Higher Area Fraction Research Articles

The effects of deformation parameters on the second phases and softening behavior of Al–Zn–Mg–Cu alloys

This study investigates the effects of deformation parameters on the second phase and softening behavior of Al–Zn–Mg–Cu alloy. The results are as follows: Firstly, the area fraction of the intermetallic phase fluctuates between 0.704 ± 0.092% and 1.886 ± 0.231% with varying deformation parameters. Secondly, in the temperature range of 270 °C to 430 °C, the area fraction of the η[Mg(Zn, Al, Cu)2] phase first increases and then decreases with rising deformation temperature, and gradually increases with decreasing strain rate. The highest area fraction is 12.613 ± 0.340% at 350 °C/0.001 s−1, and the lowest is 0.366 ± 0.068% at 470 °C/0.001 s−1. Additionally, the coarsening and dissolution of the η[Mg(Zn, Al, Cu)2] phase accelerate the dynamic recovery softening of the alloy. The sample at 350 °C/0.001 s−1 shows a low-angle grain boundary (LAGBs) percentage of 97.83% and a minimum average dislocation density of 8.493 × 102 μm2. Furthermore, at 470 °C/0.001 s−1, the Al7Cu2Fe phase has a weaker effect on stimulating nucleation and recrystallization, while the most significant promotion occurs at 430 °C/0.001 s−1. In the range of 270 °C to 350 °C and 0.1 s−1 to 0.5 s−1, the Al7Cu2Fe phase mainly stimulates the formation of sub-grains. These findings offer valuable insights for refining the grain size of alloys by regulating the content of the second phase during hot deformation.

Damage mechanisms of 2195-O aluminum alloy sheet induced by microstructural evolution during tensile deformation at different temperatures

The 2195 aluminum alloy is limited in aerospace structural components due to its poor formability at room temperature (RT) and narrow range of working parameters at hot deformation, which prompted considerable interest in understanding the microscopic damage mechanisms at different temperatures. This work focuses on the interaction between the second-phase particles and the matrix, as well as their evolving relationship to investigate the damage mechanisms of the 2195-O alloy. Particular attention was given to the nucleation mechanisms that trigger damage. SEM, BSE, and EBSD methods were employed to characterize the evolution of the microstructure during tensile tests ranging from RT to 450 °C. The results indicate that nucleation mechanisms exhibit temperature-dependent variations: At RT, a high area fraction of particles and inadequate coordination with matrix deformation lead to stress concentration on the particles, and particle fracture is the primary nucleation mechanism. Meanwhile, voids nucleate at the particle-matrix interface at 300–450 °C, where localized strain concentration is induced by differential deformation between particles and the matrix. Moreover, matrix cracking occurs at 450 °C due to a reduction in the quantity of particles and grain coarsening. Matrix-cracks tend to expand and aggregate, leading to decreased elongation at 450 °C.

Effect of TiO2 and CaO Addition on the Crystallization and Flexural Strength of Novel Leucite Glass-Ceramics.

The aim of this study was to investigate the effects of TiO2/CaO addition on the crystallization and flexural strength of leucite glass-ceramics (GC). Synthesis of translucent and high strength GCs is important for the development of aesthetic and durable dental restorations. To achieve this, experimental aluminosilicate glasses (1-3 mol% TiO2 and CaO (B1, B2, B3)) were melted in a furnace to produce glasses. Glasses were ball milled, screened and heat treated via crystallization heat treatments, and characterized using XRD, differential scanning calorimetry, dilatometry, SEM and biaxial flexural strength (BFS). Increasing nucleation hold time (1-3 h) led to a reduction in crystallite number for B2 and B3 GC, and significant differences in leucite crystal size at differing nucleation holds within and across test groups (p < 0.05). A high area fraction of leucite crystals (55.1-60.8%) was found in the GC, with no matrix microcracking. Changes in the crystal morphology were found with higher TiO2/CaO addition. Mean BFS of the GC were 211.2-234.8 MPa, with significantly higher Weibull modulus (m = 18.9) for B3 GC. Novel glass compositions enriched with TiO2/CaO led to crystallization of leucite GC of high aspect ratio, with high BFS and reliability. The study's findings suggest a potential high performance translucent leucite GC for use in the construction of dental restorations.

Thermo‐mechanical properties of epoxy composites filled with inorganic particulate fillers for robust solder mask application

AbstractFiller components play a crucial role as thermo‐mechanical reinforcement to the epoxy‐based solder mask, ensuring effective insulation and passivation. This study investigates the impact of different inorganic filler types (talc, silica (SiO2), boron nitride (BN) and barium sulfate (BaSO4)) and loadings (5 and 15 wt%) on the tensile and thermal properties of the epoxy composites. The composites were blended, cast and thermally cured. Of these composites, only 15 wt% SiO2/epoxy composite exhibits notable increments in both tensile strength and modulus, surpassing unfilled epoxy by 11.65% and 31.9%, respectively. It also displays the highest elongation at break, supported by small particle size, high specific surface area and minimal void volume fraction. For thermal tests, the addition of all fillers increases the storage modulus in both glassy and rubbery regions, especially 15 wt% talc/epoxy composite with 30.09% increment at 25 °C. Additionally, all fillers raise the glass transition temperature (Tg), notably improving it by 9 °C in the 15 wt% BN/epoxy composite. Moreover, their inclusion generally enhances the onset decomposition temperature (Tonset) and reduces weight loss during decomposition. © 2024 Society of Chemical Industry.

Mast Cells in the Microenvironment of Hepatocellular Carcinoma Confer Favorable Prognosis: A Retrospective Study using QuPath Image Analysis Software.

The insights provided by in-situ detection of immune cells within hepatocellular carcinoma (HCC) might present information on patient outcomes. Studies investigating the expression and localization of immune cells within tumor tissues are associated with several challenges, including a lack of precise annotation for tumor regions and random selection of microscopic fields of view. QuPath is an open-source, user-friendly software that could meet the growing need for digital pathology in whole-slide image (WSI) analysis. The infiltration of HCC and adjacent tissues by CD1a+ immature dendritic cells (iDCs), CD117+ mast cells, and NKp46+ natural killer cells (NKs) cells was assessed immunohistochemically in representative specimens of 67 patients with HCC who underwent curative resection. The area fraction (AF) of positively stained cells was assessed automatically in WSIs using QuPath in the tumor center (TC), inner margin (IM), outer margin (OM), and peritumor (PT) area. The prognostic significance of immune cells was evaluated for time to recurrence (TTR), disease-free survival (DFS), and overall survival (OS). The AF of mast cells was significantly greater than the AF of NKs, and the AF of iDCs was significantly lower compared to NKs in each region of interest. High AFs of mast cells in the IM and PT areas were associated with longer DFS. In addition, high AF of mast cells in IM was associated with longer OS. Computer-assisted analysis using this software is a suitable tool for obtaining prognostic information for tumor-infiltrating immune cells (iDCs, mast cells, and NKs) in different regions of HCC after resection. Mast cells displayed the greatest AF in all regions of interest (ROIs). Mast cells in the peritumor region and IM showed a positive prognostic significance.

Breaking the Ice: Exploring the Changing Dynamics of Winter Breakup Events in the Beaufort Sea

AbstractThe Beaufort Sea has experienced a significant decline in sea ice, with thinner first‐year ice replacing thicker multi‐year ice. This transition makes the ice cover weaker and more mobile, making it more vulnerable to breakup during winter. Using a coupled ocean‐sea‐ice model, we investigated the impact of these changes on sea‐ice breakup events and lead formation from 2000 to 2018. The simulation shows an increasing trend in the Beaufort Sea lead area fraction during winter, with a pronounced transition around 2007. A high lead area fraction in winter leads to greater growth of new, thin ice within the Beaufort region while also leading to enhanced sea ice transport out of the area. Despite the large export, consisting primarily of thinner first‐year ice, we find little evidence that winter breakup amplifies the advection of multi‐year ice from the central Arctic into the Beaufort Sea. Overall, the export offsets ice growth, resulting in negative volume anomalies and preconditioning a thinner and weaker ice pack at the end of the cool season. Our results indicate that large breakup events may become more frequent as the sea‐ice cover thins and that such events only became common after 2007. This result highlights the need to represent these processes in global‐scale climate models to improve projections of the Arctic.

Prognostic role of macrophages and mast cells in the microenvironment of hepatocellular carcinoma after resection

BackgroundThe prognostic significance of mast cells and different phenotypes of macrophages in the microenvironment of hepatocellular carcinoma (HCC) following resection is unclear. We aimed in this study to assess the local distribution of infiltrating macrophages and mast cells of specific phenotypes in tissues of HCC and to evaluate their prognostic values for survival of post-surgical patients.MethodsThe clinicopathological and follow-up data of 70 patients with HCC, who underwent curative resection of tumor from 1997 to 2019, were collected. The infiltration of CD68+ and CD163+ macrophages and CD117+ mast cells was assessed immunohistochemically in representative resected specimens of HCC and adjacent tissues. The area fraction (AF) of positively stained cells was estimated automatically using QuPath image analysis software in several regions, such as tumor center (TC), inner margin (IM), outer margin (OM), and peritumor (PT) area. The prognostic significance of immune cells, individually and in associations, for time to recurrence (TTR), disease-free survival (DFS), and overall survival (OS) was evaluated using Kaplan-Meier and Cox regression analyses.ResultsHigh AF of CD68+ macrophages in TC and IM and high AF of mast cells in IM and PT area were associated with a longer DFS. High AF of CD163+ macrophages in PT area correlated with a shorter DFS. Patients from CD163TChigh & CD68TClow group had a shorter DFS compared to all the rest of the groups, and cases with CD163IMlow & CD68IMhigh demonstrated significantly longer DFS compared to low AF of both markers. Patients from CD68IMhigh & CD163PTlow group, CD117IMhigh & CD163PTlow group, and CD117PThigh & CD163PTlow group had a significantly longer DFS compared to all other combinations of respective cells.ConclusionsThe individual prognostic impact of CD68+ and CD163+ macrophages and mast cells in the microenvironment of HCC after resection depends on their abundance and location, whereas the cumulative impact is built upon combination of different cell phenotypes within and between regions.

Heptatic liquid quasi-crystals by colloidal lithographic pre-assembly

HypothesisWe hypothesize that pre-assembled lithographic Brownian seven-fold quasi-crystals (QCs) of colloidal tiles at high densities can exhibit a heptatic liquid quasi-crystal (LQC) phase upon release; such heptatic LQCs can undergo heterogeneous dynamics at different length scales, reflecting the underlying symmetry, corrugation, and hierarchy of local sets of tiles. ExperimentsWe design, fabricate, and release a seven-fold QC composed of three differently shaped rhombic tiles using the method of lithographically pre-assembled monolayers (litho-PAMs). High resolution optical microscopy enables spatio-temporal particle tracking of Brownian fluctuations of many tiles in a large area over a long time. We develop an edge-proximity tessellation method for analyzing nearest neighboring particles that can be applied to assemblies and dense systems of complex shapes. FindingsA fluctuating heptatic LQC phase is identified at high tile area fractions. Heterogenous dynamics and order at different length scales indicate diverse, hierarchical motif structures. We show that certain motifs can collectively rotate without any cage breaking, leading to alterations of the local tile-structure reminiscent of phason-flips in atomic QCs; this rotation causes a slow decline in the system's spatial order. We anticipate that edge-proximity tessellation will help elucidate phase transitions of other systems made of diverse building blocks having significant geometrical complexity at multiple length scales.

The effect of oxide scale and microstructural changes during cyclic hot corrosion on high-temperature tensile properties of Rene-80 superalloy

ABSTRACT The effect of oxide scale and microstructural changes during 10, 20, and 40 hot corrosion cycles on the high-temperature tensile properties of Rene-80 superalloy at 950 °C was investigated. Due to the formation of micro-cracks and micro-voids, compressive stresses produced from Cr2O3 and NiO growth, and tensile stresses stemming from NiMoO4 transformation and Al internal oxidation, the oxide scale spalled. By increasing the hot corrosion cycles, UTS (Ultimate Tensile Strength) and El.% (Elongation) first decreased and then increased due to the propagation of intergranular vertical cracks from the oxide scale to the Rene-80 after 20 cycles. During hot corrosion cycles, YS increased due to a rise in the density of near-surface intergranular cracks close to the Rene-80/oxide scale interface resulting from micro-void linkage and γ′-depleted zone. Due to the high area fraction and the small average size of secondary γ′, UTS and YS were the highest and lowest after ten cycles, respectively.

Dissolution-induced oxide synthesis using SiO2 microparticles for oxide dispersion strengthening of Fe-based alloys

This study reports on a single-track laser surface alloying process that utilizes SiO2 powder to disperse both SiO2 particles and oxide inclusions in 316L stainless steel for oxide dispersion strengthening (ODS) purposes. In this process, the SiO2 powders partially dissolve in the melt pool, and the released silicon and oxygen atoms nucleate to form oxide inclusions in-situ within the metal matrix. This dissolution-induced oxide synthesis route demonstrated a high potential for ODS, achieving a high particle number density (6.6 × 104 mm−2) and area fraction (3.3%) comparable to that of bulk 316L samples produced via directed energy deposition. The hardness of the SiO2/316L composites reached a maximum of 232.4 HV compared to that of the 316L substrate (average 170.8 HV). The improvement in hardness was theoretically explained and quantified, significantly originating from the enhanced dislocation density strengthening mechanism resulting from the large difference in the coefficient of thermal expansion between SiO2 and 316L.

Beneficial role of the grain boundary precipitates for intergranular creep fracture of 25Cr–20Ni–Nb–N steel

Creep deformation and fracture behavior of pre-aged 25Cr–20Ni–Nb–N steel were examined to determine the effect of the M23C6 phase precipitated on the grain boundary in the initial microstructure. Aging at 873 K, 923 K, and 973 K for 500 h resulted in an area fraction of the precipitates on the grain boundary of 51%, 79%, and 89%, respectively, and the time to rupture at 873 K under 280 MPa increased with the area fraction. Additionally, the creep elongation was significantly improved by aging at 973 K, whereas that at 873 K and 923 K did not. Because the coherent matrix/M23C6 interface exhibited high crack propagation arrestability, the crack propagation path in the microstructure was the incoherent matrix/M23C6 interface and uncovered grain boundaries. The different creep deformation behaviors between the aging at 923 K or below and 973 K are discussed using the percolation theory of the crack propagation path. It was suggested that the enhanced creep properties due to the aging at 973 K were attributed to a sufficiently high area fraction of the precipitates on the grain boundary, which fragmented the crack propagation path and retarded the intergranular creep fracture.

Recrystallization and texture evolution of cold pilgered FeCrAl cladding tube during annealing at 700 °C∼1000 °C

FeCrAl alloys are being developed as potential accident-tolerant fuel cladding materials for the light water reactors due to significantly improved steam oxidation and good mechanical properties at high temperatures. In this study, the recrystallization and texture evolution of the cold pilgered FeCrAl cladding tube was investigated by means of hardness measurements and electron backscatter diffraction (EBSD) during annealing at 700∼1000 °C. The partially recrystallized maps were deconstructed into deformed, recovered, and recrystallized grain fractions based on the critical internal misorientation angle. In the early stages of recrystallization, cold pilgered cladding tubes contained a mixture of discontinuously recrystallized {111}<110> newly nucleated grains and heterogeneous deformed 〈110〉 orientation grains. The deformed microstructural inhomogeneity state could be explained based on the Taylor factor. The rate of recrystallization increased with increasing annealing temperature, which was described by the Johnson-Mehl-Avrami-Kolmogorov equation. The cladding tube showed slow recrystallization kinetics and thermally stable grains due to the pinning of the grain boundaries by the Laves precipitates. The dominant α-fiber decreased and γ-fiber increased with increasing recrystallization fraction in the cold pilgered tubes. The high area fraction and stable γ-fiber would be beneficial to the processability of the cladding tube.

Effect of cooling rate on surface properties of ZnMgAl coating and adhesion to epoxy adhesive

The importance of adhesion between ZnMgAl-coated steel and epoxy adhesive is increasing with regard to the home appliances, engineering, and automotive industries. The present study investigated the correlation between the cooling rate and the adhesion strength of ZnMgAl-coated steel and epoxy adhesive using Dolly and lap shear adhesion tests. The cooling rate of the ZnMgAl coating on the steel was controlled by N 2 gas flow rate via air knife wiping. As a result, with increasing cooling rate, the area fraction of the primary Zn and the surface roughness of the ZnMgAl coating layer increased, and finally, the adhesion strength of the ZnMgAl-coated steel and epoxy adhesive increased. Therefore, it was clearly indicated that the adhesion strength of ZnMgAl-coated steel and epoxy adhesive is strongly affected by the area fraction of the primary Zn in the coating layer. Consequently, we can conclude that the microstructure of the ZnMgAl coating comprised of a high area fraction, rough and small grain size of the primary Zn obtained by controlling the cooling rate during solidification resulted in strong adhesion. • Effects of cooling rate on adhesion of Zn-Mg-Al and epoxy adhesive was studied. • Area fraction of primary Zn increased in Zn-Mg-Al with increasing cooling rate. • Rough and small grain size of primary Zn was observed with increasing cooling rate. • Higher primary Zn fraction show higher adhesion strength to epoxy adhesive.

Achieving advanced elevated-temperature strength by tailoring precipitates in Mg-Sn-Y alloys

The Mg-Sn-Y alloys exhibiting advanced elevated-temperature strength up to 300 ℃ were newly developed by tailoring precipitates through partially substituting and increasing yttrium (Y) (2, 3.5 wt%) for tin (Sn) in Mg-2.5Sn alloy. The effects of precipitates on the room/elevated-temperature mechanical properties, and the related dynamic precipitation behavior were investigated. The elevated-temperature strengthening mechanism of the alloy was revealed. The precipitates transformed from Mg2Sn in Mg-Sn alloy to Sn3Y5 in Mg-Sn-Y alloys. The abundant Sn3Y5 nanoparticles formed in the as-extruded Mg-0.5Sn-3.5Y alloy which exhibited significant higher peak strength as 223 MPa compared to that of Mg-2.5Sn as 53 MPa. The calculation of the critical nucleation energy for dynamic precipitation indicated that the Mg-Sn-Y alloys exhibited a smaller nucleation barrier for dynamic precipitation of dense nanoscale Sn3Y5 particles compared to the Mg-Sn alloy. This barrier was further decreased with increasing Y content, as exemplified by the increased area fraction of nanoparticles in the Mg-0.5Sn-3.5Y alloy. The abundant Sn3Y5 nanoparticles can inhibit the grain boundary crack propagation, and the formed fine grains (~3.8 µm) can effectively hinder the dislocation motion. Therefore, the present work demonstrated that coupling a high area fraction of thermally stable nanoparticles with grain refinement can provide an effective approach to acquire superior elevated-temperature strength for Mg alloys.

O- and F-doped porous carbon bifunctional catalyst derived from polyvinylidene fluoride for sulfamerazine removal in the metal-free electro-Fenton process

Heteroatom-doped carbon materials can effectively activate H2O2 into •OH during the metal-free electro-Fenton (EF) process. However, information on bifunctional catalysts for the simultaneous generation and activation of H2O2 is scarce. In this study, O- and F-doped porous carbon cathode materials (PPCs) were prepared by the direct carbonization of polyvinylidene fluoride (PVDF) for sulfamerazine (SMR) removal in a metal-free EF process. The porous structure and chemical composition of the PPCs were regulated by the carbonization temperature. PPC-6 (carbonized at 600 °C) exhibited optimal electrocatalytic performance in terms of electrochemical H2O2 generation and activation owing to its high specific surface area, mesoporous structure, and optimum fractions of doped O and F. Excellent performance of the 2e− oxygen reduction reaction was found with an H2O2 selectivity of 93.5% and an average electron transfer number of 2.13. An H2O2 accumulative concentration of 103.9 mg/L and an SMR removal efficiency of 90.1% were achieved during the metal-free EF process. PPC-6 was able to stably remove SMR over five consecutive cycles, retaining 92.6% of its original performance. Quantitative structure-activity relationship analysis revealed that doped oxygen functional groups contributed substantially to H2O2 generation, and semi-ionic C–F bonds with high electronegativity were the cause of the activation of H2O2 to •OH. These findings suggest that the PVDF-derived carbonaceous catalysts are feasible and desirable for metal-free EF processes.

Effect of heat treatment parameters on microstructure, defects, and properties of Al-16Si-6Cu automotive shift fork: quantitative evaluation perspective

ABSTRACT The current study investigated the effect of heat treatment parameters, including solution treatment temperature (STT), time, and quench rate, on the microstructure, defects, and hardness of an Al-16Si-6Cu Shift fork die-cast alloy. The changes in primary silicon particle (PSP) features were examined quantitatively by optical microscopy, coupled with image analysis and SEM equipped with EDS. The biggest PSPs (27 ± 8 µm) and the highest area fraction (23%) were found in the sample solution treated at 470°C and cooled in the furnace. The hardness value increased in heat-treated samples slightly (140–148 BHN). A lower STT (420°C) and a lower ageing time (1 h) are suitable conditions for the heat treatment of an Al-16Si-6Cu die-cast alloy, in which a lower pore area fraction, 1.18, smaller pore, 4.5 μm, along with finer primary silicon, 9.5 ± 3 μm, with higher circularity, 0.38 ± 0.04, was achieved.

Effects of heat treatment on γ′ precipitates and tensile properties of a Ni-base superalloy

Different heat treatments (solution temperatures: from 1100 °C to 1140 °C) were performed to optimize the microstructures improving the mechanical properties of a wrought superalloy GH4151. The solution treatments essentially affected the area fraction of γ′ precipitates and the grain size of γ matrix. The dissolution kinetics model of primary γ′ precipitates was calculated. The results showed that the fine primary γ′ precipitates inside of grains dissolved first when the solution temperature below 1120 °C, while the coarse primary γ′ precipitates dissolved obviously as solution temperature above 1130 °C. Moreover, the grain growth occurred when the solution temperature exceeded 1130 °C. Besides, a higher area fraction of secondary γ′ precipitates with nearly spherical morphology were precipitated from the matrix during the subsequent aging process. The size of secondary γ′ precipitates increased with the increase of solution temperature. Then tensile tests were carried out at room temperature (RT) and 750 °C, the results showed that the alloy suffered solution treated at 1130 °C possessed the optimum tensile properties at 750 °C on account of the high area fraction of medium-sized secondary γ′ precipitates. However, the strength of alloy solution treated at 1140 °C decreased mainly because of the larger secondary γ′ precipitates. Meanwhile, the fracture mechanism changed from the ductile fracture to a mixed ductile and brittle fracture with the solution temperature rising.

Correlation of EDLC Capacitance with Physical Properties of Polyethylene Terephthalate Added Pitch-Based Activated Carbon.

The electric double-layer capacitor (EDLC) has attracted attention by using activated carbon (AC) as an active electrode material with a high power density and high cost-efficiency in industrial applications. The EDLC has been actively developed over the past decade to improve the power density and capacitance. Extensive studies on EDLCs have been conducted to investigate the relation of EDLC capacitance to the physical properties of AC, such as the specific surface area, pore type and size, and electrical conductivity. In this study, EDLC was fabricated with AC, and its capacitance was evaluated with the physical properties of AC. The AC was prepared using petroleum-based pitch synthesized using pyrolysis fuel oil (PFO) with polyethylene terephthalate (PET). The AC based on PFO and PET (PPAC) exhibited high specific surface area and low micropore fraction compared to the PFO-based AC without PET addition (PAC). Furthermore, the reduction of the EDLC capacitance of PPAC was smaller than that of PAC, as the scan rate was increased from 5 to 100 mV s−1. It was determined that the minor reduction of capacitance with an increase in the scan rate resulted from the development of 4 nm-sized mesopores in PPAC. In addition, a comprehensive correlation of EDLC capacitance with various physical properties of ACs, such as specific surface area, pore characteristics, and electrical conductivity, was established. Finally, the optimal properties of AC were thereupon derived to improve the EDLC capacitance.

Investigation on Viscoelastic Poisson’s Ratio of Composite Materials considering the Effects of Dewetting

A direct numerical method is introduced herein to investigate time-dependent Poisson’s ratio of solid propellant based on a representative volume element (RVE) model. Time-dependent longitudinal and transverse strains are considered in the calculation of time-dependent Poisson’s ratio under the relaxation test. The molecular dynamics (MD) packing algorithm is used to generate the high area fraction RVE model of solid propellants consisting of ammonium perchlorate (AP) particles whose radius follows lognormal distribution. In order to simulate the dewetting response of the interface between particles and matrix, the PPR model is modified and utilized during the analysis. Time-dependent Poisson’s ratio is measured under different cohesive parameters, loading conditions (loading temperature, loading rate, and fixed strain), and area fraction. Numerical results reveal that time-dependent Poisson’s ratio can be nonmonotonic or monotonic according to the different cohesive parameters. A concept of critical cohesive parameters is proposed to judge whether the monotonic property of time-dependent Poisson’s ratio appears or not. According to the numerical analysis, the cohesive contact and the shrinkage of the bulk element are two main factors which will control the change of monotonic property. All time-dependent Poisson’s ratios will increase at the beginning of the relaxation stage because the effects of cohesive contact can be ignored compared with the large shrinkage of the bulk element. However, with the increased shrinkage of the bulk element, the increased cohesive contact will defend further shrinkage at the same time. Although the shrink of the bulk element never changes its direction, the ratio of the transverse strain to longitudinal strain may decrease or keep increasing in this stage. When transverse and longitudinal strains stop to change, all time-dependent Poisson’s ratios will achieve their equilibrium values.

Effect of initial aluminium-oxygen concentration product on alumina-based inclusions in high carbon Al-killed steels during the ladle refining process

ABSTRACT The effect of different aluminium-oxygen concentration products at the start of deoxidation on the evolution of alumina-based inclusions in high carbon Al-killed steels during the ladle refining process was investigated. Results showed that the higher aluminium-oxygen concentration product at the start of deoxidation, the higher area fraction and the number density of large-sized inclusions before the slag melting, then clustered alumina-based inclusions gradually became ripening. Thermodynamic equilibrium results indicated that initial contents of the [O] were 100, 200, 300 and 400 ppm in the molten steel, then contents of the [O] at the final reaction equilibrium were 4.6, 4.9, 5.8 and 9.5 ppm, respectively. The relationship between oversaturation and size of Al2O3 inclusions showed that the larger the critical radius of nucleus, the lower the oversaturation. Meanwhile, the evolution mechanism of alumina-based inclusions during the LF refining process was also revealed.