Phase Evolution Studies Research Articles

Study of phase evolution, mechanical, and tribological behaviour of a novel β-phase strengthened Ti-alloy with Fe and Co alloying via a laser material deposition route

A new Ti64-Fe-Co alloy was studied via a laser-material-deposition method. Associated with high growth restriction factors, β-eutectoid (Fe, Co) alloying minimizes anisotropy (due to the prior columnar β-grain growth) in the laseradditive -manufacturing (AM) built Ti-parts along with enhanced properties. Fe alloying for Ti64 via laser-AM results in superior strengthening with reduced ductility, where a good combination of strength and elongation properties can be achieved for a Ti-Fe-Co system. However, studies on Ti-Fe-Co-based systems via laser processing are limited. Co possesses a similar electronic property as Fe and the Ti-Fe system accompanies further solute addition. The effect of Co alloying the Ti64-Fe system was investigated in this study via a pre-placed laser-material-deposition method. A Ti64–5Fe-5Co alloy was formulated referring to CALPHAD simulations, along with a Ti64–10Fe composition. The new Ti-alloys were fabricated via both the laser-material-deposition and conventional vacuum arc melting routes, and the characteristics of the fabricated samples were examined. XRD analysis shows the evolution of the β-Ti phase with Fe and Co alloying, which agrees with the thermodynamic phase simulation results. The corresponding SEM micrographs depicted a β-phase dominant matrix with α-dendrites, and the solidification path was discussed. Considerable grain refinement was obtained for the laser-deposited alloys compared to the arc-melted ones, with an improved hardness value twice that of the commercial Ti64. A reduced stiffness for the laser-deposited Ti64–5Fe-5Co was observed from the load-vs-displacement characteristics, indicating matrix softening with Co alloying, which might benefit the elongation properties. The studied Ti-alloy shows a 30 % improvement in the dry-sliding wear characteristic with reduced fretting and abrasion compared to the commercial Ti64. The studied Ti-alloys were located in the theoretical d-electron space and new (Bo) ̅-(Md) ̅ vectors were introduced. Further studies on this would help in extending the applicability of laser-AM-built Ti-components.

Study of phase evolution and microstructural features when modeling operating conditions of fuel cells based on lanthanum-strontium ferrite compounds

Study of phase evolution and microstructural features when modeling operating conditions of fuel cells based on lanthanum-strontium ferrite compounds

Material dependent soliton interaction dynamics in highly nonlinear fibers: A phase evolution study

Material dependent soliton interaction dynamics in highly nonlinear fibers: A phase evolution study

The beneficial effect of Fe addition in PbTe-Ni diffusion bonded thermoelectric contact interfaces – A comprehensive phase evolution study

The development of reliable interconnects in thermoelectric (TE) modules is essential for the durability and serviceability of these solid-state devices. PbTe-based devices are used in mid-temperature range applications, with Ni being the most preferred interconnect. Ni reacts with PbTe to form a binary intermetallic, Ni3Te2 (β2). The sustained growth of this phase at higher service temperatures is adversarial to the long-term reliability of interconnects. This paper reports and discusses the beneficiary role of minor Fe-addition in the Ni contact alloy to arrest such unwarranted chemical interaction while ensuring proper bonding. PbTe and Ni-Fe (Fe = 1 at.%, 5 at.%) discs are diffusion bonded at 700 °C for various holding times. The current investigation leads to three noteworthy observations: 1) the formation of Fe-enriched Ni-Fe phase islands at the interface at microscale (1 - 10 µm), (2) Fe-segregation at the local interfaces (∼ 10 nm), and (3) the growth of a Ni-rich metastable Ni3-xTe phase, not present in Ni-Te binary phase diagram. Detailed examinations of these phenomena and crystallographic relations (β2 and Ni3-xTe) are conducted through advanced analytical TEM/STEM techniques. Furthermore, the PbTe-Ni reaction formulation is modified to accommodate such a Fe-enrichment phenomenon and is validated through free energy calculations.

Hydrogen Release and Uptake of MgH2 Modified by Ti3CN MXene

MgH2 has a high hydrogen content of 7.6 wt% and possesses good reversibility under normal conditions. However, pristine MgH2 requires a high temperature above 300 °C to release hydrogen, with very slow kinetics. In this work, we utilized Ti3CN MXene to reduce the operating temperature and enhance the kinetics of MgH2. The initial temperature of MgH2 decomposition can be lowered from 322 °C for pristine MgH2 to 214 °C through the employment of Ti3CN. The desorbed MgH2 + 7.5 wt% Ti3CN can start absorption at room temperature, while the desorbed pristine MgH2 can only start absorption at 120 °C. The employment of Ti3CN can significantly improve the hydrogen release kinetics of MgH2, with the desorption activation energy decreasing from 121 to 80 kJ mol−1. Regarding thermodynamics, the desorption enthalpy changes of MgH2 and MgH2 + 7.5 wt% Ti3CN were 79.3 and 78.8 kJ mol−1, respectively. This indicates that the employment of Ti3CN does not alter the thermal stability of MgH2. Phase evolution studies through the use of X-ray diffraction and electron diffraction both confirm that Ti3CN remains stable during the hydrogen release and uptake process of the composite. This work will help understand the impact of a transition metal carbonitride on the hydrogen storage of MgH2.

Exploring the performance of Fe-Al rich sand in fly ash-based cementitious system in the context of a sustainable built environment

This research seeks to manufacture concrete by replacing fine aggregates in concrete with Fe-Al rich sand obtained from laterite scraps (mine waste) and fly ash-based cement. To reduce the colossal dumping of laterite scraps and curtail the utilisation of virgin aggregates, this study was done to utilise the laterite scraps effectively in concrete. In this study, laterite scraps were collected as rocks and processed into Fe-Al rich fine aggregates. The processed Fe-Al rich sand was employed in various amounts and substituted as fine aggregates ranging from 0 % to 100 % at 25 % intervals. The morphological properties of raw materials, clay content percentage, workability, strength, microstructure, and phase evolution studies on Fe-Al rich sand-based concrete were investigated. The workability tests such as slump, compaction factor, Vee Bee consistency, and flow table indicated that the workability values of all the Fe-Al rich sand-based mixes were lesser than the control mix. The compressive strength, splitting tensile strength, and flexural strength values of Fe-Al rich sand-based concrete were reported to be greater than those of control concrete, but up to 50 % level of replacement, they demonstrated higher values. Furthermore, the decline in strength above 50 % was evaluated in comparison to that of conventional specimens. Microstructure and phase evolution studies on Fe-Al rich sand-based concrete revealed that the strength of Fe-Al rich sand-based concrete mixes changed as hydration products formed. This work further iterates that replacing natural fine aggregates with Fe-Al rich sand as a partial alternative in concrete has a significant ecological and long-term benefits.

A study of phase evolution, crystallographic and down-conversion luminescent behaviour of monoclinic Y4Al2O9:Dy3+ nanophosphors for white light applications

Undoped Y4Al2O9 and Dy3+ doped Y4Al2O9 nanophosphors have been synthesized through urea aided combustion approach. The monoclinic phase of undoped and Dy3+ doped Y4Al2O9 nanosamples are affirmed by the results of X-ray diffraction. Diffuse reflectance (DR) spectrum and an energy band gap (5.51 eV) value for optimized Y3.96Al2O9:0.04Dy3+ sample, calculated utilizing the Kubelka-Munk theory, demonstrated the good optical quality of nanosample. Transmission electron microscope confirms the nanosize particles with some agglomeration. The synthesized nanosamples are well excited at 348 nm, exhibited yellowish-band at 576 nm with 4F9/2 → 6H13/2 and bluish-band at 483 nm with 4F9/2 → 6H15/2 transition. Firstly, luminous intensity of trivalent dysprosium ion rises and then decreases, this was because of quenching of concentration (CQ). The dipole-dipole interaction between the nearest dopant ions is responsible for this concentration quenching. Bi-exponential fitting behaviour in the focused nanophosphors confirms that there are two coordinatively different luminous centres are present in the host material for the incoming dopant ions. The luminescence decay lifetime for 4F9/2 energy level was found to be around 1.522 ms for the optimized phosphor composition. The value of integrated Y/B ratio for the samples being close to one, they can be promising candidate for white light emitting nanophosphors. The obtained outcomes authenticate the ability of Y4Al2O9:Dy3+ nanophosphor to be utilized in WLED's and other lighting appliances.

Design, preparation and study of microstructure, phase evolution and thermal stability of Ti-Co0.35-Cr0.35-Nb-Zr nanocrystalline HEA for biomedical applications

In the present study, novel Ti-Co0.35-Cr0.35-Nb-Zr high entropy alloy (HEA) has been synthesized by mechanical alloying (MA) followed by sintering at different temperatures. The microstructure and phase stability of as milled powder and sintered samples have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The density and micro-hardness values have also been calculated for the sintered samples. The atomic % of the individual element is selected based on the parametric method. After 50 h of milling, the powders transformed into a solid solution having BCC structure with a minor fraction of undissolved Zr. The crystallite size (CS) of ∼ 7 nm reveals the nanocrystalline nature of the milled powder. The DSC thermograph displays the phase transformation of the milled powder near ∼ 821 °C. After sintering at 750 °C, the sample had only β (BCC) phase, however, after sintering at 850 and 950 °C, it appeared as both β and α (HCP) phases. Micro-hardness values of the sintered samples have been found to be in the range of 460 – 580 HV which is higher than that of similar biomaterials. This study reveals that Ti-Co0.35-Cr0.35-Nb-Zr HEA can be explored as a new class of biomaterials.

A study of phase evolution of Fe-doped bismuth tantalate pyrochlore

The phase formation process of Bi2FeTa2O9.5 (sp. gr. Fd-3m) synthesized by traditional ceramic technology was studied. Bismuth orthotantalate BiTaO4 (sp. gr. Pnna) was found to be the precursor of the pyrochlore phase. The high-temperature synthesis of the iron-containing pyrochlore and the formation of a characteristic dendrite-like microstructure took place at temperatures above 900°С. The pure pyrochlore was obtained at a temperature of 1050°С. At the early stages of calcination, at a temperature close to 650 °C, the main part of iron (III) oxide, as a precursor, interacts with bismuth tantalate, and at temperatures above 950 °C, no Fe2O3 traces in the sample were found. Complex oxides Bi25FeO40 (sp. gr. I23), Bi3TaO7 (sp. gr. Fm-3m) were found as intermediate phases during the synthesis of pyrochlore. Pyrochlore of the given composition Bi2FeTa2O9.5 had a porous microstructure with a grain size of 0.5–1.0 μm. The calcination temperature did not significantly affect the microstructure of the sample. The porosity of synthesized samples with a pyrochlore structure does not exceed 21%.

Operando X-ray diffraction study of thermal and phase evolution during laser powder bed fusion of Al-Sc-Zr elemental powder blends

Elemental powder blends are an emerging alternative to prealloyed powders for high-throughput alloy design via additive manufacturing techniques. Elemental Al+Sc(+Zr) powder blends were processed by laser powder bed fusion into Al-Sc and Al-Sc-Zr alloys, with operando X-ray diffraction at the Swiss Light Source extracting the structural and thermal history of the process. The pure Sc and Zr particles were found to react with the molten Al pool at 550–650 °C, well below their respective melting temperatures. Various scan areas (1 × 1, 2 × 2, 4 × 4, and 8 × 2 mm 2 ) were studied to compare (i) the base plate “preheating” effect caused by prior laser scans, (ii) the return temperature reached after the melting scan and before the following scan, (iii) the initial cooling rate immediately after solidification, and (iv) the time spent in the “intrinsic heat treatment range”, defined as 300–650 °C, where secondary Al 3 (Sc,Zr) precipitation occurs. Microstructural analysis of the as-built samples show 110–140 nm L1 2 -Al 3 (Sc,Zr) primary precipitates at the bottom of the melt pool. The 1 × 1 mm 2 samples exhibit the most elongated grains (long axis of 10 ± 5 µm), which correlates with the highest build plate temperature and the slowest initial cooling rate (3–5 × 10 5 K/s). In comparison, the 4 × 4 mm 2 samples exhibit the smallest equiaxed grains (2 ± 0.6 µm), corresponding to the lowest build plate temperature and the fastest initial cooling rate (6–7 × 10 5 K/s). These results indicate the need for establishing a minimum feature size during part design, or for modifying the laser parameters during processing, to mitigate microstructure and performance differences across features of different sizes.

Phase evolution and conductivity study of doped gadolinium-based perovskite oxides

Phase evolution and conductivity study of doped gadolinium-based perovskite oxides

Design, Preparation and Study of Microstructure, Phase Evolution and Thermal Stability of Ti-Co0.35-Cr0.35-Nb-Zr Nanocrystalline Hea for Biomedical Applications

Design, Preparation and Study of Microstructure, Phase Evolution and Thermal Stability of Ti-Co0.35-Cr0.35-Nb-Zr Nanocrystalline Hea for Biomedical Applications

Comparative Study of Microstructure and Phase Evolution of Fecocrnial High Entropy Alloy-Matrix Wc Nanocomposite Powders Prepared by Mechanical Alloying

Comparative Study of Microstructure and Phase Evolution of Fecocrnial High Entropy Alloy-Matrix Wc Nanocomposite Powders Prepared by Mechanical Alloying

Development of Ni-Sr(V,Ti)O3-δ Fuel Electrodes for Solid Oxide Fuel Cells.

A series of strontium titanates-vanadates (STVN) with nominal cation composition Sr1-xTi1-y-zVyNizO3-δ (x = 0–0.04, y = 0.20–0.40 and z = 0.02–0.12) were prepared by a solid-state reaction route in 10% H2–N2 atmosphere and characterized under reducing conditions as potential fuel electrode materials for solid oxide fuel cells. Detailed phase evolution studies using XRD and SEM/EDS demonstrated that firing at temperatures as high as 1200 °C is required to eliminate undesirable secondary phases. Under such conditions, nickel tends to segregate as a metallic phase and is unlikely to incorporate into the perovskite lattice. Ceramic samples sintered at 1500 °C exhibited temperature-activated electrical conductivity that showed a weak p(O2) dependence and increased with vanadium content, reaching a maximum of ~17 S/cm at 1000 °C. STVN ceramics showed moderate thermal expansion coefficients (12.5–14.3 ppm/K at 25–1100 °C) compatible with that of yttria-stabilized zirconia (8YSZ). Porous STVN electrodes on 8YSZ solid electrolytes were fabricated at 1100 °C and studied using electrochemical impedance spectroscopy at 700–900 °C in an atmosphere of diluted humidified H2 under zero DC conditions. As-prepared STVN electrodes demonstrated comparatively poor electrochemical performance, which was attributed to insufficient intrinsic electrocatalytic activity and agglomeration of metallic nickel during the high-temperature synthetic procedure. Incorporation of an oxygen-ion-conducting Ce0.9Gd0.1O2-δ phase (20–30 wt.%) and nano-sized Ni as electrocatalyst (≥1 wt.%) into the porous electrode structure via infiltration resulted in a substantial improvement in electrochemical activity and reduction of electrode polarization resistance by 6–8 times at 900 °C and ≥ one order of magnitude at 800 °C.

Application of CeO2-MWCNTs nanocomposite for heavy metal ion detection in aqueous solutions by electrochemical technique

Heavy metals are most common pollutant found in the water bodies and are very toxic to the ecosystem. This work focuses on the application of cerium oxide and multiwall nanotube (CeO2-MWCNT) nanocomposites for simultaneous detection and quantification of heavy metal ions from aqueous solutions. The CeO2-MWCNTnanocomposite was prepared by hydrothermal method. The morphology, structural characterization and phase evolution studies of nanocomposites were determined by XRD, FE-SEM, XPS and TEM. The experimental results showed that the electrochemical performance of CeO2-MWCNT modified sensor for Hg2+, Pb2+, and Cu2+solutions, is promising and better than glassy carbon electrode. For quantification and calibration, differential pulse voltammetry technique was used for a broad concentration range of 5–5000 µM. The dependence of concentration of Hg2+, Pb2+, and Cu2+ions on the analytical signals can be fitted by quadratic polynomial equation. The modified sensor showed the lower detection limits of 1.98, 1.10 and 3.53 µg/l for Hg2+, Pb2+, and Cu2+,respectively. In addition, the CeO2-MWCNTbased sensor exhibited good sensitivity and high selectivity. The detection limit surpassed the lower limit defined by World Health Organization guidelines for Hg2+, Pb2+, and Cu2+. As a proof-of -concept, the suitability of the sensor was demonstrated in real water samples from tap water and river water. Correspondingly, this work demonstrated a simple and effective sensing platform for heavy metal ion detection.

Structural, morphological properties and phase stabilisation criteria of the calcia-zirconia system

ABSTRACT The phase evolution studies of zirconia, with 4–16 mol-% doping of calcium, have been carried out after sintering the pellets at 1400°C. From the X-ray diffractometer patterns, it is evident that the zirconia exists only in the monoclinic phase. However, Rietveld refinement of calcium-doped zirconia revealed the stabilisation in the monoclinic and cubic phases. With increasing calcium doping, the development of the cubic phase in zirconia is seen and at 16 mol-% doping of calcium, almost fully stabilised cubic phase of zirconia (∼97%) is achieved. The microstructure and elemental analyses of the sintered pellets are done using a field-emission scanning electron microscopy and energy-dispersive spectroscopy, respectively. Raman spectroscopic studies validate the findings of XRD. It is expected that the present study on calcium-doped zirconia opened a new channel for its potential applications in new technology such as oxygen sensors and solid electrolyte.

Phase evolution and magnetoelectric coupling studies in multiferroic Fe doped BST solid solutions

Phase evolution and magnetoelectric coupling studies in multiferroic Fe doped BST solid solutions

A gleeble-assisted study of phase evolution of Ti-6Al-4V induced by thermal cycles during additive manufacturing

The effects of thermal cycles on the phase evolution of additively manufactured (AM) Ti-6Al-4V components are comprehensively investigated by integrating direct laser deposition, Gleeble 3500 physical simulator, computational modeling, and thermodynamics analysis. A consistent martensitic microstructure is observed in the Gleeble-quenched sample at a cooling rate of 7000 °C/s, while a gradient structure (~10 mm) is observed on the top of AM-deposited samples. In-situ characterization analysis and hardness test further demonstrate that the gradient structure is composed of the α + β zone, α′+ αm zone, and α′ zone along the building direction. The location-dependent phase evolution as a result of periodically attenuated thermal cycles is then systematically explored through correlating the gradient structure and the thermal cycles from thermal models. In the early thermal cycles, the high cooling rate (>400 °C/s) and peak temperature (>980 °C) mainly leads to β →α′ transformation, generating the α′ zone on the top. β→α′+ αm and retained α′+ αm lead to the formation of α′+ αm zone due to a reduced cooling rate (25–400 °C/s). The α′+ αm further decompose to α + β at the temperature between 400 and 850 °C with a decreased cooling rate (<25 °C/s) in the later thermal cycles, resulting in the formation of α + β zone. This study provides reliable ways to investigate the phase evolution of AMed Ti-6Al-4V that is subjected to a complex AM thermal environment by using the Gleeble physical simulator and thermodynamics analysis.

Thermal decomposition, phase evolution and morphology study of combustion synthesized alumina powder – Influence of precursor pH

Here, nanocrystalline alumina powder is prepared by the glycine-nitrate combustion method, maintaining stoichiometric fuel to oxidizer ratio and two different pH conditions. The in-situ exothermic reaction occurs between an oxidizer, and fuel found to be affected by the alkalinity of the precursor solution. During combustion synthesis, spontaneous ignition occurs with the generation of gases and foamy ashes. The ash crushed into powders and then calcined at different temperatures. Thermodynamic modelling is done to calculate the enthalpy of combustions and the number of moles of gases released from the stoichiometric chemical reactions. Different characterization techniques used to study the phase formation, surface area, microstructure and morphology of the ash and calcined alumina powders. Fine crystalline α - Al2O3 powder with high surface area formed in alkaline condition. Micrographs reveal that flaky morphology of the alumina powder changed to grain type on increasing the pH of the precursor solution.

Development of graded composition and microstructure on Inconel 718 by laser surface alloying with Si, Al and ZrB2 for improvement in high temperature oxidation resistance

The present study evaluates the scope of improvement of oxidation resistance of Inconel 718 (IN718) by laser surface alloying (LSA) with Si, Al and ZrB2 using a 0.5 kW continuous wave Nd-YAG laser. The alloyed zone (AZ) is free of macro-defects (porosity, crack, etc.) and contains microstructural and compositional gradation along vertical depth from the top surface until the AZ-substrate interface. Detailed microstructural and phase evolution studies indicate that the AZ consists of multiple intermetallic phases/compounds of Si, Al or Zr with multi-phase eutectic aggregate including Ni-rich matrix phase. The identity, size, morphology and relative amount of these phases vary with LSA parameters and vertical depth within the AZ. Accordingly, the microhardness profile along depth corroborates such graded microstructure and phase aggregate confined to the AZ. Isothermal oxidation studies at 900 °C show significant improvement in oxidation resistance due to LSA in comparison to that of as-received IN718, particularly in case of LSA with Si. Post oxidation studies reveal that the oxide scale consists of adherent oxides like SiO2, Al2O3 or ZrO2, in addition to several intermetallic phases pre-existing in the AZ prior to oxidation. Thus, it follows that the intermetallic phase rich AZ developed by LSA is adherent, defect-free, strong and offers very high resistance to oxidation in IN718 at elevated temperature.