Mechanical Microstructure Research Articles

New elucidating into the microstructural evolution mechanisms and micromechanical properties of C4AF and gypsum synergistic hydration

Increasing the C4AF content significantly enhances the sulfate and impact resistance of Portland cement-based materials. However, the research on the microstructural evolution mechanisms and micromechanical properties of the binary synergistic hydration products of C4AF and gypsum is not yet sufficiently deep. This study employed thermodynamic simulations, phase structure characterization, and nanoindentation techniques to investigate the microstructure evolution of gypsum-assisted C4AF hydration. Results indicated that the final hydration product of C4AF, C3(A,F)H6, formed through the stacking of lamellar OH-AFm phases. The addition of gypsum altered the formation pathway of C3(A,F)H6, causing it to precipitate directly from an amorphous iron-aluminum gel, which resulted in smaller particles with higher crystallinity. Gypsum also filled pores in the hydration products, thereby positively influenced their micromechanical properties.

Probing the formation mechanism of hierarchical microstructures in experimental Ni-based superalloys

Hierarchical microstructures, consisting of a γ matrix with γ′ precipitates that incorporate finer-scale embedded γ precipitate, are known to enhance strength and enhanced coarsening resistance of the ordered γ′ precipitates in various nickel-based superalloys. Despite their potential benefits, the underlying origins and design principles of such hierarchical microstructures remain poorly understood due to the complex multicomponent nature of superalloys. In this study, we employ an integrated approach that combines advanced composition and microstructure analysis and computational thermodynamic and kinetic modeling to investigated the formation mechanism of the hierarchical microstructure in two experimental multi-component nickel-base superalloys. Using chemical mapping via atom probe tomograph and nucleation driving force calculations, we find that the enrichment of γ-stabilizing elements, such as Co and Cr, along with the depletion of Al within the γ′ precipitates, promotes the decomposition of the γ′ phase and the precipitation of the finer γ phase. In addition, kinetic modeling predicts the supersaturation of Co and Cr during cooling, elucidating the influence of heat treatment on solute partitioning. Our findings illustrate how alloy composition and tailored heat treatment strategies discussed can guide the design of a hierarchical γ/γ’/γ microstructure, offering a pathway towards optimizing mechanical properties in nickel superalloys through microstructure design.

Morphological evolution mechanism of microstructures involved in shaping micro-pillar arrays into microlens arrays on fused silica surfaces by CO2 laser polishing

The periodic micro-pillars on the hard-brittle fused silica surface can be shaped into the smooth and defect-free microlens arrays (MLA) by CO2 laser polishing, which can be applied in imaging and beam-shaping. However, the morphology evolution mechanism of the micro-pillars is not clear during polishing, which seriously affects the rapid preparation of high-quality MLAs. Herein, a multi-physics coupling model is established to investigate the interaction between CO2 lasers and micro-pillars on the fused silica surface, and is verified from the perspectives of temporal and spatial temperature. The steady surface temperature evolution law with laser power and spot radius is explored, based on which, the parameter ‘Window’ for polishing is determined to make the material melt and flow without ablation removal. The morphology evolution of micro-pillars is investigated as well as laser-material interaction. It is found that under laser irradiation, the micro-pillar height first increases and then decreases, and its top curvature radius increases. The surface tension makes the dominant contributions to the melting and flow of the micro-pillar materials, while the Marangoni effect and the gravity have little effect. Furthermore, to fabricate the target MLAs with the specific dimensions, the influence of micro-pillar aspect ratio (φ) on microlens surface morphology is investigated. It is found that there are two critical φ for the target MLAs. For the required MLA with the target period of 200 μm and the target height of 40 μm, when the φ is larger than 5.1, the micro-pillar array fails to be shaped into the target MLA by CO2 laser polishing. As the φ decreases, the junction of micro-pillar and the substrate sags downwards significantly, and the deviation between the shaped- and the ideal spherical contours increases. To successfully prepared the target MLA and guarantee the geometry accuracy, the minimum φ is selected to be 0.71. This work has important theoretical significance for obtaining the smooth and defect-free target fused silica MLAs with the specific dimensions by CO2 laser non-evaporative polishing.

Scale-span feature of surface analysis, macromolecular and pore structure in coal: Implications for inherent evolutionary mechanism of morphological microstructure

Morphological microstructural evolution of tectonic coal determines CBM storage and transportation mechanism as well as the occurrence of coal and gas outburst. Scale-span morphological feature of original and tectonic coals was characterized by AFM, Raman spectrum and physisorption method. The results demonstrate that metamorphism could remold the surface property of coal from rugged band to flat porous structure with pore form factor from 0.572 to 0.831, promoting the formation of regular and round pores. Tectonism facilitates ability of gas sorption in coal, breaking the basic structural integrity. Metamorphism could facilitate the ordered macromolecular structural evolution on recombination and aromatization as well as condensation; besides, tectonism may promote the evolution and development of microcrystalline structure in advance. The aforementioned results have revealed essential differences in morphological microstructure between original and tectonic coals, which are of great guiding significance to safe mining of CBM and prediction of coal and gas outburst.

Study on the Microscopic Mechanism and Performance of TPU/SBR Composite-Modified Asphalt

To enhance the service life of traditional asphalt pavement and mitigate issues such as high-temperature rutting and low-temperature cracking, this study investigates the composite modification of matrix asphalt using thermoplastic polyurethane (TPU) and styrene-butadiene rubber (SBR). Initially, the study examines the conventional properties of the composite-modified asphalt from a macro perspective, analyzing the performance variations of asphalt before and after TPU and SBR modification. Subsequently, microscopic analysis is conducted to explore the microstructure, phase structure, and modification mechanisms of the composite-modified asphalt, with a focus on understanding the underlying reasons for performance changes. The influence of TPU and SBR on asphalt performance is evaluated comprehensively. It is found that TPU-modified asphalt demonstrates superior high-temperature performance, storage stability, and elastic recovery. Conversely, SBR-modified asphalt excels in ductility at low temperatures, though its storage stability decreases with increasing dosage. Based on a thorough analysis of the conventional properties of the two types of modified asphalt, the optimal dosages of TPU and SBR are determined to be 15% and 3.5%, respectively. In the composite-modified asphalt, TPU facilitates the even distribution of chemical components, creating a more stable cross-linked network structure. The compatibility of TPU, SBR, and asphalt contributes to the good storage stability of the composite-modified asphalt. While SBR effects physical modification, TPU induces chemical modification of asphalt. Consequently, the composite modification system benefits from both physical and chemical enhancements, resulting in excellent overall performance.

Microstructure, crystallographic texture and mechanical properties of the Zn–1%Mg–1%Fe alloy subjected to severe plastic deformation

The paper covers the production, analysis of the microstructure, crystallographic texture and deformation mechanisms of the ultrafine-grained (UFG) Zn–1%Mg–1%Fe zinc alloy demonstrating unique physical and mechanical properties compared to its coarse-crystalline analogs. The zinc alloy with improved mechanical properties was developed in two stages. At the first stage, based on the analysis of literature data, an alloy with the following chemical composition was cast: Zn–1%Mg–1%Fe. Then, the alloy was subjected to high-pressure torsion (HPT) to improve mechanical properties due to grain structure refinement and implementation of dynamic strain aging. The conducted mechanical tensile tests of the samples and assessment of the alloy hardness showed that HPT treatment leads to an increase in its tensile strength to 415MPa, an increase in hardness to 144HV, and an increase in ductility to 82%. The obtained mechanical characteristics demonstrate the suitability of using the developed alloy in medicine as some implants (stents) requiring high applied loads. To explain the reasons for the improvement of the mechanical properties of this alloy, the authors carried out comprehensive tests using microscopy and X-ray diffraction analysis. The microstructure analysis showed that during the formation of the ultrafine-grained structure, a phase transition is implemented according to the following scheme: Zneutectic + Mg2Zn11eutectic + FeZn13 → Znphase + Mg2Zn11phase + MgZn2particles + Znparticles. It was found that as a result of high pressure torsion in the main phases (Zn, Mg2Zn11), the grain structure is refined, the density of introduced defects increases, and a developed crystallographic texture consisting of basic, pyramidal, prismatic, and twin texture components is formed. The study showed that the resistance of pyramidal, prismatic and twin texture components at the initial stages of high-pressure torsion determines the level and anisotropy of the strength properties of this alloy. The relationship between the discovered structural features of the produced alloy and its unique mechanical properties is discussed.

Study on the Performance of Modified Qingchuan Rock/Rubber Asphalt

This paper developed a new environmentally friendly composite modified asphalt material and studied the composite modification of Qingchuan rock asphalt (QRA) and waste tire rubber powder (RP) was studied in this paper. QRA/RP composite modified asphalt was prepared by adding these two materials as modifiers into matrix asphalt and compared with matrix asphalt and QRA modified asphalt. The basic properties of asphalt before and after aging were evaluated by the rotating thin film oven test. The high-temperature performance and permanent deformation resistance at different temperatures and frequencies were analyzed by the dynamic shear rheological test. The bending creep stiffness test was used to evaluate the low-temperature performance. In addition, the microstructure and modification mechanism of composite-modified asphalt were analyzed by scanning electron microscopy and infrared spectroscopy. The results show that QRA-modified asphalt is superior to matrix asphalt in terms of mass loss, viscosity ratio, and residual penetration, while QRA/RP composite-modified asphalt is further improved on this basis, QRA/RP composite modified asphalt can effectively improve the high and low temperature performance of asphalt.. Although the addition of RP is mainly based on physical modification, it also causes weak chemical reactions and enhances the adhesion of asphalt. The interaction between Qingchuan Rock asphalt and rubber powder significantly improves the overall stability of asphalt structure.

Interface microstructure and healing mechanism of Al/Al composites by hot compression bonding

To understand the interfacial evolution of heterogeneous aluminum alloys in detail, this study investigated bilayers and extended to investigate multilayer heterogeneous aluminum (MHA)11multilayer heterogeneous aluminum (MHA) alloys. Hot compression bonding (HCB)22Hot compression bonding (HCB) was used to investigate the interface healing mechanism of 7075Al/Pure Al at 450℃ in different processing conditions. Subsequent post-holding treatment of different durations were carried out to investigate the microstructure, the evolution of intermetallic compounds (IMCs)33intermetallic compounds (IMCs) and interfacial oxides of the bonded interface. The results show that during the bonding of dissimilar aluminum alloys, IMCs and substantial oxides formed at the layer interfaces under high temperatures and strain rates. Post-holding treatment facilitates the decomposition and transformation of these oxides, thereby enhancing interface healing. The optimal interfacial bonding between the two aluminum alloys is attained at a strain rate of 0.001 s−1 followed by a post-holding treatment for 60 min, MHA at various strains is produced using the same procedure. The prepared MHA features a continuous and flat interface, but there are still discontinuous micropores and voids. As deformation increases, the degree of recrystallization on the 7075Al side also increases. Defects progressively vanish as grain boundary migration replaces the original bonding interfaces, thereby enhancing interface bonding quality. These studies may provide guidance for the preparation of heterogeneous layered composites.

Synergistic regulation of microstructure, properties, and abrasive wear mechanism of a medium carbon dual phase steel for plowshares

In this study, a new medium carbon dual phase (DP) steel for plowshares is prepared. The quenching and partitioning process of the medium carbon steel is designed and optimised using the constrained carbon equilibrium model. The optimised process parameters are quenching temperature of 880 °C, quenching bath temperature of 190 °C and partitioning temperature of 350 °C. The microstructure of the acicular martensite matrix with 13% retained austenite was prepared, so that the good mechanical properties of tensile strength of 2007 MPa, yield strength of 1689 MPa, elongation of 11% and impact energy of 12 J are obtained. The multi-scale characterisation and abrasive wear experiments are carried out to investigate its microstructural evolution and wear mechanism under simulated working conditions. The results show that the coordinated deformation of retained austenite and martensite, as well as the trip effect, endows it with ultra-high strength and good plasticity. The recurring process of formation and spalling of the hardened layer is the main wear pattern of this medium carbon DP steel. The synergism of twinning formation and (Ti, Mo)C precipitation enhances wear resistance of this medium carbon DP steel.

Microstructural evolution mechanism and mechanical properties of La and Gd on AZ91 alloy: Experiments and first-principles calculations

The morphology and thermal stability of the Al-RE phase in Mg-Al-RE alloys are critical to their mechanical properties, particularly at elevated temperatures. In this study, AZ91, AZ91–2La, and AZ91–2La-0.6Gd alloys were prepared via gravity casting and characterized using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicate that adding La reduces the amount of the Mg17Al12 phase and introduces a long acicular Al11La3 phase. Further addition of minor amounts of Gd transforms the long acicular Al11La3 phase into a short rod-like Al11RE3 phase. Tensile tests and fracture analyses at both room and elevated temperatures reveal that the AZ91–2La-0.6Gd alloy exhibits exceptional tensile properties. First-principles calculations were used to study the modification mechanism of Gd atoms on the Al11La3 phase. Adsorption calculations show that Gd atoms stably adsorb on the Al11La3 (001) growth surface, altering its growth characteristics. These calculations also investigated the thermal stability and formation enthalpy of intermetallic phases in Mg-Al-La-Gd alloys. Additionally, the complex alloying reactions during the solidification of the Mg-Al-La-Gd multi-element alloy system were simplified. This study provides new insights into the interaction mechanisms of rare earth (RE) elements in Mg-Al series alloys. It also offers a new approach for designing heat-resistant Mg-Al-RE alloys.

High temperature electropalsticity in Aermet100 steel by decoupling electron wind effect

Aermet100 ultra-high strength steel (UHSS) is one of the highest strength-plasticity-matched metallic materials. It is widely used in critical load-bearing components in aerospace and weaponry. Compared to traditional forging processes, electropulsing assisted forming technology significantly enhances manufacturing efficiency and forming limits. Particularly in the forming of hard-to-deform materials into complex structures, it demonstrates significant application potential. However, quantitative studies on the decoupling of electron wind effects during high-temperature deformation and their impact on microstructural evolution, deformation mechanisms, and mechanical properties remain few reported, resulting in limiting the ability to select optimal process parameters in electropulsing assisted forming technology to precisely control material structure and properties. In this paper, the impact of varying degrees of electron wind effects on flow stress through high-temperature compression tests was investigated. The evolution of the microstructure was analyzed in conjunction with the thermodynamic and kinetic mechanisms of recrystallization. Moreover, the hitherto unexplained relationship between the activation of slip systems and texture components in Aermet100 UHSS is examined. Results indicate that with the enhancement of the electron wind effect, the flow stress of Aermet100 UHSS is reduced by 59.4 %. The electron wind effect not only reduces the activation energy for recrystallization but also enhances vacancy concentration, dislocation climb diffusion flux, and driving force, thus promoting continuous dynamic recrystallization. Furthermore, as the intensity of the electron wind effect increases to 0.85 Ew and above, S and Brass textures are observed for the first time. It is notable that the Dillamore texture, Brass texture, and S texture respectively activate specific slip systems (1‾ 10)[11 1‾], (0 1‾1‾)[11 1‾] and (110)[1‾ 11‾] during the hot deformation process of Aermet100 UHSS. This investigation sheds new insight into tailoring high temperature electroplasticity by regulating electron wind effects.

Microstructure Refinement via Nucleation of Intragranular Acicular Ferrite Stimulated by Ti-Containing Core-Shell Structured Particles in Low-Carbon Steel.

This study investigated the microstructure, mechanical properties, and nucleation mechanism of acicular ferrite (AF) present in hot-rolled Ti deoxidized steel. In our experiments, the impact toughness of Ti deoxidized steel is significantly increased to 144 J at -20 °C, while those Mn and Al deoxidized steels are only 9 J and 18 J, respectively. Interlocked AF is the primary microstructure of Ti deoxidized steel. The second-phase particles of the core-shell-type structure, in which Ti2O3 is the nucleus and TiO is the outermost shell, act as effective nucleating agents to stimulate AF nucleation. The low lattice disregistry between TiO and AF is the main factor contributing to the production of AF. It is also revealed that Ti2O3 and MnS fulfill the particular orientation relationship, contributing to the formation of an Mn-depleted zone (MDZ) adjacent to MnS, proposed to be one of the possible mechanisms for promoting AF nucleation.

Microstructure Design and Dimensional Engineering of Nanomaterials for Electromagnetic Wave Absorption and Thermal Insulation.

Multifunctional materials integrated with electromagnetic wave absorption (EWA), thermal insulation, and lightweight properties are urgently indispensable for the flourishing advancement of space technology, which can simultaneously prevent electromagnetic detection and resist aerodynamic heating. To achieve excellent synergistic EWA and thermal insulation performance, the elaborate regulate the microstructure and dimension of nanomaterials has emerged as a captivating research direction. However, comprehending the structure-property relationships between microstructure, electromagnetic response, and thermal insulation mechanisms remains a significant challenge. Herein, a comprehensive perspective focuses on the microstructure design encompassing various dimensions of nanomaterials, providing a comprehensive understanding of correlations among structure, EWA, and thermal insulation. First, the cutting-edge mechanisms of EWA and thermal insulation are elaborated, followed by the relationship between the dimensions of nanomaterials. Moreover, the synergistic design methods of EWA and thermal insulation are explored. Lastly, this review summarizes the corresponding shortcomings and issues of current EWA-integrated thermal insulation materials and proposes breakthrough directions for the creation of materials with superior performance.

Microstructure and mechanical properties of 9 % nickel steel welded joints using a CoCrNi filler wire for cryogenic storage tanks

A medium-entropy alloy of CoCrNi exhibits excellent cryogenic mechanical properties. It is possible to enhance the ductility of weld metal for cryogenic storage tank materials at cryogenic temperatures by employing CoCrNi alloys as filler metal. In this study, a CoCrNi multi-principal filler wire and a 308L stainless steel wire were used for welding 9 % Ni steel. The effects of the CoCrNi filler wire on the microstructure, hardness, mechanical properties, and deformation mechanisms of the weld metals were evaluated and discussed. A remarkable finding was that as the tensile temperature decreased from 298 K to 77 K, the fracture elongation of the CoCrNi joint increased by approximately 34.7 %, rather than decreasing. In contrast, a significant reduction in fracture elongation was observed in the 308L joint. The CoCrNi filler wire could promote the activation of twinning deformation in the weld metal at 77 K, thereby enhancing the ductility of the welded joints at cryogenic temperatures.

Deformation Behavior and Microstructural Evolution of Ti–6.5Al–2Zr–1Mo–1V Alloy during Isothermal Hot Compression

In this investigation, the effects of different deformation passes—namely, single pass and multipass—on the microstructural evolution and deformation mechanisms in the Ti–6.5Al–2Zr–1Mo–1V alloy are analyzed. It is observed that following a single‐pass hot compression, the extent of lamellar α phase spheroidization enhances as the temperature increases. During multipass hot compression, there is a gradual reduction in the size and concentration of equiaxed α phase, alongside an increase in spheroidization. Dislocation density escalates to 15.88%, while the proportion of high‐angle grain boundaries (HAGBs) diminishes to 75.24%. Static recrystallization occurring during the holding process facilitates dislocation annihilation. The dynamic phase transformation mechanism manifests through interfacial permeation at the primary α phase. Strain localization at the boundaries or sub‐boundaries of the primary α phase, which exhibit minimal curvature, induces elevated shear stress, thereby promoting the shearing of the primary α phase and reducing its presence. Texture components predominantly observed are <‐12‐10>//Z0 and <0001>//Z0, transitioning from <‐12‐10> to <0001> with increasing strain.

Mechanical Properties and Microstructure Analysis of Mild Steel Welding Made by GTAW

This work discusses the effect of gas tungsten arc welding (GTAW) variables on the welding transverse tensile strength and hardness of S 235JR at different groove configurations. The welding microstructure and numerical fracture mechanism are also discussed. GTAW is increasingly emerging in the local industry due to its advantages over conventional shielded metal arc welding (SMAW). The properties of steel welding have always concerned manufacturers and researchers. Since steel structures experience forces such as tensile, it’s vital that good welding has increased tensile strength. It was reported that the hardness of welding affects the welding properties and, therefore, the integration of welded structures. The groove shape of the joining ends determines the size of the FZ and affects the dilution; thus, it is important to study the groove shape due to its effect on the final properties of welding. The results showed an increased welding traverse tensile strength (251 MPa) at higher welding speeds (150 mm/min) and V-shaped groove welding. The V-shaped groove welding that obtained higher tensile strength (251 MPa) has shown higher grain boundary ferrite and PF volume friction in the FZ and finer PF in the HAZ due to its higher interpass heat input. Higher traverse tensile strength welding has shown increased bainite and lower bainite volume friction in FZ and a finer grain structure in HAZ. The failure due to tensile force starts at the welding root, according to numerical analysis, and a double V-shaped groove has shown deformation balance at the tensile test.

Microstructure, deformation and fracture mechanism of Mg-Gd-Y-Zn-Zr alloy with different rolling routes during tension

The microstructure, deformation and fracture mechanism of unidirectional rolling (UR) and cross rolling (CR) Mg-4.7Gd-3.4Y-1.2Zn-0.5Zr alloy during tension were studied. Both rolled alloys exhibit typical bimodal microstructures, with the difference being that UR alloy has elongated grains containing rod LPSO phase, while CR alloy has relatively rounded deformed grains containing lamellar LPSO phase. After tension until fracture, the LPSO phase morphology of the two alloys remains unchanged. CR alloy exhibits a higher yield strength and lower elongation than UR alloy. Although the higher average basal <a> slip Schmid factor result in the lower yield strength of UR alloy, the activation of the high proportion of non-basal slip is responsible for its higher elongation. UR alloy and CR alloy exhibit ductile fracture and quasi cleavage fracture characteristics, respectively. For UR alloy, a variety of dislocations accumulated near grain boundary and the weak slip transfer effects between grains both contributes to the propagation of grain boundary cracks. However, the effects of weak interfacial bonding between metastable lamellar LPSO phase and matrix, along with the similar orientation and higher geometric compatibility of CR alloy, lead to the rapid spread of transgranular cracks.

Evolution mechanism of inclusions and microstructure in low-alloy cast steel with cerium addition

Rare earth (RE) elements not only modify inclusions but also refine the steel's microstructure. This study investigates the evolution mechanism of cerium on inclusions and microstructure in low-alloy cast steel through experimental and thermodynamic analyses. After cerium is added to the steel, strip-like inclusions transform into spherical ones, accompanied by a reduction in size. The evolution path of inclusions follows MnS + MnS–Al2O3→Ce2O2S–Ce2S3–MnS + CeAlO3–Ce2S3–MnS with cerium addition. Notably, Ce2S3 and Ce2O2S exhibit an orientation relationship, with [1‾ 22]Ce2S3//[01 1‾ 1]Ce2O2S and (02 2‾)Ce2S3//(1‾ 011)Ce2O2S. Compared to Ce-free steel, the Ce-0.06 steel shows a reduced grain size and the absence of needle-shaped Widmanstätten structures, which may be mainly attributed to rare earth inclusions as heterogeneous nucleation of δ-Fe. This work can provide a theoretical basis for improving the overall mechanical properties of low-alloy cast steel by adding cerium.

Sintering trials and microstructural changes mechanism of analogues of americium oxides for radioisotope power systems

Radioisotope thermoelectric generators (RTGs) are deal energy supply devices for deep space and deep-sea exploration, and it is also the energy core of the operation of the working equipment. Except for 238Pu (Plutonium), 241Am (Americium) was also used as a nuclide in the radioactive energy system for future space exploration missions. In this work, neodymium oxide (Nd2O3) was used as analogues for Am2O3. Cold-press-and-sinter methods was used. Different particle parameters (morphology, size, and crystal structure) and synthesized parameters of Nd2O3 were investigated. The synthesized powders contained lath-shaped particles, and batches with different particle sizes and microscopic topography were made and sintered. The results show that the optimal precipitation temperature of Nd2O3 is 25 °C. The optimal thermal decomposition temperature range is 900 °C to 1100 °C, and the optimal thermal decomposition heating rate is 10 °C min−1. The samples of Nd2O3 pellets without cracking is obtained with relative density of 85%–90 %. The Vickers hardness of Nd2O3 pellets was also studied. This paper provides an important scientific guiding significance for the cold-press-and-sinter of radioisotope 241Am batteries in the future.

Variations in Microstructure and Collapsibility Mechanisms of Malan Loess across the Henan Area of the Middle and Lower Reaches of the Yellow River

Variations in Microstructure and Collapsibility Mechanisms of Malan Loess across the Henan Area of the Middle and Lower Reaches of the Yellow River