Influence Of Microstructural Changes Research Articles

Study on Welding Characteristics and Parameters of Gas Metal Arc Welding for A516 Grade 70 Steel with ER70S-6 and ER308LSi Filler Materials.

Welding is a crucial process in joining metals, especially in the fabrication industry. Thisresearch aimed to investigate the effects of using two different filler materials, ER70S-6 and ER308LSi, with nine combinations of wire feeder speed (WFS) and shielding gas flow rate (GFR), on weld joints. The study focused on the weld quality and material properties of Gas Metal Arc Welded (GMAW) butt joints of ASTM A516 G70 plates, characterized through visual inspection, liquid penetrant testing, tensile testing, hardness testing, and optical microscopy. Results indicated that the highest ultimate tensile strength and hardness were achieved at 4 m/min WFS and 15 L/min GFR with ER70S-6, and 5 m/min WFS and 20 L/min GFR with ER308LSi. The specimens welded with ER308LSi demonstrated superior mechanical properties compared to those welded with ER70S-6. Additionally, the study revealed the influence of microstructural changes from the base metal (BM) to the heat-affected zone (HAZ) and fusion zone (FZ), with finer and more compact grain structures contributing to higher hardness values. These findings underscore the importance of selecting appropriate filler materials, WFS, and GFR to achieve the desired weld quality and material properties for A516 G70 low-carbon steel welded joints.

Fabrication of hierarchical layered structure in Zr/Ti composite via multi-step heat treatments and its effect on the mechanical properties

The strength and ductility of metallic structural materials are two pivotal properties generally considered mutually contradictory. In the past few decades, numerous heterogeneous materials have been designed and fabricated to overcome this trade-off. Biomimetic-designed hierarchical layered (HL) materials represent a promising approach. In the present study, HL Zr/Ti materials with three hierarchical levels were fabricated via multi-step heat treatments. Scanning Electron Microscopy (SEM), Transmission electron microscope (TEM), Electron Backscatter Diffraction (EBSD), Transmission Kikuchi Diffraction (TKD), and Energy Dispersive X-ray Spectroscopy (EDS) were employed to observe the evolution of the HL microstructure. The mechanical properties of the HL Zr/Ti materials were assessed through hardness and tensile tests, analyzing the influence of microstructural changes in the diffusion layer on the overall mechanical performance. Our results demonstrated that the HL structure could introduce extra strength beyond the rule of mixtures (ROM) due to multiple-scaled hetero-deformation induced (HDI) strengthening. Additionally, the refinement of the second-level layer thickness effectively inhibited crack propagation. This research provides new insights into developing multi-level HL materials with enhanced mechanical properties through cost-effective and scalable manufacturing processes.

Texture and lattice strain evolution in a pearlitic steel during shear deformation: An in situ synchrotron X-ray diffraction study

In-situ synchrotron X-ray diffraction experiments were conducted on the pearlitic steel sample with a carbon content of 0.74% by weight. Specimens were subjected to uniaxial loading that induced shear deformation and two-dimensional diffraction patterns were acquired. The evolution of the lattice microstrain and the strain-resolved crystallographic texture development of both ferrite (α-BCC) and cementite (θ-orthorhombic) phases were followed. The analysis revealed that the texture changed from {110}<113>α to {113}<121>α component and then, stabilized at {013}<uvw>α orientations. The θ phase exhibited a weak texture in the {100, 010, and 001}θ family planes. Additionally, it was revealed that the nucleation of interfacial defects at the α/θ interface promotes the amorphization of cementite and the activation of slip systems in less densely packed {310}α planes. The influence of microstructural changes on mechanical properties is discussed.

Correlation between the microstructure and deformation behavior of a PM fine-grained duplex steel

A fine-grained duplex steel with a composition of Fe–5Mn–2Al-0.6C (wt.%) was fabricated using a powder metallurgy (PM) technology of thermomechanical consolidation by hot extrusion of powder compact. The microstructure consisted of α′-martensite, residual austenite (RA), and a small amount of Al2O3 particles. Subsequent heat treatment was performed to adjust the microstructure and mechanical properties. This study focuses on the pre-and post-heat treatment microstructure of the material, elucidates the reasons for its formation, and explains how microstructural changes influence tensile deformation behavior. The results show that the heat treatment caused the precipitation of nanoscale carbide within the martensite, which significantly increased the yield strength from 792 MPa to 1078 MPa. While heat treatment altered the size and distribution of RA regions in the microstructure, the amount of RA transformed during deformation remained proportional to the flow stress in both materials, indicating that the flow stress dictates the amount of phase transformation of ultrafine grained RA. Therefore, in the heat-treated material with a higher yield strength, a larger amount of RA transformed during the initial stage of plastic deformation, leaving less RA to sustain a work-hardening rate in subsequent deformation, resulting in a decrease in ductility from 5.5 % to 3.6 % and fracture stress from 1674 to 1453 MPa. In addition, the in-situ formed Al2O3 particles facilitated grain refinement of the extruded rod, but had less effect on the microstructure and properties of the heat-treated sample. This study serves as a valuable reference for comprehending the influence of microstructural changes in PM manganese steel on tensile deformation behavior.

Sodium salt surface interactions affect single particle combustion behavior of biomass, coal, and their chars

Sodium salt additions provide an effective route for tuning the combustion behavior of solid fuels. The salt-fuel surface interactions play a key role in combustion, as demonstrated by low heating rate experiments. High heating rate single particle studies have not investigated the effect of surface interactions and microstructural changes for sodium salt-treated fuels. In this work, the effect of three different sodium salt treatments were investigated on the single particle combustion characteristics of two distinct solid fuels and their corresponding chars. This approach probed the influence of microstructural changes and the formation of oxidation-resistive functional groups during high heating rate combustion. The separate characterization of biomass, coal, and their respective chars aimed at identifying the effect of sodium during different stages of combustion. The investigation encompassed Tunçbilek lignite (TL), olive residue (OR), and their fast pyrolysis chars (TLc and ORc) obtained from a wire mesh reactor at 600 °C. Both pristine and char particles were treated with Na2CO3, NaOH, and NaAlO2 to investigate the catalytic/inhibiting effects at different stages of combustion, namely, ignition, volatile combustion, and char combustion. All samples were burned as single particles at a high heating rate, WMR (1600 °C s−1). Treated OR samples provided earlier ignition reaching ∼ 0.4 s for OR-OH and shorter char combustion times around ∼ 2.8 s mg−1 for OR-CO3. On the contrary, treated TL samples depicted slightly higher ignition delay (3.0 s for TL-OH) and prolonged char combustion (11.2 s mg−1 for TL-OH) compared to TL (2.3 s, 8.2 s mg−1). Treated TLc samples also exhibited higher ignition delay due to the hygroscopic behavior of the sodium salts, which is more pronounced in TLc-OH (5.5 s). All treated chars exhibited shorter char combustion times except TLc-OH. Overall, sodium salt additions improved characteristic combustion times of biomass and chars while inhibiting those of lignites. The inhibitive effect of sodium salts on treated OR and ORc samples was more pronounced for TGA experiments due to the alkali interaction with the lignocellulosic component and a prolonged heating-up period. The findings demonstrate the importance of high heating rate characterization to accurately understand the sodium salt additions on combustion performance.

Influence of Microstructural Change on Crack Growth in Thermal Barrier Coating Subjected to Thermal Cycling under Temperature Gradient

Influence of Microstructural Change on Crack Growth in Thermal Barrier Coating Subjected to Thermal Cycling under Temperature Gradient

High temperature oxidation mechanisms of grain refined Fe-25Al-1.5Ta(+TaC/+(Ta,Nb)C) iron aluminides at 700 °C in air

The high temperature oxidation mechanisms of grain refined Fe-25Al-1.5Ta (at%) with TaC or (Ta,Nb)C additives were investigated at 700 °C in air for 503 h to study the influence of microstructural changes on the oxidation behaviour. While a thin and stable α-Al2O3 scale was formed at the Fe-Al matrix, additional phases were selectively oxidised leading to higher oxidation kinetics of Fe-25Al-1.5Ta with carbide additives. The selectively oxidised C14 (Fe,Al)2Ta Laves phase showed the formation of outer Fe2O3 and an inner (Al,Ta)-rich oxide, while Al-rich oxides were found along the (Al,Ta)-rich oxide/Fe-Al phase boundary and locally below Fe2O3.

The brittle-to-ductile transition of pure tungsten processed by closed dual equal channel angular pressing process

The deformation behavior of pure tungsten was investigated to understand the influence of microstructure changes on the brittle-to-ductile transition (DBT) during closed dual equal channel angular pressing (CDECAP). In the CDECAP process, four deformation regions and three processing routes were introduced and route B with high strain uniformity and low eccentric load was selected for pure tungsten. A fine-grained microstructure with high fraction of low-angle grain boundaries (LAGBs), more edge dislocations and near {011} <100> texture was developed during the microshear bands assisted continuous dynamic recrystallization (cDRX). And the hot hardness in a wide range of temperatures suggested that the brittle-to-ductile transition temperature (DBTT) reduced significantly from 276 °C to 165 °C after 3 passes. The results indicate grain boundary (GB), dislocation and texture are three important factors controlling the ductility of pure tungsten during CDECAP.

Tuning the magnetocaloric response of Gd7-xYxPd3 (2 ≤ x ≤ 6) alloys by microstructural modifications

We investigated the influence of microstructural changes on the magnetic properties and the magnetocaloric response of the Gd7-xYxPd3 (2 ≤ x ≤ 6) alloys rapidly quenched by vacuum suction casting (rc-cast samples) and melt-spinning (melt-spun samples) techniques. Quenched-in structural disorder determines magnetic and magnetocaloric properties in both series of alloys. For the rc-cast samples two distinct magnetic transitions are visible. The peak at higher temperatures is related to the ferromagnetic/paramagnetic transition of the crystalline phase. In contrast, the peak observed at low temperatures is believed to be related to the ferro-para transition of the amorphous phase and/or a spin reorientation. The Gd7-xYxPd3 alloys in the form of rapidly cooled cast exhibit the magnetic transition temperatures at 262 K, 242 K, 202 K, 153 K and 9 K, for 2 ≤ x ≤ 6 respectively. Curie temperatures of the melt-spun Gd7-xYxPd3 alloys are much lower compared to the rc-cast samples. The melt-spun Gd5Y2Pd3 orders ferromagnetically below 90 K, while Gd4Y3Pd3, Gd3Y4Pd3, Gd2Y5Pd3 and GdY6Pd3 ribbons undergo the magnetic transformation at 65 K, 40 K, 25 K, and 9 K, respectively. Investigated ribbons exhibit almost doubled magnetic entropy change in comparison to the rc-cast samples. For instance, the -ΔSm value for melt-spun and rc-cast Gd5Y2Pd3 is equal to 6.31 Jkg-1K−1 and 3.64 Jkg-1K−1, respectively. Moreover, due to the large δTFWHM of the magnetic entropy change peak, both the melt-spun and rc-cast samples exhibit large relative cooling power (RCP), reaching 466 Jkg−1 (Δµ0H = 5 T) for the rc-cast Gd5Y2Pd3. RCP values are comparable to those of some potential magnetic refrigerants.

Design of mechanical robust superhydrophobic Cu coatings with excellent corrosion resistance and self-cleaning performance inspired by lotus leaf

Various strategies have been developed to fabricate mechanical robust superhydrophobic membranes on the original substrates. However, for superhydrophobic coatings that have to be homologous to the inherently fragile substrate, their mechanical stability problems have not been satisfactorily solved. Herein, we prepared three hierarchical superhydrophobic Cu coating via facile pulse electrodeposition with microstructure size of 10–15, 30–40, and 60–70 µm, respectively. The resulting superhydrophobic coatings simultaneously exhibit excellent self-cleaning, mechanical robustness, and corrosion resistance. A hydrophobic mechanism suitable for worn superhydrophobic surfaces was proposed, which can well analyze the influence of microstructure changes on wettability. Moreover, these three coatings can withstand 15, 50, and 100 cycles of sandpaper abrasion, respectively, as the size of the microstructure increases. The results demonstrate a size effect of microstructure, which means surfaces with larger-sized microstructures can better maintain their superhydrophobicity under mechanical damage. Our findings offer a reference for improving the mechanical robustness of other superhydrophobic coatings that are homologous to the substrate.

Effect of autogenous crack self-healing on mechanical strength recovery of cement mortar under various environmental exposure

While research on self-healing of cement-based materials has recently gained considerable attention and made sizable progress, there is still ongoing debate and controversy regarding the effect of crack closing induced by autogenous self-healing on mechanical strength recovery. Despite that several techniques have been used to capture and quantify the self-healing of surface cracks, the resulting effect on mechanical strength has not, to date, been explored and quantified in a rigorous and systematic manner. Therefore, in this study, a broad array of multi-scale techniques including non-destructive shear wave velocity, high-resolution X-ray computed tomography (µCT), and 3D image analysis was deployed to examine the effects of autogenous crack self-healing on the mechanical strength recovery in various mortar specimens. The influence of microstructural changes induced by additives such as swelling compounds, silica-based additions, and carbonating minerals on strength recovery under diverse environmental exposures was further explored. The results capture the relationship between the crack closing mechanism imparted by self-healing and mechanical strength recovery, therefore elucidating the discrepancies in mechanical strength recovery results reported in the open literature.

Effect of microstructural evolution from nano to micron grain size regime towards structural, magnetic, electrical and microwave properties of gadolinium iron garnet (Gd3Fe5O12)

The influence of microstructural changes from nano to micron grain size regime towards their structural, magnetic, electrical and microwave properties of gadolinium iron garnet (Gd3Fe5O12) has been investigated systematically in this research work. Raw materials were milled via high-energy ball milling (HEBM) followed by subsequent sintering (600–1400 °C) process. X-ray diffraction (XRD) analysis had shown that single phase with garnet structure and highest crystallinity of Gd3Fe5O12 was formed at 1000 °C. The B–H hysteresis loop unveil the evolution development of magnetic behaviour (paramagnetism–ferrimagnetism) in samples thru variation of different sintering temperature. The values of linewidth (∆H) can be grouped into two groups which are; sample increased from 600 to 1000 °C due to shape and strain induced anisotropy while decreasing from 1100 to 1400 °C influenced by magnetocrystalline anisotropy with the increment of the sintering temperature.

Effect of micro‐structural changes on concrete properties at elevated temperature: Current knowledge and outlook

AbstractThe influence of microstructural changes on concrete properties at elevated temperatures is presented and discussed in this paper, as the exposure to elevated temperatures brings in marked changes in concrete thermal, mechanical and kinematic properties owing to the heat‐induced evolution of material's microstructure. The major microstructural changes consist in increasing pore size, occurrence of microcracking and activation of chemo‐physical processes in the hardened cement‐paste. These processes (like portlandite dissociation and crystalline change in quartzitic aggregate) occur above 400°C and are more pronounced in high‐strength than in normal‐strength concrete. Increasing pore size and microcracking, however, yield the largest contribution to concrete strength‐loss, that occurs mainly between 400 and 800°C, depending on aggregate type and initial moisture content in the mix. On the whole, calcareous (or carbonate) aggregate behaves better than siliceous aggregate face to increasing temperatures. Initial moisture content favors concrete thermal spalling, mostly between 200 and 400°C, but such a complex phenomenon is still open to investigation, as demonstrated by the various theories found in the literature, each with its chemo‐physical mechanisms and limitations. Three theories are discussed in this paper, and these theories together with other critical issues allow to focus on future work.

Influence of Microstructural Changes on Residual Stress Characteristics and Macro-Hardness of Submerged Arc Welded P-91 Steel Plates

Abstract: In this study, the submerged arc welded butt joint of P-91 ferritic-martensitic alloy steel plates has been chosen to examine the influence of microstructural changes on welding residual stress characteristics and macro-hardness in the weldment with two different heat input 2497.5 J/mm & 2040J/mm respectively. The stress magnitudes at a different location on the welded specimen are measured by X-ray diffraction technique at the post-weld heat-treated condition. Compressive stresses are observed in the weld zone (WZ) and tensile stresses are detected at the boundary of the heat-affected zone (HAZ) near the weld zone. Higher compressive stresses are found in the weld zone of both the specimens where maximum hardness values are observed. Different grain matrix in the microstructure contributes significantly towards the quality of weldment. Residual stress, as well as the hardness of weldment, is found to be influenced by the martensite phase transformation and dissolution of precipitates. A modeling concept is presented for dimensional analysis of martensite structure. Energy dispersive X-ray indicates the distribution of carbides at the grain boundaries. Optical micrograph substantiates the presence of δ-ferrite in the WZ.

Formation of interfacial reaction layer for stainless steel/aluminum alloy dissimilar joint in linear friction welding

One of the mechanisms for the dissimilar materials joining is the formation of interfacial reaction layers. However, this reaction is disrupted owing to the presence of oxide layers and voids, leading to lower strength, and the elimination of these factors is essential. Thus far, studies on linear fraction welding (LFW) with regard to the relationship between the joint strength and the microstructure of the base alloy and interface are lacking. Therefore, herein, the influence of microstructural changes in base alloys and interfacial structures on the joint tensile strength was investigated for the dissimilar joint between the stainless steel and an A5083 alloy after high-frequency linear friction welding at 245 Hz. After the initial joining process up to 1 s, the joint strength decreased as the friction increased. The crystal orientation analyses using electron backscatter diffraction demonstrated a minimal change in the microstructure of the A5083 alloy, particularly in the grain size in the geometric dynamic recrystallization region. This variation in the microstructure was minimal, regardless of the friction time, which was consistent with the result of the hardness distributions. The observation of microstructure using transmission electron microscopy revealed the formation of metastable Al-Fe intermetallic compounds and Al-Mg-Cr compounds derived from the reaction between the oxide layer and alloying elements in the A5083 after experiencing friction for a short time. Conversely, we confirmed the formation of a fragile boundary within the interfacial reaction layer after the exposure to friction for an extended period due to differences in the formation process of the layer: mechanical mixing or interdiffusion. Hence, it was proposed that mechanical removal as well as the interfacial reaction between the oxide layer and the Mg contained in the aluminum alloy function in removing the surface oxide layer, which plays a significant role in designing the interfacial structure and joint properties.

Influence of Microstructural Changes’ Effects on the Linear and Nonlinear Ultrasonic Parameters of Cast Stainless Steels

In this research, some nondestructive ultrasonic techniques were employed to inquire into the effect of microstructural changes induced by thermal aging and cold work on the ultrasonic response. As thermal embrittlement is a risk to the safety of nuclear power plants, a nondestructive detection method has to be developed for on-site monitoring. The austenitic stainless steel with δ-ferrite specimens were used to study the behavior of microstructural changes caused by age-treating and cold work and then examined by the velocity, attenuation, and nonlinear ultrasonic technique. The variations of the linear and the nonlinear ultrasonic parameters were related to the microstructural changes. Additionally, the experimental results suggest that the ultrasonic nonlinearity parameter of cast stainless steel is determined by the microstructure evolution caused by spinodal decomposition and the phase precipitation process.

Effect of Recovery and Recrystallization on the Damping Behaviour of A356/SiCp Composites

Damping characteristics of A356 alloy and its composites reinforced with 15 vol% SiC particles were investigated using a dynamic mechanical analyzer. Tests were done at three different temperatures 150 °C, 200 °C and 300 °C to study the influence of microstructural changes during recovery and recrystallization on the damping behaviour. Since recovery and recrystallization also depend on the heating rate, damping tests were done at slow (2 °C/min) and fast (10 °C/min) heating rates. The damping characteristics were explained with respect to the microstructure changes that took place during recovery and recrystallization.

Investigation of Structure Property Relationship of the Dissimilar Weld Between Austenitic Stainless Steel 316L and Duplex Stainless Steel 2205

In the present study, the influence of microstructural changes on the mechanical and corrosion properties of the dissimilar weld between austenitic stainless steel (ASS 316L) and duplex stainless steel (DSS 2205) has been examined and reported. The weld joint was fabricated through the use of gas tungsten arc welding process with a nickel enhanced filler metal ER 2209. The microstructural changes observed in the fusion zone such as nucleation of delta ferrite (δ), austenite (γ) reformation, precipitation of intermetallic phases and the formation of coarser ferrite phases in the HAZ have been reported. Also, the mechanical properties of the weldment such as microhardness, impact toughness and tensile properties have been correlated with microstructural changes. Potentiodynamic polarization test results showed a better electrochemical behavior for ASS 316L than with the weldment and the parent metal of DSS 2205. The austenite phase was found to be electrochemically more stable than the ferrite phase in duplex microstructure. On the other hand, achievement of the stress corrosion cracking resistance by the weldment and the parent metal of DSS was found to be excellent, whereas ASS 316L ended with surface fissures.

Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal

The aim of this work was to evaluate the different phases formed during solidification and after thermal aging of the as-welded 625 nickel-based alloy, as well as the influence of microstructural changes on the mechanical properties. The experiments addressed aging temperatures of 650 and 950 °C for 10, 100, and 200 hours. The samples were analyzed by electron microscopy, microanalysis, and X-ray diffraction in order to identify the secondary phases. Mechanical tests such as hardness, microhardness, and Charpy-V impact test were performed. Nondestructive ultrasonic inspection was also conducted to correlate the acquired signals with mechanical and microstructural properties. The results show that the alloy under study experienced microstructural changes when aged at 650 °C. The aging was responsible by the dissolution of the Laves phase formed during the solidification and the appearance of γ″ phase within interdendritic region and fine carbides along the solidification grain boundaries. However, when it was aged at 950 °C, the Laves phase was continuously dissolved and the excess Nb caused the precipitation of the δ-phase (Ni3Nb), which was intensified at 10 hours of aging, with subsequent dissolution for longer periods such as 200 hours. Even when subjected to significant microstructural changes, the mechanical properties, especially toughness, were not sensitive to the dissolution and/or precipitation of the secondary phases.

Effect of retrogression and re-ageing heat treatment on microstructure and microhardness of aluminium 7010 alloy

Aluminium alloy 7010 is subjected to retrogression and re-ageing (RRA) heat treatment to study the influence of microstructural changes on hardness. Retrogression is performed at 190 °C for different time intervals ranging from 10 to 60 minutes. Optimum time for retrogression treatment is estimated based on the retrogression time that result with equivalent mechanical properties as that of peak aged (T6) condition. Retrogression performed for 30 minutes resulted with micro hardness of 203 HV, which is equivalent to that obtained by following T6 treatment. Microstructural characterization done with the help of transmission electron microscope (TEM) indicates RRA treatment results with the coarsened and discontinuous precipitates along the grain boundary which is similar to over aged (T7) condition, where as fine and densely populated precipitates in the matrix similar to T6 condition. Coarse and discontinuous grain boundary precipitates (GBP’s) improves resistance to stress corrosion cracking. Fine and dense precipitates in the matrix ensures hardness equivalent to that of T6.