Influence Of Secondary Phases Research Articles

Influence of secondary phases on the emission behavior of YAG-based luminescent materials prepared using single and double precipitants

The emission behavior of single and double precipitants-derived Ce-doped YAG involving secondary phases is explored. Single precipitant-derived samples indicate major YAG with secondary YAP, YAM, and Al2O3, whereas double precipitant-derived samples demonstrate YAG with secondary YBO3 and Al2O3 at 1000–1400 °C. The single precipitant-derived samples did not show tunable emissions with calcination due to the contribution of yellow-green. However, double-precipitants-derived samples revealed blue and yellow-green contributions due to the involvement of YBO3 and YAG, respectively. The contribution of blue and yellow-green emissions of YAG-based materials derived from double precipitants developed tunable hues that shift from near-white to light blue on calcination.

Addressing the strength-ductility trade-off in a thermomechanical-processed high entropy alloy

High entropy alloys (HEAs) have garnered significant attention due to their exceptional mechanical behavior. However, the influence of secondary phases and dislocation substructures has yet to be thoroughly investigated. This study focuses on the incorporation of the decomposed η-phase within a face-centered cubic (FCC) microstructure at different recrystallization levels, aiming to achieve adequate ductility while maintaining strength at gigapascal levels. Various characterization techniques were employed to analyze the microstructure of both homogenized and annealed+aged conditions. Implementing a sub-micron grain size distribution and introducing a favorable dislocation substructure significantly enhanced the mechanical properties of yield strength, ultimate tensile strength, and ductility, reaching up to 1291 MPa, 1450 MPa, and 17.5%, respectively. The results highlight the influential role of grain size in facilitating the generation of geometrically necessary dislocations during plastic deformation.

Effects of Cu substitution on microstructures and microwave dielectric properties of Li2ZnSiO4 ceramics

Herein, the influence of Cu2+ substitution on the phase composition, bulk density, microstructures, and microwave dielectric properties of Li2CuxZn1−xSiO4 (0 ≤ x ≤ 0.06) ceramics prepared by a solid-state reaction were investigated. The results of XRD and mapping showed that Cu2+ substitution can avoid the influence of secondary phase on the properties of samples. According to the analysis of bulk density, microstructure and microwave dielectric properties, a proper amount of Cu substitution not only improved the sintering characteristics of Li2CuxZn1−xSiO4 ceramics, reduced the densification temperature from 1250 °C to 950 °C, but also increased the Q×f value. Furthermore, Cu2+ substitution also improved the temperature stability of the samples. Particularly, the Li2Cu0.04Zn0.96SiO4 ceramics sintered at 950 °C for 5 h possessed excellent microwave dielectric properties: εr = 5.624, Q×f = 12,764 GHz, and τf = −77 ppm/°C, exhibiting a potential for the low temperature co-fired ceramic applications.

The Influence of Secondary Phase on Impact Toughness of Alloyed Iron Aluminides

The microstructure and fracture surfaces were investigated for five Fe3Al – based iron aluminides doped by different alloying elements (Nb, Zr + C, Cr) or without addition. Generally, iron aluminides are considered as brittle material at room temperature, therefore the type and distribution of secondary phases affect the fracture behaviour. The influence of present secondary phase particles on impact toughness at room temperature was evaluated in comparison to binary alloy. The type and the volume fraction of particles affect the value of impact toughness significantly – these values decrease with increasing volume fraction of precipitates. On the other hand, the solid solution strengthening improves impact toughness.

Role of Nb in the failure of dual-phase steel in heterogeneous welds

The use of Cr-Ni austenitic steel interlayers is an effective solution for heterogeneous welds, especially in combination with high-carbon steels. High contact-fatigue resistance and resistance to impact loads are required in the case of railway crossing applications. The failure of Nb-alloyed cast Cr-Ni austenitic steel used as an insert in the flash butt resistance weld of Hadfield steel with carbon steel is the subject of the presented analyses. The identification of the failure mechanism is based on light and scanning electron microscopy and energy dispersive X-ray analyses, including electron backscattered analyses. The initiation of hot-crack defects is detected in the heat affected zone (HAZ). In contrast to the usual conditions for the formation of hot cracks in the HAZ, cracks are found solely outside the superheating zone. The decisive influence of Nb-based intermetallics formed at the phase interface of δ-ferrite and the austenitic matrix is indicated. The eutectics formation between niobium carbonitrides and the austenitic matrix is assumed to be responsible for the hot-cracking susceptibility of austenitic steel. The particular combination of the temperature gradient together with the chemical gradient leading to a localization of the critical zone is documented. The paper describes the influence of carbon redistribution at the weld interface on the morphology of delta-ferrite in different layers of the heat-affected zone. Induced structural differences are associated with Nb-particle formation. Fractographic analyses show the formation of low-melting phases in the critical layer of the HAZ. The influence of secondary phases, especially Nb-eutectic, on the degradation of austenitic steel plasticity is documented.

Influence of secondary phases in A356 MMCs on their mechanical properties at macro- and nanoscale

Metal matrix composites are very inhomogeneous materials, and their properties depend on various parameters (production process, constituents, their interfaces, etc.). The influence of SiC microparticles (40 μm) reinforcement and graphite macroparticles (200–800 μm) addition on the mechanical properties of Al–Si A356 alloy, produced by compocasting, has been assessed using macro- and nanoscale measurements of hardness and modulus of elasticity. The Al makes over 90 wt% of the A356 alloy, so the nanoscale measurements were performed on different α phase regions on each material (core of α phase, eutectic α phase, and α phase near the phase boundaries α phase/secondary phases). The results showed that there is no direct correlation between mechanical properties on macro- and nanoscale. The nanoscale results also showed that the secondary phases (SiC and graphite particles) can have significant effect on the mechanical properties on the atomic level, i.e. in the α phase regions very close to the secondary phases.

Development of highly performing TiO2 complex thin films by novel combined physico-chemical process for enhanced photo-catalytic applications

Structural, morphological, optical, photoresponse and photo-catalytic properties of TiO2 nanostructured thin films, prepared through novel combined physico-chemical (GLADOX) process by varying the electrolyte ratio have been investigated. TiO2 nanoporous structured thin films were prepared by anodization of Ti thin films, prepared on FTO substrate by using DC magnetron sputtering equipped with the glancing angle arrangement and by varying electrolyte ratio of anodization. The structural studies show that the TiO2 nanostructured thin films have a crystal structure of tetragonal with a crystalline phase of rutile with an appreciable secondary phase; monoclinic TiO. The morphological studies reveal the nanoporous structure of the GLADOX deposited TiO2 thin films. The optical studies show that the absorbance and band gap of the optimized TiO2 thin films prepared at optimized electrolyte ratio are ideal for photo-catalytic applications. The photo-catalytic properties of TiO2 nanostructured thin films were investigated by the degradation of methylene blue (MB) dye in the presence of visible light and the influence of secondary phase on the photo-catalytic performance is also investigated with the support of photoresponse studies.

Comparative study of the hot processing behavior in advanced Ni-based superalloys for use in A-USC applications

Three Ni-based superalloys, Haynes 214, Haynes 230 and Inconel 740H, have been analyzed for their mechanical behavior under conventional industrial hot-processing conditions. These and other comparable alloys are expected to be used in sCO2 heat exchanger cycles, as proposed in the Advanced Ultra-Supercritical (A-USC) program, due to their unique combination of mechanical, corrosion and creep properties. However, these alloys are difficult to form, specifically for sCO2 components, such as header pipes and manifolds, requiring optimal forming conditions. In this study, hot-deformation testing was conducted using a Gleeble 3500, to simulate temperatures and strain rates expected during industrial forming operations. The effect of using as-received material on the deformation behavior was analyzed, emulating microstructures under real conditions more accurately. The flow-stress curves for all three alloys showed the occurrence of dynamic recrystallization (DRX) with some signs of dynamic recovery, for the slowest strain rates and higher temperatures. Additionally, the influence of secondary phases on the hot deformation behavior was analyzed. The M6C-carbide in Haynes 230 showed the strongest effect, promoting recrystallization necklacing and inhibiting DRX growth. The activation energies for plastic flow were 246, 302 and 217 kJ mol−1, for Haynes 214, Haynes 230 and Inconel 740H, respectively. Hot-processing maps were generated for all alloys and suggested specific domains for optimal workability under the tested conditions. For Haynes 214, that is ε˙≤ 0.1/s and T ≥ 1050 ∘ C. For Haynes 230, it is 1050 ∘ C ≤ T ≤ 1150 ∘ C and 0.01/s ≤ε˙≤ 0.5/s. For Inconel 740H, it is 1010 ∘ C ≤ T ≤ 1075 ∘ C and 0.01/s ≤ε˙≤ 0.1/s.

Influence of secondary phases on crack initiation and propagation during fracture process of as-cast Mg-Al-Zn-Nd alloy

The influence of secondary phases on the initiation and propagation of tensile crack during the fracture process is studied by using in-situ scanning electron microscopy (SEM) tensile testing in as-cast Mg-Al-Zn-Nd alloy. Results reveal that micro-cracks initiated in divorced eutectic Mg17Al12 phase, eutectic Mg17Al12 phase, twin boundaries and interface between α+β eutectic structure and α-Mg matrix. The breaking of the divorced eutectic Mg17Al12 phase at the grain collapsing zone (GCZ) edge and the decreased effective force bearing area due to grain collapsing contributed to the propagation of transgranular cracks. Breaking of Mg17Al12 phase is accompanied by the formation of voids at the main crack tip, which provided a path for crack propagation and growth. Formation of voids can also blunt the main crack tip and divert the crack propagation direction. On the other hand, the voids difficultly form in Nd-containing secondary phases, i.e., Al2Nd and Al11Nd3, due to the superior mechanical properties and better interfacial bonding capability. Therefore, the Nd-containing compounds have an inhibitory effect on the propagation of crack of Mg alloys. Furthermore, the elastic modulus and electronic charge density difference of Mg17Al12, Al2Nd and Al11Nd3 phases have been calculated to verify the experimental results. The mechanical properties and the bonding mechanism of these phases are discussed briefly.

Influence of Secondary Phase on Intrinsic Threshold and Path of Shear-Mode Fatigue Cracks in Metals

Influence of Secondary Phase on Intrinsic Threshold and Path of Shear-Mode Fatigue Cracks in Metals

On the Stability of c-BN-Reinforcing Particles in Ceramic Matrix Materials.

Cubic boron nitride (c-BN) composites produced at high pressures and temperatures are widely used as cutting tool materials. The advent of new, effective pressure-assisted densification methods, such as spark plasma sintering (SPS), has stimulated attempts to produce these composites at low pressures. Under low-pressure conditions, however, transformation of c-BN to the soft hexagonal BN (h-BN) phase can occur, with a strong deterioration in hardness and wear. In the present work, the influence of secondary phases (B2O3, Si3N4, and oxide glasses) on the transformation of c-BN was studied in the temperature range between 1100 °C and 1575 °C. The different heat treated c-BN particles and c-BN composites were analyzed by SEM, X-ray diffraction, and Raman spectroscopy. The transformation mechanism was found to be kinetically controlled solution–diffusion–precipitation. Given a sufficiently low liquid phase viscosity, the transformation could be observed at temperatures as low as 1200 °C for the c-BN–glass composites. In contrast, no transformation was found at temperatures up to 1575 °C when no liquid oxide phase is present in the composite. The results were compared with previous studies concerning the c-BN stability and the c-BN phase diagram.

Influence of secondary phase on polymorphic phase transition in Li-doped KNN lead-free ceramics

Abstract Shifting polymorphic phase transition (PPT) to room temperatures in Li-doped KNN (KNLN) can greatly increase its piezoelectric constant. However, pure phase KNLN ceramics could hardly be obtained since secondary phases were formed inevitably during its synthesis. Here, we examined the structure, composition and distribution of the secondary phase and their influences on the phase compositions in KNLN ceramics. The results show that orthorhombic–tetragonal phase boundary cannot shift to room temperature when considerable amount of secondary phase exist in KNLN piezoceramics.

Influence of secondary phases on ferroelectric properties of Bi0.5Na0.5TiO3 ceramics

The effects of secondary phases on ferroelectric properties of Bi0.5Na0.5TiO3 (BNT) have been studied. Ceramic powders were prepared by solid state reaction employing different sintering temperatures and characterized by X-ray diffraction (XRD), Scanning Electron Microscopy and impedance spectroscopy. The perovskite structure was detected by XRD; together with small peaks corresponding to a secondary phase assigned to the Na2Ti6O13-based phase in calcined powders. In addition, morphology and the content of the secondary phase were modified by the sintering temperatures, affecting the ferroelectric properties, and ac and dc conductivities. We believe that our results can benefit not only the understanding of BNT ceramics, but also expand the range of applications.

The Effect of Subbandgap Illumination on the Bulk Resistivity of CdZnTe

The variation in bulk resistivity during infrared (IR) illumination above 950 nm of state-of-the-art CdZnTe (CZT) crystals grown using the traveling heating method or the modified Bridgman method is documented. The change in steady-state current with and without illumination is also evaluated. The influence of secondary phases (SP) on current–voltage (I–V) characteristics is discussed using IR transmission microscopy to determine the defect concentration within the crystal bulk. SP present within the CZT are connected to the existence of deep, IR-excitable traps within the bandgap.

Optical properties of Eu‐doped NaYP2O7 under UV and X‐ray excitation

AbstractEu‐doped NaYP2O7 polycrystalline samples were produced via sol‐gel method based on PVA. Structural investigation of calcined powders was made by X‐ray diffraction analysis. High crystalline purity was achieved when using molar ratio Na:Y:P of 1.15:1:2 and the presence of dopant caused no noticeable change on the structure. The influence of secondary phases on the optical properties of NaY0.99Eu0.01P2O7 was investigated by photoluminescence (PL) and X‐ray excited optical luminescence (XEOL). In general, each XEOL emission spectrum was similar to that obtained from PL. The spectroscopic properties measured indicate that the dopant occupies two sites of high symmetry on the host matrix and that the spurious phases significantly affect the luminescence yield. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of secondary phases on the tribological response of electro-discharge machined zirconia-based composites against WC–Co cemented carbide

Three ceramic composite grades, consisting of a ZrO 2 matrix and 40 vol.% WC, TiC 0.5N 0.5 or TiN phase, were completely self-developed by hot pressing powder mixtures of yttria-stabilised zirconia (Y-TZP) and distinctive WC, TiC 0.5N 0.5 or TiN powder sources. The friction and wear characteristics of the zirconia-based composites against WC–Co cemented carbide were investigated by performing dry reciprocating sliding experiments on a pin-on-plate tribometer under various normal contact forces. The generated wear was quantified using surface scanning topography. Post-mortem obtained wear volumes were correlated to real-time recorded wear depth. The ZrO 2–40 vol.% WC grade displayed more favorable tribological properties compared to the other grades with equal secondary phase content. The worn surfaces and the wear debris were analysed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), revealing several wear mechanisms such as polishing, abrasion and wear debris layer formation, mainly depending on the imposed contact load and the material composition.

Connectivity and critical currents in polycrystallineMgB2

Current transport in polycrystalline magnesium diboride is highly non-uniform(percolative) due to the presence of secondary phases and also due to the intrinsicanisotropy of the material. The influence of secondary phases on the transport properties ofMgB2 was investigated. Bulk samples were prepared from a mixture ofMgB2 and MgO powders by the ex situ technique in order to vary the MgO content systematically.The samples were characterized by resistive and magnetization measurements. The reducedMgB2 fraction is modeled by a reduced effective cross section (connectivity), which wasassessed directly by the experiments. The presence of MgO also increases thepercolation threshold, which reduces the zero resistivity (or irreversibility) field.

Influence of secondary phases during annealing on re-crystallization of CuInSe 2 electrodeposited films

Electrodeposited CuInSe 2 thin films are of potential importance, as light absorber material, in the next generation of photovoltaic cells as long as we can optimize their annealing process to obtain dense and highly crystalline films. The intent of this study was to gain a basic understanding of the key experimental parameters governing the structural–textural-composition evolution of thin films as function of the annealing temperature via X-ray diffraction, scanning/transmission electron microscopy and thermal analysis measurements. The crystallization of the electrodeposited CuInSe 2 films, with the presence of Se and orthorhombic Cu 2 − x Se (o-Cu 2 − x Se) phases, occurs over two distinct temperature ranges, between 220 °C and 250 °C and beyond 520 °C. Such domains of temperature are consistent with the melting of elemental Se and the binary CuSe phase, respectively. The CuSe phase forming during annealing results from the reaction between the two secondary species o-Cu 2 − x Se and Se (o-Cu 2 − x Se + Se → 2 CuSe) but can be decomposed into the cubic β-Cu 2 − x Se phase by slowing down the heating rate. Formation of liquid CuSe beyond 520°C seems to govern both the grain size of the films and the porosity of the substrate–CuInSe 2 film interface. A simple model explaining the competitive interplay between the film crystallinity and the interface porosity is proposed, aiming at an improved protocol based on temperature range, which will enable to enhance the film crystalline nature while limiting the interface porosity.

Geopolymers from Algerian metakaolin. Influence of secondary minerals

The influence of secondary phases (illite, quartz) on the geopolymerization reaction of metakaolin has been investigated by comparing two metakaolins, one prepared from a pure kaolinite and the other from illite- and quartz-containing Algerian kaolin from the Tamazert region, respectively. Geopolymerization was achieved by mixing the metakaolins with an alkaline sodium silicate solution at room temperature and curing at 50 °C. The products were characterized by X-ray diffraction and 29Si and 27Al MAS-NMR. The results show that the secondary phases, at the concentration used in this work, do not prevent the geopolymerization reaction.

The homogeneity range and the microwave dielectric properties of the BaZn 2Ti 4O 11 ceramics

Ceramics with a composition close to BaZn 2Ti 4O 11 were synthesized according to various substitutional mechanisms in order to verify an existence of a homogeneity range in the vicinity of this composition. Structural and microstructural investigations showed that the crystal structure of BaZn 2Ti 4O 11 was formed in the homogeneity range corresponding to the formula BaZn 2 − x Ti 4O 11 − x (0 < x < 0.1). Densely sintered BaZn 2 − x Ti 4O 11 − x (0 < x < 0.1) ceramics exhibited a dielectric constant around 30, τ f = −30 ppm/K and high Q × f values, which increased from ∼68,000 GHz at x = 0 to ∼83,000 GHz at x = 0.05. Structurally, the deficiency of Zn in BaZn 2 − x Ti 4O 11 − x (0 < x < 0.1) resulted in a slight decrease in the unit-cell volume. The influence of secondary phases in the BaZn 2Ti 4O 11-based materials on the microwave dielectric properties was also investigated. A presence of small amounts of ZnO, BaTiO 3, hollandite-type solid solutions (Ba x Zn x Ti 8 − x O 16) and BaTi 4O 9 caused a decrease in Q × f values.