Phase Formation Sequence Research Articles

Microstructure and properties of Zircaloy-4 alloy under low-temperature diffusion bonding with a Ni-plated surface

Zircaloy-4, which is used as a structural material for nuclear cladding, requires precise bonding at low temperature in nuclear power applications. We achieved this using diffusion bonding with Ni plating on the surface of Zircaloy-4. We evaluated the performance of joints at temperatures between 650 and 780 °C. At 650 °C, the joint was successfully bonded. The joint exhibited a maximum shear strength of 207 MPa at 780 °C, which was twice as high as that produced by direct diffusion bonding at 700 °C under the same parameters. The interface was analyzed by using a combination of SEM and TEM to identify the presence of multilayered intermetallic compound layers in the joints. We investigated the mechanism of interface generation and determined the sequence of phase formation by Gibbs free energy calculations to be NiZr, Ni10Zr7, NiZr2, Ni7Zr2, and Ni3Zr. Through X-ray diffraction and cross-section elemental analysis of the fractures, we observed that, at lower temperatures, the joint fracture tended to occur in the Ni layer, whereas at higher temperatures, it occurred between Ni7Zr2 and Ni3Zr. The utilization of diffusion welding with Ni plating applied to the surface of Zircaloy-4 reduces the joining temperature and enhances the properties of the joint.

Prediction of Phase Formation Sequence in Multicomponent NiCoW/Nb3Al Interface

Prediction of Phase Formation Sequence in Multicomponent NiCoW/Nb3Al Interface

Phase formation and strengthening mechanism of Zn–2 wt%Cu alloy fabricated by laser powder bed fusion

Biodegradable Zn-based alloys with stable degradation rates and excellent biocompatibility have numerous potential applications as orthopedic implant materials. In this study, a Zn–2 wt%Cu alloy is fabricated through laser powder bed fusion (LPBF), and its microstructural evolution, mechanical properties, and strengthening mechanism are investigated. The microstructure comprises equiaxed grains with an average grain size of 0.2 μm, and the phase is composed of supersaturated η-Zn phase, ε-CuZn5 phase, and a small amount of γ-Cu5Zn8 phase. The phase formation sequence during rapid solidification is γ-Cu5Zn8→ε-CuZn5→η-Zn. The hardness, yield strength, and ultimate tensile strength are increased by solution strengthening, fine-grain strengthening, and second-phase strengthening (hardness up to 84.78 HV, yield strength = 145.18 MPa, and ultimate tensile strength = 188.17 MPa). The solidification behavior and microstructure of the LPBF Zn–2 wt%Cu alloy are elucidated, providing a theoretical foundation for the design of biodegradable Zn-based alloys via LPBF.

Optimizing microwave-assisted synthesis of akermanite nanoparticles using citric acid as a chelating agent: A combined machine learning and experimental approach

This study aims to synthesize akermanite (Ca2MgSi2O7) using an eco-friendly and fast microwave-assisted method and understand the effect of using citric acid (CA) as a chelating agent to optimize the calcination temperature for synthesizing pure akermanite nanoparticles (along with a trace amount of merwinite) at low calcination temperatures. This study developed a new predictive model by machine learning-assisted modeling to advance the understanding of relationship between synthesis parameters and the resulting purity and particle size of akermanite. To evaluate the reliability of the developed model in predicting the purity and characteristics of the resultant Ak powder, the crystallization behavior and phase formation sequence of citric acid-containing samples and those without citric acid were experimentally investigated by differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. Following validation and training, the developed model indicates promising effects of citric acid on reducing crystallization temperature, enhancing purity, and decreasing particle size. The synthesized powders were further characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) analyses. For the first time, our results addressed the microwave-assisted synthesis as an effective method via experimental evidence and machine learning-assisted modeling that allows for the production of akermanite containing a trace amount of merwinite with the aid of citric acid at a relatively low calcination temperature of 950 °C. In vitro bioactivity evaluation supported the potential suitability of Ak powders for bone tissue engineering applications.

Relationship between color changes and ternary eutectic reaction in Yb/Y-co-doped SiAlON ceramics

This study investigated the relationship between the green/brown colors and Yb/Y-co-doped ternary eutectic reactions. A color difference was initially observed at 1600 °C. The green color indicates a relatively highly porous area compared to the brown color, and it was confirmed that the green color was spherical in all samples. This difference in color was analyzed through photoluminescence (PL), and it was confirmed that the reduction of Yb2+ increased at temperatures higher than 1550 °C owing to the reducing atmosphere generated by the carbon ambient. The reaction sequence of the phase formation of SiAlON exhibited a difference resulting from the reduction in Yb ions, and the sequence of phase formation improved with an increase in the content of Y substituted for Yb.

Nb Phase Position Marking for Clarifying the Formation Process of Cu-Al Composite Interfacial Phases in Continuous Composite Casting

Cu-Al composites are widely applied materials exhibiting advanced properties of both matrix metals. Controlling the brittle interfacial phases is a key factor in improving the interfacial strength of Cu-Al composites. This paper studied the interfacial formation process of Cu-Al composites fabricated by continuous composite casting. The phase formation sequence, growth direction and formation mechanism were clarified via element marking and thermodynamic calculations. The spatial distribution of the interfacial phases from the aluminum side to the copper side is as follows: the α + θ layer (α-Al + CuAl2), the θ layer (CuAl2) and the γ layer (Cu9Al4). Moreover, insular η phases (CuAl) and δ phases (Cu3Al2) exist in the γ phase sublayer. The formation sequence of interfacial phases is as follows: the θ phase, the η phase, the δ phase and the γ phase. The θ layer and α + θ layer are transformed from a liquid diffusion layer formed by scouring the surface of copper with liquid aluminum, the η and δ phases grow towards the θ layer and the γ phase simultaneously grows towards both the copper matrix and the θ layer.

Near-net forming of porous Co-Al by isothermal treatment: Phase formation sequence and diffusion kinetics

Near-net forming of porous Co-Al by isothermal treatment: Phase formation sequence and diffusion kinetics

Impact of Microstructure of Nanoscale Magnetron Sputtered Ru/Al Multilayers on Thermally Induced Phase Formation

In this study, we report on phase formation and microstructure evolution in multiscale magnetron sputtered Ru/Al multilayers upon thermal annealing in vacuum at slow heating rates of 10 K/min. By specifically adjusting the microstructure and design of the as-deposited multilayers, the formation of certain desired phases can be tuned. We demonstrate that the synthesis of single phase RuAl thin films is possible in a very controlled manner in a solid state only via thermal activation without initiating the self-propagating exothermic reactions of Ru/Al multilayers. To investigate phase formation sequences and the resulting microstructures, Ru/Al multilayers were designed via magnetron sputtering with systematic variation of bilayer modulation periods and subsequent vacuum annealing. Thin films samples were characterized by in situ high-temperature XRD, TEM imaging and diffraction. It is shown that different phase sequences appear in strong correlation with the modulation length. Depending on the multilayer design, the phase formation toward single-phase RuAl thin films happens as either a multi-step or single-step event. In particular, below a critical threshold of the modulation period, the multi-step phase formation can be suppressed, and only the desired RuAl target phase is obtained with a pronounced growth in a preferred orientation. This finding may be versatile for the targeted synthesis of intermetallic phases, contributing to further understanding of phase formation in such nanoscale multilayer systems.

AlCo-rich AlCoNiFe and AlCoNiFeCr high entropy alloys: Synthesis and interaction pathway at high heating rates

Novel AlCo-rich AlCoNiFe and AlCoNiFeCr high entropy alloys (HEAs) were prepared from the non-activated and mechanically activated (MA) quaternary Al40Co40Ni10Fe10at% and quinary Al35Co35Ni10Fe10Cr10at% mixtures. The wide temperature range of the formation of a single high entropy alloy of BCC structure in quaternary system and the formation of pure quinary AlCoNiFeCr alloy above 740 °C was predicted by thermodynamic modelling. The underlying interaction mechanism was proposed, and the effective activation energy values were deduced at high heating rates up to 2600 °C·min−1 by thermal analysis method through high-speed temperature scanner. The presence of a single-stage exothermic interaction in the non-activated and mechanically activated quaternary and quinary mixtures was attributed to HEA formation via either solid + liquid or solid + solid mechanism depending on the heating rate and mechanoactivation (MA) duration. The influence of heating rate and MA duration on the self-heating profile and reaction onset temperature was also deduced. Microstructure evolution and phase formation sequence were monitored by the examination of products quenched at characteristic temperatures at synthesis and processing of AlCo-rich AlCoNiFe and AlCoNiFeCr HEAs. The crystallite size (CS), lattice strain (LS) and lattice parameter (LP) of CoFeNiAl and CoFeNiAlCr HEAs were estimated according to MA duration. The thermal stability in argon and air flow conditions at heating rate of 40 °C·min−1 for up to 1200 °C was studied by thermogravimetric analyser complemented with X-ray diffraction analysis.

Tuning the Mn5Ge3 and Mn11Ge8 thin films phase formation on Ge(111) via growth process

We have studied the stability of manganese germanide thin films grown on Ge(111) substrates by three different growth methods: solid phase epitaxy, reactive deposition epitaxy and co-deposition. By combining X-ray diffraction and magnetic measurements, we demonstrate that we can form either Mn5Ge3 or Mn11Ge8 thin films depending on the growth processes. In the case of solid phase epitaxy, we explain the phase formation sequence by taking into consideration the kinetic and thermodynamic processes involved. Tuning phase formation of the manganese germanide thin films was determined using in situ X-ray diffraction and the effect of the thin film thickness on the Mn5Ge3 thermal stability was investigated.

Effect of ZrO2 addition on the structure and the crystallization delay in lithium disilicate based glasses

Lithium disilicate (LD) glasses in system (99-X)(1Li2O:2SiO2)-(1K2O)-XZrO2 (X ​= ​0, 1 and 2 ​mol %) have been synthesized by melt quenching technique and converted into glass-ceramics by three and four-stage heat treatment schedules. The sequence of phase formation in glass-ceramics with ZrO2 addition has been discussed. The activation energy of crystallization increases with the addition of ZrO2. Rietveld refinement and micro structural analysis show an increase in the amorphous content with the addition of ZrO2. 29Si MAS-NMR, Raman and XPS spectroscopy studies for the glasses reveal that the ZrO2 addition to LD based glasses causes network polymerization and changes the role of network modifying Li+ and K+ species into charge compensators. The increased connectivity of [ZrO6]2- units in the glass network restricts the mobility of Q2 [Si2O6]4-, Q3 [Si4O10]4- and Q4 [SiO2] units, which leads to an increase in activation energies of crystallization and hampers the devitrification ability of glasses.

Initial nucleation of metastable γ-Ga2O3 during sub-millisecond thermal anneals of amorphous Ga2O3

Beta-phase gallium oxide (β-Ga2O3) is a promising semiconductor for high frequency, high temperature, and high voltage applications. In addition to the β-phase, numerous other polymorphs exist and understanding the competition between phases is critical to control practical devices. The phase formation sequence of Ga2O3, starting from amorphous thin films, was determined using lateral-gradient laser spike annealing at peak temperatures of 500–1400 °C on 400 μs to 10 ms timescales, with transformations characterized by optical microscopy, x-ray diffraction, and transmission electron microscopy (TEM). The resulting phase processing map showed the γ-phase, a defect-spinel structure, first nucleating under all annealing times for temperatures from 650 to 800 °C. The cross-sectional TEM at the onset of the γ-phase formation showed nucleation near the film center with no evidence of heterogeneous nucleation at the interfaces. For temperatures above 850 °C, the thermodynamically stable β-phase was observed. For anneals of 1–4 ms and temperatures below 1200 °C, small randomly oriented grains were observed. Large grains were observed for anneals below 1 ms and above 1200 °C, with anneals above 4 ms and 1200 °C resulting in textured films. The formation of the γ-phase prior to β-phase, coupled with the observed grain structure, suggests that the γ-phase is kinetically preferred during thermal annealing of amorphous films, with β-phase subsequently forming by nucleation at higher temperatures. The low surface energy of the γ-phase implied by these results suggests an explanation for the widely observed γ-phase inclusions in β-phase Ga2O3 films grown by a variety of synthesis methods.

Solid-state synthesis of the Zn2SiO4:Mn phosphor: Sequence of phase formation, localization and charge state of Mn ions in the intermediate and final reaction products

The phase and structure formation of the Zn2SiO4:Mn phosphor during solid-state synthesis in air from ZnO, SiO2, and Mn2O3 was studied by differential thermal, thermogravimetric, X-ray phase diffraction, and luminescent analyses. It has been shown that the first product of their interaction is a solid solution with the spinel structure (Zn1-хMn2+х)Mn3+2O4 (700°С); with an increase in temperature, ZnMn3+2O4 heterolite is formed. When heated to 900°С, willemite Zn2SiO4 appears along with heterolite. At higher temperature, the interaction of ZnMn3+2O4 with SiO2 leads to the formation of Zn2SiO4:Mn with an impurity of rhodonite Mn2+SiO3. A further increase in temperature activates the interaction of willemite, heterolite, rhodonite, silicon and zinc oxides. At about 1250 °C, this heterophase mixture forms the final single-phase product - the Zn2SiO4:Mn phosphor.

Microstructure identification of powder in tube Nb3Al wires during rapid heating process and properties of the transformed superconductors

This paper systematically studied the microstructure and phase formation sequence in the powder in tube (PIT) Nb3Al processed by rapid heating and quenching (RHQ), which is a crucial issue to fabricate reliable high performance practical Nb3Al superconductors. Due to significantly inhomogeneous of the Nb/Al diffusion couple distance, an eutectic phase with liquid characteristic happened during the RHQ process, where the phase formation sequence is: Nb + Al → eutectic phase + NbAl3 → Nb3Al + Nb2Al → grid morphology bcc → band feature bcc with the increase of rapid heating temperature. The phase and microstructure during RHQ are mainly determined by the RHQ condition and local Nb/Al distribution that similar feature was shown in the quenched wires with initial Al content of 22–28 at.% in the raw powders. Grid and band microstructure of the bcc phase was related to the Al content of ~32 at.% and ~ 22 at.%, respectively. After transformation process at 800 °C, quenched wires with coexist of gird and band micro-structure show the best superconducting properties, including Tc, ΔTc, Birr, and Jc. The microstructure identification confirms that uniform and thin Al layer in the precursor wire plays an essential role in obtaining a homogeneous bcc solid phase.

Modification of Cantor High Entropy Alloy by the Addition of Mo and Nb: Microstructure Evaluation, Nanoindentation-Based Mechanical Properties, and Sliding Wear Response Assessment

The classic Cantor (FeCoCrMnNi) isoatomic high entropy alloy was modified by separate additions of Mo and Nb in an effort to optimize its mechanical properties and sliding wear response. It was found that the introduction of Mo and Nb modified the single phase FCC solid solution structure of the original alloy and led to the formation of new phases such as the BCC solid solution, σ-phase, and Laves, along with the possible existence of intermetallic phases. The overall phase formation sequence was approached by parametric model assessment and solidification considerations. Nanoindentation-based mechanical property evaluation showed that due to the introduction of Mo and Nb; the modulus of elasticity and microhardness were increased. Creep nanoindentation assessment revealed the beneficial action of Mo and Nb in increasing the creep resistance based on the stress sensitivity exponent, strain rate sensitivity, and critical volume for the dislocation nucleation considerations. The power law and power law breakdown were identified as the main creep deformation mechanisms. Finally, the sliding wear response was increased by the addition of Mo and Nb with this behavior obeying Archard’s law. A correlation between microstructure, wear track morphologies, and debris characteristics was also attempted.

Plasma surface treatment of GeSn layers and its subsequent impact on Ni / GeSn solid-state reaction

The plasma surface treatment of GeSn layers was monitored by quasi in-situ parallel angle-resolved X-ray photoelectron spectroscopy (pAR-XPS) and atomic force microscopy (AFM). The combination of a wet cleaning and an Ar plasma treatment appeared to be the best compromise to reduce the quantity of native oxides on GeSn surfaces without impacting the surface roughness. In particular, the passivation effect of HCl was particularly beneficial to control the regrowth of oxides at the GeSn surface before the plasma treatment and to obtain a final relative low amount of oxides.The impact of surface treatment on the solid-state reaction between Ni thin films and GeSn layers was also studied. The phase formation sequence was followed by in-situ X-ray diffraction and the morphological and electrical properties were discussed. If the overall phase formation sequence remained the same, the addition of a preclean step prior to metallization influenced the temperatures at which the Ni-rich phase appeared. As far as morphological and electrical properties were concerned, the impact of surface preparation treatments remained moderate, except for HF-treated samples which suffered from an increase of dewetting and Ni(GeSn) film agglomeration phenomena.

Key factor of sponge phase formation in commercial polyethoxylated nonionic surfactant/cosurfactant/water systems and its unique feature at interface

A sponge phase is particularly interesting in terms of its features, such as its transparency, low viscosity, low interfacial tension and so on. However, most past research on the sponge phase have focused on pure surfactants, whereas little research exists on commercial polyethoxylated nonionic surfactants that are used in cosmetics and household products. The reason is attributed to the polyethyleneoxide, hydrophilic group of nonionic surfactants, having large distributions in polymerization degree, resulting in many irregular behaviors in the phase equilibrium. In this study, the phase sequence of the sponge phase formation in a commercial polyethoxylated nonionic surfactant/cosurfactant/water system was investigated based not only on HLB, but also on the distribution of polymerization degree of the hydrophilic group to reveal the irregularity of the phase sequence. As a result, in commercial nonionic surfactant systems, the important points for sponge phase formation were revealed to be (1) selecting a surfactant having intermediate HLB, and (2) selecting a structure with sufficient lipophobicity. These factors are for preventing cosurfactant phase separation that is attributed to the wide distribution of polymerization degree of polyethyleneoxide groups. Furthermore, we demonstrated the phenomenal wetting behavior on a hydrophobic surface with unevenness and clarified that the low interfacial tension and low viscosity of the sponge phase among various self-assembling structures were the critical for the wetting behavior.

Phase transitions in thermoelectric Mg-Ag-Sb thin films

α-MgAgSb thin films are expected to be compatible with the complementary metal oxide semiconductor (CMOS) technology, and could be used to develop thermoelectric modules integrated to microelectronic devices for energy harvesting. However, bulk studies showed that the presence of secondary phases in addition to α-MgAgSb, such as the metallic phase Ag3Sb, deteriorates the thermoelectric properties. Consequently, understanding phase transformations in Mg-Ag-Sb thin films produced by CMOS-compatible magnetron sputtering is capital for the production of homogeneous α-MgAgSb thin films to be used in energy harvesting thermoelectric modules integrated into microelectronic devices. In this work, different Mg-Ag-Sb films were deposited by magnetron sputtering using either a single alloyed target with the average composition Mg1/3Ag1/3Sb1/3 or using Mg, Ag, Sb co-deposition from three elementary targets. In situ X-ray diffraction measurements were used to investigate the phase transitions in the films, aiming to determine the thermal stability of α-MgAgSb and to investigate the possibility of producing α-MgAgSb films without secondary phases. The results show that the use of the single alloyed target does not allow the production of homogenous α-MgAgSb films. The phase formation sequence observed in the films is different from bulk samples in this case. Co-sputtering of the three elements Mg, Ag, and Sb, allowing the composition of the as-deposited film to be better controlled, confirmed that the Mg1/3Ag1/3Sb1/3 stoichiometry does not allow the production of homogenous α-MgAgSb films. Contrasting with usual belief, the results show that the Ag and Sb compositions of the phases α-MgAgSb and γ-MgAgSb vary during annealing, and the phase transitions α-to-β, β-to-γ, and α-to-γ are not allotropic. These finding are of major importance for the production of the thermoelectric compound α-MgAgSb, and explain the large variations of the α-MgAgSb Seebeck coefficient reported in the literature.

Impact of Sn on the Ti/Ge solid-state reaction: Phase formation sequence, morphological and electrical properties

The impact of Sn on the solid-state reaction between Ti thin films and Ge(Sn) layers was studied. Thanks to in-situ X-ray diffraction (XRD) analyses, the phase formation sequence was first studied. Ti5Ge3 (resp. Ti5(GeSn)3) phase was formed first. This phase was consumed to the benefit of Ti6Ge5 (resp. Ti6(GeSn)5). At higher temperatures, TiGe2 (resp. Ti(GeSn)2) was the last phase to appear. The phase formation sequence appeared to be strongly impacted by the presence of Sn into the system. With Sn addition, the formation of the Ti6Ge5 phase was delayed while the Ti5Ge3 and TiGe2 phases formation was promoted at lower temperatures. These phenomena were linked to the fact that the Ti6Ge5 (resp. Ti6(GeSn)5) formation was limited by diffusion-controlled reaction while the TiGe2 formation was controlled by nucleation.The morphological evolution of Ti/Ge and Ti/GeSn systems was comparable. For a given temperature, GeSn-based samples were however slightly rougher than Ge-based samples. It was linked to Sn segregation (i.e. long-scale diffusion of Sn). On the other hand, the electrical properties evolution differed from one system to the other. For the Ti/Ge system, Rsh values remained relatively constant over the temperature range studied. Meanwhile, for the Ti/GeSn system and beyond 450 °C, a significant decrease of the resistivity was observed. It was linked to the Sn segregation and the subsequent formation of metallic Sn.

Microstructure and Corrosion Behavior of Functionally Graded Wire Arc Additive Manufactured Steel Combinations

Functionally graded materials (FGM) have gained many interests for various applications and are designed to match special requirements in local properties (e.g., corrosion behavior), which highly determines the component's lifetime. The corrosion behavior is strongly dependent on the chemical composition and the microstructure of the designed materials. Therefore, two FGM combinations are designed using wire arc additive manufacturing (WAAM) with a linear changing material deposition from G 3Si1 to G 19 9L Si (combination 1) and G 18L Nb to G 19 9L Si (combination 2). The microstructure at different positions is analyzed using optical light microscopy (OLM), scanning electron microscopy with attached energy dispersive X‐ray spectroscopy (SEM/EDS), and X‐ray diffraction (XRD). The electrochemical corrosion behavior in 0.6 m NaCl solution is determined by cyclic potentiodynamic polarization (CPDP) including SEM imaging after CPDP to determine the pit size and morphology. The phase formation sequences of ferrite (α and δ), martensite, and types of austenite are discussed regarding the chemical gradient. The pitting corrosion resistance is enhanced for both combinations in direction to G 19 9L Si due to the increase in Cr and/or Ni, while the pit morphology changes in dependence of the presence of various microstructures.