Phase Transformation Study Research Articles

Transient liquid phase bonding of Hastelloy X to Ni3Al intermetallic compound: Microstructure and phase transformation study

The microstructure of dissimilar transient-liquid-phase (TLP) bonding of Hastelloy X nickel base super alloy to Ni3Al intermetallic by AWS BNi2 filler metal at different temperatures (1000–1150 °C) and time ranges (60–180 min) was investigated. A novel study was done to correlate the phase transformation during bonding with microstructure and phase transformation using field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HR-TEM), and high temperature X-ray diffraction (HTXRD). Efforts were performed to correlate the phase transformation stages during isothermal solidification (IS), formation of Cr-Mo precipitates in diffusion affected zone (DAZ) and dissolution of nickel silicides (eutectic morphology) in athermal solidification zone (ASZ) with their respective reaction temperatures. The high tendency of Hastelloy X to react intensely with filler metal generated Mo-Cr rich phase in DAZ. The ISZ was developed across the joint area after holding at 1100 °C for 180 min. High temperature XRD results on half joint of HX revealed new phases generated at above 1050 °C including BNi2,BNi3, and Ni2Si (Ni-Si eutectic phase) confirmed by FESEM. On the other half joint (Ni3Al), no BNi phases were generated nor nickel silicides by increasing temperature as high as 1150 °C.

Synthesis and phase transformation study of nanostructured manganese oxide polymorphs

This paper presents the green synthesis of manganese oxide nanoparticles using olive leaf extract (OLE). The extract functions as both a reducing agent, responsible for converting manganese ions into nanoparticles, and a capping agent, aiding in stabilizing the formed nanoparticles. Our focus lies on investigating the thermal stability, phase transformation, and decomposition temperatures of different manganese oxide phases in powder form as a function of the calcination temperature. Since phase transformation depends on temperatures change at the nanoscale both thermogravimetric and differential scanning calorimetry (TGA, DSC) are used to determine the new phase transformation temperatures of the synthesized nanoparticles. Moreover, the phase structure and the exact stoichiometry are studied using ex-situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning/transmission electron microscopy (SEM/TEM). XRD and XPS analyses reveal the formation of amorphous MnOx at room temperature (prior to calcination), transitioning to crystalline phases (Mn2O3 and Mn3O4) post-calcination. High-resolution TEM and SEM depict the formation of nanoparticles around 15 nm in size, exhibiting different shapes. BET technique calculations give a very high specific surface area, rending these nanoparticles excellent candidates for several applications.

Serendipitous discovery of a novel polymorph of an immunosuppressant drug azathioprine: phase transformation, solubility, dissolution and stability study

A novel polymorph of an immunosuppressant drug azathioprine (AZP) is prepared (F-III) along with two solvates (2-methoxyethanol (MEE) and 1,4-dioxane (DOX)) and a monohydrate of AZP.

Phase transformation, thermal behavior, and magnetic study of new (FeSiBP)100-XCuX glassy alloys obtained by melt-spinning in air

In the current work, a new variation of the FeSiBPCu system with good glass forming ability and soft magnetic properties was developed and investigated. The effect of copper addition on the FeSiBP base alloy was studied in the system (Fe0.77Si0.08B0.1P0.05)100-xCux with x = 0, 0.25, 0.5, 0.75 and 1.0 at%. Microstructural evolution upon the annealing process was evaluated by XRD and TEM, revealing the formation of α-Fe(Si), Fe2B and Fe3(B,P) crystalline phases. VSM allowed to determine that the combination of chemical composition and microstructure with the best soft magnetic properties after the annealing corresponds with the alloy with 0.75% Cu. In addition, activation energy for glass transition and the first crystallization event were calculated using the Kissinger method. The research findings demonstrated that maintaining the relationship between the main elements, it is possible to keep the good glass forming ability with the possibility of developing a nanocrystalline structure with soft magnetic performance.Graphical abstract

Multiphase zinc and magnesium mono-substituted calcium phosphates derived from cuttlefish bone: A multifunctional biomaterials

Biomimetic calcium phosphate (CaP) systems mono-substituted with zinc (Zn2+) and magnesium (Mg2+) ions were prepared from a biogenic source (cuttlefish bone) by wet precipitation method. The results revealed that the as-prepared powders were composed of calcium-deficient carbonated hydroxyapatite (HAp), octacalcium phosphate (OCP), and amorphous calcium phosphate (ACP), while the heat-treated powders consisted of HAp, α-tricalcium phosphate (α-TCP), and β-tricalcium phosphate (β-TCP). In addition to Zn2+ and Mg2+ ions, the presence of CO32−, Sr2+ and Na + ions was detected with elemental analysis, which can be attributed to the use of cuttlefish bone as a natural precursor of Ca2+ ions. The data obtained by XRD study demonstrated the decrease in lattice parameters in the OCP and β-TCP phases for Zn-substitution and Mg-substitution in the HAp, OCP, and β-TCP phases. Zn2+ occupies the Ca(1,3,4,6,7,8) sites in OCP and Ca(1,2,3,4) sites in β-TCP, while Mg2+ occupies the Ca(2) sites in HAp and the Ca(4,5) sites in β-TCP. Phase transformation study under simulated physiological conditions for 7 days showed the transformation of OCP and ACP into the thermodynamically more stable HAp. Characterization of the zeta-potential showed positively charged populations for all prepared CaP powders, while all samples showed high bovine serum albumin adsorption capacity. The culture of human embryonic kidney cells showed that the prepared CaPs are non-cytotoxic and that viability of the cells increases during the culture period. All powders obtained showed antibacterial activity towards Gram-negative Escherichia coli and low antibacterial effect against Gram-positive Staphylococcus aureus, as determined by viability analysis during 48 h. Inhibition zone analysis and observation of the morphology after 24 h showed no antibacterial properties.

Phase transformation and crystallization study of Se100-xBix glassy alloys

Bulk Se100-xBix(x = 0, 5 and 10) glassy compositions were synthesized by the quenching method. The ingot materials were studied by X-ray diffraction, which was used to investigate the structure of the prepared compositions. Differential thermal analysis (DTA) under non-isothermal conditions was used to determine the transition temperatures, activation energies and responses of stability using various models such as Kissinger, Matusita, and Goa-Wang at four different heating rates. For a better understanding of the growth mechanism, the Avrami exponent (n) and the dimensionality of growth (m) have been studied. For the studied system, the obtained Avrami exponent values suggest surface nucleation with one-dimensional growth. The obtained results indicate that the thermal stability of the glassy samples decreases with increasing Bi content.

Evolution of Structural and Optical Properties of Cuprous Oxide Particles for Visible Light Absorption

Absorbent materials are being developed to replace semiconductor materials such as p‐type silicon, GaAs, CdTe, and quaternary compounds such as CIGS (copper indium gallium selenide). Cu2O is a potential candidate because it is non‐toxic, inexpensive, an abundant compound in the Earth’s crust, and has good optical properties, such as a high absorption coefficient. In this work, Cu2O was obtained simply by reducing Benedict’s solution with glucose in an alkaline medium (pH 10.2 ± 0.2) at 65°C. The samples were synthesized by varying glucose content from 1 g to 7 g. The results showed a phase proportion variation between 95.56% and 99.50% of the Cu2O phase. It was found that the changes in crystallite size, microstrains, particle size, and morphology are due to reaction times, which were influenced by the use of different glucose amounts. The use of a higher glucose amount in the synthesis favors a faster reaction, forming smaller crystallites with more microstrains. Lower glucose amount leads to a slower reaction giving the crystallites more time to grow, which relaxes the microstrains. When increasing glucose content, the obtained morphologies changed from cubes, irregular cubes, prismatic spheres, cauliflower‐like, to spherical shapes. The XPS spectra confirmed only the presence of chemical species such as Cu(I) and Cu(II), and chemical defects, such as oxygen vacancies (Vo), were detected in the samples. All samples presented a broad absorption range from 200 nm to 570 nm indistinctly of the morphology. The band gap showed an insignificant change from 2.04 eV to 2.09 eV when glucose was increased from 1 g to 7 g. The in-situ phase transformation study was analyzed from 25°C to 700°C. The results indicated a phase transition from Cu2O to Cu and CuO when the temperature was above 280°C.

Accelerated Isothermal Phase Transformation and Enhanced Mechanical Properties of Railway Wheel Steel: The Significant Role of Pre‐Existing Bainite

Exploring possible ways to accelerate bainite transformation kinetics and enhance mechanical properties, especially for large‐scale parts, attracted much attention both in industrial manufacturing and fundamental research. Herein, prior continuous cooling transformed bainite is introduced to promote isothermal transformation and improve strength toughness matching of bainite railway wheel steel. Phase transformation study by dilatometer indicates that the time–temperature–transformation curves of tested steel swing back at lower isothermal temperature. This acceleration effect is due to the formation of leaf‐shaped bainite at initial isothermal transformation stage. By tailoring the cooling rate, leaf‐shaped bainite can also be obtained during continuous cooling. It is confirmed that the formation of leaf‐shaped bainite during continuous cooling stage accelerates the subsequently isothermal bainite transformation. In situ microstructure evolution observation demonstrates that prior bainite/ austenite interface provides favorable nucleation site for initial isothermal bainite transformation. Moreover, pre‐existing bainite formed during continuous cooling stage can effectively divide the original austenite grain size. Concurrent enhancement of tensile strength and impact toughness in bainite wheel steel can be achieved by controlling the cooling rate.

Design Parameters for Enhanced Performance of Li1+xNi0.6Co0.2Mn0.2O2 at High Voltage: A Phase Transformation Study by In Situ XRD

The electrochemical performance of Al-doped and un-doped Li1+xNi0.6Co0.2Mn0.2O2 (NCM) cathodes was evaluated at a high cut-off voltage up to 4.6 V (vs Li/Li+) using 1 Ah pouch-type full cells and coin-type half cells. The batteries employing Al-doped NCM exhibited lower internal resistance, higher C-rate capability, and better low-temperature performance. In situ X-ray diffraction revealed that the Al-doped cathode followed a one-phase reaction route, which is attributed to enhanced Li+ diffusion due to Al doping and the relatively small and porous secondary particles. The existence of the pristine phase in undoped NCM throughout the cycling is explained by the slow diffusion of lithium in and out of the large and dense particles, leading to phase separation caused by regions with different lithium concentrations. Analysis using time-of-flight secondary ion mass spectrometry combined with a focused ion-beam scanning electron microscopy confirmed that the Li-ion distribution of undoped NCM was less homogeneous than that of the doped NCM.

Phase constitution of the noble metal thin-film complex solid solution system Ag-Ir-Pd-Pt-Ru in dependence of elemental compositions and annealing temperatures

Multiple-principal element alloys hold great promise for multifunctional material discovery (e.g., for novel electrocatalysts based on complex solid solutions) in a virtually unlimited compositional space. Here, the phase constitution of the noble metal system Ag-Ir-Pd-Pt-Ru was investigated over a large compositional range in the quinary composition space and for different annealing temperatures from 600 to 900 °C using thin-film materials libraries. Composition-dependent X-ray diffraction mapping of the as-deposited thin-film materials library indicates different phases being present across the composition space (face-centered cubic (fcc), hexagonal close packed (hcp) and mixed fcc + hcp), which are strongly dependent on the Ru content. In general, low Ru contents promote the fcc phase, whereas high Ru contents favor the formation of an hcp solid-solution phase. Furthermore, a temperature-induced phase transformation study was carried out for a selected measurement area of fcc-Ag5Ir8Pd56Pt8Ru23. With increasing temperature, the initial fcc phase transforms to an intermediate C14-type Laves phase at 360 °C, and then to hcp when the temperature reaches 510 °C. The formation and disappearance of the hexagonal Laves phase, which covers a wide temperature range, plays a crucial role of bridging the fcc to hcp phase transition. The obtained composition, phase and temperature data are transformed into phase maps which could be used to guide theoretical studies and lay a basis for tuning the functional properties of these materials.

Phase transformation study during diffusion brazing of γ-TiAl intermetallic using amorphous Ni-based filler metals

The paper aims at understanding the microstructure evolution of the diffusion brazing of γ-TiAl intermetallic compound using two Ni-based filler metals, a ternary Ni-Si-B, and a quinary Ni-Cr-Fe-Si-B. It was found that the joint region comprised of two distinct zones: analogous reaction layers adjacent to the TiAl substrates and a solidified zone at the middle of the joint region. The reaction layers consisted of separate intermetallic phases regions including ternary and binary Ti-Ni-Al intermetallic compounds. The solidified zone mainly composed of the Al1-xNi3Six isostructural solid solution and athermally Ni-boride or Ni-Cr rich borides containing eutectic microstructures at the joint centerline. The maximum shear strength was 240 MPa, and obtained by using Ni-Cr-Fe-Si-B filler metal. Fracture of the joint with Ni-Cr-Fe-Si-B filler occurred in the reaction layer/solidified zone interface, but joint with Ni-Si-B filler was fractured at solidified zone.

A new high-throughput method using additive manufacturing for alloy design and heat treatment optimization

Alloys made by Additive Manufacturing (AM) require careful design of post-heat treatment as an indispensable step of microstructure engineering to enhance performance. We developed a high-throughput approach to accelerate the heat treatment optimization for AM alloys by fabricating a long-bar sample heat-treated under a monitored gradient temperature zone for phase transformation study. This approach has been proven efficient in determining the aging temperature with peak hardness. We observed that precipitation strengthening is the predominant strengthening mechanism for the studied superalloy made by laser powder bed fusion, and the grain size variation is insensitive to temperatures between 605 and 825°C. This new approach can be applied to post-heat treatment optimization of other materials made by AM, and further assist new alloy development.

Phase transformation, thermal behavior and magnetic study of new Co80-xTaxSi5C15 (x = 0, 5) glassy/nanocrystalline alloys prepared by mechanical alloying

Abstract In the current work, new Co80-xTaxSi5C15 (x = 0, 5) alloys were prepared by mechanical alloying (MA) and the influence of milling period on their microstructure, thermal behavior, and soft magnetic properties were examined. The quantitative X-ray diffraction (XRD) analysis, revealed that while the fraction of hexagonal-close packed (hcp) Co-based solid-solution continuously declines by milling time, the content of face-centered cubic (fcc) one initially levels up and subsequently decreases. Furthermore, the microalloying with Ta markedly enhances the amorphization rate, as well as the fraction of amorphous phase from 60 wt% for Co80Si5C15 alloy to near 100% for Co75Ta5Si5C15 alloy after 120 h milling. Thermal analysis reflected the absence of supercooled liquid region (SLR) in Co80Si5C15 alloy, while Co75Ta5Si5C15 alloy shows a relatively wide SLR, with an extension of 41 K, demonstrating its high thermal stability. Magnetic measurements showed that the soft magnetic behavior of both alloys notably improves upon a certain stage of milling. It was shown that the new Co75Ta5Si5C15 glassy alloy represents a promising soft magnetic behavior, i.e., a minimum coercivity (Hc) of 1.2 kA/m, which is notably lower than a minimum value obtained for Co80Si5C15 (3.3 kA/m), as well as those reported for most other Co-based amorphous/nanocrystalline alloys prepared by MA.

Phase transformation and microstructure evolution study in various alloy systems: An insight

Phase transformations occurring in various metals like steel, titanium and super alloysis integrated and presented in this paper. In steels, the microalloying with Nb and Nb-Mo decrease in transformation temperature indicates the acceleration of transformation kineticsin turn which affect the microstructure and continuous cooling transformation (CCT) diagram. Incase of titanium alloys, the thermohydrogen treatment (THT) uses hydrogen as temporary alloying element which facilitatethe alloys to be processed at lower stresses and/or temperatures. Thermomechanical processing sschedules are designed baseds ons the β transus temperature to produce a variety of novel microstructures. In the case of crystalline materials, plastic deformations assisted by dislocations and the concentration of dislocation increases with increasing plastic strainthus becoming a precursor of twinning.Stress-strain curves for different alloys suggested the microstructural changes account for deformation induced twinning and martensite transformation.

Annealing Kinematics of Nickel Oxide Nanoparticles

The present paper reports the effects of isochronal annealing on Nickel oxide nanoparticles. The phase transformation study has been done. Nickel oxide nanoparticles were successfully synthesized using ASH SUPPORTED technique followed by annealing for 2 hours at various temperatures between 300°C and 800°C. It was observed using X-ray diffraction (XRD) that the as grown sample of nickel oxide nanoparticles has mixed phases while at 700 C it is in pure NiO phase. Particle size of the nanoparticles was around ~ 41 nm. Phase and particle size of nanoparticles were also confirmed using Transmission Electron Microscopy (TEM). The EDAX study shows the presence of pure nickel oxide (NiO) at 700 C.

Low Pressure Phase Transformations During High-Speed, High-Temperature Scratching of Silicon

Higher temperature assisted processing of silicon, such as heat-assisted diamond turning, is often being considered to improve surface integrity. At higher temperatures and under mechanical loading and unloading, caused by a moving tool, silicon deforms plastically often in association with occurrence of phase transformations. This paper investigates such phase transformations in rotational scratching of single crystal (100) p-type silicon with a conical diamond tool under various furnace-controlled temperatures ranging from room temperature (RT) to 500 °C and at scratching speeds comparable to that used in the diamond turning process (1 m/s). Phase transformation study, using Raman spectroscopy, at various crystal orientations, shows differences in phases formed at various temperatures when compared to that reported in indentation. The tendency to form phases is compared between scratched and diamond turned surfaces at RT, and also with that reported at low scratching speeds in the literature. Analytical indenting-based pressure calculations show that at higher temperatures, phase transformations can happen in silicon at significantly lower pressures. Analysis of depths of the scratched groove indicates that at temperatures beyond a certain threshold, plastic deformation and significant elastic recovery may be causing shallow grooves. Abrasive wear coefficients are thus seen to decrease with the increase in temperatures. This study is expected to help tune heat-assisted diamond turning conditions to improve surface formation.

Comparative phase transformation and magnetocaloric effect study of Co and Mn substitution by Cu in MnCoGe compounds

Structural and magnetic phase transformations and magnetocaloric effect of Mn and Co substitutions by Cu in MnCoGe have been investigated using X-ray diffraction, differential scanning calorimetry, and magnetization measurements. Increase in Cu concentration reduces the martensitic structural and magnetic phase transition temperatures. However, nearly doubling of the amount of Co substitution is required compared to Mn for an equivalent change in the structural transition temperature. A giant magnetocaloric effect, -ΔSMmax ≈ 50 J kg−1K−1 for Δμ0H = 5 T, resulting from coupling of concomitant structural and magnetic transformations near room temperature has been obtained for a sample with around 11 at% Mn-substitution. Fine tuning of Cu concentration (20 at%) in the case of Co substitution resulted in concurrent structural and magnetic transitions at around 260 K. However, the absence of a magnetostructural coupling resulted in peak entropy change of less than 4 J kg−1K−1. Samples with 15 at% or higher Co-substitution showed complex magnetic behavior and multiple magnetic transitions. The nature of magnetic phase transitions in both Co- and Mn-substituted samples have been investigated and phase diagrams for both sets of samples have been derived based on calorimetry and magnetometry results.

Tribological behavior of electroless Ni–B–W coating at room and elevated temperatures

Sodium borohydride reduced electroless Ni–B coatings possess high hardness, wear resistance, and low coefficient of friction. They are found to be suitable candidates for wear reduction of mechanical components. In a quest to achieve enhanced tribological behavior and high thermal stability, the present work reports the inclusion of W to Ni–B coatings. Electroless method is employed for Ni–B–W coating deposition on AISI 1040 steel specimens. Post deposition, the coatings are heat treated at 350 ℃, 400 ℃, and 450 ℃. Deposit characterization is carried out using energy-dispersive X-ray analysis, X-ray diffraction, and scanning electron microscopy. Inclusion of W leads to an increase in microhardness and thermal stability of Ni–B coatings. The tribological behavior of as-deposited and heat-treated Ni–B–W coatings are investigated at room and elevated temperatures (100 ℃, 300 ℃, and 500 ℃). Heat-treated coatings show lower wear rate at room temperature compared to as-deposited ones but the coefficient of friction increases. Tribological test results at elevated temperatures suggest an improvement in the wear resistance and coefficient of friction at 300 ℃ and 500 ℃ in comparison with 100 ℃. Phase transformation study post wear test indicate microstructural changes in the coating due to the in situ heat treatment at high temperature. The tribological behavior of the coatings at 100 ℃ and 300 ℃ is mainly governed by the loose wear debris and formation of debris patches, respectively. Whereas at 500 ℃, formation of protective tribo-oxide patches is also observed.

Structural Transformation and Hysteresis Behaviour of Ni46Cu4Mn45Sn5 Alloy Synthesized by Ball Milling Method

The present work reports synthesis and structural and magnetic studies of Ni46Cu4Mn45Sn5 shape memory alloy. The synthesis was done using solid state non‐equilibrium mechanical alloying (MA) technique. MA was performed in a Pulverisette‐6 ball milling machine using Tungsten Carbide (WC) bowl and balls. Ball to powder weight ratio of 10:1 and rotation speed of 300RPM were taken as milling parameters. After 20hr milling, the obtained powder was consolidated and quenched from high temperature to induce martensitic phase transformation. X‐ray diffraction (XRD) study indicates a phase mixture of austenite and martensite phase. Variation in lattice strain and crystallite size with milling time is calculated. Microstructural study reveals dual phase mixture after quenching. Phase transformation study carried out by Differential Scanning Calorimetric (DSC) indicates martensitic phase transformation of reversible nature. Vibrating sample magnetometer (VSM) has been utilized for magnetic characterization.

Frictional wear stability mechanisms of an activated carbon composite derived from palm kernel by phase transformation study

PurposeThe purpose of this paper is to investigate the mechanisms of frictional wear stability of an activated carbon composite derived from palm kernel using phase transformation study.Design/methodology/approachThe unlubricated sliding test was executed using a ball-on-disc tribometer at different loads with a constant speed, sliding distance and temperature.FindingsResults of this paper suggest that stability of friction and wear of the test materials are primarily due to the phase transformation of the composite surface layer.Research limitations/implicationsHowever, the effectiveness of the transfer layer as a medium for low friction and wear is only limited at certain applied loads.Originality/valueThis is the first study, to the authors’ knowledge, to find out the mechanisms of low frictional wear properties of an activated carbon composite derived from palm kernel using phase transformation study.