Fine Grain Research Articles

Processing of different Mg-based multiphase alloys via a combined severe plastic deformation

In this study, cyclic extrusion compression angular pressing-forward extrusion was employed to develop binary magnesium-based multiphase alloys, and subsequently analysed the microstructural, mechanical and corrosional properties of the resulting samples. The findings demonstrate that the inclusion of alloying elements in the multiphase alloys significantly enhances their microstructural, mechanical and corrosional properties. Compared to pure Mg samples fabricated using the same method, the multiphase alloys produced by this technique exhibit finer grain structures. Mechanical analysis indicates that these multiphase alloys possess higher yield and ultimate strength compared to pure magnesium. Corrosion testing reveals that all produced alloys outperform pure magnesium in various aspects. Particularly, Mg–1Zn and Mg–1Mn alloys exhibit exceptional corrosion resistance in immersion, mass loss and polarisation tests.

Colossal permittivity and excellent temperature stability of BaTiO3 based fine ceramics with controlled grain growth

Dielectric materials with colossal permittivity (CP, εr > 104) have attracted the increasing interest of researchers due to their enormous potential in the fields of sensor, capacitor, energy storage, etc. However, for the explored CP materials, their grains are too large to apply. To control grain growth, the sintering aids of MgO–Al2O3–SiO2 (MAS) cordierite glass and common suppression grain growth of MgO have been introduced to BaTiO3-0.004Y2O3-0.006MnO2 ceramics derived from the commercial BaTiO3 powder with the average grain size of 300 nm. After controlling grain growth, the fine grains with the average grain size of dg ∼300 nm and CP are achieved in BaTiO3 based ceramics sintered in reducing atmosphere. Notably, excellent temperature stability with Δεr/εr25°C lower than 17 % is gained for the present BaTiO3 based ceramics in the temperature range of −60 to 155 °C, meeting the X8S specification (ΔC/C25°C ≤±22 %, −55 °C–150 °C). Based on the X-ray photoelectron spectroscopy (XPS) and Raman spectra, the outstanding dielectric properties of the present BaTiO3 based ceramics is ascribed to the electron-pinned defect-dipole (EPDD) effect induced by YTi′−YBa∙, TiTi′−Vo∙∙−TiTi′ and YTi′−Vo∙∙−TiTi′ defect dipoles. The present BaTiO3 based fine ceramics with colossal permittivity (∼2.9 × 104), low loss (∼0.03) at 1 kHz and room temperature, excellent temperature stability and high resistivity of 3.54 × 109 Ω cm is a promising candidate for the multilayer ceramics capacitor (MLCC).

Regulated Phase Separation in Al-Ti-Cu-Co Alloys through Spark Plasma Sintering Process.

With the goal of developing lightweight Al-Ti-containing multicomponent alloys with excellent mechanical strength, an Al-Ti-Cu-Co alloy with a phase-separated microstructure was prepared. The granulometry of metal particles was reduced using planetary ball milling. The particle size of the metal powders decreased as the ball milling time increased from 5, 7, to 15 h (i.e., 6.6 ± 6.4, 5.1 ± 4.3, and 3.2 ± 2.1 μm, respectively). The reduction in particle size and the dispersion of metal powders promoted enhanced diffusion during the spark plasma sintering process. This led to the micro-phase separation of the (Cu, Co)2AlTi (L21) phase, and the formation of a Cu-rich phase with embedded nanoscale Ti-rich (B2) precipitates. The Al-Ti-Cu-Co alloys prepared using powder metallurgy through the spark plasma sintering exhibited different hardnesses of 684, 710, and 791 HV, respectively, while maintaining a relatively low density of 5.8-5.9 g/cm3 (<6 g/cm3). The mechanical properties were improved due to a decrease in particle size achieved through increased ball milling time, leading to a finer grain size. The L21 phase, consisting of (Cu, Co)2AlTi, is the site of basic hardness performance, and the Cu-rich phase is the mechanical buffer layer between the L21 and B2 phases. The finer network structure of the Cu-rich phase also suppresses brittle fracture.

Study on strengthening and toughening mechanism of Ti-Ni-Al ternary metallic-intermetallic laminated composites: Effect of interlaminar phase and Ti2Ni morphology

Further improving the strengthening and toughening properties of traditional binary metallic-intermetallic laminated (MIL) composites has become an urgent problem to be solved. In this work, a thin 0.02 mm Ni layer was added between the Ti and Al layers to prepare novel Ti-Ni-Al ternary MIL (TNA-TMIL) with multi-layer heterostructure (HS) characteristics, which significantly improved strength and toughness. TNA-TMIL composites include intermetallic layers (Ni-Al and Ni-Ti), unreacted metal layers (Ti-6Al-4V and Ni) and special morphology Ti2Ni in the Ti-6Al-4V layers. With the rise of hot-pressing temperature from 710 ℃ to 900 ℃, the eutectoid reaction and the increase of Ni element in Ti-6Al-4V alloy caused the morphology of Ti2Ni in the Ti-6Al-4V layer transition from island-like to network-like/needle-like to transition regions and finally formed needle-like Ti2Ni morphology. The electron backscatter diffraction (EBSD) analysis of the needle-like Ti2Ni shows that it has a weak cubic texture, and its fine grains are composed of dynamic recrystallization (DRX) and deformed grains. Nano-indentation and compression experiments indicated that the mechanical properties of TNA-TMIL composites are related to the different HS combinations and the morphology changes of Ti2Ni in the Ti-6Al-4V layer. This discovery may provide experience for designing and developing ternary MIL composites.

Investigation of cigarette effect and elastic-plastic behavior of green iron pellets on the roller screen efficiency

The green iron pellet demonstrates elastic–plastic deformation behavior during classification on a roller screen, which has a significant effect on its inefficiency due to the occurrence of phenomena such as the cigarette effect. This phenomenon causes the quantity and quality of produced pellets to drop by transferring the on-size pellets to the fine grain section and especially the oversized pellets to the product section. In this research, the effective factors in creating this phenomenon and the solutions to reduce it are investigated. It is observed that the optimum plastic behavior of the pellet and consequently the efficiency of the roller screen would be achieved when the green pellet is made from magnetite concentrate with 8 % moisture and 1 % bentonite, and roller screen operational parameters include feed rate of 1.5 t/h, the deck inclination angle of 13 degrees and the roll rotation speed of 150 rpm. The results obtained for the optimum fine removal efficiency, product screening efficiency, loss of production to undersize, on-size contamination, and oversize removal efficiency are 92.1 %, 93.7 %, 5.36 %, 5.23 %, and 73.2 %, respectively. The total screening efficiency of the roller screen is also estimated as 86.29 % and the cigarette effect is decreased to the most optimal state.

Microstructure evolution during high temperature rolling and effect on the mechanical properties of TiBw/Ti65 composites with network structure

In this paper, the rolled TiB whisker (TiBw)/Ti65 composites with different rolling reductions were obtained by high temperature (HT) rolling in the β single-phase region. The changes in TiBw, silicide and grain size after rolling deformation were analyzed by microstructure characterization. Based on this, the strengthening mechanism and HT deformation behavior of rolled composites were analyzed in combination with room temperature and HT tensile experiments. The results show that TiBw fractured after rolling deformation, leading to a decrease in the aspect ratio and an increase in matrix connectivity. Silicide with an average diameter of 80 nm appeared in the rolled composites. The grain was continuously refined as the rolling reduction increased. A T-type texture with the crystal C-axis parallel to the transverse direction appeared at 40% rolling reduction. The strength and plasticity of sintered TiBw/Ti65 composites were increased after rolling. With an increase of rolling reduction, the composites exhibited fine-grain strengthening below 650 °C. When tensile above 700 °C, a softening effect occurred with the decrease of grain size, that is, the yield strength decreased for grain size <3.6 μm. The strengthening mechanisms of rolled TiBw/Ti65 composites include fine grain strengthening, load transfer strengthening of TiBw, Orowan strengthening of silicide, and dislocation density strengthening. Among them, fine grain strengthening and load transfer strengthening predominated and increased as the rolling reduction increased. After tensile at 750 °C, many recrystallized grains with large misorientation appeared around the initial coarse grains and TiBw.

A novel additive repair approach for Ti-6Al-4 V based on the extreme low heat input

An innovative wire arc additive repair approach based on the extreme low heat input was proposed to repair the defect of Ti-6Al-4 V in this study. Arc was ignited between the tungsten electrode and hydrocooling Cu pipe over the substrate, avoiding arc acting on the substrate directly and resulting in a smaller heat affected zone (HAZ) and finer grains. While the top and middle region of repaired layer exhibited coarser grains with α and α’ martensite phases owing to the lower heat dissipation rate. Note that the thickness of HAZ was much lower than reported methods. And the hardness near fusion line was higher than other regions, attributed to the finer grains. The substrate was only affected by the molten droplet and little arc heat during repairing process, minimizing the thermal influence on the substrate. This study provided a novel perspective for wire arc additive repair technology.

Microstructure and characteristics of Cu-W composite prepared by W-coated Cu powder with different W contents

In this study, nanometer W particles were added to Cu matrix as reinforcement phase, aiming to maintain the excellent electrical conductivity of Cu matrix while significantly improving the mechanical performance of Cu-W composite. Cu-W composite powder with W nanoparticle coated Cu was prepared after spray drying and two-step hydrogen reduction. Cu-W composite with different W contents (0 wt%, 5 wt%, 10 wt%, and 20 wt%) were fabricated by spark plasma sintering (SPS). The coating structure can refine Cu particle size and inhibit Cu grain growth during sintering. The impact of W nanoparticles on microstructure, physical and mechanical performance of Cu-W composite was studied. The average size of the W particles dispersed in Cu matrix ranged from 71.89 nm to 106.90 nm. Electron back-scatter diffraction (EBSD) statistics indicated that Cu-5 wt%W, Cu-10 wt%W, and Cu-20 wt%W composite had a mean grain size of 0.76 μm, 0.71 μm, and 0.57 μm, respectively. Cu-20 wt%W composite had a uniform W network-Cu pool structure. The room-temperature tensile strength of Cu-20 wt%W composite was up to 421.98 MPa, with an elongation of 10.91 %; and the room-temperature compressive yield strength reached 313.83 MPa, an increase of 71.76 % compared to pure Cu. Although adding W nanoparticles caused the decrease of electrical conductivity, the conductivity of all Cu-W samples exceeded 81 %. The (111) of Cu and (110) of W showed a semi-coherent relationship with a calculated mismatch parameter δ of 0.077 and good interfacial bonding. The strength of Cu-W composite was improved by the pinning effect of W nanoparticles as a result of the combined effect of fine grain and dispersion strengthening.

Y effects on the Cu-Zr-Fe alloys’ aging behavior and properties

Cu-Zr-Fe(-Y) alloys were prepared by vacuum melting, and their microstructure, elemental distribution and mechanical properties were analyzed. The microstructure evolution, dislocation morphology and precipitated phase distribution due to aging were investigated by electron backscatter diffraction and transmission electron microscopy. The optimal process parameters for the Cu-Zr-Fe(-Y) alloy after solution treatment at 930 °C with 60% cold rolling are 450 °C aging for 120 min and 500 °C aging for 20 min, resulting in microhardness, electrical conductivity, and tensile strength of 60.9% IACS, 162.4 HV, 512.8 MPa and 54.8% IACS, 177.7 HV, 546.9 MPa, respectively. The addition of Y has a fine grain strengthening effect, resulting in an increase in hardness and strength by 9.4% and 6.6%, respectively. The precipitated Cu5Zr and γ-Fe phases pinned the dislocations and played a significant role in the aging hardening of the alloy, being the main contributors to the strengthening effects.

Synthesis of fine Na-type zeolite grains from coal fly ash and the assessment of the adsorption capability of lead ions from aqueous solutions

Fine Na-type zeolite grains (ZE) were prepared by dry milling treatment (D-ZE) or wet milling treatment (W-ZE).

Microstructural regulation and mechanical behavior of asymmetrically extruded high-content TC4p reinforced AZ31 composite

Asymmetric extrusion (AE) is frequently used to weaken the texture of magnesium (Mg) alloys to improve their mechanical properties. In this paper, to explore the influence of asymmetric extrusion on the microstructure and mechanical properties of Mg matrix composites (MMCs), we synthesized TC4/AZ31 composite sheets via ball milling coupled with sintering and then various extrusions (including conventional extrusion (CE), transverse-directional AE (TDE), and normal-directional AE (NDE)). The differences in microstructure and performance among the three processed samples were compared and analyzed using SEM, XRD, EBSD characterization and tensile testing. The results showed that the asymmetrically extruded samples achieved better mechanical properties compared to their CE counterparts. It found that the grain refinement was relatively significant and texture evolution was dispersed in AE samples compared to the CE ones, which was attributed to the TC4 particle (TC4p) disturbance and extra asymmetric shear of matrix flow. Three different macro-textures were obtained in various extruded processes, and the micro-texture of each sample changed in diverse regions. Based on grain orientation spread (GOS) analysis, the introduction of TC4p resulted in dynamic recrystallization (DRX) and particle-stimulated nucleation (PSN) effects during the AE process at 350 °C. The mechanisms of the combination of ductility and strength in the AE-processed sheets were related to the finer grains, high Schmid factor (SF), evenly distributed dislocations and scattered texture. This work can also provide the feasibility and prospects of applying asymmetric extrusion to MMCs.

Feasibility of using coal as reinforcement in dissimilar welded joints: Comparative analysis

This study explores the possibility of using coal as reinforcement in dissimilar welded joints. The study involved joints of AA5083 and AA6082 alloys, which underwent friction stir welding (FSW), friction stir processing (FSP), and FSP with added coal powder (FSP+Coal). Microstructure analysis, microhardness testing, tensile tests, and fracture surface analysis were evaluated. The results indicated that FSP+Coal joints exhibited promising mechanical properties, with failure initiation at 130 MPa and a tensile strain of 6%, and complete failure at an ultimate tensile stress (UTS) of 144 MPa and a tensile strain of 9.5%. In comparison, FSP joints showed failure initiation at 130 MPa and a strain of 8.5%, and complete failure at 90 MPa and a strain of 14%. Additionally, FSP+Coal joints demonstrated a higher average hardness (8.3% higher than FSW joints and 4% higher than FSP joints), supported by fracture surface and microstructural analyses indicating a finer grain size of 13.15 μm in FSP+Coal joints, compared to 12.79 μm in FSP joints and 39.74 μm in FSW joints.

Раціональні технологічні засади отримання коксу із заданими показниками питомого електричного опору

DOI: 10.31081/1681-309X-2024-0-1-8-15 Specialty 161. U.D.C. 661.66.2:537.311/.312 RATIONAL TECHNOLOGICAL BASES OF PRODUCTION OF COKE WITH SPECIFIED ELECTRICAL RESISTIVITY © I.V. Shulga, Ph.D. in Technical Sciences, O.V. Sytnyk, Ph.D. in Technical Sciences (State Enterprise “Ukrainian State Research Institute for Carbochemistry (UKHIN)”, 7 Vesnina str., Kharkiv, 61023, Ukraine), O.I. Zelenskii, Ph.D. in Technical Sciences, V.V. Vladymirenko (National Technical University "Kharkiv Polytechnic Institute", 2, Kyrpychova str., Kharkiv, 61002, Ukraine) The article is devoted to the practically important issue of obtaining coke with a specific electrical resistance of no more than 0.1 Ohm∙cm for the needs of blast furnace production. Achievement of this indicator should occur simultaneously with the improvement of the entire range of properties of blast furnace coke. It is noted that the concept of production of blast furnace coke of improved quality consists of the formation of a rational raw material base, ensuring proper coking technology and post-furnace coke treatment. It has been shown that the production of high-quality blast furnace coke with low resistivity requires: high sinterability and coking capacity of the charge based on highly sinterable coals; coking pressure of the coal charge not exceeding 7 kPa; coking speed not exceeding 24 mm/hour; final coking temperature of 1050-1100 °C; maximum temperature level in the heating system not exceeding 1410 °C. It is confirmed that in order to obtain a low electrical resistivity, it is necessary to produce coke with the most ordered anisotropic structure. It is shown that the resistivity of coke naturally changes when used in blast furnace production: the destruction of lumps leads to the formation of fragments of different sizes. At the same time, coarser fragments have lower resistivity values, and smaller ones, characterized by an increased concentration of structural defects that are the centers of crack formation, have a higher resistivity. After gasification with carbon dioxide, the number of structural defects increases in grains of any size due to the weakening of the surface due to chemical interaction, so the resistivity of coke increases and becomes almost equal for both coarser and finer grains. Keywords: hard coal coke, blast furnace production, resistivity, vertical temperature, final coking temperature, coke gasification. Corresponding author I.V. Shulga, e-mail: ko@ukhin.org.ua

Granulometric Analyses of Stream Sediments from Kolar River Sub-Basin, Central India

This paper focuses on a granulometric study conducted to investigate the sedimentary characteristics of channel sediments in the upper, middle, and lower reaches of the Kolar River Sub-basin. The study's primary objective is to gain a detailed understanding of sediment transport by seamlessly integrating field surveys and laboratory analyses. The study investigates grain size distribution and the deposition environment in the Kolar River Sub-basin. From sediment data, statistical measures were prepared and utilized to construct bivariate diagrams and examine the inter-relationship of various parameters. The results indicate that the upper reach exhibits poor sediment sorting, while the middle and lower reaches show more moderate sorting. Skewness values indicate dominance of coarser sediments in the upper reach, finer grain sizes in the middle reach, and a mixed distribution in the lower reach. Kurtosis values suggest concentrated distributions in specific areas of the upper and middle reaches, while the lower reach displays a broader distribution. The CM plot analysis reveals distinct sediment transport types in each reach, reflecting the energy level of water transport and sediment load. This study provides valuable insights into spatial variations in sediment dynamics, contributing to a comprehensive understanding of the overall sedimentary regime of the river. With this understanding, effective river basin management techniques, such as vegetative stabilization, check dam construction and prevention of excessive deposition can be implemented to ensure the sustainable management of the Kolar River Sub-basin. Keywords: Granulometry, Stream Sediments, Depositional Environment, Sustainable Management, Kolar River Sub-Basin, Central India

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 Sc contents on the mechanical properties and damping capacity of Al–Zn–Mg–Cu–Zr–Sc alloys with different grain structures

Al–Zn–Mg–Cu–Zr–Sc alloys with different Sc contents were fabricated by casting, deformation, and T6 treatment. Deformation methods including rolling and friction-stir processing (FSP) were used to design their grain structure. A low additive amount (0.1) of Sc cannot refine the grains of the alloy with rolling and T6 treatment, and it instead coarsened the grains. The reason was the non-uniform distribution of nanosize Al3(Sc,Zr) phases that led to the occurrence of abnormal grain growth during homogenization. Meanwhile, the alloy with only 0.1Sc exhibited finer grains after FSP and T6 treatment than the alloys subjected to the same process but with higher Sc additive amount. Alloys with rolling-induced elongated grain structure exhibited better mechanical properties, and alloys with FSP-induced fine equiaxed grain structure exhibited higher high-strain and high-temperature internal friction values. These features are important performance parameters for applications in fields where vibration and noise are sensitive. The optimum additive amounts of Sc for alloys with elongated and fine equiaxed grain structures were 0.25 and 0.1, respectively.

Strain-rate-dependent behavior of additively manufactured alumina ceramics: Characterization and mechanical testing

This study experimentally investigates the mechanical behavior of additively manufactured (AM) alumina ceramics by stereolithography technique. The AM alumina specimens with two different printing orientations (POs) are tested under quasi-static and dynamic loading rates. The material shows a quasi-static (i.e., a strain rate of 10−3 s−1) compressive strength of 1640.54 ± 99.33 MPa and 1494.25 ± 260.08 MPa for the PO1 and PO2, respectively, and a dynamic (i.e., a strain rate of 640–730 s−1) compressive strength of 3077.25 ± 174.07 MPa and 3107.33 ± 97.03 MPa for the PO1 and PO2, respectively, which are among the highest reported values for AM alumina due to the higher density and finer grain size. The strain-rate-dependent compressive strength of the material is slightly affected by the PO which is alleviated with the increase in strain rate from quasi-static to dynamic loading conditions. In contrast, the PO noticeably affects the macro-scale failure pattern. The fractography analysis shows the dominant contribution of the intergranular failure mechanism and a combination of intergranular and transgranular mechanisms under quasi-static and dynamic loading, respectively. The crack speed propagation is found to be 785 ± 174 m/s on average which is ∼68% less than that of conventional ones in the literature. The current AM alumina shows a hardness of 24.45 ± 0.88 GPa which is higher than that of the majority of other AM alumina. Overall, this study discusses the potentiality of using AM ceramics in engineering fields replacing the conventionally-made counterparts, and provides implications for designing better-performing AM ceramics.

Study on microstructure evolution and mechanical properties of similar joint of Al-Mg-Si alloy by tungsten inert gas welding

Study on microstructure evolution and mechanical properties of similar joint of Al-Mg-Si alloy by tungsten inert gas welding

Thermo-mechanical process variables driven microstructure evolution during additive friction stir deposition of IN625

Additive friction stir deposition is an innovative technique for solid-state additive manufacturing involving complex thermo-mechanical processes such as frictional heating, plastic deformation, and viscoplastic material flow, which repeats layer by layer during material deposition. The present study is an attempt to understand the relationship between the complex thermo-mechanical process attributes and the resultant microstructure in additive friction stir deposition of IN625. The estimation of thermo-mechanical process attributes, primarily temperature and strain rate during multi-layer deposition was based on the already established thermo-pseudo-mechanical description of friction stir based processes. The complex thermo-mechanical interaction associated with multi-layer material deformation, deposition, and flash formation can be attributed to variations in the average deposition temperature and the strain rate. Microstructural examination of the additive friction stir deposited sample was performed using electron backscatter diffraction. As a result of the additive friction stir deposition associated thermo-mechanical conditions, the microstructure exhibited fine equiaxed grains in the plane along the build direction along with bands of very fine grains within the interface regions between deposited layers. The observation of fine equiaxed grains and a lower degree of in-grain misorientation in the additively fabricated sample pointed to dynamic recrystallization as the governing restoration mechanism during the deposition process. The grain size refinement during additive friction stir deposition of IN625 resulted in substantial augmentation in the yield strength compared to IN625 feed material and as-cast IN625.

Geochemical Characteristics of the Mallawa Formation, and its Relationship with the History of Source Rock Formation in the South Makassar Basin, South Sulawesi

A hydrocarbon system to determine the hydrocarbon potential in an area can be determined by the presence of three main components that ensure its existence together, one of main components are source rock. The South Makassar Basin has the potential to have a petroleum system that acts as a source rock for the Mallawa Formation. Source rock is a component of the petroleum system that has the ability to produce and store hydrocarbons, where this rock is generally a rock with fine grains such as coal or shale. Oil and gas exploration in Indonesia is a common thing because there are many prospect areas that have the potential to produce hydrocarbons. The South Makassar Basin is a Tertiary sedimentary basin of land type which is geographically located along West Sulawesi to South Sulawesi and this basin occurs due to tectonics or structures with high frequency. The South Makassar Basin was formed as a result of the expansion of the Makassar Strait which occurred at no younger than the Early Paleocene age where the tectonic consequences would influence the maturation process of the source rocks in the South Makassar Basin. Apart from that, in this research a geochemical method was carried out in the form of laboratory analysis to determine the maturity of the source rock using cuttings samples. So this research provides something new in the exploration of the maturity of source rocks, which in the South Sulawesi area has a complex tectonic setting.