Microstructures of spinodal phases in Cu-15Ni-8Sn alloy

The microstructures of spinodal phases in Cu-15Ni-8Sn alloy were studied by TEM. It was found that when the alloy is completely in a as-quenched state, spinodal decomposition is quick. Ordering appears after spinodal decomposition. The ordered phase with DO₂₂ structure has three variants obtained from coarsening spinodal structure. The reason of ordering appeared after spinodal decomposition is that the content of solute atoms needed by ordering is higher than the average, which can be reached by the composition fluctuation of spinodal decomposition. It was speculated that the morphology of the ordered phase is needle-like.     

Solidification structures of high niobium containing TiAl alloys

To understand the effect of alloy stoichiometry on the microstructural development and mechanical behavior of γ-TiAl-based materials, it is necessary to have a determination of the phase relationships for the TiAl alloy system near the γ phase field. Cast structures and phases of Ti-(43-47)Al-8Nb-(1-2)Mn (at%) alloys have been studied by using scanning electron microscope and X-ray diffraction. Their solidification path and microstructure development during the solidification were analyzed. The experimental results show that the alloys with different Al contents form different macrostructures and microstructural morphologies. This indi-cates that the solidification paths are different with different Al contents. The alloy with 43Al forms equiaxed grain structure, and the solidification path is as follows:L→L+β→β→α+β→α+β cores→α₂+γ+B2 cores. Whereas the alloy with 47Al forms colum-nar grain structure, and the solidification path is as follows:L→L+β→α+β+L→α+γ+β cores→tXj+γ+BZ cores. The p phase is their primary solid phase and can be retained to ambient temperature. The alloy with 43Al solidifies completely into β phase. The peritectic reactions L+P→α and L+α→γ appear when the Al content increases to 47Al.     

CALCULATING MODEL OF MASS ACTION CONCENTRATIONS FOR Cd-Sb ALLOY MELT

According to the Cd-Sb alloy phase diagram, resistivity, heat capacity, partial molar entropy and viscosity,the structural units of this alloy melt have been determined as Cd and Sb atoms as well as Cd₃Sb₂, Cd₄Sb₃ and CdSb compounds.Based on these structural units and the coexistence theory of metallic melt structure involing compound formation,a calculating model of mass action concentrations has been deduced.The calculated mass action concentrations N_Cd are in good agreement with measured activities a_Cd. The Gibbs standard free energy of formatioin for above three compunds have been obtained too.     

Microstructure and phase composition of hypoeutectic Te–Bi alloy as evaporation source for photoelectric cathode

A hypoeutectic 60Te–40Bi alloy in mass percent was designed as a tellurium atom evaporation source instead of pure tellurium for an ultraviolet detection photocathode. The alloy was prepared by slow solidification at about 10-2 K·s-1. The microstructure, crystal structure, chemical composition, and crystallographic orientation of each phase in the as-prepared alloy were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. The experimental results suggest that the as-prepared 60Te–40Bi alloy consists of primary Bi₂Te₃ and eutectic Bi₂Te₃/Te phases. The primary Bi₂Te₃ phase has the characteristics of faceted growth. The eutectic Bi₂Te₃ phase is encased by the eutectic Te phase in the eutectic structure. The purity of the eutectic Te phase reaches 100wt% owing to the slow solidification. In the eutectic phases, the crystallographic orientation relationship between Bi₂Te₃ and Te is confirmed as [0001]_Bi2Te3//[1213]_Te and the direction of Te phase parallel to [1120]_Bi2Te3 is deviated by 18° from N(2111)_Te.     

Evaluation of precipitation hardening in TiC-reinforced Ti<Subscript>2</Subscript>AlNb-based alloys

Ti₂AlNb-based alloys with 0.0wt%, 0.6wt%, and 2.0wt% carbon nanotube (CNT) addition were fabricated from spherical Ti-22Al-25Nb powder by sintering in the B2 single-phase region. Phase identification and microstructural examination were performed to evaluate the effect of carbon addition on the hardness of the alloys. Carbon was either in a soluble state or in carbide form depending on its concentration. The acicular carbides formed around 1050℃ were identified as TiC and facilitated the transformation of α₂+B2 → O. The TiC was located within the acicular O phase. The surrounding O phase was distributed in certain orientations with angles of 65° or 90° O phase particles. The obtained alloy was composed of acicular O, Widmanstatten B2+O, and acicular TiC. As a result of the precipitation of carbides as well as the O phase, the hardness of the alloy with 2.0wt% CNT addition increased to HV 429±9.     

Microstructure Study of Ti-24Al-14Nb-3V Alloy

The microstructure of Ti-24Al-14NB-3V intermetallic alloy with solution treated was investigated by trans mission electron microscopy (TEM) and selected area electron diffraction (SAD) in conjunction with X-ray energy dispersive spectroscopy (EDS) techniques. It shown that φ=50% ductile β₀-phase and small amount of O phase,and α₂ with the number of dislocations having c-component resulted in increasing slip system of the material, have contributed to a good combination of strength and ductility at room temperature. Owing to some reciprocal planes of similarity between α₂ and O Phases, to distinguish both of two phases, a series of diffraction patterns obtained by tilting around one reciprocal direction of the phase are needed based on the systematic extinction and reciprocal planes sequences occurred in the diffraction patterns, if those patterns are not containing one of three reciprocal unit vectors, a*, b*, c* in terms of the crystal unit cell, a, b, c.     

Effect of Li content on the microstructure and properties of lead-free piezoelectric(K0.5Na0.5)1-xLixNbO3 ceramics prepared by SPS

Lead-free piezoelectric (K_0.5Na_0.5)_1-xLi_xNbO₃ (x = 0at%-20at%) ceramics were synthesized by spark plasma sintering (SPS) at low temperature and the effects of LiNbO₃ addition on its crystal structure and properties were also studied. When the Li content was less than 6at%, a single proveskite phase with the similar structure of (K_0.5Na_0.5)NbO₃ was formed; and a secondary phase with K₃Li₂Nb₅O₁₅ structure was observed in the 6at% < x < 20at% compositional range. Furthermore, LiNbO₃ existed as the third phase when the Li content was higher than 8at%. The grain sizes increased from 200-500 nm to 5-8 μm when the K₃Li₂Nb₅O₁₅ and LiNbO₃ like phases were formed. With increasing Li content, the relative density of the ceramics first decreased from 97% to 93% and then kept constant. The piezoelectric coefficient d₃₃, dielectric constant, and planner electromechanical coupling factor exhibited a decreasing tendency with increasing Li content because of the decrease in density and the formation of the secondary phase such as K₃Li₂Nb₅O₁₅ and LiNbO₃. The formation of dense microstructure with a single phase is necessary in improving the properties of the (K_0.5Na_0.5)_1-xLi_xNbO₃ ceramics.     

Kinetics of Hydrogen Absorption in Hydrogen Storage Alloy

Hydrogenation kinetics of MLNi_3.8(Co,Mn,Al)_1.2 and MLNi_3.7(Co,Mn,Al)_1.2Cu_0.1 alloy in α + β phase at the temperature range of 30~70 ℃ has been studied. The kinetic mechanism of hydrogen absorption is not affected by initial hydrogen pressure. Temperature does not influence the rate of hydrogen absorption obviously. In the prior and later period of hydrogen absorption the rate-controlling step is chemical reaction and hydrogen diffusion in the hydride phase respectively for MLNi_3.8(Co,Mn,Al)_1.2 alloy. Adding Cu, the rate-controlling step changes from chemical reaction to the nucleation and growth of β phase in the prior period and the process of hydrogen absorption still controlled by diffusion in the later period.     

Transient spinodal decomposition during annealing of rapidly solidified Al-10Sr alloy

Rapidly solidified Al-10Sr alloy ribbons were prepared using a single roller melt spinning technique. The annealing process of the rapidly solidified Al-10Sr alloy has been carried out using differential scanning calorimetry (DSC). The microstructure of as-annealed Al-10Sr alloy has been characterized by transmission electron microscopy (TEM). The equilibrium AUSr phase is dominant in the as-annealed alloy. Besides the Al₄Sr phase, an AlSr phase is also found in the alloy isothermally annealed at 873 K for 90 min. Furthermore, a modulated nanostructure was observed in the alloy isothermally annealed at 873 K for 90 min. With further prolonged annealing time, however, the AlSr phase disappears in the as-annealed alloy. The dependence of particle size and growth rate on annealing time as well as the modulated structure shows that the occurrence of the AlSr phase may be due to the spinodal decomposition.     

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.     

Effect of stoichiometry and Cu-substitution on the phase structure and hydrogen storage properties of Ml-Mg-Ni-based alloys

To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were studied. Nonsubstituted Ml_0.80Mg_0.20(Ni_2.90Co_0.50-Mn_0.30Al_0.30)_x (x=0.68, 0.70, 0.72, 0.74, 0.76) alloys and Cu-substituted Ml_0.80Mg_0.20(Ni_2.90Co_0.50-y Cu_y Mn_0.30Al_0.30)_0.70 (y=0, 0.10, 0.30, 0.50) alloys were prepared by induction melting. Phase structure analysis shows that the nonsubstituted alloys consist of a LaNi₅ phase, a LaNi₃ phase, and a minor La₂Ni₇ phase; in addition, in the case of Cu-substitution, the Nd₂Ni₇ phase appears and the LaNi₃ phase vanishes. Thermodynamic tests show that the enthalpy change in the dehydriding process decreases, indicating that hydride stability decreases with increasing stoichiometry and increasing Cu content. The maximum discharge capacity, kinetic properties, and cycling stability of the alloy electrodes all increase and then decrease with increasing stoichiometry or increasing Cu content. Furthermore, Cu substitution for Co ameliorates the discharge capacity, kinetics, and cycling stability of the alloy electrodes.     

Cold Rolling Texture in Ordered CuZn Alloy

The texture of 80% cold rolling CuZn ordered alloy was investigated. The development of rolling texturein 50%Cu-50%Zn(at.) alloy has been characterized by a inhomogenous {111} fiber texture with strong {111} <112> component, which is significantly different from the conventional Cu-Zn alloys. The main characters of cold rolling textures in ordered CuZn alloy are obviously similar to that in IF steel with bcc structure or ordered Fe₃Al-based alloys with imperfect B2 structure. From the rolling texture obtained by experiments and simulations,it can be estimated that main deformation mechanism are characterized by the activation of slip systems with <111> Burgers vector in CuZn ordered alloy.     

Precipitation behavior of B2-like particles in Fe-Cu binary alloy

The precipitation behavior in Fe-Cu binary alloy was investigated under transmission electron microscope (TEM) during aging at 650℃ for the time range of 100 s to 300 h. In addition to the zones with higher copper content and ε-Cu were observed, a metastable phase with B2-like structure was found in the early stage of the precipitation process, which is quite different from the equilibrium copper phase shown in the Fe-Cu binary phase diagram and has perfect coherent relationship to the α-Fe matrix. The appearance of B2-like structure is very important concerning the mechanism of aging strengthening effect and mechanical properties of corresponding engineering steels and alloys containing copper.     

Effects of high-pressure rheo-squeeze casting on the Fe-rich phases and mechanical properties of Al-17Si-(1,1.5)Fe alloys

The effects of high pressure rheo-squeeze casting (HPRC) on the Fe-rich phases (FRPs) and mechanical properties of Al-17Si-(1,1.5)Fe alloys were investigated. The alloy melts were first treated by ultrasonic vibration (UV) and then formed by high-pressure squeeze casting (HPSC). The FRPs in the as-cast HPSC Al-17Si-1Fe alloys only contained a long, needle-shaped β-Al₅FeSi phase at 0 MPa. In addition to the β-Al₅FeSi phase, the HPSC Al-17Si-1.5Fe alloy also contained the plate-shaped δ-Al₄FeSi₂ phase. A fine, block-shaped δ-Al₄FeSi₂ phase was formed in the Al-17Si-1Fe alloy treated by UV. The size of FRPs decreased with increasing pressure. After UV treatment, solidification under pressure led to further refinement of the FRPs. Considering alloy samples of the same composition, the ultimate tensile strength (UTS) of the HPRC samples was higher than that of the HPSC samples, and the UTS increased with increasing pressure. The UTS of the Al-17Si-1Fe alloy formed by HPSC exceeded that of the Al-17Si-1.5Fe alloy formed in the same manner under the same pressure. Conversely, the UTS of the Al-17Si-1Fe alloy formed by HPRC decreased to a value lower than that of the Al-17Si-1.5Fe alloy formed in the same manner.     

Effect of Ni addition on microstructure and mechanical properties of Al-Mg-Si-Cu-Zn alloys with a high Mg/Si ratio

The effect of adding 0.03wt% Ni on the microstructure and mechanical properties of Al-Mg-Si-Cu-Zn alloys was systematically studied. The results reveal that the number density of spherical Fe-rich phases within grains increases with the addition of Ni, accompanied by the formation of Q (Al₃Mg₉Si₇Cu₂) precipitates around the spherical Fe-rich phases. Additionally, Ni addition is beneficial to reducing the grain size in the as-cast state. During the homogenization process, Q phases could be completely dissolved and the grain size could remain basically unchanged. However, compared with the Ni-free alloy, the Fe-rich phase in the Ni-containing alloy is more likely to undergo the phase transformation and further form more spherical particles during homogenization treatment. After thermomechanical processing, the distribution of Fe-rich phases in the Ni-containing alloy was further greatly improved and directly resulted in a greater formability than that of the Ni-free alloy. Accordingly, a reasonable Ni addition positively affected the microstructure and formability of the alloys.     

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.     

Microstructure,mechanical, and corrosion properties of extruded low-alloyed Mg–xZn–0.2Ca alloys

The microstructure, mechanical, and corrosion properties of extruded low-alloyed Mg-xZn-0.2Ca (x=0, 1.0, 2.0, 3.0) alloys were investigated in this study. Findings from scanning electron microscope, X-ray diffraction and transmission electron microscopy results indicate that the amount of ternary Ca₂Mg₆Zn₃ phase, as the only secondary phase in 1.0Zn, 2.0Zn, and 3.0Zn alloys, gradually increases with the addition of Zn, while the Mg₂Ca phase was observed in the Mg-0.2Ca alloy only. Zn has a strong effect on the orientation and intensity of textures, which also influence mechanical behaviors, as revealed by electron back-scatter diffraction. Among all the alloys, the Mg-2.0Zn-0.2Ca alloy obtains the maximum tensile strength (278 MPa) and yield strength (230 MPa). Moreover, Zn addition has an evident influence on the corrosion properties of Mg-xZn-0.2Ca alloy, and Mg-1.0Zn-0.2Ca alloy exhibits the minimum corrosion rate. This paper provides a novel low-alloyed magnesium alloy as a potential biodegradable material.     

HOT CORROSION BEHAVIOR OF Ni-BASED SUPERALLOY WITH HIGH Cr CONTENTS -PART 1.EXPERIMENTAL STUDY

A systematic study of the effects of Ti, Ta and Nb on the hot corrosion behavior of alloy system Ni-16Cr-gAl-2W-1Mo-4Co-(0~4)Ti-(0~4)Ta-(0~4)Nb (at%) was conducted. The results showed that, in certain compositional regions, the hot corrosion resistance in 75% Na₂SO₄+25%NaCl molten salt of the expermental alloys was similar to that of IN738LC alloy. The hot corrosion property balances with other properties, which provides the basis for selecting alloy compositions to develop single crystal superalloys of high performance hot corrosion resistance.     

Mechanism of α-Cr precipitation and crystallographic relationships between α-Cr and δ phases in Inconel 718 alloy after long-time thermal exposure

To study the precipitation mechanism of α-Cr phase in Inconel 718 alloy, the samples after long-time aging at 650 and 677℃ were examined by microstructural observations and chemical phase analysis methods. Combining the thermodynamics and kinetics calculation results, α-Cr always precipitates in the vicinity of δ phase, because δ phase rejects Cr into the γ-matrix when growing. The selected area diffraction patterns confirm that the crystallographic relationships of α-Cr with δ phase are (010)_δ//(1 10)_α-Cr and [100]_δ//[111]_α-Cr. A graphic model is also presented to show the crystallographic relation between α-Cr and δ phases.     

Microstructure and magnetostrictive performance of NbC-doped<100>oriented Fe-Ga alloys

The <100> oriented Fe₈₃Ga₁₇ alloy rods with various NbC contents less than 1at% were prepared by the directional solidification method at a growth rate of 720 mm·h-1. Low NbC-content was found to affect the oriented grain growth and slightly improve the <100> orientation. Flat grain boundaries in the alloys with low NbC contents less than 0.2at% became greatly curved at higher NbC contents, and a large amount of Nb-rich precipitates were observed in the alloys with high NbC contents. Small amounts of NbC, less than 0.2at%, resulted in an increase in magnetostrictive strain due to the improvement of the <100> orientation, and a high magnetostrictive strain value of 335×10-6 under a pre-stress of 15 MPa was obtained in the 0.1at% NbC-doped alloys. The magnetostrictive performance obviously decreased with the NbC addition higher than 0.5at%, and the strain sensitivity under no pre-stress was lower than that in the binary Fe-Ga alloy.