Microstructural Modifications Research Articles

SiC nanoparticles additions to squeeze-cast Mg-5.0Al-2.0Ca-0.3Mn alloy: An evaluation of microstructure and mechanical properties

The influences of the SiC nanoparticles (SiCnp) content on the microstructural modification and mechanical properties of the squeeze-cast Mg-5.0Al-2.0Ca-0.3Mn (AXM520) alloy have been investigated. The concentrations of the SiCnp are varied from 0.5 to 3.0 (wt%), and the nanocomposites (NCs) are abbreviated as NC0.5SiC, NC1.0SiC, NC2.0SiC and NC3.0SiC. The as-cast microstructures of the AXM520 alloy and NCs consist of an α-Mg phase, a eutectic of α-Mg and (Mg,Al)2Ca (C36), and an Al8Mn5 phase. Additionally, the SiC phase is also present in the NCs. The continuous network of the C36 phase is fragmented and becomes discontinuous as the content of the SiCnp increases in the NCs. All the NCs exhibit superior tensile and compressive properties than the AXM520 alloy. The NC2.0SiC exhibits the best tensile properties among the NCs employed. The YS of the NCs improves with the increase in the SiCnp content up to 3.0 (wt%). The UTS and %El of the NCs increase up to 2.0SiCnp (wt%), and beyond that, the same declines owing to the agglomeration of the nanoparticles. The discontinuous network of the C36 phase in the NCs inhibits crack propagation, leading to their improved %El. All the NCs exhibit higher strain-hardening exponent (n) and strain-hardening rate (SHR) compared to the AXM520 alloy. The superior ‘n’ and SHR exhibited by the NCs were attributed to the grain refinement and dislocations generation. The strengthening from CTE mismatch contributes the most to the overall strengthening of the NCs. The ‘Zhang and Chen’ model is modified by introducing an agglomeration factor, and the predicted YS of the NCs matches pretty well with the experimentally obtained values.

Comparison of the Erosive Wear Resistance of Ductile Cast Iron Following Laser Surface Melting and Alloying

This article presents research results on the influence of the laser surface melting and alloying processes on the erosive wear resistance of ductile cast iron. For the research, an EN-GJS 350-22 ductile cast iron surface was laser-melted and laser-alloyed with titanium powder in an argon and nitrogen atmosphere. Solid-particle erosion tests were carried out on the laser-melted and -alloyed surface layers and the base material according to the ASTM G76-04 standard with 30° and 90° impingement angles. The erosive wear resistance results were correlated with Vickers hardness and microstructural test results with the use of SEM (scanning electron microscopy), TEM (transmission electron microscopy), EDS (energy dispersive spectroscopy), and XRD (X-ray diffraction). The mechanisms of erosive wear were also analyzed for the laser-treated surface layers and the base material. The research showed that the laser melting and alloying processes with titanium powder had a positive effect on the hardness and erosive wear resistance of the ductile cast iron surface due to microstructure modification. Moreover, despite the lower hardness of the laser-alloyed surface layers, their composite microstructure had a positive impact on the erosive wear resistance in comparison to the laser-melted surface layers.

3D Printed MXene-Based Wire Strain Sensors with Enhanced Sensitivity and Anisotropy.

Stretchable strain sensors play a crucial role in intelligent wearable systems, serving as the interface between humans and environment by translating mechanical strains into electrical signals. Traditional fiber strain sensors with intrinsic uniform axial strain distribution face challenges in achieving high sensitivity and anisotropy. Moreover, existing micro/nano-structure designs often compromise stretchability and durability. To address these challenges, a novel approach of using 3D printing to fabricate MXene-based flexible sensors with tunable micro and macrostructures. Poly(tetrafluoroethylene) (PTFE) as a pore-inducing agent is added into 3D printable inksto achieve controllable microstructural modifications. In addition to microstructure tuning, 3D printing is employedfor macrostructural design modifications, guided by finite element modeling (FEM) simulations. As a result, the 3D printed sensors exhibit heightened sensitivity and anisotropy, making them suitable for tracking static and dynamic displacement changes. The proposed approach presents an efficient and economically viable solution for standardized large-scale production of advanced wire strain sensors.

Investigation of Hydrogen Embrittlement Effect on Microstructure Mechanical Properties and Fracture of Low-Carbon Steels

Steel hydrogen embrittlement (HE), a complex and multifaceted issue, can lead to sudden and catastrophic failure, without significant plastic deformation, making it a critical concern in the industrial sector. The present investigation focuses on the evaluation of HE effects regarding microstructure, mechanical properties degradation and type of fracture of AISI 1010 low-carbon steel, after accelerated hydrogen cathodic charging. Hydrogen was diffused electrolytically in 0.2 Μ H2SO4 solution, containing 3g/L of NH4SCN, using a cathodic current density of 10 and 20 mA/cm2, for 6 and 18 h. Mechanical properties were investigated through slow-rate tensile tests, as well as Charpy V-notch (CVN) impact tests, to determine the value of fracture toughness, both in uncharged and electrochemically pre-charged specimens. Vickers microhardness tests were conducted on the cross-sections of the hydrogen charged samples to evaluate embrittlement susceptibility, due to the presence of dissolved hydrogen. The microstructure modification was carried out through light optical (LOM) and scanning electron microscopy (SEM), in conjunction with an energy-dispersive X-ray detector (EDS). Slow scan X-ray diffraction (SSXRD) was also conducted for crystal structure analysis. The microstructure analysis showed the presence of large amounts of secondary cracks and cavities into the steel matrix, due to hydrogen diffusion and its accumulation at various sites. Hydrogen charging caused a significant gradual elongation decrease of the parent material, from 25% to 6.73%, in case of embrittlement at 20 mA/cm2 for 18h. Accordingly, after 18 h of exposure, the impact energy decrement was determined at 31.5%, at a current density of 10 mA/cm2, whereas the corresponding reduction at 20 mA/cm2 reached 68%.

Microstructure and performance modification of PVDF ultrafiltration membrane via adjusting the composition of coagulation Bath

AbstractIn this paper, the effect of the composition of a nonsolvent bath on the physicochemical properties of the polyvinylidene fluoride (PVDF) ultrafiltration membranes were comprehensively investigated using the nonsolvent‐induced phase separation method. Three additives (ethanol, glycerol, or NaCl) were added to the water coagulation bath respectively to obtain different membranes. It was found that the microstructure of the membranes changed from finger‐like structure to the sponge‐like structure with the increase of additives concentration, which successfully improved the retention and mechanical properties of the membranes. In addition, the membrane surface became smoother and more hydrophilic. The membrane fabricated in 30 wt% glycerol bath exhibited outstanding comprehensive properties of retention and anti‐fouling, with a water flux of 243.5 L/(m2 h), a bovine serum albumin rejection of more than 90%, and a flux recovery rate of 97%. From mechanism analysis, the addition of ethanol, glycerol, or NaCl to the coagulation bath altered the thermodynamic stability of the polymer system, and slowed down the rate of solvent and nonsolvent diffusion from a kinetic perspective. This research provides important clues for optimizing the membrane properties, such as flux, rejection, and strength.

The Scratch Resistance of a Plasma-Assisted DUPLEX-Treated 17-4 Precipitation-Hardened Stainless Steel Additively Manufactured by Laser Powder Bed Fusion

The Scratch Resistance of a Plasma-Assisted DUPLEX-Treated 17-4 Precipitation-Hardened Stainless Steel Additively Manufactured by Laser Powder Bed Fusion

A new laboratory‐based method to experimentally induce diagenetic modifications in human bone tissue using archaeological gravesoils

AbstractThe conditions of the burial environment trigger microstructural modifications and physical‐chemical changes in the bone, such as chemical dissolution, increase of crystallinity, chemical exchanges, collagen degradation and changes in porosity, hence to reproduce these patterns is a challenging task. This work presents a new method to accelerate the diagenetic processes in the laboratory. Artificial aging is obtained by immersion at 80°C in “enriched” solutions derived from the leaching of gravesoils, maintaining the same pH, for 1 month, on modern bones collected from an autopsy. Two distinct solutions from two graves of the necropolis of Travo (IT) (7th–8th century AD) were adopted. The induced damage patterns, on the bone microstructure and the organo‐mineral fraction, have been compared with those observed on buried skeletal elements from the same graves, by providing a multi‐analytical approach (BSE‐SEM, EMPA, FT‐IR, MP‐AES). Bioapatite parameters, such as crystallinity index and Ca/P molar ratio, evolved similarly and, in some cases, reached the same values of buried bones. Conversely, in the absence of microbial activity, the organic fraction better survived the artificial aging. For the same reason, the porosity due to bioerosion was absent in the artificially aged samples, whereas the biological pores and the post‐mortem fractures exhibited the same histomorphology. It is believed that the opportunity of reproducing the diagenetic changes by replicating the chemical environment of the burial site at the laboratory scale is of great interest to forensic science and archaeology (e.g., to reconstruct the burial environment).

Microstructure Modification and Ductility Improvement for TaMoNbZrTiAl Refractory High Entropy Alloys via Increasing Ti Content

Microstructure Modification and Ductility Improvement for TaMoNbZrTiAl Refractory High Entropy Alloys via Increasing Ti Content

A brief review of machine learning-assisted Mg alloy design, processing, and property predictions

Owing to the hexagonal close-packed (HCP) crystal structure inherent in Mg alloys, strong basal texture can readily be induced through the processes of rolling or extrusion. The anisotropy of the texture of Mg alloys impacts their stamping and forming capabilities, limiting their use in certain applications. Microalloying and shear deformation are currently the most common methods of weakening the texture of Mg alloys. Many shearing processes have been extensively studied, and given that they require complex equipment and make it difficult to achieve mass production, major attention has turned to studying the design of microalloys. Traditional trial-and-error approaches for developing micro-alloying confront many challenges, including longer test cycles and increasing expenses. The rapid advancement of big data and artificial intelligence opens up a new channel for the efficient advancement of metallic materials, specifically the application of machine learning to aid in the design of Mg alloys. ML modeling can be used to find correlations between features and attributes in data, allowing for the development and design of high-performance Mg alloys. The article provides an extensive overview of machine learning applications in Mg alloys. These include the discovery of high-performance alloys, the selection of coating designs, the design of Mg matrix composites, the prediction of second phases, the microstructure modification, optimization of rolling or extrusion parameters, and the prediction of mechanical and corrosion properties. In conclusion, challenges and prospects for the rational design of alloys with machine learning support were discussed.

Microstructure modification in Ba-doped SnO2-based ceramics with promising thermal conductivity and electrical properties

In this paper, the thermal conductivity of Ba-doped SnO2 varistors was tested using the heat flow method, and it was found that the thermal conductivity is related to the grain boundary barrier of the samples. Introducing the reduction of impurity phases and point defects is an effective method to enhance the thermal conductivity of SnO2-based varistors. Energy dispersive spectrograms indicate that the content of spinel Co2SnO4 doped with 1mol% Ba is the least when the arrester is operated at 40°C. The positive and negative charge defects are fully compensated, thereby reducing phonon scattering and improving the thermal conductivity of the samples. Spinel Co2SnO4 occupies the position of the effective grain boundary, so the reduction of Co2SnO4 and the compensation of positive and negative defects also effectively increase the grain boundary barrier. When the doping amount of Ba is 1mol%, the optimal potential barrier height is 1.48eV, the nonlinear coefficient is 45, the leakage current is 0.8μA/cm2 and the voltage gradient is 418V/mm.

Fabrication of reinforced Al–Mg composite by TiC particles via FSW: Microstructure and tribology study

In this article, wear and microstructure behaviors of dissimilar Al–Mg joints made by friction stir welding (FSW) with the addition of TiC nanoparticles under different welding parameters were investigated. Optimal joining conditions were achieved by a combination of various rotational and traverse speeds and the best microstructure evolution, mechanical properties, and tribological behaviors were achieved for specimens joined at rotational and traverse speeds of 850 rpm and 50 mm/min, respectively. It was shown that the TiC particles play a prominent role in the microstructure modification and enhanced mechanical properties of weld samples due to the recrystallization process and pinning effect. The maximum hardness and strength values of 241 HV and 168 MPa, respectively were obtained for the weld sample made by optimal condition. The friction coefficient and wear volume loss for weld samples fabricated at 850 rpm and 50 mm/min is comparatively less compared to other conditions due to the highest grain refinement, homogenous distribution of particles, and highest hardness characteristics. The major wear happened because of adhesion, abrasion, plastic deformation, delamination, and oxidation.

Microstructural modifications of lime-based mortars induced by ceramics and nanoparticle additives

Lime-based mortars are one of the principal choices for building and restoration projects, owing to their unique qualities and material compatibility. Admixtures have long been incorporated to enhance the performance and durability of mortars, with ceramics being a traditional choice. More recently, the addition of nanoparticles has been explored as a means to further improve these properties. However, the effective optimization of the complex interplay between additives in lime-based mortars, which is crucial for enhancing their sustainability, remains an ongoing area of research. This study investigated the effects of red-clay ceramic aggregates (RCC) and nanoparticle-based solutions of Ca(OH)2 and SiO2 on the mineralogy, hydraulicity, surface properties, pore structure, and mechanical properties of lime-based mortars. The addition of nanoparticle-based solutions increased the carbonation reactivity, whereas the ceramic aggregates caused a more extensive conversion of portlandite to calcite on the external faces, indicating reduced porosity during the carbonation process. Pozzolanic reactions and the formation of new calcium silicate compounds were observed, along with improved compaction, smoother surfaces, and microcrack formation. The porosity increased with the addition of the ceramic aggregates, whereas the addition of nanoparticles significantly increased the number of pores in the mesoporous range. The specific surface area of the mortars increased with the inclusion of ceramic aggregates and nanoparticles, whereas the open porosity increased and the density and compressive strength decreased with the addition of nanoparticles and associated pozzolanic reactions that occurred with the inclusion of ceramic aggregates. These findings lay the groundwork for future improvements in the formulation of lime-based mortars to balance hydraulicity, surface characteristics, and mechanical performance while preserving porosity.

Modification of electro gas weld metal microstructure reflecting mechanical property specifications in cruise vessel shipbuilding

AbstractTo identify the microstructural factors effecting the electro gas welding (EGW) weld metal properties, this study investigated the influence of different prototype welding consumables and shielding gases on the microstructural composition and mechanical-technological properties. The aim was to adjust the weld metal properties as a trade-off between strength, ductility, and impact toughness to fulfill typical weld metal material specifications in cruise vessel shipbuilding under consideration of the manufacturing conditions at European shipyards. The microstructure is analyzed by quantitative metallography of the ferritic matrix, martensite-retained austenite (M/A) constituents, and non-metallic inclusions (NMI). The influence of the Ni content, the deoxidation concept by variation of Si and Ti contents, and different shielding gas activity by variation of the Ar proportions is discussed. The interaction of ferritic matrix with high acicular ferrite content of about 70 ± 10%, the existence of larger grain boundary ferrite formations, and the M/A morphology plus distribution are considered as the determining factors for the material properties.

Multiscale analysis of traditional and non-traditional additive amended expansive soil-A comparative evaluation

The expansive soils have always been complex and problematic for construction purposes and challenging for the geotechnical fraternity. However, structural alterations and chemical stabilization methods have been practiced successfully in many practical applications. These soils interact with the chemical additives based on the chemical composition, curing period and quantity. The stabilization methods have also focused on non-traditional, eco-friendly additives, which can be a suitable alternative to conventional alkaline additives. However, extensive experimentation is required at various testing levels to understand the stabilization mechanism and the longevity of the additives in the soil medium. The present study uses lime, a conventional additive and a non-traditional additive-lignosulphonate (LS), to stabilize the expansive soil. The interaction mechanism of soil and the additives is investigated at macroscale and microscale levels to understand the modifications rendered to the virgin soil. The effect of the additives in terms of quantity and curing period is studied with respect to plasticity characteristics, strength development and microstructural modifications. The interaction behaviour of soil and the additive is compared at each level, and a probable interaction mechanism is proposed for both additives from this study. The criticality of lime amendment depends on the curing effect and the quantity. A strength improvement factor of 9 and 2 is observed for lime and LS amendment. The compressive/tensile strength ratio is higher for lime amendment, indicating excessive brittleness compared to LS. The conventional additives contribute to higher strength and brittleness, as opposed to lower strength gain and less brittleness of non-conventional additives.

Synergistic enhancement of strength and ductility in novel solid-stir continuous extrusion: Influence of heterogeneous microstructure and alloy chemistry

Friction stir-derived solid-state processes leverage the synergistic effect of frictional heating and intense shear deformation to achieve localized microstructural modification for the improvement of mechanical properties. In the present work, a novel processing route called solid-stir extrusion (SSE) has been explored for continuous, high-rate extrusion of a high strength non-age-hardenable-AlMgSc alloy. In the current study, loss of strength associated with frictional heating during the process is mitigated as elevated strength is observed in as-extruded condition, thereby eliminating the need for post process heat treatment. The effect of process attributes on mechanical property and microstructure evolution was investigated. The SSE process caused extensive grain refinement and fragmentation of thermally stable Al3Sc intermetallic periodically at shear bands, which contributes to the elevated mechanical strength. The spatial variation in mechanical properties and microstructural heterogeneity was characterized using nanoindentation and microstructural correlation. The current findings indicate the significance of the process-specific alloy design approach to increase performance of material in as-processed condition.

Impact of Microstructural and Surface Modifications on the Ti-45Nb Alloy’s Response to Bio-Environment

Impact of Microstructural and Surface Modifications on the Ti-45Nb Alloy’s Response to Bio-Environment

In Situ Microstructure Modification Using a Layerwise Surface-Preheating Laser Scan of Ti-6Al-4V during Laser Powder Bed Fusion.

An innovative in situ thermal approach in the domain of LPBF for Ti-6Al-4V fabrication has been carried out with results directing towards an improved fatigue life without the need for post-processing. The thermal process involves an additional laser scan with different process parameters to preheat the selected regions of each layer of the powder bed prior to their full melting. This preheating step influences the cooling rate, which in turn affects surface characteristics and subsurface microstructure, both of which are directly correlated with fatigue properties. A thorough analysis has been conducted by comparing the preheated samples with reference samples with no preheating. Without any additional thermal processing, the preheated samples showed a significant improvement over their reference counterparts. The optimized preheated sample showed an improved prior β-grain distribution with a circular morphology and thicker α laths within the even finer prior β-grain boundaries. Also, an overall increment of the c/a ratio of the HCP α has been observed, which yielded lattice strain relaxation in the localized grain structure. Furthermore, a less-profound surface roughness was observed in the preheated sample. The obtained microstructure with all these factors delivered a 10% improvement in its fatigue life with better mechanical strength overall.

The effects of submerged laser peening, cavitation peening, and shot peening on the improvement of the torsional fatigue strength of powder bed fused Ti6Al4V produced through laser sintering

This study demonstrates the improvement in the fatigue strength of additive manufacturing (AM) metals such as laser-based powder bed fusion of metals by post-processing. Titanium alloy samples manufactured by powder bed fused (PBF) Ti6Al4V produced through laser sintering (LS), treated by submerged laser peening (SLP), cavitation peening (CP), and shot peening accelerated via a water jet (SPwj), were subjected to torsional fatigue testing and compared with the as-built specimen. At SLP, the samples were treated by laser ablation (LA) and laser cavitation (LC) which was developed following LA. A cavitating jet was used for CP. For comparison, conventional post-processing using SPwj was also performed. To characterize the microstructural modification caused by the three post-processing methods, the cross-section of the treated surface was observed by electron backscatter diffraction. The fatigue strengths at 107 cycles were found to be 217, 361, 313, and 285 MPa for the as-built, SLP, CP, and SPwj specimens, respectively. The primary factors contributing to fatigue strength improvement by post-processing were surface smoothing and the introduction of compressive residual stress. The experimental observations were used to derive correlation formulas to estimate the fatigue life improvement due to post-processing as the function of the surface roughness and surface residual stress.

Smart Textile Flexible MnCo2O4 Electrodes: Urea Surface Modification for Improved Electrochemical Functionality.

Surface microstructure modification of metal oxides also improves the electrochemical performance of metal oxide nanoparticles. The present investigation demonstrates how varying the urea molar content during the hydrothermal process altered the surfaces of MnCo2O4 nanoparticles. Successive increases of 0.1 M in urea concentration transformed the surface shape of MnCo2O4 nanoparticles from flower-like to sheet-like microstructures. Excellent electrochemical performance of MnCo2O4 nanoparticles was demonstrated in an aqueous 1 M KOH electrolyte. The improved MnCo2O4 nanoparticles have been employed to develop an asymmetric supercapacitor (ASC). The ASC device exhibits an energy density of 13 Wh/kg at a power density of 553 W/kg and a specific capacitance of 29 F g-1 at a current density of 4 mA/cm2. The MnCo2O4 nanoparticle electrode demonstrates remarkable electrocatalytic activity in both HER and OER. The MnCo2O4 electrode shows overpotential for HER and OER at 356 mV and 1.46 V, respectively. The Tafel slopes for HER and OER of the MnCo2O4 electrode are 356 mV/dec and 187 mV/dec, respectively.

A microstructural modification strategy to improve thermal conductivity of tool steels produced by laser powder bed fusion

Laser additive manufacturing is a promising technology for producing tools with complex geometry. The tools for hot working applications typically require high thermal conductivity to reduce thermal stresses. However, the relationship between thermal conductivity and the unique microstructure created by Laser Powder Bed Fusion (LPBF) is not yet fully understood.In this study, we investigated the thermal conductivity of AISI M50 in the as-built and different heat-treated conditions. As-built samples exhibited anisotropy and low thermal conductivity. The low thermal conductivity can be improved after heat treatments by modifying the microstructure. Moreover, the influence of each microstructural characteristic was interpreted. Thereby, a correlation between thermal conductivity and microstructure can be addressed. With this knowledge, we proposed a suitable heat treatment concept for improving the thermal conductivity of additively manufactured tool steels.