Microstructure Formation Process Research Articles

COMPUTER SIMULATION OF THE STRESS-STRAIN STATE OF BAR BLANKS MADE OF ALLOY 7075

The article presents a study of the characteristics and technological parameters of bar blanks made of aluminum alloy 7075, depending on the temperature and the forming process. The main goal is to determine the stress-strain state at various temperatures during the production of blanks, which contributes to understanding the mechanism of formation of the structure and properties of bar blanks. To do this, a computer simulation of the process based on the finite element method is used, using the Forge3D software environment. The results obtained confirm the uneven structure in the volume of workpieces, with a pronounced intensity of deformation in the surface layers. The formation of workpieces at different temperatures (200 and 250 °C) showed differences in stress intensity and strain rate, which is important for understanding the processes of formation of microstructure and material properties. Special attention is paid to the influence of temperature on the formation of stresses in the rods, as well as their distribution in thickness and length. The results obtained can be used to optimize the technological parameters of the aluminum alloy forming process in order to improve the quality of the final product and production efficiency. In general, the scientific conclusions of this study contribute to the further development of aluminum alloy processing technologies and their application in various industries. Keywords: computer modeling, finite element method, numerical model, processing technology, Forge3D, deformation characteristics, microstructure formation process.

Analysis of thin-plate martensite microstructure in steel focusing on incompatibility and its visualization

The thin-plate martensite microstructure in an Fe-29.50Ni-0.34C (wt%) alloy was analyzed to understand the factors that affect the variant pairing tendency. We focused on the rigid body rotation Ql/k at the variant/variant junction planes derived by the rank-1 connection, because the factor Ql/k corresponds to the incompatibility in the junction plane. Theoretical analysis showed that three types of variant pairs (type I: V1/V17, type II: V1/V6, and type III: V1/V16) had a small degree of incompatibility (θ). These pairs accounted for 70% of the total microstructure. The formation frequency followed the order type II > type I > type III in both thin-plate and lenticular martensite microstructures, applying a correction that makes the factors that reduce the correlation between the observed two-dimensional and actual three-dimensional formation frequencies of the variant pairs irrelevant. For the type III variant pairs, the crystal orientation did not strictly follow the orientation relationship that the invariant plane condition specified. We succeeded in mapping this deviation using data obtained by electron backscatter diffraction (EBSD). Both the deviation angle and axis were well explained by Ql/k. The deviation angle was significant in the vicinity of the junction plane and decreased with distance from the junction plane. Although this could only be visualized for the type III pairs, its detection should be possible in other shape memory alloys through the use of a higher angular resolution for the EBSD measurements. Information regarding the spatial distribution of this incompatibility helps us understand the formation process of the martensite microstructure.

Unique microstructure formations during low-temperature partitioning after intercritical annealing in low alloy multi-phase TRIP steel and their mechanical behavior clarified by in-situ synchrotron X-Ray diffraction

Strong attentions have been paid to low-carbon multi-phased steels showing transformation induced plasticity (TRIP) effect as good candidates for automotive applications due to their good mechanical balance between strength and ductility. However, details of complicated microstructural evolutions during thermo-mechanical processing and the roles of constituent phases on mechanical properties have not yet been fully clarified. In the present study, the formation process of multi-phased microstructures in a low alloy steel (Fe-0.2C-1.6Mn-1.4Si-1.0Ni-0.5Al: wt.%) during intercritical annealing in austenite + ferrite temperature (830 °C) and subsequent partitioning heat-treatment at lower temperature (400 °C) were systematically investigated. The phase fraction of ferrite (F), martensite (M), and retained austenite (A) significantly changed with increasing the holding time at 400 °C. It was observed that austenite transformed into ferrite during the heat-treatment at 400 °C to form newly formed ferrite having different characteristics. The ferrite in the final microstructures was categorized into four types (Type I, II, III and IV), based on their morphologies and other features. The ferrite newly formed at 400 °C (Type II, III, IV) were concluded to be formed by massive or bainitic transformation from their characteristics, i.e., morphologies, existence of surface relief, dislocations and misorientations, chemical compositions, and thermodynamic considerations. Long-range diffusion of substitutional elements did not occur in the phase transformation, but interstitial carbon diffused and enriched into austenite, resulting in large fractions of retained austenite at room temperature. Tensile mechanical properties of the obtained multi-phase steel were systematically clarified by in-situ synchrotron X-Ray diffraction. Tensile elongation increases with increasing the holding time at 400 °C, because the amount of retained austenite increased with the partitioning heat-treatment and they showed the TRIP effect through deformation-induced martensitic transformation during tensile deformation. On the other hand, the best strength-ductility balance was obtained in the specimen experienced the shortest heat-treatment at 400 °C.

Tribofilm formation mechanism and friction behavior of polycrystalline diamond compact after cobalt leaching added molybdenum disulfide nanoparticles in different base oils

To investigate the friction and wear properties of polycrystalline diamond compact after cobalt leaching(PDCACL)and the formation mechanism of lubricating oil film under different base oil lubrication conditions, AFM, SEM, EDS and XPS were used to analysis and discuss the friction behavior, microstructure and friction film formation process of PDCACL after adding nano molybdenum disulfide in different base oils. The results showed that there are differences in the speed and thickness of the friction protective film formed by PDCACL under different kinds of base oil lubrication environment. The physical and chemical properties of base oil are the key factors affecting the wear mechanism of PDCACL and the formation of friction film.

Microstructure and properties of WC–Co cemented carbide/40Cr steel joints brazed at low–temperature with Ag–Cu–In–Ti filler alloy

WC–Co cemented carbide/steel brazed at low–temperature is of significant scientific and technical interest. In this study, the interface microstructure between the filler alloy and WC–Co and 40Cr steel, the formation process of the joint microstructure, and the effect of brazing temperature on the microstructure and properties of joints were systematically studied. The filler alloy was bonded by forming a TiC reaction layer with WC–Co and 40Cr steel, which enhanced the retention of the filler layer on the joint. The microstructure of the joint was a WC–Co/TiC reaction layer/TiCo reaction layer/Cu2InTi + eutectic structure (Ag [s, s] + Ag–doped Cu7In3 + Cu4In) + Cu [s, s]/TiC reaction layer/40Cr steel. Moreover, the maximum average shear strength of the joint (brazed at 740 °C) reached 258 MPa, which is approximately 60% higher than those reported in the literature. The fracture behavior of the joint was mainly affected by the distribution of the Cu2InTi intermetallic compounds in the filler layer and the diffusion of Co from the cemented carbide.

Supersolidus Liquid Phase Sintering and Heat Treatment on Atomic Diffusion Additive Manufacturing Produced Ledeburitic Cold Work Tool Steel*

Abstract In this work, the possibility of manufacturing complex-shaped components from a carbon-martensitic hardenable cold-work steel (1.2379; X153CrMoV12; D2) is investigated. For this purpose, cube-shaped samples with an edge length of 10 mm were produced using the fused-filament fabrication process, which were post-compacted after solvent debinding by supersolidus liquid-phase sintering. Using the knowledge of liquid phase volume content as a function of temperature, supersolidus liquid phase sintering experiments were performed. The microstructure formation process was characterized by electron microscopy and X-ray diffraction. The microstructure and hardness of the processed samples were compared in the heat-treated condition with the properties of the same steel 1.2379 (X153CrMoV12; D2) in the as-cast, deformed and heat-treated condition. The results demonstrate effective post-densificationc close to theoretical density of cold-work tool steel samples fabricated by fused-filamet fabrication using supersolidus liquid-phase sintering at 1280 °C. The defect-free microstructure in the heat-treated state is characterized by a martensitic matrix and eutectic Cr-rich M7 C3 and small amounts of V-rich MC carbides. The hardness of the annealed Supersolidus liquid phase sintering samples are 681 ± 5 HV10, which is above the level of the reference material 1.2379 (629 ± 7 HV10) in the as-cast, formed and heat-treated condition.

Simulation of nucleation and growth of austenite in duplex stainless steels – metallurgical study on weld metal of duplex stainless steel SUS329J1

The microstructure of duplex stainless steels is formed by dendrite growth in the primary ferrite-phase and by subsequent solid-state transformation to the secondary austenite-phase. In this study, formation of austenite by solid-state transformation in duplex stainless steels was evaluated. The nucleation and initial growth of austenite was simulated by the software TC-PRISMA. The formation temperatures of austenite in previous works were corresponding to the calculation obtained by adjusting the interfacial energy. Moreover, the microstructure formation process both in grain boundary and intragranular was simulated using a multi-phase field method (MICRESS software). The growth of austenite was assumed to be under paraequilibrium considering the diffusion control of nitrogen and its morphology was assumed to be an acicular growth. The microstructure morphologies were relatively similar to those obtained by the experiments. The simulation method in this study can analyse complex microstructural morphology as well as predict the composition distributions. This method is considered to be highly effective in designing duplex stainless steels and in evaluating the microstructure morphology in welding process.

Phase-field and dislocation-based crystal plasticity analysis on lath martensitic structures formation in polycrystalline metastable austenitic steel

Although strength of TRIP steels can be compatible with ductility owing to deformation-induced martensitic transformation, there is currently no model describing simultaneously the deformation and microstructure formation processes of TRIP steel. In this report, we introduce the basis vectors of martensitic transformation derived in the previous report into the crystal plasticity model and develop a new material model based on a dislocation-based crystal plasticity model coupled with a multi-phase-field one. Also, we consider plastic deformation of austenite phase for more realistic analyze. After that, we use this model to reproduce the formation process of martensitic lath-block structure in a metastable austenitic polycrystal. As a result, it is shown that the microstructure of lath martensite is numerically formed in a polycrystalline micro-specimen using 6 variants in a CP group.

The Study of the Formation Process of Microstructure and Properties during Laser Alloying of the Surface of the Structural Steels

Development and implementation of new methods of high-energy surface treatment of structural steels is one of the priorities of modern materials science One of the urgent problems of power engineering is the development of effective processing technologies that allow parts to provide the required properties of working surfaces. The use of laser technologies helps to increase wear resistance, corrosion resistance, reduce the duration of chemical and thermal treatment time and other technological characteristics that can improve the quality, durability and efficiency of parts, increase economic and environmental effects.

Diamond microfabrication by imprinting with nickel mold under high temperature

Diamond is a key material for quantum devices and sensors, microelectromechanical systems, and the next-generation electronic devices. Microfabrication technology of single-crystal diamond (SCD) for device fabrication and processing is required but hardly established. For example, photolithographic techniques using plasma induced etching for the microfabrication of the diamond devices induce damage to its diamond and deteriorate the device-performances. To overcome this problem, we proposed a plasma-free imprint lithographic technique of SCD using nickel (Ni) mold at high temperatures. Prior to contacting with SCD, the native surface oxide film of the Ni mold was reduced by a hydrogen annealing treatment. Then, the samples were contacted with Ni mold closely, and annealed at various temperatures from 800 to 1200 °C for 30 min, aiming at the formation of the microstructure on the SCD surface by imprinting the structure of Ni mold based on the carbon solid solution reaction into Ni. After removing the Ni and the formed graphite by acid treatment from the SCD surface annealed at 1000 °C, imprints with Ni shape structure are revealed on the SCD surface. This microstructure formation processes requires only short periods of time without any specific equipments. Therefore, this diamond imprint lithography is significant and practical for the development of diamond applications.

Analisis Scanning Electron Microscopy pada Nacre Sinanodonta (Anodonta) woodiana (Lea, 1834)

Chinese pond shell, Sinanodonta (Anodonta) woodiana (Lea, 1834), is a freshwater bivalve that has essential ecological and economic functions. The microstructure of the nacre is of great interest and is the main attraction for the development of pearl farming. This study aims to describe the microstructure and composition of biomineral elements of the nacre at several shell sizes of S. woodiana. The shell is cut with a small forcepon the ventral margin with a size of 3-5 mm for Scanning Electron Microscpy (SEM). SEM images display that a shell layer consists of periostracum, prismatic and nacre layers. The surface of the nacre layer is an irregular or labyrinth patterned. The nacre tablets are hexagonal, glued to each other, so the nacre tablets become polygonal. Moreover, the microstructure of the nacre tablets is like a brick wall, and the thickness of tablets from 0.43 μm to 0.59 μm. The composition of the biomineral elements are C, O, Ca, and the mineralization mechanism is under the control of aquatic environmental factors that help the process of microstructure formation in nacre.

Interfacial microstructure evolution and formation process of the joints prepared by diffusion bonding on DD6 nickel-based single crystal superalloy

Nickel-based single crystal superalloy DD6 was diffusion bonded in vacuum at 1170 °C under 55 MPa for 2–6 h. Two processes, direct bonding and bonding with interlayer, were designed for comparison. A pure 4 μm nickel (Ni) foil was selected for the interlayer. The joint strength was measured via shear test, whereas the joint microstructure and element distribution were analyzed via scanning electron microscope, electron probe analyzer and transmission electron microscope. The results indicated that the joint direct bonded for 6 h achieved the best joint quality at approximately 353 MPa of shear strength. In this case, the joint morphology and microstructure were characterized by microvoids and carbide precipitation. In contrast, in the joints bonded with interlayer, both carbide precipitation and microvoids disappeared. When 4 μm nickel foil was used as an interlayer, the foil/DD6 interface became less distinct as the bonding time prolonged. When the bonding time reached 6 h, the γ′ phase crystals connected each other with the misorientation distribution of the joint less than 5°, and maximum shear strength of 727 MPa was obtained. The fracture morphology has a mixed ductile-brittle feature.

Formation Process of Microstructure in Laser Powder Bed Fusion with WC Cemented Carbide Powder

Formation Process of Microstructure in Laser Powder Bed Fusion with WC Cemented Carbide Powder

Numerical investigation of solidification microstructure formation in sequential YSZ droplet impact under supersonic plasma spraying

A coupled CFD and diffuse interface model was developed to predict the dynamic process of solidification microstructure formation of sequential yttria-stabilized zirconia (YSZ) droplet impact under supersonic plasma spraying. The numerical model relies on the explicit finite difference solution of the Navier-Stokes and energy balance equations, coupled with the Cahn-Hilliard equation, to track liquid-gas interface, and of a phase field model for solidification microstructure formation involving polycrystalline growth to trace solid-liquid interface. Extensive simulations, differing in the status of the first droplet and the impacting parameters of the second one, were carried out. The results reveal that solidification microstructure still follows a columnar pattern if the second droplet lands on the first that is just starting spreading, and that the growth direction around the contact region in the second splat will be obviously skewed by fluid flow if the first has been solidified, owing to earlier and easier nucleation on the top surface of the first splat, thus confirming the epitaxial growth across the splat-splat interface. Computed results are also compared with thermal spray experiments, with gratifying agreement obtained.

Improving the behaviors of foam concrete through the use of composite binder

The most important task in the production of foam concrete is the selection of silica-containing components from both natural and technogenic raw materials, the use of which can not only reduce the consumption of the most energy-intensive and expensive component of foam concrete/Portland cement, but also allows to control the process of structure formation. The novelty of the paper is to identify the scientific patterns of the process control to foam concrete microstructure formation by using the system “Portland cement - opoka marl-fly ash” as a composite binder. The composite binders obtained by mechanochemical activation of Portland cement, opoka marl and fly ash were prepared as the novel compositions, based on which the concretes with improved behaviors are created. The physico mechanical characteristics of the concretes were researched by a series of tests including heat intensity of hydration, shrinkage, average density, and compressive strength, in addition to the durability characteristics (freeze-thaw resistance, vapor permeability) and thermal conductivity. The morphology and microstructure of the obtained cement pastes and concretes was studied by a complex of methods, including SEM images, XRD analysis and DTA analysis. For the first time, the scientific data on the properties of the composite binders and the foam concrete based on it were obtained. The nature of the influence of fly ash on the microstructure formation processes of the foam concrete mix for wall materials is revealed. The composite binders obtained by milling components have a compressive strength of up to 60 MPa with cement savings of up to 40%. Based on the composite binder, the foam concrete with a density of 500–700 kg/m3 with a compressive strength of up to 4.26 MPa were obtained.

Inhomogeneous microstructure and its evolution of laser melting deposited 24CrNiMo steel: From single-track to bulk sample

The microstructure of 24CrNiMo steel samples fabricated via laser melting deposition (LMD) is inhomogeneous, and has not received enough attention. To study the inhomogeneous microstructure and its evolution rule during LMD, single-track, single-layer, and multi-layer samples were fabricated via LMD. The microstructure, grain size, and texture intensity of the samples were analysed by optical microscopy, scanning electron microscopy, and electron backscatter diffraction. In addition, the hardness and strength were measured, and the evolution of the temperature field was simulated using the finite element method. The results indicate that heat accumulation during the LMD process caused the substrate temperature to rise. The higher the substrate temperature, the lower the cooling rate of the molten pool. Thermal accumulation not only altered the rules of microstructure change, but also caused grain refinement and weakened the texture. In addition, the thermal cycle caused phase transformation of the previously formed microstructure, resulting in grain refinement and weakening the texture. Thermal cycle and thermal accumulation caused the microstructure of multi-track samples to become inhomogeneous. The uneven microstructure made the hardness distribution irregular, and caused the macro-mechanical properties of the LMD 24CrNiMo sample to fluctuate in a relatively large range. In this study, the microstructure evolution of the LMD process was comprehensively traced, and the formation process of inhomogeneous microstructure was revealed.

Assessing the freezing process of early age concrete by resistivity method

In order to prevent damage to concrete due to early age freezing, it is very important to monitor the microstructure formation process and strength development of early-age concrete in winter construction. A resistivity method is presented in this study to assess the freezing process of early age concrete at different negative ambient temperatures. The results show that the freezing temperature leads to a sharp rise in resistivity of concrete. The evolution of resistivity can be divided into three stages, which are cooling and nucleuses formation stage, rapid crystallization stage and crystallization finish stage. In addition, some characteristic values, such as blocking time t1, maximum ice content time t2 and freezing rate α, are extracted from the resistivity-time relationship curve and further clarify the freezing process of concrete. There is a good log-linear relationship between resistivity and compressive strength, which can be used to predict the extent of frost damage to concrete. Moreover, the monitoring results of outdoor concrete resistivity confirm that this method is suitable for the evaluation of concrete frost damage on site during winter construction.

Investigation on interlayer phase morphology evolution of “Ex‐Situ” toughened composite laminate

The numerical simulation on the interlayer phase morphology evolution of “Ex‐Situ” toughened laminate was performed in this study. Specifically, the diffusion process of thermoset (TS) resin into thermoplastic (TP) resin was modeled incorporating the negative effect of resin curing reactions. The dynamic process of polymerization‐induced phase separation in TP/TS blends was predicted by the modified Cahn–Hilliard equation, in which the concentration‐dependent mobility was used to describe dynamic asymmetry between TP resin and TS resin, and the mixing free energy of the blends contained the contribution of resin curing reactions. The phase morphology evolution of polysulfone/epoxy blends in the interlaminar region was analyzed numerically, and the results indicated that the diffusion process resulted in the concentration‐gradient distribution of epoxy resin in interlayer, and when the concentration‐gradient decreased, the interlayer phase morphology developed from the coexistence of different microstructures to the presence of a single structural form. The post‐curing temperature played a more important role in the phase separation than that in resin curing reaction, and the separated structures were only observed in the local region of interlayer under low post‐curing temperature, due to small driving force of phase separation. Moreover, the movements of epoxy molecules dominated the microstructure formation process. POLYM. COMPOS., 40:3644–3656, 2019. © 2019 Society of Plastics Engineers

Simulation of Microstructure Formation Process in Fe-23Cr-6Ni-3Mo-0.1N Alloy Using Multiphase Field Method

Simulation of Microstructure Formation Process in Fe-23Cr-6Ni-3Mo-0.1N Alloy Using Multiphase Field Method

Microstructure Characterization of AlSi10Mg Fabricated by Selective Laser Melting Process

Multi-scale microstructure observation and three dimensional finite element thermal analysis of AlSi10Mg alloy fabricated by selective laser melting (SLM) process were demonstrated in order to understand the microstructure formation process during SLM fabrication. The unique hierarchically microstructures were observed: (1) the “fish scale” microstructure corresponding to a part of molten pool consists of columnar and equiaxed grains and (2) these grains contain a substructure of α-Al surrounded by Si particles. It is revealed that a supersaturated Si concentration due to the predicted rapid cooling rate on the order of 106 oC/s. In addition, the base temperature during the fabrication increases gradually with some peak temperature of each laser path as the laser scan has proceeded on a powder layer. Although the thermal changes cause no melting of the AlSi10Mg except directly fused region by selective laser so called molten pool, those are capable of causing precipitation and/or clustering.