Effect Of Second Phase Research Articles

Structural, Magnetic, and Transport Properties of Ti(Fe,Re)2Sn Heusler Alloys

This study investigates polycrystalline samples of TiFe2−xRexSn (with x = {0, 0.02, 0.04, 0.06, 0.2}) synthesized using conventional arc-melting and spark plasma sintering. Structural and morphological analysis shows that low Re substitutions result in good phase purity with minor traces of secondary phases, while higher Re content leads to the segregation of additional phases. The magnetism and electrical resistivity of the samples are affected by inherent Fe–Ti atomic disorder, with the effects of secondary phases becoming more prominent in the samples with higher Re content. The Seebeck coefficient values increase only for TiFe1.98Re0.02Sn, while the power factor increases for x = {0, 0.02, 0.04}, reaching maximal values for x = 0.02 at ~ 300 K and x = 0.04 at ~ 325 K, i.e., (2.22 ± 0.2) × 10−4 Wm−1 K−2. The thermal conductivity of the samples increases with x, resulting in modest values of the figure of merit, with the maximum achieved for x = 0.02 at 325 K, i.e., 0.015 ± 0.002.

Study on the synergistic effect of second phases and product films to significantly improve the corrosion resistance of Mg-Gd-Y-Nd alloy

A uniform and compact product film with the same microstructure as Mg substrate is formed on the surface of Mg-RE alloy in NaCl solution, which still keeps in good condition after immersion for 5 months. Formation mechanism of the special film was investigated by electrochemical measurements, transmission electron microscopy (TEM), scanning kelvin probe microscopy (SKPM) and finite element modelling (FEM). The results show that fine and evenly distributed second phases provide reasonable galvanic effects, resulting in uniform self-corrosion of substrate, the stable “skeleton structure” of second phases and product film PBR of 1.33 also play key roles in corrosion resistance.

Effect of Secondary Phase on Passivation Layer of Super Duplex Stainless Steel UNS S 32750: Advanced Safety of Li-Ion Battery Case Materials.

Aluminum, traditionally the primary material for battery casings, is increasingly being replaced by UNS S 30400 for enhanced safety. UNS S 30400 offers superior strength and corrosion resistance compared to aluminum; however, it undergoes a phase transformation owing to stress during processing and a lower high-temperature strength. Duplex stainless steel UNS S 32750, consisting of both austenite and ferrite phases, exhibits excellent strength and corrosion resistance. However, it also precipitates secondary phases at high temperatures, which are known to form through the segregation of Cr and Mo. Various studies have investigated the corrosion resistance of UNS S 32750; however, discrepancies exist regarding the formation and thickness of the passivation layer. This study analyzed the oxygen layer on the surface of UNS S 32750 after secondary-phase precipitation. The microstructure, volume fraction, chemical composition, and depth of O after the precipitation of the secondary phases in UNS S 32750 was examined using FE-SEM, EDS, EPMA and XRD, and the surface chemical composition and passivation layer thickness were analyzed using electron probe microanalysis and glow-discharge spectroscopy. This study demonstrated the segregation of alloy elements and a reduction in the passivation-layer thickness after precipitation from 25 μm to 20 μm. The findings of the analysis aid in elucidating the impact of secondary-phase precipitation on the passivation layer.

The semi-continuous (Mg,Al)2Ca second phase on Mg-Al-Ca-Mn alloys as an efficient anti-corrosion anode for Mg-air batteries

Developing high anti-corrosion and good discharge properties of magnesium based alloys for Mg-air batteries is still in challenge. In this work, a series of Mg-Al-Ca-Mn (AMX) alloys are prepared, and the second phases on AMX alloys are adjusting by varying the Al content. The AMX alloys with 3 wt% Al (denoted as AMX311) exhibits the excellent anti-corrosion behavior with a corrosion current density of 85.7 μA cm−2 and a low corrosion rate (4.1±0.21 mm y−1) in the 3.5 wt% NaCl solution. Furthermore, AMX311 shows lower hydrogen evolution volume (20.9±1 ml/cm2) and weight loss (5.8±0.3 mg) compared to other contrast samples. The outstanding electrochemical corrosion performance of AMX311 is attributed to the Al-rich oxide film which slowing corrosion at the initial stage and the formation of semi-continuous (Mg,Al)2Ca phase which can acts as a physical barrier to prevent the electrolyte from further corroding the magnesium matrix. Moreover, the AMX311 exhibits the highest discharge voltage (-1.471 V) and a peak specific energy of 1684.7±30.0 mW h g−1 at 20 mA/cm2, due to its superior corrosion resistance and reduced chunk effect. This work provides a good guide for designing advanced Mg-based alloys and an excellent insight into the effect of second phase on the corrosion and discharge performance of Mg-air batteries anode materials.

Effect of Secondary Phase on Electroless Ni Plating Behaviour of Super Duplex Stainless Steel SAF2507 for Advanced Li-Ion Battery Case.

The development of Li-ion battery cases requires superior electrical conductivity, strength, and corrosion resistance for both cathode and anode to enhance safety and performance. Among the various battery case materials, super duplex stainless steel (SDSS), which is composed of austenite and ferrite as two-phase stainless steel, exhibits outstanding strength and corrosion resistance. However, stainless steel, which is an iron-based material, tends to have lower electrical conductivity. Nevertheless, nickel-plating SDSS can achieve excellent electrical conductivity, making it suitable for Li-ion battery cases. Therefore, this study analysed the plating behaviour of SDSS plates after nickel plating to leverage their exceptional strength and corrosion resistance. Electroless Ni plating was performed to analyse the plating behaviour, and the plating behaviour was studied with reference to different plating durations. Heat treatment was conducted at 1000 °C for one hour, followed by cooling at 50 °C/s. Post-heat treatment, the analysis of phases was executed using FE-SEM, EDS, and EPMA. Electroless Ni plating was performed at 60-300 s. The plating duration after the heat treatment was up to 300 s, and the behaviour of the materials was observed using FE-SEM. The phase analysis concerning different plating durations was conducted using XRD. Post-heat treatment, the precipitated secondary phases in SAF2507 were identified as Sigma, Chi, and CrN, approximating a 13% distribution. During the electroless Ni plating, the secondary phase exhibited a plating rate equivalent to that of ferrite, entirely plating at around 180 s. Further increments in plating time displayed growth of the plating layer from the austenite direction towards the ferrite, accompanied by a reduced influence from the substrate. Despite the differences in composition, both the secondary phase and austenite demonstrated comparable plating rates, showing that electroless Ni plating on SDSS was primarily influenced by the substrate, a finding which was primarily confirmed through phase analysis.

Effect of Second Phase on the Tensile Properties of a High‐Mn High‐Al Austenitic Lightweight Steel Processed by Thin‐Strip Casting

The effects of the second phase on the tensile properties of a high‐Mn high‐Al austenitic lightweight steel processed by thin‐strip casting and subsequently aged at 600 °C for different times are studied. Depending on the aging time, the second phase includes short‐range ordered (SRO) phase, nanosized κ phase, and/or microsized κ phase. At aging time of 1 min, the 2 nm SRO phase precipitates and evolves into 6 nm intragranular κ phase when the time is 60 min, and microsized intergranular κ phases exist at austenite grain boundaries at aging time of 480 min. The precipitation of SRO phase increases the yield strength from 470 to 610 MPa, and the elongation only decreases from 55.9% to 52.1%, with ductile fracture for 380 MJ m−3. Although the precipitation of intragranular κ phase increases the yield strength to 910 MPa, but elongation decreases to 33.4%, there is a mixture of ductile and brittle fracture for 316 MJ m−3. The presence of intergranular κ phase increases the yield strength to 960 MPa, but reduces the elongation to only 3.6% with brittle fracture for 35 MJ m−3. All the second phases reduce strain hardening rate, and SRO has smaller effect.

Quantifying the influence of microstructure on the corrosion of Mg-Li alloys by using X-ray CT

The microstructure of multi-component Mg-Li alloys played a decisive role in their corrosion properties due to the potential differences between the matrix and the secondary phases. In this study, the effects of secondary phases (AlLi, AlX(Gd, Y, Mn), and Mg2Sn) on the corrosion behavior of Mg-Li alloys have been quantified by using in situ X-ray CT. The microstructure-property correlation was established between the type, morphology, distribution, and dimensions of the secondary phases and the microscopic corrosion behavior. The corrosion parameters, such as average equivalent diameter, distance, number density, and volume fraction of the secondary phases and corrosion pits, were quantified as a function of corrosion time. The dominating secondary phase was identified by combining SKPFM analysis and electrochemical testing, giving quantitative information on corrosion control by designing secondary phases.

Effects of Secondary Phase on Electrochemical Performance of Co-Free High Entropy Spinel Oxide Anodes for Lithium-Ion Batteries

High entropy oxide (HEO) anode materials have recently gained significant attention in lithium-ion batteries (LIBs) due to their exceptional cycling stability, high specific capacity, and unique adjustable properties. The exclusive feature of HEO allows the use of endless element combinations to create new electrode materials with exciting and unexplored properties. In the context of Li-ion battery anode materials, unlike conventional thinking, where a single-phase high entropy oxide (HEO) is considered sufficient and necessary for delivering good electrochemical performance, we report here that this is not a necessary condition. This study demonstrates the advantages of a secondary phase in HEO. Two types of Co-free high entropy spinel oxide (HESO) are synthesized using solvothermal and hydrothermal methods, resulting in single-phase cubic HESO (HESO (C)) and binary-phase (cubic + tetragonal) HESO (HESO (C+T)), respectively. The secondary tetragonal spinel phase introduces phase boundaries and defects/oxygen vacancies in HESO (C+T), which can improve the redox kinetics and reversibility during electrode lithiation/delithiation. The minor tetragonal phase in the HESO (C+T) anode sustains after cycling, largely reducing the morphology deterioration due to improved reversibility, thus contributing to enhanced cyclability. Density functional theory calculation is performed to assess the phase stability of cubic spinel, tetragonal spinel, and rock-salt structures, and validate the cycling stability of the HEO electrodes upon lithiation/delithiation. This is the first time that the effects of a secondary phase in HEO on the electrochemical properties have been reported. A HESO (C+T)||LiNi0.8Co0.1Mn0.1O2 full cell delivers an energy density of ~610 Wh kg−1, demonstrating a great potential of the HESO (C+T) for use in LIBs. The results provide useful guidelines for designing new high-performance anode materials for LIBs.

An improved cellular automaton model of dynamic recrystallization and the constitutive model coupled with dynamic recrystallization kinetics for microalloyed high strength steels

This study analyzed the deformation behavior of Nb–Ti microalloyed high strength steel at strain rates of 0.001–0.1 s−1 and deformation temperatures of 1050–1150 °C using hot compression tests. The deformation activation energy of 321.1 kJ/mol was calculated based on the stress-strain curve, and the characteristic points on the flow stress curve were extracted. In contrast, the relationship equation between the characteristic points and the Zener-Hollomon parameter was established. A modified dynamic recrystallization (DRX) kinetics model was proposed based on the stress-strain data, considering the strain rate and deformation temperature. A high-precision constitutive model was established based on the dislocation density evolution phenomenological model, which couples with the modified DRX kinetics model. Furthermore, an improved DRX cellular automaton (CA) model was constructed, which comprehensively took into account a series of processes such as dislocation density evolution, recrystallization nucleation, and grain growth. Notably, the model also embedded the pinning effect of second phase (SP) particles on the DRX process. The improved CA model can control the pinning force by adjusting the size and volume fraction of SP particles and can accurately predict the evolution characteristics of DRX and the average austenite grain size of Nb–Ti microalloyed high strength steels during thermal deformation. The development of an improved CA model can be extended to apply to the DRX evolution of other microalloyed steels, and the model provides a powerful tool and method for understanding the thermal deformation behavior and microstructural evolution of microalloyed steels.

Microstructure, corrosion and mechanical properties of as-cast Mg-Zn-Y with different Zn-to-Y ratios

As-cast Mg-8Zn-xY (x = 1.4, 3.4, and 6.7; wt%) alloys containing I-phase, mixed I- and W-phases, W-phase were prepared, respectively. With the decrease of Zn/Y ratio, the second phase gradually changes from discontinuous network structure to continuous network structure. The effect of second phase on the corrosion resistance of Mg-Zn-Y alloy was studied in detail by testing the hydrogen evolution, polarization curve, corrosion morphology and Volta potential. The results show that Mg-8Zn-3.4Y alloy containing mixed W- and I-phases has the best corrosion resistance. The good corrosion resistance can be attributed to the network structure of mixed W- and I-phases which can prevent the extension of corrosion. In addition, Mg-8Zn-3.4Y alloy exhibits the yielding strength of 123 MPa, ultimate strength of 219 MPa, and elongation to fracture of 14 %. The good combination of corrosion and mechanical properties for the current alloy is helpful for the further application.

Effect of secondary phases on the selectivity of CO2 reduction properties of Mg-based alloy

It is a great challenge to achieve adsorption and desorption of H2 on magnesium-based metal materials under room temperature and ambient pressure. To address this problem, we proposed a strategy to tailing the secondary phases in Mg alloy to directly drive catalytic reactions, and utilizing ambient sunlight-driven solar energy to convert heat energy to promote the adsorption and reaction of H2 and CO2 gas. Thus, the magnesium-based materials can convert CO2 into CO and CH4 under sunlight. Here we report a magnesium-based material LiAlSiO4/Mg, where MgO/Mg interface and Li4SiO4 particles play different roles in production CO or CH4 under varied solar energy. The large amount of MgO reduced the adsorption of H2 on Mg, while the existence of Li4SiO4 enhanced the production rate of CO. This work explores the functional applications of main-group alloys and paves the way towards ambient sunlight-driven adsorption and use of hydrogen.

The effect of secondary phases on microstructure and irradiation damage in an as-built additively manufactured 316 L stainless steel with a hafnium compositional gradient

Additive manufacturing (AM) or rapid prototyping has become a crucial tool for reducing both cost and time while increasing efficiency in qualifying structural materials for reactor use. In this study, directed energy deposition (DED) was used to develop an as-built 316 L stainless steel sample with three regions of increasing Hf-dopant to study the effects of Hf on the irradiation response of the material. Morphological and microstructural changes were analyzed before and after 2 MeV proton irradiation at 360 °C to a damage of 2.5 dpa at ∼ 10 µm below the surface. The addition of Hf effectively suppressed radiation-induced damage (dislocation loops, radiation-induced segregation) due to enhanced point defect recombination. The radiation damage seen in the as-built sample was further compared to a thermo-mechanically treated counterpart of the same fabrication and irradiation parameters which was found to behave superiorly. The increased radiation resistance of this material may be attributed to the as-built microstructure, which includes undissolved Hf particles, delta ferrite grains and cellular sub-grain boundaries that can hinder defect motion.

The effect of secondary phase on corrosion behaviors of the titanium–zirconium–molybdenum alloy

The effect of secondary phase on corrosion behaviors of the titanium–zirconium–molybdenum alloy

Effect of the Second Phases on Composite Spinning-Extrusion Forming and Mechanical Properties of Al-Cu-Li Alloy.

The aim of this work is to investigate the effect of different second phases on the composite spinning-extrusion forming and mechanical properties of Al-Cu-Li alloy. With that purpose, four kinds of second phases blanks were controlled using preheating treatment, composite spinning-extrusion forming and mechanical properties test. Then, the correlation between the second phases and mechanical properties was further analyzed using electron backscattered diffraction and transmission electron microscopy. The results indicated that different second phases of Al-Cu-Li alloy can be regulated via reasonable preheating treatment. In addition, different second phases in the blank have various influences on composite spinning-extrusion forming, microstructure and mechanical properties of cylindrical parts. Dissolving the coarse second phases particles and precipitating the Al3Zr dispersoid in the blank can effectively improve the composite spinning-extrusion forming, inhibit the abnormal growth of recrystallized grains, and significantly enhance the mechanical properties of cylindrical parts with ribs. After regulation, the average grain size of the cylindrical parts is refined from about 90 μm to about 45 μm, and the average diameter of T1 phase is refined from 107 nm to 77 nm. In addition, the ultimate tensile strength, yield strength and elongation of cylindrical parts are increased from 555 MPa to 588 MPa, 530 MPa to 564 MPa, and 9.1% to 11%, respectively.

Improved barrier effect of hierarchical micro-nano precipitate framework in magnesium-aluminum alloy for corrosion mitigation

The galvanic effect of second phases in Mg alloys often does harm to corrosion resistance. Here, a hierarchal micro-nano β phase framework is proposed to improve the barrier effect of the second phase in high-aluminum-containing Mg-Al alloy, which can be achieved through facile heat treatment. Compared to pristine and solid-solution-processed β phases, this designed β phase framework effectively mitigates the corrosion in 0.6 M NaCl solution because of the formation of a brick-and-mortar structured corrosion product layer.

Approaches for the preparation of dense ceramics and sintering aids for Sr/Mg doped lanthanum gallate: focus review

This review focuses on Sr/Mg doped lanthanum gallate and its use as a dense electrolyte for medium-temperature solid oxide electrochemical devices. Methods for synthesizing the material are discussed, including techniques that lower the temperature required to attain a single-phase crystalline structure. The effects of secondary phases and grain size on conductivity of ceramics are also investigated. Moreover, the techniques used for compacting electrolyte powder and reducing energy expenses, as well as the impacts of sintering aids on ceramic properties, are analyzed. The potential advantages and disadvantages of the proposed alterations to generate an electrolyte from doped lanthanum gallate are evaluated.

(Digital Presentation) Effects of Secondary Phases in Stainless Steel on Corrosion Resistance

Stainless steels are widely used because of their high corrosion resistance. It is well known that Mo improves the pitting corrosion resistance of stainless steels1, 2).Mo dissolves at the passive region of stainless steels because of transpassive dissolution. In this study, we tried to provide dissolved species of Mo into the solution by utilizing transpassive dissolution of Mo. The type 304L stainless steel containing Mo phases was fabricated and corrosion resistance was measured. For fabrication of samples, Spark Plasma Sintering (SPS) was used because non-equilibrium microstructure can be obtained by short sintering time and low temperature.Type 304L stainless steel containing Mo phases was fabricated by SPS of type 304L gas atomized powder and 2.5 mass% of Mo powder. Sintering temperature was 1100℃ and it kept for 20 min. The specimen surface was polished down to 1 μm using a diamond paste. The same procedure was applied for fabricating sintered type 304L as comparison material.The as-polished and etched surfaces of the samples were observed by an optical microscope. A field emission scanning electron microscope equipped with an energy-dispersive X-ray spectroscopy system was also used to observe the surface of the samples.From the observation of sample surface, it was found that the samples contained many voids. Mo phases were also observed in entire surface. In Mo phases, the concentration of Mo was more than 90 mass%, and other elements were hardly detected.To assess the corrosion resistance, potentiodynamic polarization curves were measured in 0.1 M NaCl (pH 6.0). Electrode area was set from 100 µm × 100 µm to 5 mm × 5 mm depend on the measurement. Specimens were covered by epoxy resin except electrode area.Polarization curve of the samples were unstable because of the presence of voids. In measurement of Type 304L (SPS), current density increased with increasing potential and no passivation was occurred. On the other hand, in the case of type 304L containing Mo phases (SPS), increase of dissolution currents was inhibited with dissolution of Mo phases. After polarization, the surfaces of the samples were observed. Mo phases were preferentially dissolved, but the possibility of improvement of pitting corrosion resistance by dissolved Mo species from Mo phases.If the effect of dissolved species of Mo can be obtained by Mo oxide was investigated. The sample was fabricated by sintering of mixed powder of 304L and MoO3 powder. After the polarization measurement, no pitting was observed. This indicate that corrosion resistance was improved.References; Saito, I. Muto and Y. Sugawara, Mater.Trans., 61 (2020), 2248-2251 Nishimoto, I. Muto, Y. Sugawara, N. Hara, J.Electrochem.Soc., 166 (11), C3081-C3089

Experimental analyses and numerical modeling of the microstructure evolution of aluminum alloy using an internal state variable plasticity-based approach coupled with the effects of second phase

Continuous dynamic recrystallization (cDRX) is an effective way to refine the microstructures of materials with high stacking fault energies during their hot working. However, investigation of the influence of grain boundaries and second phases on the microstructure evolutions of these materials using conventional cDRX models is challenging. Accordingly, herein a cDRX model characterized with micron-scale second phases distributed along the grain boundaries was developed by an internal state variable plasticity-based approach. Geometrically necessary dislocation (GND) densities generated near the second phase and grain boundary were calculated by considering strain concentration in the grain, which affected the evolution of dislocation density at the subgrain boundary. The cDRX model considers an original grain as a collection of subgrains and represents the subgrains as a compound structure consisting of subgrain boundaries with relatively high dislocation densities and a subgrain interior with significantly low dislocation density. Changes in the misorientations of subgrains can be accurately determined by tracking and analyzing the evolutions of the dislocation densities of subgrain boundaries. Accuracy of the developed cDRX model was verified by comparing the hot compression data of 5052 and 2A14 Al alloys acquired using this model with the corresponding experimental results. The predicted values of variables, including flow stress, subgrain size, and the fraction of low-angle grain boundary, were in appropriate agreement with the experimental results. Effects of temperature and strain rate on the microstructure evolution of the 2A14 Al alloy were investigated. Based on the influences of strain concentration near the grain boundary and second phase on the dislocation density of the 2A14 Al alloy, the reasons for the enhancement of the occurrence of cDRX and improvement of the mechanical properties of the 2A14 Al alloy by the second phase and grain boundary are explained. The results of this study provide a direction for the subsequent improvement of the proposed cDRX model with second phases inside the grain.

Microstructural evolution of AA7050 alloy wires during tandem hot rolling (THR) and cold-drawing process

A novel processing route, the combination of two-step tandem hot rolling (THR) and cold drawing, was recently developed to produce AA7050 wire products. The evolution of second phases, grain microstructures, and micropores during the whole process was thoroughly studied. The specific effect of second phases on continuous dynamic recrystallization (CDRX) and grain refinement was also systematically investigated, which was of great significance to optimize the processing parameters and further improve the mechanical properties of AA7050 wires. Firstly, both the strip-shaped microscale and tens-of-nanometer MgZn2 primary phases are observed in the as-received extruded sample. The strip-shaped primary MgZn2 phases break and gradually spheroidize throughout the THR process, with some of them redissolving into the Al matrix. However, the nanoscale MgZn2 phases are obviously coarsened and equiaxed only during the second-step THR process. After the first-step THR process, the coarse columnar grains are refined to thin fibrous grains due to the occurrence of CDRX, and a high number of dislocations are stored in the recrystallized structures. During the second-step THR process, only dynamic recovery occurs and no obvious CDRX is observable. This may be due to the coarsening of nanoscale MgZn2 phases, which reduces the driving force of recrystallization by attracting and combining with other solute atoms. The following two-step cold-drawing process has little influence on the primary MgZn2 phases, but promotes the formation of refined and equiaxed grains due to the recurrence of CDRX. This may be because the larger coarsened MgZn2 phases accelerate the recrystallization nucleation and increase the driving force of recrystallization.

Investigation on fatigue crack propagation behaviors in the thickness direction of 2519A aluminum alloy thick plate

2519A aluminum alloy thick plate is a promising structural material in the military industries, owing to its low density, high tensile strength and excellent ballistic performance. However, the delamination crack in the thickness direction (ND) of this alloy restricts its further application in light armors. The fracture mechanism of the alloy under the thickness direction fatigue load (ND fatigue load) remained unclear. In this work, the influence of microstructures on the fatigue crack propagation (FCP) behavior in the thickness direction of the alloy was investigated. Compared with the alloy subjected to rolling direction fatigue load (RD fatigue load), the alloy under the ND fatigue load is more susceptible to fracture with weak FCP resistance due to the effect of the coarse second phase. The FCP mode of the alloy under the ND fatigue load is mainly intergranular crack propagation. The fracture mechanism of the alloy under ND fatigue load mainly has three aspects. Firstly, due to the bridging effect of the second phase, the FCP of the alloy is accelerated under the ND fatigue load, and the delamination cracks occur easily. Secondly, the crack tends to expand along grain boundaries (GBs) due to the large percentage of GB when the alloy is subjected to ND fatigue load. Thirdly, the crack is inclined to propagate grains with a small twist angle of GB and a high Schmid factor. Moreover, when the orientation factor difference between two grains is large, the crack is more likely to extend along the GB of the grains.