Microstructural State Research Articles

Systematic investigation of performance and productivity in laser powder bed fusion of Ti6Al4V up to 300 µm layer thickness

Within the realm of metal additive manufacturing, laser powder bed fusion (PBF-LB) has maintained a dominant role by offering exceptional geometric freedom, fine feature resolution and fine microstructure features. However, low productivity still presents a bottleneck in the adaptation of PBF-LB in most industrial contexts. In recent literature, build-up rates have shown to improve notably when thicker powder layers are employed. However, systematic analyses linking processing parameters, productivity, microstructural state and mechanical properties are lacking. This study aims to fill this gap for Ti6Al4V alloy with powder layer thicknesses in the range of 60 µm to 300 µm, specifically using system-agnostic process parameters applicable to the majority of currently available commercial AM systems. The results revealed that Youngs modulus (∼110 GPa) and yield strength (∼1.1 GPa) remain comparable to ‘conventional’ PBF-LB Ti6Al4V throughout the investigated range of layer thickness. At the same time elongation to failure decreases from 11.4 ± 2.7% at 60 µm to 8.4 ± 1.1% at 180 µm and finally to 2.0 ± 0.3% at 300 µm, which was microscopically correlated with increased occurrence of lack-of-fusion porosity in layers exceeding 180um. It was also demonstrated that the changes in the parent β phase texture arising from process changes could have contributed to decreased ductility at thicker layers. Ultimately, while productivity increases with layer thickness up to 8.76 mm3/s at 300 µm, the achievable build rate appears to plateau around 300 µm layer height and require further expansion of the laser power characteristics to enable additional gains without compromising mechanical performance.

Thermomechanical Pathways for Accurate Microstructural Control of Ti–7Ag Alloy: Towards a New Generation of Antibacterial Materials for Medical Applications

This study delved into exploring microstructural states in a Ti–7Ag alloy to achieve targeted functional and structural properties. Specifically, the focus was on attaining a homogeneously precipitated state and a solid solution, known for their potential to combine functional traits like corrosion resistance and antibacterial activity with structural properties such as mechanical strength. However, obtaining these optimized microstructures presents challenges due to kinetic considerations. A key finding of this study was the crucial role of a pre-deformation stage, prior to heat treatment, to create an even distribution of fine Ti2Ag precipitates. Moreover, we demonstrated that starting from this precipitated state, a controlled dissolution step could yield a single-phase solid solution with similar grain size. Therefore, a tailored set of thermomechanical treatments was developed to achieve both microstructures, and these metallurgical states were fully characterized combining SEM (BSE imaging and EDS analysis), TEM, and XRD. Associated mechanical properties were also assessed by tensile testing. In addition, the process was proven to be robust enough to overcome potential industrial problems, such as slow cooling rates when water-quenching large ingots. Considering the limited existing documentation on microstructural features in Ti–Ag alloys, this work on this model alloy significantly advanced our current understanding of the broader Ti–Ag alloy system by providing new data and showcasing a tailored approach involving thermomechanical treatments.

One-step ultrasound-assisted recovery of yellow-orange-red natural coloring from defatted annatto seeds: A cleaner processing alternative

The interest in natural colorants derived from sustainable processes has prompted research into obtaining bixin from defatted annatto (Bixa orellana L.) seeds. Bixin is a compound that imparts yellow-orange-red coloration, known for its high biodegradability, low toxicity, and wide industrial applicability. Meanwhile, high-intensity ultrasound (HIUS) technology has emerged as a promising method for extracting natural colorants, offering higher yields through shorter processes and minimizing thermal degradation. Although some studies have demonstrated the efficiency of HIUS technology in bixin extraction, research on the effects of acoustic cavitation on the properties of the colorant remains limited. Therefore, this study aimed to investigate the influence of HIUS-specific energy levels (0.02, 0.04, 0.12, and 0.20 kJ/g) on the chemical, physical, and morphological characteristics of annatto extracts containing bixin and geranylgeraniol. Single-step extractions of bixin using ethanol as a solvent were evaluated at various acoustic powers (4.6, 8.5, 14.5, and 20 W) and extraction times (0.5, 1, 3, and 5 min) to determine their impact on the yield of natural colorant extraction. Increasing the acoustic power from 4.6 to 20 W and extending the extraction time from 0.5 to 5 min resulted in higher yields of natural colorant, likely due to the effects of acoustic cavitation and increased heat under more intense conditions. However, elevated levels of mechanical and thermal energy did not affect the chemical properties of the colorant, as indicated by UV–Vis and FTIR spectra. Conversely, higher specific energies yielded colorants with a more intense red hue, consistent with increased bixin content, and altered the microstructure and physical state, as observed in X-ray diffractograms. Nevertheless, these alterations did not impact the solubility of the colorant. Therefore, employing a cleaner extraction procedure aided by one-step ultrasound facilitated the recovery of natural colorants and contributed to the biorefining of annatto seeds, enabling the production of a rich geranylgeraniol colorant through a sustainable approach.

Evaluation of chromium coatings deposited by standard and bipolar high-power impulse magnetron sputtering (HiPIMS & B-HiPIMS) for nuclear power applications

Chromium coatings, as deposited onto Zircaloy-4 through direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS), are evaluated for usage in advanced nuclear fuel applications. While traditional magnetron sputtering has been documented extensively in literature, HiPIMS remains relatively novel and unexplored within this application space, especially when the sputtering source voltage waveform is modified with the addition of a positive “kick pulse”, as in the case of bipolar HiPIMS (B-HiPIMS). Rigorous analysis of the microstructure and residual stress state of these coatings are correlated to electrochemical observations and 84-day, 360 °C autoclave weights gains to predict the performance of the films within a non-irradiated pressurized water reactor (PWR) environment. Under this scrutiny, differences and similarities are revealed between DCMS, HiPIMS, and B-HiPIMS. It is demonstrated that monolithic Cr coatings deposited by HiPIMS and B-HiPIMS outperform those deposited by DCMS, while exhibiting an order of magnitude reduction in autoclave weight gain relative to the Zircaloy-4 nuclear grade material.

Investigation into electrochemical catalytic properties and electronic structure of Mn doped SrCoO3 perovskite catalysts

High activity, long lifetime and low-cost cathode catalyst plays an irreplaceable role in oxygen reduction reactions process. In the present work, SrCoO3 and SrCo0.875Mn0.125O3 perovskite are prepared by sol–gel method and first principles calculation to study the role of Mn doping. The characterizations of phase, microstructure and valence state of elements demonstrate that Mn doping stabilizes the cubic structure of SrCo0.875Mn0.125O3 perovskite and forms a porous structure with large specific surface area. The high-valence and multivalent states of Co and Mn are produced, which provide abundant active sites for oxygen reduction reaction. The charge transfer resistance (1.820 Ω·cm2), Tafel slope (88 mV dec−1), discharge capacity (4.173 mWh/cm2), and positive shift of onset potential and half-wave potentials reveal that the SrCo0.875Mn0.125O3 perovskite is a promising cathode catalyst. Mn doping helps the O p-band center move up relative to the Fermi level, and adsorption energy of O2 and formation energy of oxygen vacancies increase. The improvement of these parameters has a positive effect on predicting the catalytic activity of SrCo0.875Mn0.125O3 perovskite. The possible oxygen reduction reaction mechanism of SrCo0.875Mn0.125O3 perovskite is discussed. Mn doping accelerates the transport process of SrCo0.875Mn0.125O3 perovskite.

A new perspective on Lüders band formation in medium-Mn steels based on Lüders-strain-rate and dislocation evolution

Propagating Lüders bands with pronounced strain localization are often observed in medium-Mn transformation-induced plasticity (TRIP) steels, which adversely limits the application of such alloys in engineering structures. The present work aims to understand this phenomenon from a dislocation-based perspective, with a focus on the specific role of dislocation multiplication. The material studied is a typical dual-phase medium-Mn steel with a ferrite matrix and a second phase of retained austenite. A warm-rolling process was used as a pre-straining approach to adjust the microstructure of the material, such that materials with two different microstructural states can be obtained: as-received material and pre-strained material. They show distinct differences in initial dislocation density. Stress-controlled rather than conventional strain-controlled tensile testing was adopted, which allowed the Lüders band to develop in an unconstrained manner. In this way, the intrinsic Lüders-strain-rate can be obtained. The results show that the Lüders band-related mechanical parameters, including Lüders strain, Lüders-strain-rate and yield stress drop, all depend on the initial microstructure state and the dislocation evolution process during Lüders band formation. In particular, Lüders-strain-rate is a critical microstructure-sensitive factor. It is closely related to the dislocation multiplication in the formation of Lüders band, which can be characterized and quantified using scanning transmission electron microscope and synchrotron X-ray diffraction. Finally, a quantitative relationship between Lüders-strain-rate and dislocation multiplication rate is established, which allows providing a better understanding of the exceptional Lüders band phenomenon in medium-Mn steels.

Microstructure degradation and residual low cycle fatigue life of a serviced turbine blade

AbstractThis paper was attempted to investigate the microstructure degradation and low cycle fatigue (LCF) performance of a serviced K465 Ni‐based superalloy turbine blade. LCF tests were carried out with small‐scale plate specimens sampled from the blades. Relationship between residual LCF life and microstructure state was estimated. The results indicate that the coarsening of γ/γ′ phases was the most significant microstructure degradation mode for the serviced blades. Both the γ matrix width and the γ′ precipitate diameter increased with the increase of service duration, while the γ′ precipitate volume fraction slightly decreased. The most severe microstructure degradation occurred at the leading edge along the chord direction, particularly at 50–70 % airfoil spans. The residual LCF life exhibited an accelerated decrease characteristic as increases of microstructure degradation degree. The coarsened microstructure diminished shear resistance of the superalloy, which resulted in additional accumulated inelastic deformation and a corresponding reduction in LCF life.

Structural and Mechanical Properties of Hot Rolled CuAlBe Non-Spark Alloy Explosion

Explosion protection is of particular importance for safety as explosions also endanger the health of workers due to the uncontrolled effects of flames and pressure, the presence of harmful reaction products and the consumption of oxygen in the ambient air breathed by workers. CuAlBe alloy is proposed as a solution for mechanical actuators such as gears that work in environments with possible explosive atmosphere. Made of CuBe master alloy and pure aluminum in a induction furnace the material present large grains in melted state. After the hot rolling (heated 600s at 900°C) of the ingots small variation of chemical composition was observed based on the oxidation of the material, appearance of small cracks on the edges and a preferential orientation of the grains along the lamination direction. Scanning electron microscopy (SEM) was used to characterize the microstructural states of CuAlBe as laminated and heat treated states.

High-performance electromagnetic wave absorption by two-dimensional mesoporous monolayer Ti3C2Tx MXene

Transition metal carbide MXene, with its unique chemical composition, structure and sizeable particular surface area, is widely applied in wave absorption. However, the high conductivity of MXene resulted in an impedance mismatch that prevented electromagnetic waves from entering the material to achieve dissipation, and thus, tuning the intrinsic properties of pure MXene to obtain excellent electromagnetic wave absorption is still a challenge. Here, we strengthen the absorption of electromagnetic waves by generating titanium vacancies through hydrogen peroxide etching and thus forming micro-sized wrinkles with porous MXene. Porous MXene possesses an excellent microstructure and surface state, abundant porous defects, and moderate electrical conductivity, allowing it to achieve well-matched impedance, dipole polarization, and conduction loss, thus inheriting excellent electromagnetic wave absorption (EWA) properties. Therefore, the porous MXene achieves a strong absorption of − 63.31 dB and an adequate absorption bandwidth (EAB) of 6.88 GHz at a matched thickness of 2.39 mm with a fill ratio of 6 wt%.

Study on bending fretting fatigue behaviour of 15-5PH stainless steel with different fretting regimes

The failure of the aircraft spline shaft was attributed to overstressing, cyclic bending loads, and other complex conditions. This study investigates the bending fretting fatigue behaviours and failure mechanisms of 15–5PH stainless steel. The study analysed the residual stress, microstructure, morphology, and chemical state of the worn surface and the fatigue failure mechanisms. The results showed that fretting wear significantly reduces the bending fatigue life. The surface residual stress transitions from compressive to tensile stress states. The value of residual stress increased, and the oxygen content of the worn surface was higher in the mixed fretting regime. Fatigue fractures occur at a depth of 50–100 µm below the surface in the present experiment.

Effect of microstructure on the corrosion-friction behavior of low-carbon martensitic stainless steel

The effect of microstructure on the corrosion-friction behavior of 11Cr4NiMo steel was investigated for three different microstructure states. Quenched martensite and low-temperature tempered martensite with high density dislocations exhibit severe wear under the dual effects of corrosion and abrasion, and their wear mechanism include three-body wear, adhesive wear, and fatigue wear. While high-temperature tempered microstructure mixed structure of tempered martensite, reversed austenite, and M23C6 carbides exhibits weakened wear. Reversed austenite greatly promotes the generation of a dense and stable passivation film with corrosion product of α-FeOOH, and plays a lubricating role and attenuates three-body wear. Utilizing the passivation film induced by corrosion to improve the wear resistance of materials is of great significance in engineering applications.

The role of process parameters and printing position on meltpool variations in LPBF Hastelloy X: Insights into laser-plume interaction

Meltpool dimensions play a pivotal role in defining the defects and microstructure state of Laser Powder Bed Fusion (LPBF) builds. Therefore, it is crucial to investigate variations in meltpool geometries under different process conditions. In this work, we fabricated single tracks of LPBF Hastelloy X (HX) alloy under 36 printing conditions and examined the corresponding cross-section meltpool dimensions at two locations across the build platform. This investigation demonstrates the impacts of laser power, scan speed, powder layer thickness, and printing locations on resultant meltpool dimensions. As expected, we observed that meltpool dimensions increase as laser power increases or scan speed decreases. It was also concluded that thicker powder layers lead to wider and shallower meltpools due to reduced laser energy penetration into the solid beneath the powder layer. Additionally, the meltpool dimensions show variations dependent on deposition locations due to the different levels of interaction of the laser and its induced vapor plume, resulting in shallower and wider meltpools. These findings provide a systematic understanding of meltpool dimension variations across various process conditions for LPBF HX alloy, which ultimately offer insights into the formation of defects and microstructure features.

Performance Degradation of a Double-Perovskite PrBaCo2O5+δ Cathode Operating under a CO2/H2O-Containing Atmosphere.

The electrochemical activity and stability of the PBCO electrode are investigated under the annealing processes in an atmosphere containing CO2/H2O for solid oxide fuel cells (SOFCs). The electrochemical impedance spectrum results unequivocally confirm the significant deterioration in PBCO cathode performance upon annealing under ambient air conditions, particularly when exposed to CO2/H2O atmospheres. Microstructure and surface chemical state analyses reveal the segregation of BaO on the PBCO surface, and the formation of insulating BaCO3 degraded the electrochemical performance. CO2 and H2O exhibit a significant induced effect on the segregation of Ba in PBCO to the surfaces, thereby causing a rapid decline in electrode performance. Additionally, the analysis of volume relaxation reveals that the presence of oxygen in the electrode environment can also influence the deposition process occurring on the surface of the electrode. However, this phenomenon is not observed in N2. This study emphasizes the impact of various gases present in the working atmosphere on surface-separated BaO, which consequently plays a pivotal role in the activity and long-term stability of PBCO electrodes.

Effect of CaCl2 on the micromorphology of a self-thickening agent (TZXJ) for acidizing diversion

The effect of CaCl2 on the micromorphology of a self-thickening agent (TZXJ) was investigated. This study involved analyzing the compositional changes in acid solutions during acid–rock reactions. It combined dynamic light scattering and viscosity testing to confirm that the presence of CaCl2 enhances the aggregation strength of the TZXJ network structure in acid solutions. This enhancement is macroscopically evident as an increase in viscosity. Incorporating 10 % CaCl2 as a promoter into a fresh acid solution, the hydrodynamic radius (Rh) distribution of TZXJ in varying reaction stages was analyzed using dynamic light scattering experiments. The results indicated that the promoter CaCl2 further strengthens the network association of the TZXJ acid solution, thereby improving its thickening capability. Investigating the viscosity of TZXJ aqueous solutions with varying concentrations of CaCl2 revealed that TZXJ exhibits notable salt-thickening effects and can withstand saturated CaCl2 solutions. The microstructural aggregation state and morphology of TZXJ in aqueous solutions were characterized at different CaCl2 concentrations. Dynamic light scattering results demonstrated an increase in the Rh of TZXJ solutions with CaCl2 concentrations. In particular, the mean Rh of a 0.8 % TZXJ solution increased from 150.8 nm to 3078.93 nm. Ultraviolet spectral analysis confirmed that the absorption intensity of the TZXJ solutions increased with CaCl2 concentration, indicating a strengthened network aggregate structure in the TZXJ solutions. Microscopic observations using environmental scanning electron microscopy and transmission electron microscopy revealed that under the influence of calcium chloride, the microstructure of TZXJ transitions from a non-associated, linear carbon chain skeleton to a dense, aggregated network structure. The findings of this study offer theoretical insights for researching polymers resistant to extreme concentrations of CaCl2.

Microstructure and high-temperature tribological properties of Ti–6Al–4V alloy treated by laser shock peening

The high-temperature wear resistance plays an important role for Ti–6Al–4V alloy components working in extreme environments, especially vital for avoiding unexpected failure. However, the reasonable method of surface modification should meet the requirement of improving in wear resistance and less decreasing in mechanical properties simultaneously, which brings a great challenge. In the present research, the laser shock peening (LSP) technique was applied to optimize the superficial layer of Ti–6Al–4V alloy by different processing. The microstructure, elastic modulus, nano-hardness and high-temperature tribology properties of the LSP processed Ti–6Al–4V were investigated to reveal the improving effect. The results demonstrate the LSP processing transforms the dual-size grain structure to relative homogeneous grain structure and forms the gradient nano-structure in superficial layer. With the increasing of LSP processing numbers, the density of geometrically necessary dislocation (GND) decreases obviously, but the density of statistically stored dislocation (SSD) rises significantly, which promotes the increase of total dislocation density compared with the as-received (AR) alloy. Due to the crystal evolution, the Ti–6Al–4V alloy with three-times LSP processing has the lowest wear rate which is less than half of the as-received state. The observations on worn surface and adjacent cross-sectional microstructure reveal the severe scratching and many inner microcracks in the AR sample but the slight scraping and few inner microcracks in the three-times LSP processed sample. Considering the elevated nano-hardness and elastic modulus, the improved tribological properties should be mainly attributed to the optimized microstructure and dislocation state by LSP processing. The present research provides a more reasonable method to improve the high-temperature wear properties of Ti–6Al–4V alloy.

Hydrogen Embrittlement of Ti-Al6-V4 Alloy Manufactured by Laser Powder Bed Fusion Induced by Electrochemical Charging

The 3D printing of Ti-Al6-V4 alloy is subject to much current investigation, with Laser Beam Powder Bed Fusion (PBF-LB/M) being one of the most applied technologies. Ti-Al6-V4 alloy, despite its great material properties, is susceptible to hydrogen penetration and consequent embrittlement. The level of susceptibility to hydrogen penetration depends on the microstructural state of the alloy. In this work, we compare the effect of electrochemical charging by hydrogen on Ti-Al6-V4 alloy prepared by PBF-LB/M, either in the as-built state or annealed, and conventionally prepared alloy. At the same charging conditions, considerably different hydrogen concentrations were achieved, with the as-built 3D-printed material being the most susceptible. The changes in mechanical properties are discussed in relation to changes in microstructure, studied using microscopy, X-ray, and electron diffraction techniques.

Hydrothermally synthesized MnCo2O4 nanoparticles for advanced energy storage applications

We observed the impact of reaction time on the electrochemical performance of MnCo2O4 nanoparticles, specifically focusing on the overgrowth of nanoparticles over the nanostructure. We characterized the synthesized nanomaterial using XRD, SEM, and XPS techniques to analyze its crystal structure, surface microstructure, and chemical states, respectively. The electrode prepared via a 5-hour hydrothermal reaction exhibited an outstanding areal capacitance of 144 mF/cm2 at a current density of 1A/g. Furthermore, it demonstrated an areal energy density of 4.1 μWh/cm2 at a power density of 0.225 mW/cm2. We assembled an asymmetric supercapacitor (ASC) configuration, MCO-5 h//AC, using MCO-5 h and activated carbon (AC), which showcased exceptional areal capacitance, areal energy density, and power density. These characteristics make it highly suitable for practical applications in energy storage. Overall, our findings highlight MCO-5 h as a promising electrode for energy storage applications.

Dysprosium oxide (Dy2O3) layer effect on the interface possessions of Au/n-GaN Schottky diode as an interlayer and its chemical and microstructural features

The work reveals the design of Au/dysprosium oxide (Dy2O3)/n-GaN metal/insulator/semiconductor (MIS)-type structures with a dysprosium oxide interlayer and investigates its microstructural and chemical states using XRD, TEM and XPS approaches. The outcomes confirm that the Dy2O3 film exists on the n-GaN. The electrical properties of the MIS structure are probed by I–V and C–V procedures. A superior rectifying type with a small leakage current was acquired for the MIS structure rather than the Au/n-GaN Schottky diode (SD). Results showed that the MIS structure has a better barrier height (Φb) (0.91 eV) than the SD (0.82 eV), representing that the Dy2O3 layer modifies the Φb. Using Cheung's, Norde and ΨSP-V plots, the Φb of the SD and MIS structure are derived and the values are nearly similar, representing that the approaches applied here are valid. The predicted NSS of the MIS structure is two orders smaller than the SD, implying that the Dy2O3 interlayer substantially lowers the NSS. The Poole-Frenkel emission is the foremost current transport at a lower bias, though Schottky emission (SE) is ruled as the current transport at a higher bias of the SD. Nevertheless, the SE is prevailing in the current transport in the MIS structure. Consequences endorse that the Dy2O3 layer can be suitable for building of MIS/MOS devices.

Influence of Heat Treatment Parameters on the Microstructure of 17-4 PH Single Tracks Fabricated by Direct Energy Deposition

Post-fabrication heat treatment (PFHT) is one of the most applied strategies for achieving the desired microstructure and mechanical resistance on additive manufactured components because of the non-equilibrium microstructural state of the material in the as-built condition. In particular, during PFHT, 17-4 PH martensitic stainless steel is mainly strengthened by the precipitation of Cu-rich nanometric particles and Nb carbides into the metal matrix. In this work, the influence of specifically designed PFHTs on the microstructural and mechanical properties of 17-4 PH single tracks fabricated via direct energy deposition was studied. Different solubilization and aging times, as well as a direct aging strategy, were considered. Optical microscopy, X-ray diffractometry, and transmission electron microscopy were used to investigate the microstructure evolution induced by the PFHTs. Moreover, Vickers microhardness measurements were performed to evaluate the increase in mechanical strength. In all cases, the heat-treated single tracks showed a mean microhardness higher than that of the depositions in the as-built condition. In the single tracks subjected to solution treatment, followed by aging for about 100 h, the presence of both Cu-rich precipitates and Nb carbides was assessed; conversely, when directly aged from the as-built condition, only Nb carbides were detected. In the latter case, the carbides were finer and closer to each other than those in the single tracks aged after the solution treatment.

Feasibility study of wire arc additive manufactured P91 steel by cold metal transfer deposition

The objective of this study was to analyze and evaluate the feasibility of utilizing Wire Arc Additive Manufacturing (WAAM) technology for the constructing components made from P91 steel, which is widely used material for high-temperature applications. The utilization of the Cold Metal Transfer (CMT) method enables the deposition of thin steel walls by virtue of its low heat input. Samples collected from the deposited wall have been tested in two different microstructural conditions, in the as-built (AB) condition and in a normalized and tempered (NT) condition. The latter condition is the microstructural state commonly employed for producing components used in power plants. This post-deposition heat treatments (PDHT) comprise a normalization process conducted at 1050 °C for 40 min, followed by a tempering step at 760 °C for 2 h. The results of mechanical testing and microstructural characterization were then compared against the established standards for commercial P91 steel. SEM-EDAX, XRD, and EBSD analyses were employed to conduct a comprehensive microstructural examination of the samples. The hardness of the AB samples ranged from 384 to 439 HV, while the NT samples had a hardness range of 205 to 223 HV. In terms of tensile strength, the AB samples demonstrated a range of 1064 to 1266 MPa, whereas the NT samples exhibited a range of 635 to 626 MPa. These results were found to be consistent with the observed strong texture and grain orientations in the {001} and {111} planes, as revealed by the EBSD analysis. The NT components demonstrated significant strength, ductility, hardness, and toughness compared to the specified ASTM standards. Based on the test performance and feasibility criteria, this process has significant potential as an additive manufacturing method suitable for complex boiler components.