Kind Of Microstructure Research Articles

Microstructure, hardness and creep properties for P91 steel after long-term service in a ultra-supercritical power plant

3 P91 pipes enduring 5∼6 × 104 h service had been found in an ultra-supercritical power plant. Hardness tests, microstructure observation(OM, SEM/EBSD, TEM/EDS) and creep rupture tests were performed, and the relationship between hardness, microstructure and creep rupture strength were discussed. Results showed that 1 of the 3 pipes still featured lath martensite, and its mechanical properties complied with relevant criteria. Other 2 pipes were characteristic of a mixture of ferrite and highly recovered martensite. Their hardness and creep rupture strength experienced severe degradation. Laves phase was observed in all 3 pipes. The most distinctive feature of the 2 low hardness pipes was their coarse and intragranularly distributed M23C6. This might be caused by abnormal heat treatments which could lead to the mixed microstructure of martensite and ferrite, and this kind of microstructure would degrade fast during service. Thus the low hardness had nothing to do with the precipitation of Laves phase.

Active steering of omni-droplets on slippery cross-scale arrays by bi-directional vibration

Directed droplet manipulation is paramount in various applications, including chemical micro-reaction and biomedical analysis. The existing strategies include some kinds of gradients (structure, inherent wettability, and charge density), whereas they suffer from several limitations, such as low velocity, limited volume range, poor durability, and inefficient environmental suitability. Moreover, active bi-directional reversal of omni-droplets remains challenging because one kind of microstructure at a single scale cannot acquire two kinds of net results of mechanical interaction. Herein, we report an active and directional steering of omni-droplets utilizing bi-directional (vertical and horizontal) vibration on slippery cross-scale structures consisting of macro millimeter-scale circular arc arrays and micro/nanometer-scale slant ratchet arrays, which are fabricated by femtosecond laser patterned oblique etching and lubricant infusion. The physical mechanism of active droplet steering lies in the relative competition between the forces under vertical and horizontal vibration, which mainly arise from the circular arc arrays and slant ratchet arrays, respectively. Various steering modes, including climbing and programmable manipulation, can be realized. Our work is applicable to a wide range of potential applications, including circuit on/off and droplet-based chemical micro-reaction, particularly in the field of high-throughput omni-droplets operation.

Formation and Evolution of Micro/Nano Periodic Ripples on 2205 Stainless Steel Machined by Femtosecond Laser

The preparation of micro/nano periodic surface structures using femtosecond laser machining technology has been the academic frontier and hotspot in recent years. The formation and evolution of micro/nano periodic ripples were investigated on 2205 stainless steel machined by femtosecond laser. Using single spot irradiation with fixed laser fluences and various pulse numbers, typical ripples, including nano HSFLs (‖), nano LSFLs (⟂), nano HSFLs (⟂) and micro grooves (‖), were generated one after another in one test. The morphologies of the ripples were analyzed, and the underlying mechanisms were discussed. It was found that the nano holes/pits presented at all stages could have played a key role in the formation and evolution of micro/nano periodic ripples. A new kind of microstructure, named the pea pod-like structure here, was discovered, and it was suggested that the formation and evolution of the micro/nano periodic ripples could be well explained by the pea pod-like structure model.

Parametric shell lattice with tailored mechanical properties

Along with the development of additive manufacturing, people can fabricate microstructures with complicated geometry that achieve outstanding mechanical properties beyond traditional materials. Shell lattice is a kind of microstructure that consists of a continuous, smooth shell. It has been fabricated as an ultra-low-density material called Shellular, which provides excellent strength and stiffness and has significant multi-functional applications such as heat radiation, permeability, and diffusivity. Most shell lattices in the literature are based on triply periodic minimal surface (TPMS). However, TPMSs are derived from limited types of implicit functions and thus have limited material space. This work proposes the parametric shell lattice (PSL), a type of shell lattice described by a simple and efficient parametric model. The parametric model consists of a skeleton and a set of generation parameters, from which the shell structure can be derived. Various shell lattices with different topologies can be extracted from the parametric model by controlling the generation parameters. Then, a parametric shape optimization method is used to optimize the generation parameters to obtain the PSL with target mechanical properties. A group of PSLs with tailored mechanical properties, including isotropic elasticity, tailored Young’s modulus, shear modulus, and Poisson’s ratio, are designed. Physical experiments demonstrate that the designed PSLs could realize elastic isotropy and high stiffness compared with TPMS lattices. Thanks to the parametric representation, the geometric characteristics of PSL are preserved during the optimization procedure. In addition, the PSL also possesses high efficiency in storage and slicing for additive manufacturing.

Feasibility analysis of obtaining tri-modal microstructure by multi-pass conventional forging combined with dual heat treatment for near-α titanium alloy with different initial microstructures

Conventional forging followed by dual heat treatment (near-β and two-phase field heat treatments) is a feasible technique aimed at obtaining tri-modal microstructure in near-α titanium alloys. In view of the enlargement and integration of aerospace structural parts as well as the microstructure diversification of original billet, the Ti–6242S alloy specimens with three different initial microstructures were subjected to multi-pass conventional forging and dual heat treatment. The flow behavior and microstructure evolution of material were analyzed. The results indicated that lamellar α has a stronger ability to coordinate deformation than equiaxed α. The more lamellar α in the microstructure, the slower the microstructure reconstruction during deformation interruption. It is feasible to obtain tri-modal microstructure by any pass conventional forging and dual heat treatment for the initial equiaxed or duplex microstructure, and two passes are more appropriate. The difference between initial equiaxed and duplex microstructures is gradually eliminated through a series of microstructure evolutions during the subsequent heat treatment. For initial lamellar microstructure, a kind of microstructure with multi-scale equiaxed α can be formed after multi-pass conventional forging. The spheroidization fraction of lamellar α is significantly increased with the increase of deformation pass. Tri-modal microstructure can be obtained through three-pass forging and dual heat treatment.

Bioinspired Metal-Intermetallic Laminated Composites for the Fabrication of Superhydrophobic Surfaces with Responsive Wettability.

Hundreds of copper and titanium foils were applied to prepare biomimetic metal-intermetallic laminated composites by diffusion bonding. The cross sections of the obtained diffusion bonded bulks were etched selectively with FeCl3 solution to get regular microarray structures. This kind of microstructure was controlled accurately and promptly by simple parameter adjustment. The etched surfaces were modified with 1-dodecanethiol, and the water contact angles (WCAs) were measured. The relationship between the microstructure and wettability of the achieved material was discussed, and the reason for the anisotropic wettability was also analyzed. Then etched surfaces were anodized in different electrolyte solutions to obtain different nanostructures. The morphology and chemical compositions of the surfaces were analyzed. The surfaces with CuO nanostructures by modification show superhydrophobicity with self-cleaning, on which the WCA and water sliding angle are 160.9° and 0.8°, respectively. The surfaces with TiO2 nanostructures without modification show ultraviolet light-responsive wettability. After modification with 11-mercaptoundecanoic acid and 1-decanethiol, the surfaces also exhibit pH-responsive wettability. The superhydrophobic surfaces with responsive wettability have potential applications in biotechnology and microfluidics.

The influence of columnar to equiaxed transition on deformation behavior of FeCoCrNiMn high entropy alloy fabricated by laser-based directed energy deposition

Abstract This study investigates the columnar to equiaxed transition (CET) and deformation behavior of a FeCoCrNiMn high entropy alloy (HEA) fabricated by laser-based directed energy deposition (DED). The results show that two kinds of microstructure can be obtained in the as-built HEAs by changing laser scanning speed: one kind of microstructure is formed at a low scanning speed and composed of near fully equiaxed grains; the other is formed at a high scanning speed and composed of columnar grains. These two different microstructures are closely related to the CET, which is decided by the ratio of thermal gradient and solidification rate in the molten pool. Additionally, compared with traditional HEAs, as-built HEAs show a heterogeneous grain-size distribution and high dislocation density, as well as improved tensile properties, one of which (Yield strength = 330 MPa; Ultimate tensile strength = 630 MPa; Fracture elongation = 55%) is similar to the properties of wrought HEAs. Moreover, the as-built HEA with equiaxed grains shows a higher work hardening rate than the as-built HEA with columnar grains and the equiaxed microstructure has the characteristics of intergranular microcracks, the columnar microstructure shows the characteristics of intragranular microcracks. The deformation behavior was investigated using in-situ high-resolution digital image correlation methods, and the result shows that the difference in work hardening rate is closely related to the texture formed during deposition.

Detwinning-twinning behavior during compression of face-centered cubic twin-matrix layered microstructure

In this paper, we have examined the mechanical response of a face-centered cubic layered twin – matrix system, which has been generated in Cu–Al alloy single crystal. This kind of microstructure was obtained by specially designed uniaxial tension experiments of Cu-9at.%Al single crystals oriented for “easy” glide. It has been shown, that detwinning system, which operates along the twinning plane, may at specific crystallographic conditions totally dominate the process of plastic deformation. The detwinning system was activated in a confined area that creates a localized deformation regions in the form of kink bands that were found to be hierarchical in formation (i.e. higher order kinking within already existing kink bands). This mode of plastic deformation generates lattice rotation that was identified to occur around normal to the plane of shear of the active detwinning system. Hence, the paper gives direct experimental prove of the importance of detwinning systems on the mechanical properties and deformation texture analysis of face-centered cubic materials.

The role of eutectic colonies in the tensile properties of a Sn–Zn eutectic solder alloy

The growth of eutectic colonies in Sn–Cu, Sn–Zn and Sn–Ag–Cu eutectic alloys has already been reported in the literature. However, relationships between this kind of microstructure and mechanical properties remain undetermined for solders. The use of water-cooled copper (Cu) and AISI 1020 low-C steel molds and the eutectic Sn-9 wt.%Zn alloy make it possible to address this matter. The samples grown in the Cu mold demonstrated higher solidification rates than those developed in the low-C steel mold. Overall, the microstructure is constituted by Zn-lamellae embedded in a Sn-rich matrix. The Zn lamellae are not only uneven in thickness but also irregularly perforated. Due to Cu dissolution into the alloy, a small fraction of Cu5Zn8 intermetallic particles formed during solidification of the Sn-9 wt.%Zn alloy in the Cu mold. The contamination with Cu appears to be responsible for the improvement in the distribution of Zn-lamellae. The decrease in spacing between broken lamellae measured from SEM images, as well as a higher number of Zn particles per area, explain such occurrence. Ductility and tensile strength of different samples could allow the establishment of relationships among properties vs. eutectic colony spacing. For the Cu mold, the motion of Cu towards the alloy as well as higher solidification rates, allowed microstructures to be formed combining 60% of strain to fracture and 52 MPa of ultimate tensile strength. These achievements are mainly due to the finest spacings of both the eutectic colony (λc = 36 μm) and the Zn lamellae (λL=0.9 μm), besides homogeneous distribution of Cu across the resulting microstructure.

Abrasive wear behavior of WC-10Co-4Cr cladding deposited by TIG welding process

The aim of the present study is to fabricate a highly wear resistant WC-10Co-4Cr cladding on AISI 304 stainless steel using TIG welding process. The effect of current and speed on the microstructure, hardness, and abrasive wear of the cladding was investigated. Tribological behaviour of the claddings slided against SiC emery paper was examined using pin-on-disc tribometer. FESEM, XRD and EDS spectrums were used to analyse the microstructure of cladding. Different parametric combination of current and speed has been used to produce the variation in heat input during the cladding. Process parameters, such as current and speed influence the solidification time which results in different kind of microstructure. The results revealed that the TIG cladding deposited at low heat input produces a hard and wear resistance cladding. Increase in hardness and wear resistance was attributed to the partially melted WC grains reinforced in CoCr matrix. SEM images showed the formation of wear tracks on the surface of worn out cladding. The wear tracks was formed due to the plastic deformation and extrusion of CoCr matrix. However, the cladding developed at low heat input shows relatively smooth surface with lesser depth of wear tracks.

Polymer optical bridges for efficient splicing of optical fibers

We present an application of optonumerical methodology for improvement of functional parameters of polymer optical bridges that connect two optical fibers. To fully determine and improve the properties of this kind of microstructure, experimental methods are combined with numerical modeling. The parameters describing the functionality of the polymer optical bridges are optical losses (insertion and return), which determine the usability of those elements as optical fiber splices. These parameters are the function of such features as refractive index distribution, microstructure geometry, and propagation of the light wavelength. To analyze the relation of those features on the functional parameters of the studied microstructures, the experimental results are compared to the ones obtained with simulations. Numerical modeling of the aforementioned optical bridges is performed by means of the finite-difference time-domain method. Experimental methods consist of optical diffraction tomography, which is used to obtain a full three-dimensional refractive index distribution of optical bridge, and measurement of optical losses. Implementation of the proposed methodology in iterative procedure allows the optimization of the fabrication procedure to produce efficient and reliable optical splices with desired functional parameters—insertion loss at the level of 0.2 dB and return loss above 60 dB.

Formation and evolution of tri-modal microstructure during dual heat treatment for TA15 Ti-alloy

Dual heat treatment (near-β heat treatment + (α+β) heat treatment) provides an effective way for the acquisition of a tri-modal microstructure in TA15 titanium alloy, and this kind of microstructure is found to possess excellent comprehensive performance. The temperature difference between near-β and (α+β) heat treatments determines the content of secondary lamellar α phase in the final tri-modal microstructure. During near-β heat treatment, the volume fraction of equiaxed α phase decreased sharply to 8%–9%, and equiaxed α phase with grooves on the surface broke up due to phase transformation and then spheroidized. Martensite was formed after water quenching, and it decomposed into a large number of secondary lamellar α phase at the initial stage of (α+β) heat treatment. Afterwards, parts of the decomposed lamellae dissolved, and the rest grew through the merging of adjacent lamellae. In the meantime, the content of equiaxed α phase increased to about 20%. Tertiary lamellar α phase precipitated from high temperature β phase together with residual β phase to form transformed β matrix during subsequent air cooling. Eventually, tri-modal microstructure is formed, and its mechanical properties meet the requirements of aviation forgings.

Tri‐core photonic crystal fiber based refractive index dual sensor for salinity and temperature detection

AbstractThis article discusses the tri‐core photonic crystal microstructure fiber for the process of simultaneous sensing for salinity and temperature of water substances. This kind of microstructure is preferred in many sensing application to scale the detection process in micrometer range. In this novel sensor, the sensitivity is calculated through coupling mechanism by tracking wavelength shift of various concentrations of salinity and temperature using finite element method. The sensible samples are in liquid and are infiltrated into the framed hollow cavity. Based on the coupling principle between silica substrate and the analyte material, the sense of the salt as well as temperature is obtained. Finally, it is noted that sensitivity of the salt level in water as 5404.9 nm/RIU for x polarization direction and 5674 nm/RIU for y polarization direction have been calculated with the temperature sensitivity of 4 nm/°C in the same water substances.

Closed-loop optimization and investigation of bistable interlocked structure

BI (bistable interlock), which exists in some creatures and is nowadays applied in engineering, is a kind of micro-structure with two distinct stable positions. In this study, the physical properties and other characteristics of the BI are investigated and the geometric parameters of the BI are optimized. Initially, to filter unimportant factors for individual interlocked structure, GSA-HDMR (global sensitivity analysis - high dimensional modeling representation) is firstly performed through a closed-loop method. An optimization of structure with multiple interlocked sutures is carried out by several novel algorithms to find the optimal design that makes the structure the most stable. The optimal design obtained by the PSO (particle swarm optimization) method turns out to be the best. To improve the modeling efficiency and make the above procedures adaptive and easy to be controlled, the GSA (global sensitivity analysis) and optimization procedures are modeled in ABAQUS based on Python Language.

Laser-arc hybrid welding of thick HSLA steel

A standard laser-arc hybrid welding (S-LAHW) and LAHW with preplaced cut wire inside the groove before welding were studied and compared. The S-LAHW setup revealed problems with filler wire delivery to the root, resulting in substantial hardness increase due to bainitic-martensitic transformation. The applied finite element modeling confirmed significant cooling rate increase in the root area for deep penetration welds. Preplacement of cut wire prior to welding reduced hardness providing improved welds with higher homogeneity. This method was subsequently applied for multi-pass welding that revealed insufficient nucleation of acicular ferrite on non-metallic inclusions (NMIs). It is implied that a critical cooling rate has been exceeded where the NMIs become inactive, resulting in a microstructure consisting of a martensite and bainite mixture. This kind of microstructure is clearly harmful for the weld metal toughness.

Computational material design for acoustic cloaking

A topology optimization technique based on the topological derivative and the level set function is utilized to design/synthesize the micro-structure of a pentamode material for an acoustic cloaking device. The technique provides a micro-structure consisting of a honeycomb lattice composed of needle-like and joint members. The resulting metamaterial shows a highly anisotropic elastic response with effective properties displaying a ratio between bulk and shear moduli of almost 3 orders of magnitude. Furthermore, in accordance with previous works in the literature, it can be asserted that this kind of micro-structure can be realistically fabricated. The adoption of a topology optimization technique as a tool for the inverse design of metamaterials with applications to acoustic cloaking problems is one contribution of this paper. However, the most important achievement refers to the analysis and discussion revealing the key role of the external shape of the prescribed domain where the optimization problem is posed. The efficiency of the designed micro-structure is measured by comparing the scattering wave fields generated by acoustic plane waves impinging on bare and cloaked bodies.

Influence of injection molding on the flexural strength and surface quality of long glass fiber-reinforced polyamide 6.6 composites

Abstract The objective of this paper was to process a polyamide 6.6 composite reinforced with long glass fibers (50 wt.%) using a design of experiments to determine the processing conditions that simultaneously maximize the flexural strength and the surface quality of the molded composite. The analyzed factors were the barrel temperature profile, the injection speed and the screw speed. To maximize the flexural strength response variable and the surface quality, all studied parameters should be maintained at the higher levels. The analysis of microstructure of composites molded demonstrates that this combination of parameters promotes a greater orientation of the fibers in the outer layers, as well as prevents the migration of glass fiber to surface of the composite. This kind of microstructure is favorable to a better surface quality, and a greater flexural strength.

Evaluation of damage induced by high irradiation levels on α-Ni-Ni3Si eutectic structure

Diluted alloys of the binary system Ni–Si have been used as target of beam of ions, electrons, neutrons and so on because in this kind of alloy occurs transformations order–disorder, when the temperature is raised. This fact has permitted to evaluate the phenomena associated with the damage induced by irradiation (DII). The results of these works have been employed to understand the behavior under irradiation of complex alloys and to evaluate the reliability of the results of mathematical simulation of the evolution of the DII. The interest in the alloy system Ni-Si has been reborn due to the necessity of developing materials, which have better resistance against the corrosion on more aggressive environments such as those generated on the nuclear power plants or those that exist out of the Earth's atmosphere. Now, a growing interest to use concentrated alloys of this binary system on diverse fields of the materials science has been taking place because up to determined concentration of silicon, a regular eutectic is formed, and this fact opens the possibility to develop lamellar composite material by directional solidification. However, nowadays, there is a lack of fundamental knowledge about the behavior of this type of lamellar structure under aggressive environments, like those mentioned before. Hence, the task of this work is to evaluate the effect that has the irradiation over the microstructure of the concentrated alloy Ni22at%Si. The dendritic region of the hypereutectic alloy consists of an intermetallic phase Ni3Si, whereas the interdendritic region is formed by the alternation of lamellas of solid solution α-Ni and intermetallic phase Ni3Si. Such kind of microstructure has the advantage to get information of the DII over different phases individually, and at the same time, about of the microstructure influence over the global damage in the alloy. The hypereutectic Ni22at%Si alloy was irradiated perpendicularly to its surface, with 3.66 MeV – Ni ions up to 380 dpa at 650°C in a Tandetron linear accelerator. The level of irradiation dose was chosen similar to the irradiation conditions of the next-generation nuclear reactors. The theoretical maximum depth of the DII (maximum depth of damage (MDD)) was calculated as 1.35 µm using the SRIM-2013 program; the laminar microstructure of the eutectic was simulated using the lattice parameters of the eutectic before irradiation. The experimental MDD was 1.47 µm, as determined through transmission electron microscope (TEM) images and the DII was characterized using µX-ray diffraction and TEM. The elimination of cubic phase of the intermetallic Ni3Si, the suppression of lamellae of the α-Ni phase, the generation of dislocation loops and lines, all of these changes generated by the irradiation are clear evidences that the DII was severe. Based on theoretical and experimental evidence, we propose that the amount of phases, alternate of lamellae with different chemical concentrations of silicon and lamellae spatial distribution have a direct relation with the severe evolution of the DII.

Study of matrix microstructure of SiCf/Ti–43Al–9V composites

Four different microstructures of the Ti–43Al–9V alloy were obtained through heat treatment or thermal deformation process. Alloys with different microstructures were cut and ground into thin foils. The foils would be used to fabricate the SiC fibre reinforced composites via foil–fibre–foil method. Then, the matrix microstructures of composites were investigated by means of optical microscopy, scanning electron microscopy and microarea X-ray diffraction. The results show that near lamellae and massive gamma microstructure transform into duplex during the consolidation process, but the transformation mechanism of the two microstructure is different. Fully lamellae microstructure remains in the matrix, while B2 phase precipitates in the matrix. Duplex microstructure does not change during the consolidation process. No matter what kind of microstructure the foils have, there is only gamma phase formed close to the fibres in the matrix of composites.

Flow Behaviour of M2 Steel Alloy during Semi Solid Isothermal Rapid Compression

The key to all semisolid processes is spherical and non-dendritic particles suspended in a liquid matrix. This special kind of microstructure causes the semisolid material to behave like a non-Newtonian fluid dependent on time and shear rate. Semi solid metal processing gives less shrinkage and porosity, non-macro segregation, lower flow stress, good formability and increased die life compared with conventional production methods. Therefore, semi solid processing introduces a good option for massive forming of high temperature alloys. Here, by partial remelting of M2 tool steel alloy under rapid compression test, deformation mechanism of steel alloy and its correlation to rheological properties were investigated. Flow stress for M2 tool steel alloy corresponding to solid fraction above 55% derived at constant strain rate and holding time. In order to investigate the parameter involved in this process, in the second stage of experiments the ram speed and holding time are variable. The analysis of the derived curves shows that the semisolid slurries exhibit a pseudo plastic behavior dependent on stain rate and temperature. The classical power law model used to describe the rheological and thixotropic dependence.