Microstructural Evolution Research Articles

Understanding the Microstructure Evolution during Laser Metal Deposition of HSS M4 Obtained from Various Building Strategies, through Thermal Modelling, and Both Microstructural and Mechanical Characterizations

Understanding the Microstructure Evolution during Laser Metal Deposition of HSS M4 Obtained from Various Building Strategies, through Thermal Modelling, and Both Microstructural and Mechanical Characterizations

Microstructure Evolution and Temperature/Stress Field Simulation of Laser Cladded EA4T Axle Steel with Inconel 625 Alloy

Microstructure Evolution and Temperature/Stress Field Simulation of Laser Cladded EA4T Axle Steel with Inconel 625 Alloy

Influence of Nitrogen Content on the Microstructure Evolution and Oxidation Resistance toward Ambient Air of CrAlSiN Coatings Deposited by FCVAD Technique.

In this study, CrAlSiN coatings with nitrogen contents ranging from approximately 42 to 54 at. % were deposited and subsequently exposed to temperatures of 700 or 900 °C for 2 h in ambient air to investigate the impact of nitrogen content on the microstructure evolution and high-temperature oxidation resistance. It was found that the CrAlSiN coating with nitrogen content of 42-45 at. % exhibited an amorphous/nanocrystalline hybrid structure, comprising pure metallic Cr and (Al,Cr)N phases within the matrix, as determined by the TEM, XRD, and XPS analysis. In contrast, as the nitrogen content exceeded 52 at. %, the coatings transformed to a dominantly columnar structure featuring solely Cr(Al)N phase. The CrAlSiN coating with a nitrogen content of ∼52 at. % retained amorphous fraction of around 20% but demonstrated superior oxidation resistance with the lowest parabolic rate constant of 1.1 × 10-14 cm2/s at 900 °C compared to other coatings. This enhanced performance was primarily attributed to the high stability of Cr(Al)N phase and formation of a fine-columnar/amorphous microstructure devoid of metallic Cr, resulting in a significantly thin (∼60 nm) yet dense Al2O3-rich monolayer atop the coating surface during the oxidation. Conversely, substoichiometric CrAlSiN coatings with N content ≤45 at. % would form a thick Cr2O3 outer layer over an underlying Al2O3 layer. Additionally, elemental segregation of Cr, Si, and Al was observed in all CrAlSiN coatings after exposure to 900 °C for 2 h, which was induced by the spinodal decomposition of the ternary nitride phases.

Microstructural Evolution and Damage Mechanism of Water-Immersed Coal Based on Physicochemical Effects of Inorganic Minerals

Coal seam water injection technology enables seam permeability enhancement and facilitates outburst risk reduction. This study investigated the microscale effects of water infiltration on coal and the evolution mechanisms of its mechanical properties. To this end, we systematically analyzed dynamic changes (such as mineral composition, pore structure, and mechanical performance) in coal soaked for various durations using X-ray diffraction, low-field nuclear magnetic resonance (NMR), and uniaxial compression testing. The results indicate: (1) the coal NMR T2 spectrum displays three characteristic peaks, corresponding to rapid water absorption, uniform transition, and stabilization stages of soaking traditionally divided according to peak area variation trends. (2) The coal strength decreases with progressive soaking, influenced by water content, pore volume, mineral composition, etc. Its compressive strength and elastic modulus drop by 22.4% and 19.5%, respectively, compared to the initial values. (3) The expansion of clay minerals during immersion reduces average pore size. In contrast, quartz particle displacement, pore water movement, and soluble mineral dissolution increase pore volume, reducing the overall structure strength. (4) The dominant factors driving the degradation of mechanical properties vary across immersion stages, including water content and specific mineral concentration. This work offers new insights into how hydraulic technology alters coal seams, providing theoretical support for optimizing water injection strategies in the seam.

Effect of Gd Addition on Hot Deformation Behavior and Microstructure Evolution of 7075 Aluminum Alloy

Effect of Gd Addition on Hot Deformation Behavior and Microstructure Evolution of 7075 Aluminum Alloy

An Analysis of Dynamic Recrystallization During the Reduction Pretreatment Process Using a Multiscale Model

In this study, a multiscale model is developed through secondary development (UMAT and UEXTERNALDB) in Abaqus with the objective of simulating the thermal deformation process with dynamic recrystallization behavior. The model couples the finite element method (FEM) with the multiphase field model (MPFM), thereby establishing bidirectional coupling between macroscopic mechanical behavior and microstructural evolution. A comparison between the single-element hot compression simulation and experimental results demonstrates that the model accurately simulates both the macroscopic mechanical behavior and microstructural evolution during the thermal deformation process, thereby exhibiting high precision. Simulations of the reduction pretreatment (RP) process under different reduction amounts and billet surface temperatures demonstrate that increasing the reduction amount and billet surface temperature significantly enhances both plastic deformation and the volume fraction of dynamic recrystallization in the billet core. This results in the closure of core voids and the refinement of the core microstructure, thereby providing valuable guidance for the development of optimal reduction pretreatment (RP) processes.

Evolution of microstructure, texture, and mechanical performance of Mg-13Gd-2Er-0.3Zr alloy by double extrusion at different temperatures

Evolution of microstructure, texture, and mechanical performance of Mg-13Gd-2Er-0.3Zr alloy by double extrusion at different temperatures

Impact of Partitioning Temperature Parameters during the Quenching and Partitioning Process on Medium Carbon Steels with Two Different Alloying Strategies

Quenching and partitioning (Q&P) heat treatments have recently gained attention as promising methods for the third generation of advanced high‐strength steels, particularly in industrial applications like automotive. This study investigates the microstructural evolution during Q&P in two medium‐carbon high‐silicon and aluminum‐alloyed steels, exploring potential additional phase transformations controlling the final structure. The choice to focus on Si and Al‐ medium‐carbon steel is linked to the lower cost of these elements compared to commonly alloying elements like Ti, Cr, Mo, and V, while still achieving high mechanical properties through Q&P. The Q&P process is analyzed by varying the volume fraction of primary martensite (M1) at 0.25, 0.50, and 0.75, with partitioning temperatures ranging from 350 to 550 °C for 30 min. At 350 °C, a significant volume fraction of stabilized austenite (up to 0.3) is observed. However, concurrent reactions such as nanostructured bainite and martensite formation lead to deviations from the theoretical constrained carbon equilibrium (CCE). At higher temperatures (450–550 °C), tempering reactions, including cementite precipitation and pearlite formation, reduced the austenite final fraction. The study highlights that heat treatment design, particularly partitioning temperature, must be tailored to the specific steel composition due to the varying effects of Si and Al.

Dental evidence for extended growth in early Homo from Dmanisi.

Human life history is characterized by an extended period of immaturity during which there is a disjunction between cerebral and somatic growth rates1. This mode of ontogeny is thought to be essential for the acquisition of advanced cognitive capabilities in a socially complex environment while the brain is still growing2. Key information about when and how this pattern evolved can be gleaned from the teeth of fossil hominins because dental development informs about the pace of life history3-5. Here we show that the first evolutionary steps towards an extended growth phase occurred in the genus Homo at least 1.77 million years ago, before any substantial increase in brain size. We used synchrotron phase-contrast tomography6 to track the microstructural development of the dentition of a subadult early Homo individual from Dmanisi, Georgia. The individual died at the age of 11.4 ± 0.6 years, shortly before reaching dental maturity. Tooth growth rates were high, similar to rates in living great apes. However, the Dmanisi individual showed a human-like delayed formation of the posterior relative to the anterior dentition, and a late growth spurt of the dentition as a whole. The unique combination of great-ape-like and human-like features of dental ontogeny suggests that early Homo had evolved an extended growth phase before a general slow-down in life history, possibly related to biocultural reproduction7 rather than brain growth.

Characterization of microstructural evolution and mechanical properties of Cu-Ni-Cr alloys deformed by ECAP

In recent years, Cu-Ni-Cr alloy materials have been broadly applied in the marine industry. However, owing to its dendritic microstructure, this material is an obstacle to the manufacturing process, particularly in the metal-forming process. In this study, an equal-channel angular pressure (ECAP) process is proposed to improve the material microstructure and mechanical properties. A single pass of the ECAP was performed at room temperature, and the microstructural evolution and mechanical properties of the material were characterized. The ECAP compressed and tensioned the microstructures on the top and bottom surfaces, respectively. The microstructures on the front and back surfaces were similar because they were sheared. This also caused a tear-off of the dendritic microstructure. Based on the changes in the characterization of the microstructural evolution, the ultimate tensile strength increased by 32% to approximately 680 MPa, and the elongation decreased by 200% to approximately 8%. The microhardness distribution was irregular on the front and back surfaces, causing nonuniform deformation. However, the microhardness increased by an average of 35% to approximately 270 HV. Consequently, the nonuniform microstructural evolutions and mechanical properties of each surface must be considered when applying the ECAP process to improve the mechanical properties of Cu-Ni-Cr alloy materials.

Microstructural and phase evolution in Nb–Si intermetallic thin films deposited using the pulsed laser ablation technique

Microstructural and phase evolution in Nb–Si intermetallic thin films deposited using the pulsed laser ablation technique

Microstructure Evolution of Super304H Steel Used in a Service Power Station Boiler

The microstructure and structure of a Super304H superheater steel pipe after 47,000 h were analyzed by metallographic microscope, scanning electron microscope (SEM), and EDS, and its mechanical properties were measured by hardness meter. The results show that the austenitic grains appear on the outer wall of Super304H steel pipe after service, while the SEM and metallographic microscope tests show that the outer wall particles are coarse. There is an obvious corrosion layer on the outer surface, and the thickness of the corrosion layer on the windward surface is significantly higher than that on the leeward surface. The inner surface is refined and the hardness of the material is significantly increased; the outer surface, the inner surface, and the center all grow abnormally. In this case, the room temperature tensile strength and impact performance of the rough crystal area of the outer wall of the Super304H steel pipe are reduced and fracture along the crystal. Supervision should be strengthened to eliminate the safety risks caused by the abnormal growth of the outer wall austenite grain. The results of crystal phase microscopy show that the main structure of the material still maintains the basic structure of austenitic steel, and particle aggregation mainly occurs in the sub-inner layer of the inner and outer surface. Compared with the lee surface, the middle body structure is basically the same, but whether the thickness of the corrosion layer on the inner surface or the outer surface increases, the deformation degree of the deformation layer is greater. The hardness measurement finds that the hardness of the corrosion layer is caused by the increase in Super304H steel surface stress. In case of pipe explosion accident, the highest chance of pipe explosion here should be closely observed.

Effect of aging temperature on the microstructural evolution and mechanical properties of 18Ni (200) maraging steel

Herein, we used transmission electron microscopy (TEM), electron backscattering diffraction (EBSD), and X-ray diffractometry (XRD) to investigate the effects of different aging temperatures on reversed austenite and precipitates in 18Ni (200) maraging steel, as well as their evolving patterns of cryogenic toughness and strength. Aging at 510 °C was found to enhance cryogenic toughness at −196 °C and deliver peak strength, which is attributable to the significant aging-strengthening effect and the reversed austenite. Furthermore, this study investigated the factors that contribute to the formation and high stability of reversed austenite and quantitatively assessed the contributions of aging strengthening, dislocation strengthening, and grain-boundary strengthening to yield strength at various aging temperatures.

Study on Microstructure Evolution Characteristics of Coal in Low Temperature Oxidation Stage in Goaf of Longfeng Coal Mine

ABSTRACT Low temperature oxidation of coal is the nature of oxidation of coal with oxygen molecules at temperatures below its oxidation critical point or ignition point, usually from ambient temperature to about 200°C. Air leakage and uneven oxygen distribution significantly impact coal spontaneous combustion in goaf. Understanding the changes in free radicals and functional groups during low-temperature oxidation of coal under different oxygen concentrations is crucial for preventing and controlling residual coal self-ignition. This study employs Fourier transform infrared spectroscopy to analyze the effects of varying oxygen concentrations (3%, 5%, 9%, 15%, 21%) on functional groups and structural parameters during coal’s low-temperature oxidation. Results indicate that increasing oxygen concentration promotes the consumption of oxygen-containing functional groups, reducing their content from 71.9% to 52%. Concurrently, the activity and content of aromatic hydrocarbon functional groups rise rapidly from 4.8% to 52.6%. The aliphatic hydrocarbon structure shows a downward trend, indicating its minimal presence. Aromatic ring condensation increases coal sample aromaticity, suggesting higher maturity and weaker hydrocarbon generation potential, with minimal effect from oxygen concentration. Early-stage reactions show little change in coal’s basic structure, and coal-oxygen reactions remain low in low oxygen environments. This study provides an important basis for understanding the mechanism of coal spontaneous combustion in goaf and formulating effective prevention measures for coal spontaneous combustion.

Effect of Cerium-based Inoculant Addition on the Development of Microstructure and Mechanical Properties of Centrifugally Cast High-speed Steel

Effect of Cerium-based Inoculant Addition on the Development of Microstructure and Mechanical Properties of Centrifugally Cast High-speed Steel

Investigating the influence of ferric oxide grade alumino‐silicate cenosphere particulates and heat treatment on the microstructural evolution and mechanical properties of Al6061/ferric oxide alumino‐silicate cenosphere (x weight %) composite

AbstractThe main aim of this investigation is to fabricate aluminum 6061 composites with three different weight percentages of ferric oxide grade alumino silicate cenosphere (1 wt.%, 3 wt.%, and wt.%) by the stir‐casting process. The fabricated cast composite and T6 heat‐treated composite is used to obtain a fundamental understanding of various weight percentages of the cenosphere and the influence of heat treatment on the microstructural changes, mechanical characteristics, the mechanism of fracture, and the interface between the aluminum‐matrix and ferric oxide grade alumino‐silicate cenosphere particulates. Tensile and compressive tests with a constant strain rate (0.5 mm ⋅ min−1) were carried out to study the strength and to find a correlation between the various weight fractions of cenosphere and heat treatment. Investigations of the changes in the microstructure of the aluminum ferric oxide grade alumino silicate cenosphere composite and the fractography of the fracture surface are investigated using optical and scanning electron microscope. X‐ray diffraction was utilized to confirm the results obtained from optical and scanning electron microscope analyses for phase characterization validation. A maximum of 30 % increase in hardness value, 20 % increase in tensile strength value, 33 % increase in maximum compressive strength value, and 2 % increase in elongation values are observed in heat‐treated composite when compared to cast composite.

Strength and microstructural development in concrete pavements by blended copper tailings powder and copper tailings sand

This study investigated the effects of replacing cement with copper tailings powder on pavement concrete performance. Concrete pavements were prepared by substituting 5 %, 10 %, and 15 % of the cement with copper tailings powder. Additionally, 70 % of the river sand (0.6–0.15 mm) was replaced with copper tailings sand of a fixed particle size. The study aimed to understand how this combined replacement affected the mechanical and microstructural properties of the concrete. Tests revealed that two hours of mechanical milling was optimal for activating the copper tailings powder, resulting in a Pozzolanic activity index of 82 %. Concrete specimens with 5 % copper tailings powder achieved the highest flexural strength (6.21 MPa) and compressive strength (52.8 MPa). Furthermore, this replacement level resulted in the lowest porosity and highest resistivity. Scanning electron microscope images revealed that increasing the amount of tailing powder reduced the degree of hydration within the microstructures. However, the specimens with both tailings powder and sand exhibited better compactness and homogeneity in their internal pore structures compared to those with only tailings sand. It suggests a beneficial microfilling effect from the tailings powder.

Hot Deformation Behavior and Microstructure Evolution of the Maraging Stainless Steel

Hot deformation behavior of the maraging stainless steel is studied in temperature range from 900 to 1150 °C and strain rate from 0.1 to 10 s−1. When the deformation temperature is 900−950 °C, the abnormal stress increase is observed at the end of the flow curves. Transmission electron micrographs reveal that the Laves phase at the interface between prior austenitic (γ) and high‐temperature ferrite (δ) impedes hot deformation. The microstructure analysis shows that the dynamic recrystallization (DRX) mechanism of γ and δ is discontinuous DRX and continuous DRX, respectively. When the specimens are deformed at 950 °C, the extent of DRX at a strain rate of 5 s−1 is higher than at 0.1 s−1. This anomaly is due to adiabatic heating causing the actual deformation temperature at high strain rate () to be higher than at low , indicating that DRX is more influenced by temperature compared to . The influences of adiabatic heating and friction are corrected. Strain‐dependent constitutive equation is developed based on the revised flow curves, yielding an average absolute relative error of 4.69% and a correlation coefficient of 0.99; the prediction accuracy exceeds 90% when the relative error is within 10%.

Development of significantly hard hypereutectoid plain carbon steel through incomplete austenitization based cyclic quenching treatment

AbstractIn this investigation hot rolled steel bars of 1.24 weight % carbon steel are subjected to incomplete austenitization based cyclic quenching treatment. Each cycle consists of inserting the specimen in an electric resistance furnace at a temperature of 894 °C and holding for a short duration (6 minutes), followed by oil quenching to the room temperature. Such a typical thermal cycling results in the evolution of a novel microstructure that comprises of large clusters and blocks of cementite in a matrix of martensite after 3 and 4 cycles. Accordingly, a significantly high hardness (7.13 GPa) is achieved on execution of 3 cycles which envisages a new pathway of incomplete austenitization based cyclic quenching treatment for development of new‐generation plain carbon hypereutectoid tool steel.

Pore Microstructure and Dynamic Evolution Characteristics of Unfrozen Water during the Freezing Process of Coal with Different Moisture Contents

Pore Microstructure and Dynamic Evolution Characteristics of Unfrozen Water during the Freezing Process of Coal with Different Moisture Contents