Search Results (266)

Difficult, extreme operating conditions of parabolic antennas under precipitation and sub-zero temperatures require the creation of effective heating systems. The purpose of the research is to develop a multilayer coating containing two metal-ceramic layers, epoxy composite layers, carbon fabric, and an outer layer of basalt fabric, which allows for effective heating of the antenna, and to study the properties of this coating. The multilayer coating was formed on an aluminum base that was subjected to abrasive jet processing. The first and second metal-ceramic layers, Al₂O₃ + 5% Al, which were applied by high-speed multi-chamber cumulative detonation spraying (CDS), respectively, provide maximum adhesion strength to the aluminum base and high adhesion strength to the third layer of the epoxy composite containing Al₂O₃. On this not-yet-polymerized layer of epoxy composite containing Al₂O₃, a layer of carbon fabric (impregnated with epoxy resin) was formed, which serves as a resistive heating element. On top of this carbon fabric, a layer of epoxy composite containing Cr₂O₃ and SiO₂ was applied. Next, basalt fabric was applied to this still-not-yet-polymerized layer. Then, the resulting layered coating was compacted and dried. To study this multilayer coating, X-ray analysis, light and raster scanning microscopy, and transmission electron microscopy were used. The thickness of the coating layers and microhardness were measured on transverse microsections. The adhesion strength of the metal-ceramic coating layers to the aluminum base was determined by both bending testing and peeling using the adhesive method. It was established that CDS provides the formation of metal-ceramic layers with a maximum fraction of lamellae and a microhardness of 7900–10,520 MPa. In these metal-ceramic layers, a dispersed subgrain structure, a uniform distribution of nanoparticles, and a gradient-free level of dislocation density are observed. Such a structure prevents the formation of local concentrators of internal stresses, thereby increasing the level of dispersion and substructural strengthening of the metal-ceramic layers’ material. The formation of materials with a nanostructure increases their strength and crack resistance. The effectiveness of using aluminum, chromium, and silicon oxides as nanofillers in epoxy composite layers was demonstrated. The presence of structures near the surface of these nanofillers, which differ from the properties of the epoxy matrix in the coating, was established. Such zones, specifically the outer surface layers (OSL), significantly affect the properties of the epoxy composite. The results of industrial tests showed the high performance of the multilayer coating during antenna heating. Full article

This study systematically investigates the homogenization-induced Laves phase dissolution kinetics and recrystallization mechanisms in laser powder bed fusion (L-PBF) processed IN718 superalloy. The as-built material exhibits a characteristic fine dendritic microstructure with interdendritic Laves phase segregation and high dislocation density, featuring directional sub-grain boundaries aligned with the build direction. Laves phase dissolution demonstrates dual-stage kinetics: initial rapid dissolution (0–15 min) governed by bulk atomic diffusion, followed by interface reaction-controlled deceleration (15–60 min) after 1 h at 1150 °C. Complete dissolution of the Laves phase is achieved after 3.7 h at 1150 °C. Recrystallization initiates preferentially at serrated grain boundaries through boundary bulging mechanisms, driven by localized orientation gradients and stored energy differentials. Grain growth kinetics obey a fourth-power time dependence, confirming Ostwald ripening-controlled boundary migration via grain boundary diffusion. Such a study is expected to be helpful in understanding the microstructural development of L-PBF-built IN718 under heat treatments. Full article

Understanding the limitations of cold-formed aluminum alloys in practice applications is essential, particularly due to the risk of substructural changes and a reduction in strength when exposed to elevated temperatures. In this study, the thermal stability of the ultra-fine-grained (UFG) structure formed by equal channel angular pressing (ECAP) at room temperature and the mechanical properties of the AlSi7MgCu0.5 alloy were investigated. Prior to ECAP, the plasticity of the as-cast alloy was enhanced by a heat treatment consisting of solution annealing, quenching, and artificial aging to achieve an overaged state. Four repetitive passes via ECAP route A resulted in the homogenization of eutectic Si particles within the α-solid solution, the formation of ultra-fine grains and/or subgrains with high dislocation density, and a significant improvement in alloy strength due to strain hardening. The main objective of this work was to assess the microstructural and mechanical stability of the alloy after post-ECAP annealing in the temperature range of 373–573 K. The UFG microstructure was found to be thermally stable up to 523 K, above which notable grain and/or subgrain coarsening occurred as a result of discontinuous recrystallization of the solid solution. Mechanical properties remained stable up to 423 K; above this temperature, a considerable decrease in strength and a simultaneous increase in ductility were observed. Synchrotron radiation X-ray diffraction (XRD) was employed to analyze the phase composition and crystallographic characteristics, while transmission electron microscopy (TEM) was used to investigate substructural evolution. Mechanical properties were evaluated through tensile testing, impact toughness testing, and hardness measurements. Full article

This paper studies the effect of reversible hydrogen alloying of the TC4 alloy on the microstructure, phase composition, and mechanical properties before and after equal-channel angular pressing. It is shown that the introduction of 0.3% hydrogen followed by quenching from a temperature of 850 °C leads to the formation of a thin-plate α″-martensite, which made it possible to implement 6 passes (ε ~ 4.2) of pressing at 600 °C. As a result of the deformation of the TC4-H alloy and subsequent thermal vacuum treatment to remove hydrogen, an ultrafine-grained structure with an average size of the α-phase of 0.15 μm was formed, which led to strengthening of the alloy to 1490 MPa with a relative elongation of about 5% at room temperature. The reasons for a more significant refinement of the grain/subgrain structure and an increase in the tensile strength of the hydrogenated alloy after equal-channel angular pressing in comparison with hydrogen-free TC4 alloy are discussed. Full article

Austenitic stainless steel inevitably undergoes deformation during application, and it is necessary to study the properties of deformed steel. This article investigates the evolution of microstructure, mechanical properties, and corrosion resistance of plastic-deformed 304 steel, the evolution law of structure and properties of steel is revealed. As a result, it was found that with the increase in deformation, the grains of 304 steel were destroyed, and many small subgrains were generated internally, resulting in a significant decrease in grain size. At the same time, the content of martensitic transformation in stainless steel increased significantly. The characteristics of the surface passivation film of stainless steel also change during the deformation process. Meanwhile, with the increase in deformation, the nanohardness and wear resistance of 304 steel gradually increase, but its corrosion resistance gradually decreases. Analysis suggests that microstructural changes such as grain size and phase transformation in stainless steel lead to an improvement in its mechanical properties, while the generation of defects during deformation and changes in surface passivation film characteristics result in a deterioration of its corrosion resistance. This study can provide a reference for the forming and performance optimization of metals and has high theoretical significance and practical value. Full article

In the Direct Energy Deposition (DED) process, the deposited material experiences intricate thermo-mechanical processes. Subsequent thermal cycling can trigger Dynamic Recrystallization (DRX) under suitable conditions, with specific strain and temperature parameters facilitating grain refinement and homogenization. While prior research has examined the impact of thermal cycling in continuous wave (CW) lasers on DRX in 316 L stainless steel deposits, this study delves into the effects of pulsed wave (PW) laser thermal cycling on DRX. Here, the thermo-mechanical response to PW cyclic thermal loading is empirically assessed, and the evolution of microstructure, grain morphology, geometric dislocation density (GND), and misorientation map during PW DED of 316 L stainless steel is scrutinized. Findings reveal that DRX is activated between the 8th and 44th thermal cycles, with temperatures fluctuating in the range of 680 K–750 K–640 K and grains evolving within a 5.6%–6.2%–5.2% strain range. After 90 thermal cycles, the grain microstructure undergoes significant alteration. Throughout the thermal cycling, dynamic recovery (DRV) occurs, marked by sub-grain formation and low-angle grain boundaries (LAGBs). Continuous dynamic recrystallization (CDRX) accompanies discontinuous dynamic recrystallization (DDRX), with LAGBs progressively converting into high-angle grain boundaries (HAGBs). Elevated temperatures and accumulated strain drive dislocation movement and entanglement, augmenting GND. The study also probes the influence of frequency and duty cycle on grain microstructure, finding that low pulse frequency spurs CDRX, high pulse frequency favors DRV, and the duty cycle has minimal impact on grain microstructure under PW cyclic thermal load. Full article

Single-lip deep-hole drilling is a key technology for the precision machining of high-temperature nickel-based alloy pore structures in aero engines. However, the intense thermo-mechanical coupling effects during machining can easily lead to surface integrity deterioration, and the correlation mechanism between microstructure and properties remains unclear. By adjusting the spindle speed and feed rate, a series of orthogonal experiments were carried out to study the integrity characteristics of the machined surface, including surface morphology, roughness, work hardening, and subsurface microstructure. The results reveal gradient structural features along radial depth: a dynamic recrystallized layer (RL) at the surface and a plastically deformed layer (PDL) containing high-density subgrains/distorted grains in the subsurface. With the increase in the spindle speed, the recrystallization phenomenon is intensified, the RL ratio of the machined-affected zone (MAZ) is increased, and the surface roughness is reduced to ~0.5 μm. However, excessive heat input will reduce the nanohardness. Low feed rates (<0.012 mm/rev) effectively suppress pit defects, whereas high feed rates (≥0.014 mm/rev) trigger pit density resurgence through shear instability. Progressive material removal rate (MRR) elevation drives concurrent PDL thickness reduction and RL proportion growth. Optimal medium MRR range (280–380 mm³/min) achieves synergistic RL/PDL optimization, reducing machining-affected zone thickness (MAZ < 35 μm) while maintaining fatigue resistance. These findings establish theoretical foundations for balancing efficiency and precision in aerospace high-temperature component manufacturing. Full article

316LN stainless steel (316LN SS) with a gradient structure was produced by ultrasonic surface rolling processing (USRP). The surface quality of the 316LN SS specimen was improved significantly after the USRP. The experimental results showed that with an increasing number of rolling passes, the thickness of the gradient structure layer increased, and the microhardness decreased in a gradient from the surface to the matrix. The results also indicated that the optimal parameters were as follows: 220 rad/min lathe speed, 0.11 mm rolling space, 0.2 rad/min feed rate, and 5 rolling passes. Under these parameters, the tested surface residual compressive stress (SRCS) value was nearly 32 times higher than that achieved after conventional processing on the surface of 316LN stainless steel. Moreover, the microstructure exhibits an increase in the subgrain boundary density and low-angle grain boundaries (LAGBs, misorientation < 15°) of the steel, providing an easy way to enhance the properties, including the mechanical and corrosion resistance of 316LN stainless steel. Full article

The purpose of this study is to investigate the effects of process parameters on the microstructure and mechanical properties of the Hastelloy X (HX) alloy using a laser powder bed fusion (L-PBF) process. A combined experimental and numerical approach was used to evaluate the influence of the energy density distribution and temperature evolution on the microstructure, defects, and mechanical properties. After the specimens were built on SUS304 substrate by the L-PBF, the microstructure and defects in the specimens were analyzed by SEM and EBSD analysis methods, and then the hardness and the tensile tests were performed. The cooling rate under different laser conditions was obtained by the finite element method (FEM). The results show that a low volume energy density (VED) was applied to the unmelted powder particles, and a high energy density resulted in spherical defects. In addition, the microstructures were found to coarsen with increasing the energy density along with a tendency to strengthen the (001) texture orientation in both x–y and x–z planes. Compared to the parts with the thermal history from numerical results, the low cooling rate with high energy density had larger crystal grains elongated along the building direction, coarser sub-grains, resulting in a reduction in microhardness and yield strength together with an increase in elongation for the L-PBF HX alloy. The presented results provide new insights into the effects of parameters and the cooling rates. It can play an important role in optimizing the L-PBF processing parameters, identifying the cause of defects, and controlling the cooling rates for the crystallographic texture in such a way as to guide the development of better metrics for designing processing parameters with the desired mechanical properties. Full article

A high-pressure torsion (HPT) with a number of revolutions (n) of up to 10 and an advanced method of accumulative HPT (AccHPT), n = 10 with subsequent post-deformation annealing (PDA) at 500 and 600 °C, were applied to a biodegradable Fe-30Mn-5Si (wt.%) alloy. The effect of HPT, AccHPT and AccHPT with PDA on the microstructure, phase composition, microhardness and electrochemical behavior in Hanks’ solution was studied. HPT with n = 1 and 5 resulted in forming a mixed submicrocrystalline (SMCS) and nanocrystalline (NCS)structure, while HPT, n = 10 and AccHPT, n = 10 resulted in a predominant NCS with grain/subgrain sizes of 15–100 nm and 5–40 nm, respectively. PDA after AccHPT resulted in a mixture of SMCS and NCS. HPT, n = 5, n = 10 and AccHPT, n = 10 led to a transition from a two-phase (γ-austenite and ε-martensite) state after reference quenching, and HPT, n = 1 to a single-phase state (stress-induced and deformed ε-martensite), while the AccHPT, n = 10 with PDA results in a two-phase state of γ-austenite and cooling-induced ε-martensite, similarly to reference heat treatment (RHT). The increase in n resulted in the microhardness increasing up to its maximum after AccHPT, followed by a slight decrease after PDA. HPT and AccHPT led the biodegradation rate to decrease as compared to the initial state. PDA after AccHPT at 500 and 600 °C resulted in a two-phase state corresponding to an elevated biodegradation rate without significant material softening. The observed electrochemical behavior features are explained by changes in a combination of the phase state and the overall level of crystal lattice distortion. Full article

Hip joint implants are among the most prevalent types of medical implants utilized for the replacement of damaged joints. The utilization of modern implant materials, such as cobalt–chromium alloys, stainless steel, titanium, and other titanium alloys, is accompanied by challenges, including the toxicity of certain elements (e.g., aluminum, vanadium, nickel) and excessive Young’s modulus, which adversely impact biomechanical compatibility. A mismatch between the stiffness of the implant material and the bone tissue, known as stress shielding, can lead to adverse outcomes such as bone resorption and implant loosening. Recent studies have shifted the focus to β-titanium alloys due to their exceptional biocompatibility, corrosion resistance, and low Young’s modulus, which is close to the Young’s modulus of bone tissue (10–30 GPa). In this study, the microstructure, mechanical properties, and phase stability of the Ti-38Zr-11Nb alloy were investigated. Energy dispersion spectrometry was employed to confirm the homogeneous distribution of Ti, Zr, and Nb in the alloy. A subsequent microstructural analysis revealed the presence of elongated β-grains subsequent to rolling and quenching. Furthermore, grinding contributed to the process of recrystallization and the formation of subgrains. X-ray diffraction analysis confirmed the presence of a stable β-phase under any heat treatment conditions, which can be explained by the use of Nb as a β-stabilizer and Zr as a neutral element with a weak β-stabilizing effect in the presence of other β-stabilizers. Furthermore, the modulus of elasticity, as determined by tensile testing, exhibited a decline from 85 GPa to 81 GPa after annealing. Mechanical tests demonstrated a substantial enhancement in tensile strength (from 529 MPa to 628 MPa) concurrent with a 32% reduction in elongation to fracture of the samples. These alterations are attributed to microstructural transformations, including the formation of subgrains and the rearrangement of dislocations. This study’s findings suggest that the Ti-38Zr-11Nb alloy has potential as a material of choice due to its lower Young’s modulus compared to traditional materials and its stable β-phase, which enhances the implant’s durability and reduces the risk of brittle phases forming over time. This study demonstrates that the corrosion resistance of titanium grade 2 and Ti-38Zr-11Nb is comparable. The material in question exhibited no evidence of cytotoxic activity in the context of mammalian cells. Full article

Cu-based alloys and composites are popular to prepare electroconductive parts. However, their processing can be challenging, especially in case of composites strengthened with oxides. To save the necessary time and costs, numerical simulations can be of help when determining the deformation behaviour of (newly introduced) materials. The study presents a combined method of strengthening of Cu by adding 5 wt.% of La₂O₃ particles and performing shear-based deformation by equal channel angular pressing (ECAP). The effects of the method on the microstructure, mechanical properties, and thermal stability of the composite are examined both numerically and experimentally. The results showed that the La₂O₃ addition caused the maximum imposed strain to be higher for the composite than for commercially pure Cu, which led to the development of subgrains and shear bands within the microstructure, and a consequent increase in microhardness. The numerical predictions revealed that the observed differences could be explained by the differences in the material plastic flow (comparing the composite to commercially pure Cu). The work hardening supported by the addition of La₂O₃ led to a significant increase in stress and punch load during processing, as well as contributed to a slight increase in deformation temperature in the main deformation zone of the ECAP die. Certain inhomogeneity of the parameters of interest across the processed workpiece was observed. Nevertheless, such inhomogeneity is typical for the ECAP process and steps prospectively leading to its elimination are proposed. Full article

In the framework of the geological mapping of sheet “n. 425—Asinara Island” (NW Sardinia, Italy) of the Italian National Geological Mapping Project (CARG Project), three late- to post-collisional Variscan intrusive units are recognized: (i) Castellaccio Unit; (ii) Punta Sabina Unit; and (iii) sheeted dyke complex. Granitoid rocks from these intrusive units intruded into the medium- to high-grade metamorphic micaschist and paragneiss and the migmatitic complex. A range of deformation microstructures from sub-magmatic to low-temperature subsolidus conditions are recognized. The main observed microstructures are represented by chessboard patterns in quartz and by feldspar sub-grain rotation dynamic recrystallization, indicative of deformation at high-temperature conditions (T > 650 °C). Solid-state high-temperature deformations (T > 450 °C) are provided by feldspar bulging, myrmekites, quartz grain boundary migration and sub-grain rotation dynamic recrystallization. Low-temperature sub-solidus microstructures (T < 450 °C) consist of quartz bulging, mica kinks, and feldspar twinning and bending. These features highlight that the three intrusive units recorded tectonic stresses, which affected the granitoids during cooling without developing a strong penetrative meso/microstructural fabric, as observed in other sectors of the Variscan orogen. The complete sequence of deformation microstructures, recorded in all intrusive units, suggests a weak but still ongoing deformation regime during granitoid emplacement in the Variscan orogen of northwestern Sardinia. These observations are similar to the features highlighted in other sectors of the southern Variscan belt and suggest a complex interplay between transpressional-induced exhumation of the middle/deep crust and magma intrusion. Full article

The present study aims to assess the impact of hot isostatic pressing (HIP) treatment on refractory high-entropy alloy (HEA) WTaMoNbV produced by the laser powder bed fusion (LPBF) process. This was carried out by examining the functional properties of this HEA in terms of mechanical and environmental performance. The microstructure of the tested HEA was evaluated using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Mechanical properties were examined via compression tests, while environmental behavior was evaluated by immersion tests and potentiodynamic polarization. The obtained results demonstrate that HIP treatment improved the alloy’s density from 11.27 to 11.38 g/cm³ and increased its ultimate compression strength by 11.5% (from 1094 to 1220 MPa). This modest favorable effect was attributed to the improvement in bulk properties by eliminating a large part of the sub-grain boundaries and reducing the amount of inherent printing defects, mainly in the form of internal cracking. The advantages offered by HIP were also manifested in surface quality improvement from N11 to N10 grades and enhanced environmental performance, reducing pitting density from 34,155 to 9677 pits/cm². Full article

The developed microstructures and their deformation behavior were studied in a high-strength low-alloy steel subjected to tempforming, i.e., tempering followed by large-strain rolling at temperatures of 823 K or 923 K. Tempforming has been recently proposed as an advanced treatment for low-alloy steels in order to substantially increase their impact toughness at low temperatures. However, the mechanical properties, especially the fatigue behavior, of tempformed steels have not been studied in sufficient detail. The present study, therefore, is focused on the strengthening mechanisms of the tempformed steel, placing particular emphasis on the low-cycle fatigue behavior. Tempforming resulted in a lamellar-type microstructure with a high dislocation density and dispersed Cr₂₃C₆ carbide particles. The size of the latter particles increased from 25 nm to 40 nm with an increase in tempforming temperature. The transverse grain size and dislocation density comprised 550 nm and 2.6 × 10¹⁵ m⁻² after tempforming at 823 K or 865 nm and 1.8 × 10¹⁵ m⁻² after processing at 923 K, respectively. Tempforming led to significant strengthening, which was attributed to high-density dislocations arranged in low-angle subboundaries. The yield strength of 1140 MPa or 810 MPa was observed for the steel samples tempformed at 823 K or 923 K, respectively. The low-cycle fatigue behavior depended on the plastic strain amplitude, which, in turn, was controlled by the previous strengthening under tempforming conditions besides the total strain amplitude. An increase in the plastic strain amplitude promoted fatigue softening that was caused by a decrease in the dislocation density as a result of subgrain coalescence. Full article