Number Of Secondary Phases Research Articles

Thermal conductivity of binary Al alloys with different alloying elements

This work investigates the physical properties of several binary Al-Si/Ni/Fe/Cu/Mg alloys with varying alloying element contents and microstructures. The findings indicate that as the content of alloying elements increases, the number of secondary phases in binary Al alloys rises, and these phases become coarser. In hypereutectic compositions, primary phases in Al-Ni and Al-Fe alloys take on a needle-like morphology with high aspect ratios, forming a dendritic network. Regarding properties, in the hypoeutectic region, both thermal conductivity and electrical conductivity of binary alloys initially decrease sharply, followed by a more gradual decline with the addition of alloying elements. This trend occurs because thermal conductivity is mainly influenced by supersaturated solid solutions. In hypereutectic Al-Ni and Al-Fe alloys, the presence of large, needle-like primary phases significantly hinder the heat transfer, resulting in a more apparent reduction in both thermal conductivity and electrical conductivity. Among the five binary alloys, Al-Ni and Al-Fe alloys, which have lower solute concentrations of alloying elements in the Al matrix, exhibit the highest thermal and electrical conductivity. Furthermore, with increasing alloying element contents, the phonon thermal conductivity of Al-Si alloy increases more markedly compared to other alloys. The study will offer a fundamental understanding for the development of advanced alloy.

Influence of solid solution treatment on fatigue crack propagation behavior in the thickness direction of 2519A aluminum alloy thick plates

2519A aluminum alloy thick plates have excellent applications in the military industry due to their superior ballistic resistance and fatigue properties. However, the delamination cracking along the thickness direction of this alloy hinders its further utilization. To address this issue and enhance the fatigue properties of this alloy, the effect of single-stage solid solution treatment (SST) and two-stage solid solution treatment (DST) on the fatigue crack propagation (FCP) behavior in the thickness direction of the alloy was investigated. Compared to the optimum SST, the volume fraction of the secondary phase of the alloy was reduced by 28.6% after DST. The precipitated phases were finer with more uniform distribution, and the volume fraction and number density of the precipitation increased by 47% and 30%, respectively. The DST resulted in a lower fatigue crack growth rate (FCGR) and an increase of 2.92% in the critical stress intensity factor value (ΔKcr). The crack propagation mode of the alloy after SST was inter/transgranular crack propagation, while it was transgranular after DST. The aspect ratio of grain and the number of secondary phases in the alloy decrease after DST. Meanwhile, the grain boundary (GB) precipitation phase spacing, the precipitation-free zone (PFZ) width, and the spacing between the secondary phases increase. These changes result in decreased crack sources in the alloy and reduced the bridging effect of secondary phases on fatigue cracks, thus improving the fatigue performance of the alloy.

Effect of Niobium on Sintering Process of Gamma Phase Uranium Alloys Fuel Pellets

Abstract As a candidate material for metallic fuel, U-Mo metal fuel pellets are the most promising. U-Mo and U-Mo-Nb alloy pellets with a certain porosity were successfully prepared by the process of hydrogenation/dehydrogenation—compression molding—argon liquid-phase sintering. In order to study the effect of Nb addition on γ phase uranium alloy fuel pellets, microstructure and thermophysical properties of the samples were investigated using scanning electron microscope (SEM), in situ synchrotron X-ray diffraction (XRD), and differential scanning calorimeter (DSC) measurements. Results showed that with the increase of Nb content in the pellets from the nonadd to micro-adding, Nb can facilitate the diffusion of Mo into the U matrix, resulting in the formation of a metastable γ-U phase. Meanwhile, during the same liquid phase sintering process of U-Mo fuel pellets, with the increase of Nb content, the number of secondary phases in U-Mo fuel pellets gradually decreased, while the size and number of voids of the secondary phases decreased. The specific heat capacity and thermal diffusivity of porous γ phase uranium alloys fuel pellets with different density were measured and thermal conductivity from 100 °C to 600 °C were calculated according to the experiment results. It is suggested that the thermal conductivity will increase with the density of pellets increasing.

The effect of step cooling treatment on the microstructure of Cu2ZnSnS4 film and its electric property

Flexible Cu2ZnSnS4 (CZTS) thin-film solar cells have the advantages of high flexibility, lightweight, and easy storage, which can provide portable and clean energy for various portable electronic and communication devices and vehicles. In this work, CZTS thin film deposited on flexible aluminum foil were prepared by vacuum magnetron sputtering and sulfide annealing in a tubular furnace. A step-by-step cooling way was applied to the annealing stage aiming at tuning the formation of CZTS, that is, when the slow cooling reached a target temperature (400 °C, 350 °C, 300 °C, 250 °C), a rapid cooling was triggered by opening the tube furnace lid. The effects of step cooling on the micro structure and property of CZTS film were studied by X-ray diffraction, Raman scattering, energy dispersive spectroscopy, scanning electron microscopy and current-voltage (I-V) characteristic curve test. The experimental results showed that all samples have CZTS phase and the Al/CZTS interface exhibited ohmic contact. And the formation of secondary phases like SnS, Sn2S3 and Cu31S16 in the sample film can be tuned by the step cooling treatments. The sample treated at 300 °C had the highest CZTS content, the average grain size of CZTS was 45 nm and the number of secondary phases was fewer. Beside, the I-V curve revealed that this sample had the lowest resistance. The experimental results in this work indicate the feasibility of Al as a substrate and back electrode for CZTS thin film.

Comparative Study on Electrical Conductivity of CeO2-Doped AlN Ceramics Sintered by Hot-Pressing and Spark Plasma Sintering.

Aluminum nitride (AlN) ceramics were prepared by both Hot-pressing (HP) and Spark-Plasma-Sintering (SPS) using cerium oxide as the sintering aid. The characterization of AlN raw powder denoted the presence of an amorphous layer that led to the formation of aluminum oxide. During the sintering process, CeO2 introduced as a sintering aid was reduced into Ce2O3. The latter reacted with aluminum oxide to form a transient liquid phase that promotes sintering by both HP and SPS. A reactional path leading to the formation of secondary phases, such as CeAlO3 and CeAl11O18, has been proposed according to the pseudo-binary Al2O3 – Ce2O3. Ceramics obtained from HP and SPS are presented as similar, except for the secondary-phase distribution. The influences of secondary phase composition and distribution on electrical conductivity were evaluated by leakage current measurements. The mechanism of DC conduction and the global conductivity of ceramics were discussed according to the sintering process and the number of secondary phases.

Optimizing the structural, morphological and thermoelectric properties of zinc oxide by the modulation of cobalt doping concentration

A study is conducted to determine the effects of cobalt doping concentration on structural, morphological and thermoelectric properties of Zinc Oxide (ZnO). To test this hypothesis, cobalt doped zinc oxide nano-particles are prepared by hydrothermal method by modulating the Cobalt (Co) concentration from 0.1 to 0.5. The X-Ray Diffraction (XRD) and Raman data is suggested that crystallinity of grown samples is found to be decreased by increasing the concentration of Co atoms. The poor crystallinity of the sample having higher concentration of Co atoms is due to the emergence of secondary phases. The value of Seebeck coefficient is also improved with doping as indicated by the high Seebeck value (250 µV/°C) of Zn0.5Co0.5O. This enhancement of Seebeck coefficient is linked with the number of secondary phases. In contrast, electrical conductivity is reduced due to the generation of the impurity level close to the conduction band. In conclusion, at higher doping content, the overall power factor is enhanced with a slow increase in Seebeck coefficient and decrease in electrical conductivity by doping content.

Tribological Performance of CoCrMo Alloys with Boron Additions in As-Cast and Heat-Treated Conditions

The present study evaluates the effect of boron additions on the tribological performance of CoCrMo alloys. The alloys were prepared with boron ranging from 0.06 to 1 wt%. The materials were characterized using metallographic techniques, scanning electronic microscopy, and roughness and hardness tests. Tribological evaluation was made by means of ball-on-disc tests for sliding distances of 4, 8 and 12 km. The samples were in the as-cast condition and after a heat treatment at 1200 °C for 1 h, finished by water quenching. The results showed that wear resistance was influenced by the microstructure and the number of secondary phases. The volume loss decreased as the boron content increased. Due to hard phases, abrasion wear was observed. Delamination fatigue was also detected after long sliding distances. Both wear mechanisms diminished in higher boron content alloys.

Microstructure of 7N01 Aluminum Alloy Microalloyed with Er and Zr in the Homogenization Process

The microstructure and segregation of 7N01 aluminum alloy microalloyed with Er and Zr before and after homogenization process at 470 °C for 24 h have been investigated using transmission electron microscope (TEM), and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscope (EDS) and transmission electron detecter (STEM). SEM images and EDS line scan results showed that there were dendritic segregation of Mg and Zn and micron-sized primary phases along dendrites in the as-cast alloy. The primary phases were mainly Al2Mg3Zn3 containing Al, Zn, Mg and Mn. And a small amount of primary phases were the particles containing Al, Zn, Mg, Mn, Cr and Er and the particles containing Al, Zn, Mg, Er, Mn, Fe and Cr. After homogenization at 470°C for 24 h, dendritic segregation of Mg and Zn was eliminated, Al2Mg3Zn3 and the particles containing Al, Zn, Mg and Mn were basically dissolved. The particles containing Al, Zn, Mg, Mn, Cr and Er and the particles containing Al, Zn, Mg, Er, Mn, Fe and Cr remained. Meanwhile, TEM and STEM images showed that a large number of secondary phases appeared after the homogenization, which were mainly distributed in the inter-dendrite area. EDS results showed that the block-shaped and rod-shaped phases with the width of 10-70 nm and length of 100-500 nm were the particles containing Al, Cr and Mn or Al, Mg, Cr and Mn, and the ellipsoid secondary phase with the size of 50-100 nm was MgZn2.

Corrosion and cracking characteristics upon aging of hyper duplex stainless steel weld

ABSTRACTIn this study, the effects of Mo content and aging temperature on the corrosion characteristics of newly designed hyper duplex stainless steel welds were investigated. Each specimen was aged at 600°C for 1–100 h, and weld cracking occurred when the 6 wt-% Mo specimen was aged for more than 40 h. In addition, electron backscatter diffraction and X-ray diffraction analysis found that the number of secondary phases increased as aging time increased. Based on the potentiodynamic polarisation test for assessing the corrosion characteristics according to the aging time, the corrosion resistance decreased sharply after 40 h, when cracking occurred.HighlightsWhen aging treatment for more than 40 h was performed on 6 wt-% Mo specimen, weld crack occurred.High hardness values above 450 Hv0.5 were measured in specimens aged more than 40 h.Secondary phases such as σ-phase and χ-phase were observed in specimens aged for more than 40 h.The specimens aged for more than 40 h showed a rapid decrease in corrosion resistance.

Microstructure of Mg96Zn2Y2 alloy joint formed by resistance spot welding

Mg96Zn2Y2 alloy sheets were welded by employing a resistance spot welding technique. The microstructures of the joint were observed and analyzed using scanning electron microscopy and transmission electron microscopy to investigate the difference between it and those of the base material. The joint comprises a base metal zone, heat-affected zone, fusion zone, and nugget. In the heat-affected zone, the dissolution of secondary phases occurred locally. In the fusion zone, the α-Mg grains were coarsened; and the secondary phase was transformed into a network distribution. In the nugget, the α-Mg grains were approximately 30 μm in diameter; and most of the secondary phase possessed a long-period stacking-ordered structure of 18 periods rhombohedral lattice. The results reveal that the number of secondary phases and Mg3Zn3Y2 compounds formed in the nugget were smaller than those observed in the base metal.

OPTIMIZATION OF TEMPERATURE HARDENING FOR IMPROVING THE HEAT RESISTANCE OF TOOL STEEL 4Х5MФ1С IN VARIOUS WORKPIECES. PART 2. THE CHOICE OF THE MODE OF HARDENING STEEL 4Х5MФ1С TO INCREASE THE HARDNESS AND HEAT RESISTANCE AFTER TEMPERING

A new mode of heat treatment, including oil quenching from temperature 1150 °C with tempering at 500–650 °С for 1,5 hours was developed. The effect of increasing the level of hardening and the heat resistance is determined by more complete dissolution of the steel matrix, the coarsening of grains and morphology of the primary phase of the structure and as a result of high temperature heating and increasing of the number of secondary phases as a result of the tempering. The results of the work could be used in production of working parts is highly resourceful tool for heat forming.

Effect of Yb substitution in Bi-2212 ceramics prepared by laser floating zone technique

In the present work, the influence of Yb substitution for Bi on the structural, electrical and magnetic properties of textured Bi-2212 ceramics has been investigated. X-ray diffraction studies indicated that the major peaks correspond to the Bi-2212 phase. The SEM images clearly show that there is an increase in the number of secondary phases with raising Yb content while all samples maintain similar grain morphology. Magnetic analysis of all samples has been done by magnetic hysteresis measurements, indicating that an enhancement in the M-H loops is obtained by a low Yb doping. The critical current density of samples was calculated from the M-H curves by using Bean’s critical state model, indicating that sample with 0.05 Yb substitution possesses the highest J c values.

Effect of Charge-balancing Species on Sm3+ Incorporation in Calcium Vanadinite

ABSTRACTApatites are often seen as good potential candidates for the immobilization of halide-rich wastes. In particular, phosphate apatites have received much attention in recent years, however, their synthesis often produces complicated multi-phase systems, with a number of secondary phases forming [1.2]. Calcium vanadinite (Ca5(VO4)3Cl) demonstrates a much simpler phase system, with only a single Ca2V2O7 secondary phase which can easily be retarded by the addition of excess CaCl2. However, when doping with SmCl3 (as an inactive analogue for AnCl3) the Sm forms a wakefieldite (SmVO4) phase rather than being immobilized within the vanadinite, a result of having to form an energetically unfavourable Ca vacancy in order for the lattice to remain neutral overall. It has been postulated that charge-balancing the lattice via co-substitution of a monovalent cation will be less disfavoured and therefore help stabilise formation of a (Ca5-2xSmxAx)(VO4)3Cl solid solution (A = monovalent cation). This has been investigated using a combined modelling and experimental approach. Static lattice calculations performed using Li+, Na+ and K+ as charge-balancing species have shown the energy cost to be less than half that of charge-balancing via formation of a Ca vacancy. As a result, solid state synthesis of (Ca5-2xSmxLix)(VO4)3Cl, (Ca5−2xSmxNax)(VO4)3Cl and (Ca5-2xSmxKx)(VO4)3Cl solid solutions have been trialled, and analysis of the resulting products has shown a significant reduction in both the SmVO4 and Ca2V2O7 secondary phases across all dopant levels.

Calcium Vanadinite: An Alternative Apatite Host for Cl-rich Wastes

ABSTRACTApatites are often seen as good potential candidates for the immobilization of halide-rich wastes and, in particular, chlorapatite (Ca5(PO4)3Cl) has received much attention in recent years. However, synthesis of chlorapatite waste-forms can produce a complicated multi-phase system, with a number of secondary phases forming, including β-TCP (Ca3(PO4)2), spodiosite (Ca2(PO4)Cl) and pyrophosphate (Ca2P2O7), many of which require elevated temperatures and extended calcinations times to reduce. Calcium vanadinite (Ca5(VO4)3Cl) demonstrates a much simpler phase system, with calcination at 750 °C yielding Ca5(VO4)3Cl together a small quantity of a Ca2V2O7secondary phase, the formation of which can be retarded by the addition of excess CaCl2. Characterization of compositions doped with SmCl3as an inactive analogue for AnCl3show the Cl to be immobilized in the vanadinite whilst the Sm forms a wakefieldite (SmVO4) phase.

Microstructural, mechanical and tribological characterisation of roll materials for the finishing stands of the hot strip mill for steel rolling

The microstructure, mechanical and tribological properties for three different materials, high speed steel, high chromium iron and indefinite chill iron, used for hot strip mill work rolls have been evaluated. Microstructural characterisation was performed using light optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The mechanical and tribological properties were evaluated using micro-Vickers indentation and scratch testing in combination with post-test microscopy. The microstructures of the investigated materials were found to be rather complex with a number of secondary phases and also materials with similar nominal composition display significant differences with respect to distribution, size and morphology of carbides. Scratch testing, including detection of friction coefficient, acoustic emission and penetration depth, gives valuable information concerning the mechanical and tribological response on a microscopic level of the investigated materials. Type, amount, distribution, size and morphology of the secondary phases in the materials have a strong impact on the surface deformation and wear mechanisms during scratching. Cracking and chipping are frequently observed in connection to the ridges surrounding the scratches. However, cross-sectional analyses of the scratched microstructures reveal that cracking of the brittle carbide phases may extend to significant depths>100µm, reducing the mechanical strength of the material. Based on the results, it is believed that a more isotropic microstructure, e.g., obtained via a powder metallurgy process, with finer carbides would result in improved properties and performance in a hot rolling application.

Compositional Sensitivity of Microstructures and Thermoelectric Properties of Ag1−x Pb18Sb1+y Te20 Compounds

This study reports microstructural investigations of Ag1−xPb18Sb1+yTe20, i.e., Ag-deficient and Sb-excess lead-antimony-silver-tellurium-18 (LAST-18: x ≠ 0, y ≠ 0). Two different length scales are explored. The micrometer scale was evaluated by scanning electron microscopy (SEM) to analyze the number of secondary phases as well as composition. Site-specific focused ion-beam liftout of transmission electron microscopy (TEM) lamellae from thermoelectrically characterized samples was accomplished to investigate the structure on the nanometer scale. TEM was performed to reveal the shape and orientation relationship of nanoprecipitates. The study is completed with results for the thermoelectric properties for different values of x and y.

Microstructure analyses and thermoelectric properties of [formula omitted

This study reports microstructural investigations of long-term annealed Ag1−xPbmSb1+yTe2+m (m=18, x=y=0, hereinafter referred to as AgPb18SbTe20) (Lead–Antimony–Silver–Tellurium, LAST-18) as well as of Ag1−xPb18Sb1+yTe20, i.e. Ag-deficient and Sb-excess LAST-18 (x≠0,y≠0), respectively. Two different length scales are explored. The micrometer scale was evaluated by SEM to analyze the volume fraction and the number of secondary phases as well as the impact of processing parameters on the homogeneity of bulk samples. For AgPb18SbTe20, site-specific FIB liftout of TEM lamellae from thermoelectrically characterized samples was accomplished to investigate the structure on the nanometer scale. High-resolution TEM and energy-filtered TEM were performed to reveal shape and size distribution of nanoprecipitates, respectively. A hypothesis concerning the structure–property relationship is set out within the frame of a gradient annealing experiment. This study is completed by results dealing with inhomogeneities on the micrometer scale of Ag1−xPb18Sb1+yTe20 and its electronic properties.