Dependence Of Microstructure Research Articles

Dependence of microstructure and mechanical properties on solidification condition of directionally solidified Zn-55Al-1.6Si alloys

Dependence of microstructure and mechanical properties on solidification condition of directionally solidified Zn-55Al-1.6Si alloys

Seeding Layer Effect on the Microstructure of Hydrothermally Grown α‐Manganese Dioxide Nanowires on Three‐Dimensional Graphene Foam

AbstractHydrothermal synthesis is a straightforward approach for producing high‐yield manganese dioxide (MnO2) nanostructures with efficient morphological control at low temperatures. This study investigates the microstructural dependency of hydrothermally grown α‐MnO2 nanowires (NWs) on pre‐treatment conditions on the substrate surface. Within this scope, α‐MnO2 NWs were synthesized on chemical vapor deposition (CVD)‐based graphene foam (GF) substrates pre‐treated via potassium permanganate (KMnO4) solution as a seeding layer with different concentrations (0.025, 0.050, 0.075, 0.1 M). A direct α‐MnO2 NWs growth (without pre‐treatment) was also performed on GF by hydrothermal method. The seeding layer effect on the NWs growth was elaborated to comprehend the process‐structure correlations by characterizing the resultant graphene foam/α‐MnO2 nanowires (GF/α‐MnO2 NWs) nanocomposites through Scanning Electron Microscopy (SEM), Raman Spectroscopy, X‐Ray Diffraction (XRD), and X‐Ray Photoelectron Spectroscopy (XPS). SEM, XRD, and Raman Spectroscopy revealed the successful acquisition of highly crystalline α‐MnO2 in one‐dimensional nanowire morphology on the high‐quality GF. Moreover, XPS results confirmed that all nanocomposites comprise α‐MnO2 and graphene without chemical degradation. Consequently, slight changes in solution concentration of seeding layers caused a noticeable alteration in the nanowire's structure, which could ensure effective control of nanocomposite properties without sacrificing the high purity of each component.

Microstructural Dependence of the Impact Toughness of TP316H Stainless Steel Exposed to Thermal Aging and Room-Temperature Electrolytic Hydrogenation.

This work deals with the effects of two individual isothermal aging experiments (450 °C/5000 h and 700 °C/2500 h) and the subsequent room-temperature electrolytic hydrogen charging of TP316H stainless steel on its Charpy V-notch (CVN) impact toughness and fracture behavior at room temperature. Microstructural analyses revealed that aging at 700 °C resulted in the abundant precipitation of intermediary phases, namely, the Cr23C6-based carbide phase and Fe2Mo-based Laves phase, whereas aging at 450 °C resulted in much less pronounced precipitation of mostly intergranular Cr23C6-based carbides. The matrix phase of 700 °C-aged material was completely formed of austenitic solid solution with a face-centered cubic (FCC) crystal structure, whereas an additional formation of ferritic phase with a base-centered cubic (BCC) structure was detected in 450 °C-aged material. The performed microstructure observations correlated well with the obtained values of CVN impact toughness, i.e., a sharp drop in the impact toughness was observed in the material aged at 700 °C, whereas negligible property changes were observed in the material aged at 450 °C. The initial, solution-annealed (precipitation-free) TP316H material exhibited a notable hydrogen toughening effect after hydrogen charging, which has been attributed to the hydrogen-enhanced twinning-induced plasticity (TWIP) deformation mechanism of the austenitic solid solution. In contrast, both aging expositions resulted in significantly lowered hydrogen embrittlement resistance, which was likely caused by hydrogen trapping effects at the precipitate/matrix interfaces in thermally aged materials, leading to a reduced TWIP effect in the austenitic phase.

Integrated experimental and computational study on the effect of hydrogen in mechanical responses of pure tungsten

Hydrogen irradiation profoundly changes the microstructure and morphological characteristics of tungsten, ultimately resulting in the modifications to its mechanical properties. Unfortunately, the specific mechanisms through which hydrogen irradiation influences the mechanical behavior of tungsten have not been clearly elucidated. Therefore, this study aims to further improve the understanding of the impact of hydrogen irradiation on the mechanical responses and its microstructure dependence in tungsten by employing two advanced techniques: nano-indentation experiments and Molecular dynamics (MD) simulations. The experimental findings revealed that deuterium (D) exposure decreased the maximum shear stress required for the incipient plasticity and led to the occurrence of multiple pop-ins. Particularly noteworthy was the most remarkable change in mechanical behaviors observed prominently in the recrystallized tungsten after D exposure. The microstructure dependence of irradiation-induced change in mechanical responses was investigated by two series of MD simulation, indentation and dislocation glide simulation, focusing on the independent effects of each irradiation-induced defect type (interstitial, substitutional, vacancy, vacancy-hydrogen (Vac-H) cluster, void-hydrogen (Vo-H) cluster) on dislocation activities. Based on the MD simulations, it was eventually revealed that Vo-H clusters were the most influential agent affecting dislocation activities. They not only lowered the pop-in stress by heterogeneous dislocation nucleation but also caused strain serration by a continuous pinning/unpinning process during dislocation glide. Consequently, we concluded that the dominant presence of d-induced Vo-H clusters facilitated the onset of plastic yielding and led to multiple pop-in phenomena in recrystallized tungsten, whereas inserted hydrogen caused minimal change in mechanical responses by interacting with pre-existing dislocation in cold-rolled tungsten.

Thickness dependence of microstructure and thermoelectric performance in Ag2Se films

With the increasing demand for energy autonomy in electronic systems, the research on thin-film-based energy harvesting devices has garnered significant attention. In this work, Ag2Se films with varying thicknesses on quartz glass substrates were fabricated using the magnetron sputtering technique and a straightforward selenization reaction. Charge transport and thermoelectric performance of these films were investigated in the low-temperature range of 300 K to 400 K. Considerable high room-temperature power factor (>2000 μW m-1 K-2) was achieved as the thickness of films exceeded 1000 nm, attributed to the favorable orientation and crystallization. A 5-leg thermoelectric prototype was assembled with 1600 nm-thickness Ag2Se film because of its highest power factor of 2530 μW m-1 K-2 at 300 K. Maximum output power density of 29.8 W m-2 and 87.7 W m-2 were obtained at the temperature difference of 30 K and 50 K respectively, surpassing the majority of the previous reports.

High-Throughput Microstructural Characterization and Process Correlation Using Automated Electron Backscatter Diffraction

The need to optimize the processing conditions of additively manufactured (AM) metals and alloys has driven advances in throughput capabilities for material property measurements such as tensile strength or hardness. High-throughput (HT) characterization of AM metal microstructure has fallen significantly behind the pace of property measurements due to intrinsic bottlenecks associated with the artisan and labor-intensive preparation methods required to produce highly polished surfaces. This inequality in data throughput has led to a reliance on heuristics to connect process to structure or structure to properties for AM structural materials. In this study, we show a transformative approach to achieve laser powder bed fusion (LPBF) printing, HT preparation using dry electropolishing and HT electron backscatter diffraction (EBSD). This approach was used to construct a library of > 600 experimental EBSD sample sets spanning a diverse range of LPBF process conditions for AM Kovar. This vast library is far more expansive in parameter space than most state-of-the-art studies, yet it required only approximately 10 labor hours to acquire. Build geometries, surface preparation methods, and microscopy details, as well as the entire library of >600 EBSD data sets over the two sample design versions, have been shared with intent for the materials community to leverage the data and further advance the approach. Using this library, we investigated process–structure relationships and uncovered an unexpected, strong dependence of microstructure on location within the build, when varied, using otherwise identical laser parameters.

Process-induced microstructural variations in laser powder bed fusion of novel titanium alloys: A comprehensive study on volumetric energy density and alloying effects

This study explores the effect of in-situ alloying and volumetric energy density (VED) on the microstructure of Laser Powder Bed Fusion (L-PBF) fabricated Ti alloys. Pure Ti, Ti–5Cu, and Ti–5Cu–1Si (wt%) samples were printed using elemental powders with varying VEDs. This study investigates the influence of VED and Cu/Si additions on the growth restriction factor (Q) and columnar-to-equiaxed transition of the β phase. Pure Ti samples exhibited coarse, prior columnar β grains with an average diameter of 106 μm, and a grain shape factor greater than 3.0. In contrast, both Ti–Cu and Ti–Cu–Si samples displayed a significant fraction of equiaxed prior β grains with a near-spherical morphology. Additionally, Cu/Si addition refined the prior β columnar grains, reducing their average diameter to 37 μm and 25 μm in Ti–Cu and Ti–Cu–Si, respectively. Furthermore, the study reveals a strong dependence of microstructure on VED in the Ti–5Cu–1Si alloy. Higher VED promotes a more uniform distribution of solute elements and a lower thermal gradient, resulting in finer equiaxed β grains with an average diameter of 4.9 μm, compared to samples printed at lower VEDs. The addition of Cu and Si also significantly refined the lath-like α phase and decreased the c/a ratio of the Ti HCP lattice, introducing lattice microstrains in the Ti–Cu and Ti–Cu–Si alloys. These findings demonstrate the potential of in-situ alloying and VED optimization for tailoring microstructures in novel Ti alloys fabricated via L-PBF, paving the way for achieving superior mechanical properties.

Influence of CrAlN layers on the microstructure, thermal stability, oxidation and corrosion resistance of AlN/CrAlN multilayers

Recently, the development of AlN-based multilayers has raised interest due to the probability of improved performance from both Al-addition and multilayer architecture. Here we prepared AlN/Cr1-xAlxN (x = 0.44 and 0.64) multilayers, with monolithic AlN and Cr1-xAlxN coatings as reference. The dependence of microstructure, mechanical properties, thermal stability, oxidation and corrosion resistance on Al content of CrAlN layers were investigated in detail. The AlN/Cr0.56Al0.44N (low-Al ML) shows a superlattice feature with single-phase face-centered cubic (fcc) structure and its hardness is 29.7 ± 1.0 GPa, which is ∼4.8 GPa higher than the theoretical value from rule of mixture. While the increase of Al content in CrAlN layer leads to a mixed cubic and wurtzite structure of AlN/Cr0.36Al0.64N (high-Al ML) with semi-coherent interface. Accordingly, the high-Al ML only has a hardness of 16.9 ± 0.4 GPa. During annealing, AlN/Cr1-xAlxN multilayers reveal hindered decomposition of CrN bonds, compared with the corresponding Cr1-xAlxN monoliths. The low-Al ML possesses the best thermal stability, reflected by its high hardness maintained up to 1000 °C, which is 100 °C higher than Cr1-xAlxN monoliths. Additionally, AlN/Cr1-xAlxN multilayers show improved oxidation resistance, with high-Al content in CrAlN layers favorable for such resistance. After oxidation at 1100 °C for 15 h, the low-Al ML and high-Al ML generate oxide scales with thicknesses of ∼1.6 and ∼1.4 μm, respectively, compared to the fully oxidized Cr0.56Al0.44N and ∼1.8-μm-thick oxide scale of Cr0.36Al0.64N. In electrochemical experiments, the corrosion current density (Icorr) of multilayer coatings decreases, compared to their corresponding monolithic coatings.

Temperature/stress dependence of stress rupture behavior and deformation microstructure of an advanced superalloy for additive manufacturing

A self-developed crack-free advanced superalloy ZGH451 fabricated by direct energy deposition (DED) was applied to investigate the microstructure evolution, stress rupture behavior, and deformation mechanisms at moderate-high temperatures and high-low stress conditions. The high Ta/Al ratio induces large misfit lattice stress and low stacking fault energy of alloy, resulting in approximate cubic γ′ phases in dendrites and the formation of initial dislocation tangles. After the stress rupture test at 760 °C/780 MPa, high content cubic γ′ phases, small size of voids as well as preserved dislocation tangles are observed, showing stable structures with high-stress rupture resistance. High content and suitable size of cubic γ′ phases, initial dislocation tangles, and L-C locks hinder the dislocation motion, which decreases the minimum strain rate and prolongs life significantly, forming four stress rupture stages. Hence, the deformation mechanism is determined by dislocation piled-up on γ/γ′ interface, formation of stacking faults in γ′ phases, and dislocations shearing γ′ phases. However, the microstructure exhibits uneven structures composed of large sizes of rafted γ′ phases and voids at 980 °C/260 MPa. The rafted structure and high temperature provide continuous channels and enough energy for dislocation motion, resulting in the increase of minimum strain rate, decline of life, and typic three stress rupture stages, even though there are obstacles to dislocation movement caused by dislocation networks. The deformation mechanism transforms to form dislocation networks on γ/γ′ interface and dislocations shearing γ′ phases. Besides, the decomposition of carbides on GBs also depends on temperature, which decomposes into harmful chain-like M23C6 carbides at moderate temperatures and reinforced granular-shaped M6C carbides at high temperatures. The applied stress always decreases mechanical properties due to its degradation of microstructure induced by elongating the precipitates and defects.

Direct FE2 multiscale modeling of hydrogen-induced cracking in reactor pressure vessels

Leveraging on a recently developed multiscale simulation method, we propose a pioneering strategy for the multiscale analysis of hydrogen-induced cracking in reactor pressure vessels that considers micro-voids, their influences on hydrogen diffusion as well as the operating pressure of the vessel. In the finite element analysis, the nodal lattice hydrogen concentration and displacements are exchanged bi-directionally between the macroscale and microscale within a monolithic solution procedure. During the analysis, the voids are shown to cause non-uniform lattice hydrogen diffusion and the trapping effect, resulting in inter-void hydrogen accumulation, is demonstrated. Based on the hydrogen concentration on the void surfaces, the void hydrogen pressure was calculated for the hydrogen-induced cracking analysis. It was found that both internal shearing and necking failure modes exhibited micro-structure dependence. The internal shearing mode caused oriented through-wall propagation of cracks in the vessel pressure while the internal necking mode promoted void nucleation in the reactor pressure vessel. As a result, during the early stages of void evolution, the oriented internal shearing of the dispersed small voids showed a high possibility to induce through-wall failure of the reactor pressure vessel.

The microstructure and precipitated phase dependence of plastic deformation and fracture mechanism in repaired IN718 alloy by directed energy deposition

This work studied microstructural evolution, precipitate behaviors, and micro-hardness distribution along the built direction of directed energy deposited IN718 alloy. In combination with digital image correlation and crystallographic orientation analysis, the plastic deformation and fracture mechanisms of coarse columnar grains were explored in detail. The columnar grains in the deposition zone (DZ) grow along the <001> direction in the crystallography and gradually widen with increasing built height. The misorientation angle per unit length within individual columnar grains first decreases and then slows down to ∼ 0.07 °/μm when the deposition height is ∼ 1.8 mm. The micro-hardness in the DZ is gradually decreased along the built direction, which may be due to the increasing average columnar grain width and primary dendrite arm spacing, as well as reducing the volume fraction of the γ'' + γ' phases. During the uniaxial tensile loading, most plastic deformation always occurs in the DZ irrespective of the lowest hardness in the heat-affected zone (HAZ). The nucleation of microvoids is ascribed to the granular Laves phase debonding from the γ matrix. The number of microvoids gradually decreases with increasing distance from the fracture surface, which may be attributed to the strain-controlled nucleation of microvoids. EBSD results substantiated that the columnar grains near the fracture surface occur to severe lattice rotation, leading to the Kernel misorientation angle distribution in each grain interior increasing to about 1° ∼ 4°.

Microstructure, Mechanical Properties, and Lead–Bismuth Eutectic Corrosion Behaviors of FeCrAlY-Al2O3 Nanoceramic Composite Coatings

Seven FeCrAlY-Al2O3 nanoceramic composite coatings are deposited on F/M steel via plasma spraying and laser remelting. A systematic investigation is conducted to examine the dependence of microstructure, mechanical properties, and lead–bismuth eutectic (LBE) corrosion resistance on the nano-Al2O3 addition and different Cr and Al contents. With the increase in Al content in FeCrAlY, gradual refinement of the coating grains occurs. The addition of nano-Al2O3 promotes the elemental segregation and precipitation of the second phase. The nano-Al2O3 notably enhances the mechanical properties of the coatings that are primarily attributed to second-phase and fine-grain strengthening. After LBE corrosion tests, intergranular corrosion morphology could be observed, where the contents of Cr and Al significantly influence the corrosion behavior of the coatings at varying temperatures.

Effect of different initial tempers on creep aging behavior of 2195 aluminum-lithium alloy

Five kinds of 2195 aluminum-lithium alloys with different initial tempers were obtained through different heat treatment methods. The creep aging test with a constant stress of 140 MPa, at 180 °C, mechanical tensile test at room temperature and the scanning electron microscope (SEM) observation were used to study the dependence of microstructure and properties on the initial tempers of 2195 aluminum-lithium alloy under creep aging forming conditions. The results show that the creep deformation of the alloy with re-solution initial temper is the largest, followed by the solid solution, over-aging and peak aging tempers, while the aged alloy with the regression temper has the smallest creep deformation. The order of yield and tensile strength from high to low is re-solution &gt; solid solution &gt; peak aging &gt; over-aging &gt; regression treatment. The order of elongation to fraction from large to small is solid solution &gt; re-solution &gt; peak aging &gt; over aging &gt; regression treatment. Finally, the high-strength and ductility mechanism of the creep-aged alloy with the re-solution temper was revealed: uniformly distributed fine strengthening phase (T1 phase) within the grain and narrowed precipitation-free zone at grain boundaries.

Sputtering pressure dependence of microstructure and magnetoresistance properties of non-uniform Co–ZnO nanocomposite film

Co-ZnO metal–semiconductor nanocomposite films have become the focus of attention in recent years since their magnetoresistance (MR) effect at room temperature (RT). In this study, non-uniform Co-ZnO nanocomposite films were prepared by magnetron co-sputtering method. With sputtering pressure increasing, the formation of ferromagnetic Co clusters is suppressed effectively, and the metallic-state superparamagnetic Co particles are dispersed, which form the tunneling transport paths in the Co-ZnO films at high Co content. As the sputtering pressure increases from 0.3 Pa to 1.2 Pa, the RT -MR value of the films increases from 0.41 % to 11.85 %, and the saturation magnetization of the films rises from 6.3 kGs to 7.3 kGs and then decreases to 6.7 kGs. It is noteworthy that the low-field MR field sensitivity at 1000 Oe is enhanced by about 10 times from 0.5 Pa to 1.2 Pa. This provides a reference for the application of low-magnetic field detectors.

Initial microstructure and temperature dependence of irradiation defects evolution in tungsten

Using the object kinetic Monte Carlo (OKMC) method and the sink strength model, we systematically investigated the influence of the initial microstructure and temperature on the aggregation, migration, removal, and resulting size distribution of defects emerging in tungsten (W) under neutron irradiation. It is found that the probability of defect absorption at grain boundaries is generally higher than that at dislocations. This suggests that the grain size (2 ∼ 20 μm) has a stronger effect on the evolution of irradiation defects compared to dislocation density (1010 m−2 ∼ 1013 m−2). As the grain size increases, the number of residual defects decreases but the size distribution of vacancies is basically unchanged. Besides initial microstructure, the evolution of radiation damage also depends on the irradiation temperature. The increase in temperature induces an initial increase in the number density of voids, and then followed by subsequent decreases, corresponding to the peak density at 800–1000 K. Furthermore, the defect evolution in irradiated W with different initial microstructures and temperatures is simulated, and the calculated results are compared with recent experiments. These results help us to understand the role of the initial microstructure of the material in the evolution of the irradiation defects.

Dependence of microstructure and properties in additive manufactured 18Ni300 on heat treatment and surface enhancement

Selective laser melting (SLM) known as a rapid manufacturing technology can fabricate complex and dense metallic components of 18Ni300 with excellent properties. The performance of 18Ni300 can be improved by intermetallics using heat treatment, not including anti-corrosion property. In this study, the effects of heat and coating treatments on microstructure and properties of 18Ni300 fabricated by SLM were investigated. The characterization results indicated that grain coarsening, dislocation reduction, and texture strengthening occurred after the optimal heat treatment. The sequential processing of 820 °C for 2 h and 480 °C for 3 h can maximize the microhardness (increased by 74 %) and ultimate tensile strength (increased by 79 %), accompanying cost of Charpy impact (reduced by 43 %) and elongation (decreased by 32 %). However, excessively high or low aging temperature and time can lead to insufficient performance improvement because of austenite reversal. In addition, the great interface bonding is observed after the laser cladding coating treatment, and the wear resistance maintains well while improving the anti-corrosion property significantly with low quality loss.

Sputter-grown two-dimensional α-MoO3 thin films: Microstructure dependence on growth conditions

Van der Waals epitaxy is an emerging technology for transferring freestanding films grown at high temperatures onto arbitrary substrates using two-dimensional epitaxial layers. This study investigates the microstructure and growth of α-MoO3 thin films prepared via sputtering. Under a narrow deposition temperature range, epitaxial α-MoO3 thin films were successfully grown on SrTiO3 substrates. The films were characterized by a flat surface morphology, corresponding to (0k0) planes, without undergoing reaction with the substrates. To examine the growth behavior and surface morphological variation of the α-MoO3 thin films under various process parameters, we modified the Ar:O2 ratio, working pressure, sputtering power, and crystal structure of the substrates. Transmittance electron microscopy confirmed the epitaxial growth of the α-MoO3 thin films on (001)-oriented SrTiO3 substrates with a two-dimensional layer structure. Finally, we demonstrate the morphological evolution of the α-MoO3 thin films etched in heated water as a function of soaking time. The etching results suggest that the α-MoO3 thin films are promising sacrificial layers for the transfer of large-scale epitaxial thin films onto flexible substrates. External control of the strain states of transferred freestanding thin films by bending or stretching provides new perspectives for the design of flexible or wearable electronic devices.

Dependence of Microstructure of Thermally Evaporated CuI Films on the Flow Rate of Argon Gas

Dependence of Microstructure of Thermally Evaporated CuI Films on the Flow Rate of Argon Gas

Effects of Oxygen Pressure on the Microstructures and Nanomechanical Properties of Samarium-Doped BiFeO3 Thin Films.

In this study, samarium (Sm-10at%)-doped BiFeO3 (SmBFO) thin films were grown on platinum-coated glass substrates using pulsed laser deposition (PLD) to unveil the correlation between the microstructures and nanomechanical properties of the films. The PLD-derived SmBFO thin films were prepared under various oxygen partial pressures (PO2) of 10, 30, and 50 mTorr at a substrate temperature of 600 °C. The scanning electron microscopy analyses revealed a surface morphology consisting of densely packed grains, although the size distribution varied with the PO2. X-ray diffraction results indicate that all SmBFO thin films are textured and preferentially oriented along the (110) crystallographic orientation. The crystallite sizes of the obtained SmBFO thin films calculated from the Scherrer and (Williamson-Hall) equations increased from 20 (33) nm to 25 (52) nm with increasing PO2. In addition, the nanomechanical properties (the hardness and Young's modulus) of the SmBFO thin films were measured by using nanoindentation. The relationship between the hardness and crystalline size of SmBFO thin films appears to closely follow the Hall-Petch equation. In addition, the PO2 dependence of the film microstructure, the crystallite size, the hardness, and Young's modulus of SmBFO thin films are discussed.

Control of grain density by varying lattice mismatch in FePt-C film for heat assisted magnetic recording

Controlling the number density of grains in magnetic recording media is critical for improving the areal density of the recording. Herein, we report the dependence of grain density and microstructure of FePt-based granular films for heat-assisted magnetic recording media on the lattice mismatch between the FePt films and substrates SrTiO3, MgAl2O4, MgO and TiO2. The grain density and grain size of the FePt films increased and decreased, respectively, with the increasing lattice mismatch between the films and substrates. The optimum lattice mismatch for the FePt-based granular films was found to be 8%, which corresponds to the MgO substrate. FePt films grown on TiO2 substrate, which had the largest lattice mismatch of 16%, showed poor morphology and low grain density. The results imply that an underlayer with which a film develops a suitable mismatch plays a key role in controlling the microstructure and magnetic properties of the film.