with high bonding energy) to the triplet state (low bonding energy). The maximum ultimate tensile strength of 532 MPa was obtained at B = 4 T with 30 pulses, which was 20.7% higher than that of the initial sample, primarily because of dislocation strengthening. At B = 2 T, the elongation was at its maximum of 9.3%, representing an increase of 12% compared with the initial sample, while the associated ultimate tensile strength (447 MPa) was still higher than that of the untreated sample (440 MPa). The relationship between mechanical properties and microstructure was analyzed, and the improved properties observed in this work are explained by the transition of the electron spin state and the piling up of dislocations.     

Microstructure and mechanical properties of multi-principal component AlCoCrFeNiCu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloy

By introducing Cu, AlCoCrFeNiCu _x (x values in molar ratio, x = 0, 0.1, 0.5, 1.0, 1.5, 2.0, and 2.5) alloys were designed and prepared. The effects of Cu on microstructure and properties of AlCoCrFeNi alloy were investigated. The introduction of Cu results in the formation of Cu-rich FCC solid solution phase when Cu content is low. There are two FCC solid solution phases, i.e., Cu-rich FCC solid solution phase and phase transformation-induced FCC solid solution phase, when the Cu content is more than 1.0. Both the yield stress and plastic strain of alloy show a turning point when the Cu content is 0.5. Among the seven alloys, Cu_0.5 alloy exhibits the largest yield stress of 1187 MPa and the lowest plastic strain of 16.01 %.     

Phase Equilibria of the Co-Mo-Zr Ternary System at 1000 °C

The isothermal section of the Co-Mo-Zr ternary system at 1000 °C was investigated by using 29 alloys. The annealed alloys were examined by means of x-ray diffraction, optical microscopy, and electron probe microanalysis. It was confirmed that three ternary phases, λ₁ (Co_0.5-1.5Mo_1.5-0.5Zr, hP12-MgZn₂), ω (CoMoZr₄) and κ (CoMo₄Zr₉, hP28-Hf₉Mo₄B), exist in the Co-Mo-Zr ternary system at 1000 °C. And the experimental results also indicated that there are sixteen three-phase regions at 1000 °C. Thirteen of them were well determined in the present work: (1) (γCo)?+?Co₁₁Zr₂?+?Co₂₃Zr₆, (2) (γCo)?+?Co₂₃Zr₆?+?ε-Co₃Mo, (3) Co₂₃Zr₆?+?ε-Co₃Mo?+?μ-Co₇Mo₆, (4) (Mo)?+?μ-Co₇Mo₆?+?Co₂Zr, (5) (Mo)?+?Co₂Zr?+?λ₁, (6) (Mo)?+?Mo₂Zr?+?λ₁, (7) λ₁?+?Mo₂Zr?+?CoZr, (8) Co₂Zr?+?CoZr?+?λ₁, (9) Mo₂Zr?+?CoZr₂?+?ω, (10) κ?+?Mo₂Zr?+?ω, (11) CoZr₂?+?liquid?+?ω, (12) (βZr)?+?liquid?+?ω and (13) (βZr)?+?κ?+?ω. The homogeneity of λ₁ spans in the range of 28.66-50.77 at.% Co and 15.71-37.03 at.% Mo, and that for ω is within the range of 18.66-23.64 at.% Co and 8.53-14.68 at.% Mo. The homogeneity range for κ is from 8.09 at.% to 9.94 at.% Co and 23.13 at.% to 25.58 at.% Mo. The maximum solubility of Zr in μ-Co₇Mo₆ phase, Mo in Co₂Zr phase and Co in Mo₂Zr phase were determined to be 6.17, 11.27 and 9.14 at.%, respectively. While the solubility of Zr in ε-Co₃Mo and (γCo) phases, Mo in Co₁₁Zr₂ and CoZr phases were detected to be extremely small. According to this work, the Co₂₃Zr₆ phase contained 15.61 at.% Mo and 12.7 at.% Zr. In addition, the maximum solubility of Co and Zr in (Mo) phase and Mo in (γCo) phase were measured to be 3.50, 5.44 and 7.40 at.%, respectively.     

Analysis of Plastic Flow Instability During Superplastic Deformation of the Zn-Al Eutectoid Alloy Modified with 2 wt.% Cu

The aim of this work is to analyze the plastic flow instability in Zn-21Al-2Cu alloy deformed under 10^?3 s^?1 and 513 K, which are optimum conditions for inducing superplastic behavior in this alloy. An evaluation using the Hart and Wilkinson–Caceres criteria showed that the limited stability of plastic flow observed in this alloy is related to low values of the strain-rate sensitivity index (m) and the strain-hardening coefficient (γ), combined with the tendency of these parameters to decrease depending on true strain (ε). The reduction in m and γ values could be associated with the early onset of plastic instability and with microstructural changes observed as function of the strain. Grain growth induced by deformation seems to be important during the first stage of deformation of this alloy. However, when ε > 0.4 this growth is accompanied by other microstructural rearrangements. These results suggest that in this alloy, a grain boundary sliding mechanism acts to allow a steady superplastic flow only for ε < 0.4. For ε values between 0.4 and 0.7, observed occurrences of microstructural changes and severe neck formation lead to the supposition that there is a transition in the deformation mechanism. These changes are more evident when ε > 0.7 as another mechanism is thought to take over.     

Improved High-Temperature Microstructural Stability and Creep Property of Novel Co-Base Single-Crystal Alloys Containing Ta and Ti

The influence of Ta and Ti additions on microstructural stability and creep behavior in novel Co-Al-W base single-crystal alloys has been investigated. Compared to the ternary alloy, the γ′ solvus temperature and γ′ volume fraction were raised by individual additions of Ta and Ti, and increased further in the quinary alloy containing both alloying additions. In contrast to ternary and quaternary alloys, an improved microstructural stability with the stable γ–γ′ two-phase microstructure and more than 60% γ′ volume fraction existed in the quinary alloy after prolonged aging treatment at 1050°C for 1000 h. The creep behavior at 900°C revealed lower creep rates and longer rupture lives in the quaternary alloys compared to the ternary alloy, whereas the quinary alloy exhibited even better creep resistance. When the creep temperature was elevated to about 1000°C, the creep resistance of the quinary alloy exceeded the previously reported Co-Al-W-base alloys and first-generation Ni-base single-crystal superalloys. The improved creep resistance at approximately 1000°C was considered to be associated with high γ′ volume fraction, γ′ directional coarsening, and dislocation substructure, which included γ–γ′ interfacial dislocation networks and the sheared γ′ precipitates containing stacking faults and anti-phase boundaries.