Desired Microstructure Research Articles

Designing a new ultra-high strength steel with multicomponent precipitates under material genetic design

Ultra-high strength steels with excellent strength, ductility and toughness have become one of indispensable high-performance structural materials. The development of ultra-high strength steels with higher performance has been widely concerned to break the strength-ductility trade-off. This study proposes a material inverse design strategy that combines material genetic design with thermodynamic calculation to search for new alloys with desirable microstructure and optimal strengthening contributions. Based on the advancement of the 'Pareto Front', a new steel with superior properties was successfully screened from 390,625 candidate individuals, which was verified by experiments. The experimental results show that a new steel Fe-0.25C-14.8Ni-17.0Co-2.54Mo-1.56Cr-0.53Al-1.06Cu-0.38V (wt. %) has been successfully developed. After quenching-cryogenic-aging process, the new steel achieved a superior combination of strength, ductility and toughness, with a yield strength of 2.2 GPa, an elongation-to-failure of 10% and a V-notch impact energy of 15 J. Multi-scale microstructure characterization indicates that such superior property synergy arises from the unique microstructure: lath martensite matrix with high-density dislocations and interstitial solid soluble carbon atoms, embedded fine M2C, NiAl and Cu-rich nanoprecipitates. We present an in-depth discussion on the origins of superior strength/ductility/toughness combinations of the new steel to validate the design strategy and provide an accessible pathway exploiting high-performance ultra-high strength steels.

Achieving superior mechanical and corrosion properties in medium-thickness Ti-6Al-4 V alloy joints by back heating assisted friction stir welding below β-phase transformation temperature

The equiaxed microstructure formed below the β-phase transition point of Ti alloys generally exhibits an excellent balance of mechanical properties and corrosion resistance. However, this desirable microstructure is impossible to be obtained in fusion welded joints but is prospective to be achieved by the solid-state friction stir welding (FSW) technique. Unfortunately, it generally generates bottom defects and severe tool wear in medium-thickness Ti alloy joints when conventional FSW was conducted below the β-phase transition point. In this study, 6 mm thick Ti-6Al-4 V plates were joined by both the conventional FSW and back heating assisted FSW (BHAFSW). Defects caused by significant tool wear and bottom phase transition differences occurred in the conventional FSW. It was found that the hardness difference between the base material (BM) and the tool increased to 35.6 % from 500 °C to 900 °C. The back heating (150 °C) was used to control welding temperatures remaining the 900 °C, thus largely reducing the tool wear by increasing the hardness difference. In addition, the back temperature compensation increased the bottom temperature and controlled the phase transition position from the bottom to the middle of the joint. The shoulder pressure contributed to the compression of the defects, and the defects were eliminated by increasing the pressure at the phase transition position. A significantly refined equiaxed microstructure with an average grain size of ∼0.9 μm was achieved below the β-phase transition temperature in the stir zone via back heating assisted FSW, while a bimodal structure with an average grain size of 3.5 μm was formed near the β-phase transition temperature. Inconspicuous reduction of the strength was detected for the joints (98 % of the BM) which possess equiaxed microstructures, and the corrosion resistance of the joints was enhanced compared to the BM. This superior synergy of mechanical and corrosion properties exceeded the majority of Ti alloy joints previously reported. This study provided an effective method for obtaining medium-thickness Ti alloy joints with ultrafine equiaxial structures with superior mechanical properties and corrosion resistance.

Transformations in laser track microstructures for a quasicrystal-reinforced Al-Cu-Fe-Cr alloy

Aluminum-quasicrystal composites are attractive candidate alloys for additive manufacturing, but the cost of evaluating such systems can be prohibitive. Recently, surface laser glazing studies have been used to show that desirable composite microstructures can be formed in an Al85Cu6Fe3Cr6 alloy under a wide range of laser processing parameters. Here the thermal stability of these laser track microstructures has been evaluated by performing in situ scanning transmission electron microscopy heating experiments on specimens produced by focused ion beam milling from the center of the tracks. The initial track microstructures exhibited a uniform phase mixture with 70 % by volume of I-phase quasicrystalline dispersoids in a FCC Al matrix with a film of Al2Cu at the interface. Preliminary ramped heating experiments were used to identify the temperatures at which transformations occurred and then isothermal experiments on fresh samples were used to monitor the progress of these processes. For temperatures of up to 450 °C the only significant changes were a redistribution and coarsening of the Al2Cu phase with a gradual increase in the Fe content of the phase. At higher temperatures, the I-phase decomposed to form a mixture of crystalline ω-Al7Cu2Fe and μ-Al4Cr phases. The I-phase decomposition proceeded by ejection of Cu and Fe with the remaining Cr-rich regions transforming to the Al4Cr approximant phase. The implications of these phenomena for use of the alloy in additive manufacturing are discussed.

Bi2O2CO3/g‐C3N4 Catalyst for Photocatalytic Coupling of Benzylamine under Mild Conditions

AbstractThe photocatalytic conversion of benzylamine into imine is promising for industrial production and environmental protection. To develop photocatalysts with desirable compositions and microstructures is key to achieve high activity and selectivity. Here we propose the immobilization of Bi2O2CO3 on g‐C3N4 for the photocatalytic conversion of benzylamine. The Bi2O2CO3/g‐C3N4 catalyst possesses improved light absorption capacity, electron transmission rate and reduced electron‐hole recombination than pure Bi2O2CO3. It can efficiently catalyze benzylamine coupling reaction under mild conditions, i. e., at room temperature, with air as oxidant and no additional oxidant involved. The maximum turnover frequency value of N‐benzylbenzaldimine reaches 1555.3 μmol g−1 h−1 under this condition. The Bi2O2CO3/g‐C3N4 catalyst has potential in other photocatalytic reactions.

Diffusion bonding of dissimilar materials for space applications via hot isostatic pressing

In this work, hot isostatic pressing diffusion bonding (HIP DB) behaviour of dissimilar materials such as niobium (Nb), platinum (Pt) and titanium alloy (Ti6Al4V) were assessed, especially for thrust combustion chamber used in rocket engines. In particular, the development of an oxidation-resistant layer for pure Nb using Pt was addressed. The diffusion layer analysed by scanning electron microscopy (SEM) shows a successful reaction between pure Nb and Pt with the generation of a 20 µm thick, fully dense reaction layer. Furthermore, the DB of pure Nb with Ti6Al4V was also investigated to evaluate the possibility of joining Nb and Ti6Al4V dissimilar materials for space applications. HIP-DBtrials presented in this work demonstrate the possibility of replacing the conventional R-512 E di-silicide coating with a Pt layer and the fusion welding of Nb and Ti6Al4V with solid state HIP-DBjoining to obtain a defect-free joint with a desirable microstructure at or near the interface.

Reinforcement learning for cooling rate control during quenching

PurposeThe premise of this research is that the coupling of reinforcement learning algorithms and computational dynamics can be used to design efficient control strategies and to improve the cooling of hot components by quenching, a process that is classically carried out based on professional experience and trial-error methods. Feasibility and relevance are assessed on various 2-D numerical experiments involving boiling problems simulated by a phase change model. The purpose of this study is then to integrate reinforcement learning with boiling modeling involving phase change to optimize the cooling process during quenching.Design/methodology/approachThe proposed approach couples two state-of-the-art in-house models: a single-step proximal policy optimization (PPO) deep reinforcement learning (DRL) algorithm (for data-driven selection of control parameters) and an in-house stabilized finite elements environment combining variational multi-scale (VMS) modeling of the governing equations, immerse volume method and multi-component anisotropic mesh adaptation (to compute the numerical reward used by the DRL agent to learn), that simulates boiling after a phase change model formulated after pseudo-compressible Navier–Stokes and heat equations.FindingsRelevance of the proposed methodology is illustrated by controlling natural convection in a closed cavity with aspect ratio 4:1, for which DRL alleviates the flow-induced enhancement of heat transfer by approximately 20%. Regarding quenching applications, the DRL algorithm finds optimal insertion angles that adequately homogenize the temperature distribution in both simple and complex 2-D workpiece geometries, and improve over simpler trial-and-error strategies classically used in the quenching industry.Originality/valueTo the best of the authors’ knowledge, this constitutes the first attempt to achieve DRL-based control of complex heat and mass transfer processes involving boiling. The obtained results have important implications for the quenching cooling flows widely used to achieve the desired microstructure and material properties of steel, and for which differential cooling in various zones of the quenched component will yield irregular residual stresses that can affect the serviceability of critical machinery in sensitive industries.

Investigation structural heterogeneities in hydrogenated nanocrystalline silicon thin films from argon-diluted silane dusty plasma PECVD

This study presents a novel approach for achieving a high deposition rate of nanocrystalline hydrogenated silicon (nc-Si:H) thin films using dusty plasma, eliminating the need for hydrogen dilution. Contrary to conventional beliefs, the research demonstrates that crystalline seeds can nucleate directly from the plasma environment itself. The investigation explores the relationship between plasma parameters and the degree of crystallinity in the deposited films, along with the characterization of structural inhomogeneities throughout the film's thickness. Raman spectroscopy, X-ray diffraction, and Transmission Electron Microscopy (TEM) are utilized for detailed analysis. The results reveal intriguing variations in crystallinity along the film's thickness, with higher crystallinity observed near the surface compared to regions closer to the substrate interface. In-depth analysis of grain size variation reveals that the average crystallite size decreases near the surface and increases in the bulk volume of the material. Additionally, deposition parameters, specifically power and pressure, are found to influence grain sizes, with higher values promoting larger grain growth. Notably, the observation of conical growth in layers deposited from dusty plasma presents a promising avenue for achieving controlled and desirable microstructures. This study sheds light on the critical influence of deposition parameters on film properties and the potential of dusty plasma for achieving desirable microstructures in nc-Si:H thin films. The findings offer valuable insights for tailoring thin film properties in diverse technological applications.

Optimal Control of Material Microstructures

Abstract In this paper, we consider the optimal control of material microstructures. Such material microstructures are modeled by the so-called phase-field model. We study the underlying physical structure of the model and propose a data-based approach for its optimal control, along with a comparison to the control using a state-of-the-art reinforcement learning (RL) algorithm. Simulation results show the feasibility of optimally controlling such microstructures to attain desired material properties and complex target microstructures.

Advances in Nickel-Containing High-Entropy Alloys: From Fundamentals to Additive Manufacturing.

High-entropy alloys (HEAs) are recognized as a class of advanced materials with outstanding mechanical properties and corrosion resistance. Among these, nickel-based HEAs stand out for their impressive strength, ductility, and oxidation resistance. This review delves into the latest advancements in nickel-containing HEAs, covering their fundamental principles, alloy design strategies, and additive manufacturing techniques. We start by introducing HEAs and their unique properties, emphasizing the crucial role of nickel. This review examines the complex relationships between alloy composition, valence electron concentration (VEC), and the resulting crystal structures. This provides insights into design principles for achieving desired microstructures and mechanical properties. Additive manufacturing (AM) techniques like selective laser melting (SLM), electron beam melting (EBM), and laser metal deposition (LMD) are highlighted as powerful methods for fabricating intricate HEA components. The review addresses the challenges of AM processes, such as porosity, fusion defects, and anisotropic mechanical properties, and discusses strategies to mitigate these issues through process optimization and improved powder quality. The mechanical behavior of AM-processed nickel-based HEAs is thoroughly analyzed, focusing on compressive strength, hardness, and ductility. This review underscores the importance of microstructural features, including grain size, phase composition, and deformation mechanisms, in determining the mechanical performance of these alloys. Additionally, the influence of post-processing techniques, such as heat treatment and hot isostatic pressing (HIP) on enhancing mechanical properties is explored. This review also examines the oxidation behavior of nickel-containing HEAs, particularly the formation of protective oxide scales and their dependence on aluminum content. The interplay between composition, VEC, and oxidation resistance is discussed, offering valuable insights for designing corrosion resistant HEAs. Finally, this review outlines the potential applications of nickel-based HEAs in industries such as aerospace, automotive, and energy, and identifies future research directions to address challenges and fully realize the potential of these advanced materials.

Tensile Properties and Fracture Analysis of Duplex (2205) and Super Duplex (2507) Stainless Steels, Produced via Laser Powder Bed Fusion Additive Manufacturing

Additive manufacturing of duplex (DSS) and super duplex stainless steel (SDSS) has been successfully demonstrated using laser powder bed fusion (LPBF) in recent years. Owing to the high cooling rates, as-built LPBF-processed DSS and SDSS exhibit close to 100% ferritic microstructures and require heat treatment at 1000–1300 °C to obtain the desired duplex microstructure. In this work, the mechanical properties of DSS and SDSS processed via LPBF were investigated in three building directions (vertical, horizontal, diagonal) and three processing conditions (as-built, stress-relieved, annealed, and quenched) using uniaxial tensile testing. As-built samples exhibited tensile and yield strength greater than 1000 MPa accompanied by less than 20% elongation at break. In comparison, the water-quenched samples and samples annealed at 1100 °C exhibited elongation at break greater than 34% with yield and tensile strength values less than 950 MPa. Stress relief annealing at 300 °C had a negligible impact on the mechanical properties. Austenite formation upon high-temperature annealing restored the reduced ductility of the as-built samples. The as-built and stress-relieved SDSS showed the highest yield and tensile strength values in the horizontal build direction, reaching up to ≈1400 and ≈1500 MPa (for SDSS), respectively, as compared to the vertical and diagonal directions. Fractographic investigation after tensile testing revealed predominantly a quasi-ductile failure mechanism, showing fine size dimple formation and cleavage facets in the as-built state and a fully ductile fracture in the annealed and quenched conditions. The findings in this study demonstrate the mechanical anisotropy of DSS and SDSS along three different build orientations, 0°, 45°, 90°, and three post-processing conditions.

Effect of Interlayer on Flatness and Adhesion of Aerosol-Deposited Yttrium Oxide Coating.

In this study, Y2O3 coating is used as an interlayer between Al2O3 substrate and a ceramic coating; this is in order to minimize the morphological distortion produced by a single deposition of the ceramic coating on the Al2O3 substrate, which is performed using the aerosol method. The interlayer coating, which comprises the Y2O3 phase, is deposited on the Al2O3 substrate using an e-beam evaporator. The crystal structure of the powder that was used to process the coating is identified as cubic Y2O3. In contrast, the crystal structure of the top-coating layer and interlayer indicates the presence of two kinds of Y2O3 phases, which possess cubic and monoclinic structures. The single Y2O3 coating without an interlayer exhibits microcracks around the interface between the coating and the substrate, which can be attributed to the stress that occurs during aerosol deposition. In contrast, no cracks are found in the aerosol-deposited Y2O3 coating and interlayer, which show a desirable microstructure. The single Y2O3 coating and the Y2O3 coating with an interlayer exhibit similar hardness and elastic modulus values. Nevertheless, the Y2O3 coating with an interlayer exhibits a higher level of adhesion than the single Y2O3 coating, with a value of 14.8 N compared to 10.2 N.

Influence of Solution Treatment Process on the Properties of Duplex Stainless Steels: A Comparative Study on Microstructure and Corrosion Properties of UNS S32205 and UNS S32760

The study investigated the effect of the solution treatment process on the corrosion behavior and microstructure of the duplex stainless steel. It was also aimed to reveal this effect comparatively depending on the chemical composition and alloying element content. For this purpose, UNS S32205 and UNS S32760 alloys were treated at 1000 °C, 1020 °C and 1040 °C for an hour. A solution treatment temperature was determined according to Thermo-Calc analysis. The examined samples were characterized by an optical microscope, scanning electron microscope, and XRD analysis. Also, electrochemical impedance spectroscopy and potentiodynamic polarization analyses revealed the corrosion properties of solution-treated samples. Microstructural studies showed that enhanced solution treatment temperature increased ferrite content for both alloys. A lower solution treatment temperature caused the formation of sigma in the microstructure of S32760 alloy. On the other hand, the charge transfer resistance of the passive layer was reduced after solution treatment at 1000 °C and 1020 °C, indicating decreasing corrosion resistance. A higher austenite ratio in S32205 led to pitting, while corrosion resistance improved with higher treatment temperatures. The presence of the sigma phase in S32760 significantly impacted corrosion properties by increasing ion transfer on the surface, leading to reduced corrosion resistance. It was determined that solution treatment at 1040 °C was appropriate for both alloys to achieve the desired microstructure and corrosion properties.

An Investigation into the Microstructures and Mechanical Properties of a TIG Welding Joint in Ti-4Al-2V Titanium Alloy

The Ti-4Al-2V (wt. %) titanium alloy has garnered widespread applications across diverse fields due to its exceptional strength-to-weight ratio, high toughness, specific strength, and corrosion resistance. The welding of Ti-4Al-2V titanium alloy components is often necessary in manufacturing processes, where the reliability of a welded joint critically influences the overall service life of these components. Consequently, a comprehensive understanding of the welded joint’s microstructure and mechanical properties is imperative. In this study, Ti-4Al-2V titanium alloy was welded using multi-layer and multi-pass TIG welding techniques, and a detailed examination was conducted to analyze the microstructure and grain morphology of each microzone of the welded joint. The results revealed the presence of an initial α phase and a secondary lamellar α phase in the heat affected zone (HAZ). Meanwhile, the fusion zone (FZ) primarily comprised a coarse secondary α phase and a small amount of an acicular martensitic α’ phase. Both the recrystallization zone and the superheated zone exhibited a distinct preferred orientation, with grains smaller than 10 μm accounting for 65.9% and 55.1%, respectively. To assess the mechanical properties of the various microzones and the typical microstructure within the welded joint, nanoindentation tests were performed. The results indicated that the recrystallization zone possessed a higher nanohardness (3.753 GPa) than the incomplete recrystallization zone (3.563 GPa) and the superheated zone (3.48 GPa). Among all the microzones, the FZ exhibited the lowest average nanohardness (3.058 GPa). Notably, the basket-weave microstructure demonstrated the highest average nanohardness, reaching 3.93 GPa. This was followed by the fine-grain microstructure, which possessed a slightly lower nanohardness. The Widmanstätten microstructure, on the other hand, exhibited the lowest nanohardness among the three microstructures within the HAZ. Therefore, the basket-weave microstructure stands out as the most desirable microstructure to achieve in the welded joint. In summary, this study provides a comprehensive characterization and analysis of the microstructure and properties of Ti-4Al-2V titanium alloy TIG welds, aiming to contribute to the optimization of the TIG welding process for Ti-4Al-2V titanium alloy.

Topical drug delivery by Sepineo P600 emulgel: Relationship between rheology, physical stability, and formulation performance

The objective of this present work was to develop and optimize oil-in-water (O/W) emulsion-based gels, namely emulgels that allow maximum topical drug delivery while having desired microstructure and acceptable physical stability. Emulgels containing 2.0 wt% lidocaine were prepared using various concentrations (0.75–5.0 wt%) of Sepineo P600. Their droplet size distribution, physical stability, rheological behaviors, in vitro drug release, and skin permeation profiles were evaluated. Results show that the concentration of Sepineo P600 significantly influenced the microstructure, rheology, and physical stability of the emulgel formulations. The physico-chemical properties also reveals that at least 1.0 wt% Sepineo P600 was needed to produce stable emulgel formulations. All formulations exhibited non-Newtonian shear-thinning properties which are desirable for topical applications. Both the release and permeation rates decreased with increasing viscosity and rigidity of the formulation. The lower the complex modulus of the emulgels, the higher the steady-state flux of the drug through the skin. Adding Sepineo P600 to emulgel systems resulted in increased rheological properties, which in turn slowed the diffusion of the drug for in vitro release. Although as expected skin permeation was rate limiting since in vitro release was 3 to 4 log-fold faster than skin flux. However, an interesting finding was that the derived skin/vehicle partition coefficient suggested the ionic interaction between lidocaine and Sepineo polymer reducing the free drug, i.e., thermodynamic activity and hence the flux with increasing Sepineo P600 concentration. Overall, this study has provided us with valuable insights into understanding the relationship between the microstructure (rheology), physical stability and skin drug delivery properties which will help to design and optimize topical emulgel formulations.

Hot deformation behaviors and microstructure evolution of a supersaturated nickel-based superalloy

The hot deformation behaviors and microstructure evolution of a supersaturated Ni-based superalloy GH4742 were investigated by isothermal compression tests. The deformation temperature range encompassed γ' sub-solvus (1000–1075 °C) and super-solvus (1100–1150 °C), with strain rates ranging from 0.001 s−1 to 1 s−1. Separate Arrhenius-type constitutive equations were established considering the re-precipitation of the γ' phase. The correlation coefficient between the calculated stresses and the experimental data was as high as 0.997, which indicated that the rheological behaviors of the material during hot deformation processes could be accurately analyzed by the constitutive relationship. Additionally, the activation energies for the γ + γ' two-phase region and the γ single region were calculated to be 949.08 kJ.mol−1 and 437.66 kJ.mol−1, respectively. Microstructural analysis revealed that the partial dynamic recrystallisation (DRX) occurred in the γ' sub-solvus regime whereas the full DRX occurred in the γ' super-solvus regime. The low DRX fractions in the γ' sub-solvus regime were attributed to the presence of near-spherical re-precipitated γ' phase, which effectively suppresses the nucleation and growth of new grains. The deformed grains were oriented in the <101> direction parallel to the compression direction. Meanwhile, the non-monotonic relationship between the degrees of DRX and strain rate was observed due to the adiabatic temperature rise. The retarding effects of solute elements on the grain growth in the γ' super-solvus regime were determined by comparing the recrystallized grain sizes from theoretical analysis and experiment values. This work can provide guidance for understanding the deformation behaviors of the alloy and achieving desired microstructures.

Evaluating consumer 3D printing nozzles as a low cost alternative for mesophase pitch-derived carbon fiber production

Synthetic fibers, such as Kevlar fibers, SiC fibers, and carbon fibers, are essential components for constructing high performance structures. Whether for engineering, sports, energy storage (batteries and supercapacitors), or aerospace applications, fiber microstructure plays a critical role in fiber properties and functionalities. However, studying fiber nozzle configurations and spinning parameters to achieve the desired microstructure remains challenging, costly, and time consuming. Here, mesophase pitch-derived fibers were used as an example to demonstrate that low cost, commercially available 3D printer nozzles can “print” fibers. Four different nozzles were used to “print” fibers and the effects of their features on fiber properties were observed and compared to other lab spun and commercial pitch-derived CF. A longer orifice length resulted in higher modulus fiber whereas a larger draw-down ratio yielded a stronger fiber. The findings provide a new opportunity for 3D printer hardware application and open opportunities for developing low-cost fibers.

Effects of Induction Plasma Spheroidization on Properties of Yttria-Stabilized Zirconia Powders for Thermal Barrier Coating Applications.

In this study, the induction plasma spheroidization (IPS) technique was adopted to improve the microstructure and properties of the traditional agglomerated ZrO2-7wt%Y2O3 (YSZ) powders used in thermal barrier coating (TBC) applications. Compared with agglomerated YSZ powders, IPS-treated powder has a more desirable microstructure, and the overall performance of the spray powders for TBC preparation is significantly improved. Specifically, IPS-treated powder has a dense, solid, defect-free, and chemically uniform microstructure, and its apparent density, flowability, and powder strength are significantly improved, which is believed to substantially enhance the coating performance when prepared with this IPS-treated powder.

Additive Manufacturing of Nanocellulose Aerogels with Structure-Oriented Thermal, Mechanical, and Biological Properties.

Additive manufacturing (AM) is widely recognized as a versatile tool for achieving complex geometries and customized functionalities in designed materials. However, the challenge lies in selecting an appropriate AM method that simultaneously realizes desired microstructures and macroscopic geometrical designs in a single sample. This study presents a direct ink writing method for 3D printing intricate, high-fidelity macroscopic cellulose aerogel forms. The resulting aerogels exhibit tunable anisotropic mechanical and thermal characteristics by incorporating fibers of different length scales into the hydrogel inks. The alignment of nanofibers significantly enhances mechanical strength and thermal resistance, leading to higher thermal conductivities in the longitudinal direction (65mWm-1K-1) compared to the transverse direction (24mWm-1K-1). Moreover, the rehydration of printed cellulose aerogels for biomedical applications preserves their high surface area (≈300m2g-1) while significantly improving mechanical properties in the transverse direction. These printed cellulose aerogels demonstrate excellent cellular viability (>90% for NIH/3T3 fibroblasts) and exhibit robust antibacterial activity through in situ-grown silver nanoparticles.

Evaluation of the Thermal Stability and Micro-Modification Mechanism of SBR/PP-Modified Asphalt.

To evaluate the thermal stability of composite polymer-modified asphalt, thermoplastic elastomer styrene-butadiene rubber (SBR)/polypropylene (PP) pellets were prepared using a hot-melt blending technique, with butyl rubber powder and waste polypropylene pellets as raw materials. The effects of different evaluation indexes on the thermal stability of SBR/PP-modified asphalt were investigated using a frequency scan test and a multi-stress creep recovery (MSCR) test, and the compatibility of SBR/PP particles with asphalt was studied using the Cole-Cole diagram and microstructure images. The tests show that, firstly, the performance grade (PG) classification of asphalt can be improved by adding an SBR/PP thermoplastic elastomer to enhance the adaptability of asphalt in high- and low-temperature environments, and the evaluation separation index can reflect the high-temperature storage stability of composite-modified asphalt more reasonably. Additionally, the larger the rubber-to-plastic ratio the worse the high-temperature thermal stability of composite-modified asphalt. Moreover, the addition of additives to the composite particles can promote the SBR/PP particles in the asphalt to be more uniformly dispersed, forming a more desirable microstructure and improving the thermal stability of composite-modified asphalt. Ultimately, the semicircular curve of the Cole-Cole diagram can reflect the compatibility characteristics of the two-phase structure of SBR/PP-modified asphalt, which can be used as an auxiliary index to evaluate the compatibility of polymer-modified asphalt.

Enhancing the microstructure and mechanical properties of CrCoFeNiAl high-entropy alloy produced by hot press sintering through laser remelting

Herein, laser remelting (LR) and hot press sintering (HPS) were combined to process high-entropy alloy (HEA) and strengthen desirable microstructure. The microstructural changes of HEA before and after LR processing were experimentally investigated. In Scanning Electron Microscope (SEM) and electron backscatter diffraction (EBSD) observations, it was found that the microstructure of the remelting zone was mainly composed of dendritic isometric crystals, and the laser remelting technique can refine the grain structure of HEA. The combined strengthening features of dislocations and twinning were observed by Transmission electron microscopy (TEM), and the phase structure of the grains was analyzed in conjunction with the X-ray diffraction(XRD) analysis, confirming the presence of B2 with BCC solid-solution and FCC phase. Finally, micron-sized scratches, tensile experiments and microhardness experiments were performed, and it was found that the Mechanical properties of the remelting zone were significantly enhanced. It was demonstrated that the strengthening of HEA, sintered by LR and HPS techniques, is due to the synergistic influence of various strengthening mechanisms, such as fine grain strengthening, dislocation strengthening, solid-solution strengthening and twinning strengthening.