Grain Size Reduction Research Articles

Effect of Si addition on microstructure and performance of a biomedical Ti-Nb-Zr-Ta alloy prepared via powder hot extrusion

In this study, TNZT-xSi ((Ti53Nb35Zr7Ta5)100-xSix, x=0, 1.4, 2.3, wt.%) alloys are prepared by powder hot extrusion. The effect of Si addition on microstructure, mechanical properties, corrosion resistance and in vitro apatite formation ability of TNZT-xSi alloys is investigated. The as-extruded TNZT alloy mainly consists of elongated BCC grains. The addition of Si leads to the precipitation of fine (Ti, Zr)2Si (S2) particles from the BCC matrix. With the increase of Si content, the volume fraction of recrystallized grains rises significantly, and the microstructure of extruded alloys tends to transform from elongated to equiaxed grains. It’s indicated that the introduction of S2 particles activates the dynamic recrystallization process during hot extrusion and results in an obvious reduction in the overall grain size. Compared with the TNZT-0Si base alloy, the tensile strength of TNZT-2.3Si alloy is improved from 726MPa to 983MPa, with the elongation declining from 28.0% to 9.5%. The TNZT-xSi alloys exhibit higher corrosion potential (Ecorr) and lower corrosion current density (Icorr) than Ti-6Al-4V alloy in simulated body fluid, due to the formation of more stable oxides such as Nb2O5, ZrO2 and Ta2O5. Furthermore, TNZT-xSi alloys have apatite formation ability superior to Ti-6Al-4V. These results suggest that TNZT-xSi alloys may have the potential as a biomaterial for implant applications.

Phase Evolution, Dielectric, and Electric Behavior of Sm‐Doped BCTO Ceramic Fabricated by Semi‐Wet Method

AbstractBi(2/3)‐xSmxCu3Ti4O12 (BSCTO x = 0.05, 0.10, and 0.20) ceramics are synthesized using semi‐wet technique and an extensive investigation into their structural, morphological, and elemental properties, alongside dielectric and impedance behaviors, is meticulously carried out. X‐ray powder diffraction analysis unequivocally confirmed the formation of a monophasic BCTO cubic phase without any discernible secondary phases. and the crystallite size of the BSCTO ceramic, obtained by X‐ray diffraction using Debye Scherrer formula, range from 62 to 81 nm. Rietveld analysis reveals that ceramics have a body centered cubic structure with space group Im‐3. The Scanning electron microscope image displays the dense microstructure of the ceramics, while EDX analysis unveils the elemental composition of resulting products. Doping with Sm3+ induced a notable reduction in grain size, as observed through Scanning electron microscope and Atomic Force Microscope analyses, indicating Sm3+ hindered grain growth during sintering, potentially resulting in reduced dielectric constant (ε′). Dielectric constant and dielectric loss of the composition (x = 0.2) are found to be 152 and 0.04, respectively at room temperature (1 kHz). Impedance characteristics revealed a substantial increase in grain boundary resistance, leading to improved dielectric loss. The AC conductivity of BSCTO ceramics exhibited a frequency‐dependent increase satisfying to Johncher's power law.

High energy storage performance of lead‐free Nb‐modified (Bi0.2Na0.2Ca0.2Ba0.2Sr0.2)TiO3 high‐entropy ceramics

AbstractOwing to the intrinsic chemical disorder of microscopic composition, perovskite high‐entropy ceramics exhibit dielectric relaxation behaviors and are favorable for energy storage performance. In this work, (Bi0.2Na0.2Ca0.2Ba0.2Sr0.2)(Ti1−xNbx)O3 (BNCBST‐xNb, 0.01 ≤ x ≤ 0.25) ceramics were prepared using a hydrothermal method. The results indicate that Nb doping into BNCBST induces lattice expansion and deepens dielectric relaxation. Moreover, the BNCBST‐xNb ceramics exhibit a great enhancement of electrical breakdown strength (Eb) with Nb content, which results from the reduction of grain size, the increase of resistivity, the decrease of oxygen vacancies, and the enlargement of band gap width. Consequently, the BNCBST‐0.15Nb system presents an outstanding Eb of 497 kV/cm with excellent recoverable energy density (Wrec = 3.85 J/cm3) and efficiency (η = 87.7%), accompanying by the wide temperature stability (Wrec and η vary within ± 9.8% and ± 1.4% at 40–100°C) and fast discharge rate (t0.9 = 88 ns). The significant improvement of Eb and energy storage properties suggest that our research offers an effective strategy for developing lead‐free energy storage ceramics.

Mechanical alloying of AlCoCrFe and AlCoCrFeNi: Design and experimental evaluation of medium- and high-entropy alloy particles for cold spraying

The manufacturability of equiatomic high-entropy alloy (HEA) particles with single- and dual-phase crystal structures using the high-energy mechanical alloying (HE-MA) method was explored in this study. Following a material design-of-experiment (DoE) curriculum, particles were synthesized in a planetary mill. Milling times varied while operating under two distinct HE-MA manufacturing regimes: the conventional approach (simultaneous milling of constituent elements) and the sequential method (progressive milling with the introduction of elements in a specific order). Within the conventional regime, equiatomic AlCoCrFe and AlCoCrFeNi blends were milled, focusing on the influence of incorporating nickel (Ni) as a transient element into the base composition. This led to an equivalent particle size distribution ranging from 5 to 100 μm. Notably, the presence of Ni resulted in an increased fraction of the face-centered cubic (FCC) phase, coupled with a simultaneous reduction in grain and crystallite sizes, thereby enhancing the overall material strength. This knowledge was applied to the design and synthesis of a target equiatomic FeNiCoCrAl HEA system. In this context, individual elements were added to the starting/milled Fe + Ni alloy at four-hour intervals, in line with the sequential milling regimen. The results showed an interesting evolution: the conventionally milled AlCoCrFeNi particles exhibited a dual-phase body-centered cubic (BCC) and FCC structure, with a composition of 55% BCC and 45% FCC phase fractions, while the sequentially milled FeNiCoCrAl particles demonstrated a single-phase BCC structure after 24 h of milling.

Rice Grains from Slightly Saline Field Exhibited Unchanged Starch Physicochemical Properties but Enhanced Nutritional Values

This study aims to investigate grain quality and nutritional values of rice (Pokkali, a salt-tolerant cultivar; RD73, a new cultivar improved from KDML105 introgressed with Saltol QTL from Pokkali, and KDML105, a moderately salt-susceptible cultivar) grown under non-saline (0.04–0.87 dS/m) and slightly saline (1.08–4.83 dS/m) field conditions. The results revealed that salinity caused significant reduction in grain size but significant increments in reducing sugar and total protein contents in the grains. Nevertheless, the amounts of starch in the grains of KDML105 and Pokkali rice genotypes were unaffected by the stress. The starch granule size distribution was also unaffected by salinity. Interestingly, only starch from Pokkali was significantly diminished in amylose content, from 19.18% to 16.99%. Accordingly, parameters relating to starch gelatinization, retrogradation, and pasting properties of KDML105 and RD73 were unaffected by salinity; only Pokkali showed a significant increase in percentage of retrogradation along with a significant reduction in gelatinization enthalpy. In the saline field, total phenolic content and antioxidant capacity in the grains of all rice cultivars tended to increase, particularly in Pokkali. On average, essential element contents in grains from the saline-treated plants showed a 33%, 32%, 32%, 22%, 20%, 11%, and 10% increase in total P, N, K, Mg, Zn, Fe, and Ca content, respectively. Interestingly, total Fe content exhibited the greatest percentage of increments in KDML105 (187%). Taken together, cultivation of rice in the slightly saline field did not alter its eating and cooking qualities, while enhanced some nutritional properties such as proteins, minerals, and secondary metabolites like phenolic compounds.

Simulation of defect evolution in tungsten during annealing by developing a vacancy and interstitial-type defect evolution model

In this work, a Vacancy and Interstitial-Type Defect Evolution (VITDE) model is developed to study the annealing and clustering behaviors of the irradiation-induced defect in tungsten (W). The post annealing of W-ion damaging at 300 K (called post-damaging annealing) and simultaneous annealing of W-ion damaging (called dynamic annealing) are simulated. In the post-damaging annealing case, the W is damaged by 20 MeV W-ion irradiation for 1h at 300 K, then the damaged W is annealed for 1h via increasing the temperature to 1000 K. In the dynamic annealing case, the defect evolution under simultaneous damaging and annealing is simulated using the same parameters as Case 1. The simulation results indicate the dynamic annealing case has lower induced defects concentration than the post-irradiation annealing case, which is in qualitative agreement with the experiment. The diffusion of interstitial, vacancy, di-interstitial and di-vacancy, and the cluster properties in the defect annealing are investigated and larger size Vn clusters are observed in dynamic annealing case than in post-damaging annealing case. The dependences of the defect evolution on material temperature (T) and grain size are revealed. By increasing the T, the defect concentration is decreased, which reproduces and explains the experimental result. The Vn trap amount with the reduction of grain size for two cases show a larger difference at T = 400 K, observing the Vn trap amount is unchanged for post-damaging annealing, whereas it is significantly increased by dynamic annealing.

Correlation of microstructure, texture, and mechanical properties of friction stir welded Joints of AA7075-T6 plates using a flat tool pin profile

This study investigates the influence of square and hexagon tool pin profiles on the butt joint of AA7075-T6 plates through friction stir welding. In contrast to the AA7075-T6 base metal with a grain size of 32.736 μm, both square (4.43 μm) and hexagon (5.79 μm) pin profiles led to a significant reduction in grain size within the stir zone (SZ) of the weld cross-section. The SZ region exhibited a gradient in recrystallization and a notable fraction of high angle grain boundaries, attributed to continuous dynamic recrystallization influenced by variations in temperature and strain rate. Pole figure analysis revealed predominant shear texture elements (B/ B‾ and C) with minor A1*/A2* and A/ A‾, indicating elevated strains within the SZ. Orientation distribution function (ODF) analysis identified recrystallization texture elements such as Goss {110} <001>, cube {001} <101>, and P {011} <112>, along with shear texture components F {111} <112> and rotating cube (H) {001} <110>. Tensile and nanoindentation analyses demonstrated that the weld joint using a square-shaped pin profile exhibited higher strength, elongation, and elastic modulus compared to other weld joints. These findings suggest that the square tool pin geometry enhances material flow and grain refinement during welding, thereby improving the mechanical properties of the joint.

The Effect of Cold Rolling on the Corrosion Behaviour of 5083 Aluminium Alloys

Aluminium–magnesium alloys find widespread application in diverse industrial and technological fields owing to their unique characteristics such as lightweight nature, favourable physical and mechanical properties, corrosion resistance and cost-effectiveness. During production, these alloys often undergo various forming processes that significantly affect the morphology and microstructure of their surface layers. Consequently, the surface properties, including corrosion resistance, are notably influenced by these treatments. In this study, the impact of cold rolling on the corrosion behaviour of the 5083 aluminium alloy, which is considered as an important alloy for the aerospace and naval industry, was investigated. The 5083 Al alloy underwent a cold-rolling process, resulting in specimens with reduced average thicknesses of 7% and 15%, respectively. The microstructure of the alloy was examined by using X-ray diffraction, optical and scanning electron microscopy techniques. Furthermore, the corrosion behaviour of both the as-received and cold-rolled aluminium alloy specimens was evaluated through potentiostatic and potentiodynamic corrosion measurements. The experimental results demonstrated that higher cold deformation percentages, within the specified experimental parameters, led to an enhanced corrosion resistance for the alloy. This improvement was primarily attributed to the reduction in grain size induced by recrystallization and to the formation of a passivating aluminium oxide film.

Energy storage mechanism and refinement engineering of SiO2-B2O3-Nb2O5 complex glass-ceramic doped with La2O3

Rare earth doping has demonstrated promising potential in improving material properties. This paper explored the influence mechanism of La2O3 on SiO2-B2O3-Nb2O5 (SBN) system energy storage glass-ceramic. The results reveal a significant impact of La2O3 doping on the physical properties, microstructure, and energy storage performance. Firstly, we observed the influences on the breakdown field strength through its effect on the grain size, density, and conductivity. The larger radius of La3+ triggers lattice vibrations, leading to a reduction in grain size and an increase in density. Moreover, the electronic shielding effect of the 4f layer reduces conductivity, which subsequently enhances the breakdown resistance. The dielectric constant exhibits improvements due to La2O3 doping. Increased crystallinity and polarization strength, along with the f-f transition of La3+ and reduced domain area, result in a peak dielectric constant at L4. Consequently, the energy storage performance is enhanced.

Corrosion Behavior of Nickel–Titanium Continuous-Casted Alloys

Variations in the corrosion behavior of biomedical NiTi alloys in Cl− containing and acidic environments present a problem with their biological implantation. The objective of this research was to evaluate the synergy of the microstructure, the corrosion behavior, and the biocompatibility of novel continuous-cast NiTi alloys and to compare them with commercial NiTi alloys. The two alloys have a practically identical nominal chemical composition, but they differ in production technology. The continuous casting technology involved vacuum induction melting of the basic components and vertical continuous casting, while the commercial NiTi alloy was produced through a process of casting, hot rolling, and forming into square shapes. The microstructure was revealed to determine the surface area and size of grains. The corrosion of a commercial nickel–titanium alloy and one prepared by a novel continuous casting method in acidic and chloride-containing solutions was studied via analytical and electrochemical tests. Localized corrosion characteristics related to oxide properties, when exposed to 9 g L−1 NaCl solution, were examined with focused ion beam analysis and subsequent microchemical analysis of the formed corrosive products. Corrosion potential over time and the oxide film resistance were analyzed using linear polarization measurements. To obtain a preliminary estimate of biocompatibility, human fibroblast cells were used in indirect contact, i.e., alloy conditioning medium. The continuous casting method resulted in a reduction in the average grain size in comparison to the commercial sample and better corrosion stability of the sample in an acidic environment. Also, in a solution of 9 g L−1 NaCl the commercial sample showed high values for the corrosion current density (jcorr = 6 μA cm−2), which indicated low corrosion resistance, while the continuous casting sample possessed much better corrosion stability and lower values for the corrosion current density (jcorr = 0.2 μA cm−2). In line with that, elemental analysis of the corroded surfaces showed higher Cl− ion deposition over the surface layer of the commercial sample, suggesting local oxide breakdown. Moreover, NiTicc reached a value three times higher for polarization resistance (Rp = 270 kΩ cm2) over time in comparison to the commercial sample (Rp~100 kΩ cm2). Biocompatibility evaluation showed that human fibroblast cells exhibited altered metabolic activity. An MTT assay showed that cells’ mitochondrial activity dropped below that of control cells in the presence of both materials’ supernatants.

Investigating the microstructure and mechanical properties of 316L/TiB2 composites fabricated by laser cladding additive manufacturing

In this paper, the 316L stainless steel matrix composite strengthened by TiB2 was successfully fabricated using laser cladding additive manufacturing technology. The microstructures of 316L/TiB2 with the addition of TiB2 (mass fractions of 0, 3 and 6, respectively) were characterised. Hardness tests and tensile tests were conducted to evaluate the physical and mechanical properties of the samples. The results indicated that all prepared samples exhibit a complex cellular microstructure composed of sub-grains. The matrix phase was verified as γ austenite with a honeycomb-like reinforcement phases forming along the boundaries. Further analysis revealed the net-like reinforcements were (Fe,Cr)2B and M3B2 (M is Cr, Fe, Mo, Ni, Ti) phases. The Microhardness of the samples with 0 wt%,3 wt% and 6 wt% of TiB2 were 148 HV, 170 HV and 186 HV, respectively. The addition of 3 wt% and 6 wt% TiB2 composites increased the yield strength by 22 % and 29 %, respectively, compared to 316L composite. Also, the tensile strength and modulus of elasticity of the reinforcement composites were improved by 8 % and 13 %, respectively. However, the elongation of the reinforcement composites was reduced by 36 % and 47 %, respectively. The reinforcement with high strength and modulus is formed in 316L/TiB2 composite, which leads to a reduction in grain size while enhancing the density of large-angle grain boundaries. Multiple strengthening effects dominated by Orowan strengthening were simultaneously experienced during the preparation process, which improved the mechanical properties of the composites.

The effect of heat treatment on the microstructure and mechanical properties of multilayer AA6061 alloy fabricated by additive friction stir deposition

Multilayer AA6061 aluminum alloy components were successfully fabricated by the additive friction stir deposition (AFSD). The effect of heat treatment on the microstructure and mechanical behavior of the aluminum alloy components was studied. Due to dynamic recrystallization, AFSD AA6061 sample presented a 93.2% average reduction in grain size as compared to base material (BM) (∼ 39.13 µm). Abnormal grain growth was observed in the AFSD-HT sample, and the average grain size of AFSD-HT sample was 592 µm. There was an occurrence of texture formation in the AFSD and AFSD-HT samples, mainly due to severe shear deformation during AFSD process. The maximum texture density of AFSD-HT sample was increased to 17.84. In the BM sample, apart from the β" strengthening phases, hard-brittle intermetallic compounds of Al5FeSi aggregated along the boundaries of the coarser grains. Due to the high temperature generated during the process of AFSD, the β" strengthening phases dissolved into the matrix, and significantly reduced the strength and hardness. After heat treatment, the AFSD AA6016 alloy recovered 18% of its strength at a loss of 2.8% ductility. High density β" strengthening phases precipitated, resulting in increased strength and hardness.

Estimation of pore structure and permeability in tight carbonate reservoir based on machine learning (ML) algorithm using SEM images of Jaisalmer sub-basin, India

Analyzing the pore structure in carbonate reservoirs plays a crucial role in predicting fluid flow characteristics within these formations. The goal of the study was to use machine learning techniques for pore structure analysis and estimation of permeability in carbonate reservoirs. We implemented these algorithms by examining 2D scanning electron microscope (SEM) images of carbonate samples from the Jaisalmer sub-basin captured at various magnifications. In the initial stage of the analysis, various binarization algorithms were applied to determine carbonate sample porosity. Among these algorithms, the MaxEntropy algorithm gave a porosity value closely aligned with those obtained through petrography analysis. We employed the watershed algorithm to find the pore network parameters of carbonate samples at various magnifications. We observed that changes in magnification affected pore network parameters, resulting in a reduction in pore size distribution, throat radius, and grain size. Subsequently, we employed the numerical lattice Boltzmann method (LBM) to estimate the permeability of carbonate samples and compared to values derived from well logs. We employed machine learning (ML) algorithms, specifically Artificial Neural Network (ANN) and Support Vector Machine (SVM), to predict the permeability of carbonate samples. The input features for these models were the pore network parameters, while the LBM permeability values served as the output. We examine the prediction performance of these methods against the measured LBM permeability by conducting the error analysis and the coefficient of determination (R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${R}^{2}$$\\end{document}) calculation. Our findings revealed that the ANN models outperformed the SVM models. Specifically, the ANN model displayed an impressive R2 value of 0.892, along with root mean square error (RMSE), mean squared error (MSE) and, mean absolute error (MAE) values of 1.927, 3.716 and 1.580, respectively. In contrast, the SVM model yielded an R2 value of 0.849, with RMSE, MSE and, MAE values of 2.324, 5.401 and, 2.166 respectively, when assessed on testing data of measured permeability. This study found that ANN is more dependable, robust, and precise than SVM in forecasting carbonate sample permeability.

Cu and Er modified barium zirconium titanate (BaZr0.05Ti0.95O3) ceramics: Composition-dependent dielectric properties

Cu2+ and Er3+ doped BaZr0.05Ti0.95O3 (BZT) ceramics were prepared using the solid-state reaction method, where amount of CuO + Er2O3 was fixed at 2 wt.% and different CuO : Er2O3 molar ratios (i.e. 1:1, 1:2, 1:3, 2:1 and 3:1) were used. The influence of Cu2+ and Er3+ doping on crystal structure and dielectric properties of the samples sintered at 1300 ?C was investigated. X-ray diffraction analysis confirmed the formation of a single-phase material and tetragonal crystal structure with P4mm symmetry. Microstructural analysis conducted with a scanning electron microscope revealed well-defined and uniformly distributed grains across the surface of the sintered samples and reduction of grain size and density with doping. The highest energy storage density of 40.51mJ/cm3 with an energy efficiency of 78.8% was obtained in the sample with CuO : Er2O3 molar ratio of 2:1. The doped BZT ceramics have high dielectric constant and significantly lower tangent loss in comparison to the undoped BZT. The dielectric data confirm the non-Debye behaviour for all the samples. Impedance spectroscopy and electrical modulus analysis indicated that conduction in the materials was influenced by both the grains and grain boundaries. The AC conductivity is described by the Jonscher?s universal power law, whereas DC conductivity follows a dependency based on the Arrhenius?s theory. The results revealed a conduction mechanism characterized by non-overlapping small Polaron tunnelling up to 340?C and a transition to correlated barrier hopping conduction above 340?C within the selected temperature range for all the samples. According to the Arrhenius fitting of DC conductivity the activation energy of the undoped BaZr0.05Ti0.95O3 sample is 0.168 eV and decrease with doping to 0.138 and 0.131 eV for the sample with lower Cu2+ contents (CuO : Er2O3 molar ratios of 1:2 and 1:3, respectively).

Effect of additional cooling during friction stir welding on structure and properties of aluminum alloy joints

The mechanical and corrosion properties of welded joints of sheets with a thickness of 5 mm made of the Al–Cu– Mg system alloy in the T state (hardening and natural ageing) and the 1565сhN116 alloy with a thickness of 3 mm, obtained by friction stir welding (FSW) in air and in water, are studied. It is established that additional cooling of the welded joint by water helps to increase the ultimate strength of the weld, slightly changing the properties of the welded joint. The destruction of the welded joint in both cases occurs along the thermo-mechanical affected zone. The strength of the welded joint of the Al–Cu–Mg system alloy and the 1565chN116 alloy is 0.8 and 0.95...0.99 of the strength of the base metal, respectively. When FSW of the Al–Cu–Mg system alloy in the T state in water, in comparison with welding in air, there is an increase in the microhardness of the mixing zone by 20 % and a decrease in the grain size in it from 9.8 to 4.8 μm. For the 1565chN116 alloy under the same conditions, an increase in the microhardness of the metal of the thermo-mechanical affected zone and the mixing zone by about 12 % and reduction of grain size in the mixing zone from 6 .8 to 4.5 μm is detected. At the same time, both for the Al–Cu–Mg system alloy in the T state and the 1565chN116 alloy during FSW in water, the length of the heat-affected zone decreases by about 1.6—2.2 times compared to FSW in air. For both alloys, an increase in the cooling rate during FSW leads to an increase in resistance against intercrystalline corrosion of all zones of the welded joint by about 1.5—2 times.

Improved mechanical properties of high-speed extruded BA53 alloy through long-range water-cooling system

A recently developed Mg–5Bi–3Al (BA53, wt%) alloy exhibited remarkable extrudability despite its high alloying content. However, when subjected to high-speed extrusion with a die exit speed of 67 m/min, grain coarsening of recrystallized grains occurs, increasing their size from 12.1 to 26.4 μm due to excessive heat generation during extrusion. Herein, a long-range water-cooling system is installed immediately after the extrusion die to mitigate grain coarsening and attain finer grains in the high-speed extruded alloy. The results demonstrate that the use of the cooling system leads to a significant reduction in the average grain size (from 26.4 to 15.7 μm) of the BA53 alloy extruded at high speed. Furthermore, grain refinement led to notable increases in the ultimate tensile strength (from 255 to 276 MPa) and elongation (from 7.5% to 8.6%) of the alloy. These enhancements in strength and elongation are primarily attributed to the enhanced grain-boundary hardening effect and suppression of twinning during tension, both of which are consequences of grain refinement. This study underscores the effectiveness of a long-range water-cooling system, comprising water spraying over a length of 2 m, in achieving grain refinement during high-speed extrusion of the BA53 alloy and improving both the strength and ductility of the alloy after high-speed extrusion.

Effect of Grain-Size and Textural Weakening in Polyphase Crustal and Mantle Lithospheric Shear Zones

Strain localization to form narrow plate boundary shear zones in Earth’s lithosphere requires a significant amount of strain weakening. Here we investigate the relative contributions of grain-size-sensitive weakening versus textural weakening in polyphase shear zones in granitoid and peridotitic rocks through two-dimensional centimetre-scale bulk simple shear numerical models. The models deploy both constant grain size (only textural weakening) and dynamic grain-size evolution based on the paleowattmeter. Our results reveal that for granitoid rocks, textural weakening dominates, especially at temperatures around 550 °C, while grain-size-sensitive weakening plays a secondary yet significant role. For peridotitic rocks, intense weakening is evident below temperatures of ~1000 °C due to grain-size reduction, while textural weakening has a minor effect on weakening for experiments above 1000 °C. Two-dimensional experiments are compared to one-dimensional, single-phase models to reveal the effect of geometrical complexities in stress and grain-size evolution. These results are discussed in the context of natural lithospheric shear zones and are compared with established piezometers for individual mineral phases. Our findings underscore the vital role of grain-size-sensitive rheologies, particularly in the mantle lithosphere, for the initial weakening of ductile shear zones. These insights offer quantitative constraints that advance our understanding of the long-term strength of lithospheric plate boundaries.

Discontinuous dynamic recrystallization behavior and texture evolution of large-size pure titanium flat ingot via electron beam cold hearth melting during short process direct hot rolling

Large-size pure titanium ingots melted by single electron beam cold hearth melting (EBCHM)) could be rolled into large-width and heavy-weight titanium strip coils using short process without forging. It is crucial to study the large-span refinement mechanism from highly coarse grains, whose sizes are in the order of ∼cm, to micronmeter. In this study, the recrystallization mechanism and texture evolution of pure titanium with a size of 1570 × 200 × > 8000 mm was investigated by multi-pass simulated rolling and experimental rolling. The results indicated the hot deformation can result in marked reduction in grain size of the as-cast grain, from 3 to 5 cm to 17–23 μm. The discontinuous dynamic recrystallization (DDRX) mechanism of a pure titanium ingot during direct multi-pass hot deformation causes the reconstruction of as-cast microstructure and refinement of hot rolling microstructure. Furthermore, DDRX occurred, during hot deformation, and was accompanied with weakening of deformation texture. Raising the initial hot deformation temperature results in a modification of the texture type of the {0001} crystal plane. The strength of the texture experiences a decrease initially and then eventually an increase. This alteration in strength is inversely related to the degree of dynamic recrystallization. Based on the simulated rolling experiment, the results of experimental rolling also found the coarse as-cast grains was broken and reconstructed. It has strength (average yield strength: 334 MPa, ultimate tensile strength: 371 MPa), ductility (total elongation: 30 %). Such a combination of mechanical properties makes the hot rolling plate a potential choice for sheet practical application.

High strain rate mechanical behavior of Ti-6Al-4V with micro–macro correlation under compressive loading

The application of Ti6Al4V in lightweight structures subjected to impact loads necessitates a comprehensive understanding of its dynamic response under high strain rates to ensure the safety and reliability of these components. In this paper, the macroscopic compressive mechanical behavior of Ti6Al4V under high strain rates was investigated through the split-Hopkinson pressure bar (SHPB) technique at both room temperature and 200 °C, followed by microstructure analysis of the compressed specimens, carried out employing a combination of optical microscopy (OM) and electron backscatter diffraction (EBSD), and elastic modulus and hardness measurements, performed by a nanoindentation instrument. At room temperature, both the modulus and strain hardening exponent of Ti6Al4V exhibited an initial increase before the strain rate reached 1000s-1, after which they decreased at 3400s-1. Meanwhile, the flow stress continued to rise with increasing strain rate. Microscopic observations revealed that twinning played a substantial role in the strain hardening effects. Notably, the basal slip system of the hcp (hexagonal close packed) α phase did not display a more favorable trend, while the c+a type slip systems became more active. Under a strain rate of 5000s-1, discontinuous dynamic recrystallization emerged as the dominant mechanism, resulting in an increased frequency of low-angle grain boundaries, as well as a reduction in grain size and dislocation density. These results provide a basis for explaining the mechanical behavior of Ti6Al4V under high strain rates and offer insights for the establishment of material models that take into account microstructure deformation mechanisms.

Multiple enhancement on the magnetic and electric properties of SrM hexaferrites by phase-change perovskite additives

M−type strontium (SrM) hexaferrites, which possess a high saturation magnetization, coercivity, and maximum magnetic energy product, have been widely used as permanent magnets in electric machines. However, emerging high-speed and high-power electric machines put forward higher requirements on the loss characteristics of ferrites at high frequencies and high temperatures. Here, the effects of two phase-change perovskite additives, barium titanate (BTO) and BTO-based ceramic with a positive temperature coefficient (PTCC), on the magnetic properties, electrical properties, and their temperature dependence of SrM hexaferrite are reported. The spatial concentration distribution and diffusion kinetics of the perovskite additives are investigated, showing their accumulation at the grain boundaries and gradual diffusion into the crystallites. Due to the high melting points, the addition of BTO and PTCC at the grain boundaries hinder the grain growth and reduce the grain size. Due to the strong pinning effect of the impurities near the grain boundaries and the reduction of grain size, enhancement in coercivity up to 10 % as well as an increase of 225 % in resistivity are observed. More interestingly, a positive temperature dependence of the resistivity is achieved by adding various amounts of PTCC. These results demonstrate the capability of phase-change perovskite additives to achieve simultaneous enhancement in multiple electromagnetic and temperature properties of SrM hexaferrite.