Search Results (3,026)

The research presented in this paper is part of a larger project concerning high-manganese alloys with different chemical compositions (mainly in manganese content from 21 to 31 wt.%). The presented examination results concern the analysis of the microstructure and textures in high-manganese X85MnAl29-9 steel, an age-hardenable steel, during aging at 550 °C for various times. X85MnAl29-9 steel was first hot rolled and subsequently cold rolled up to a 30% reduction. The samples were aged after deformation at 550 °C for various times in an argon atmosphere and cooled in air. The studies include X-ray phase analysis, texture measurement and observation of the microstructure by light microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), as well as microhardness measurement. Research using scanning and transmission electron microscopy identified carbides in the analyzed samples. The results indicate that, when aging takes place, precipitation of κ′-carbide in an austenitic matrix and carbide κ at grain boundaries occurs. The appearance of satellites on diffraction patterns suggests that (Fe, Mn)₃AlC nano-carbides are formed within the austenite matrix by a spinodal decomposition mechanism after the alloy is subjected to long-term aging, which is a key element for structure analysis in the design of safety systems. The use of shorter aging times (up to 24 h) leads to an increase in hardness caused by the precipitation of small κ′-carbide particles in the matrix. However, long aging times (100 h) lead to an increase in the precipitation of the carbide phase (κ and κ′), i.e., the steel becomes overage, which results in a decrease in hardness. Full article

Welded cable composed of nickel–chromium (Ni-Cr) alloy and copper is a crucial component in the resistance heating technology used for heavy oil production. Tungsten inert gas (TIG) welding was employed to join the copper and Ni-Cr alloy using copper filler wire, and the stability of the welded joint was analyzed under high-temperature service conditions. We examined the changes in the microstructure and properties of the welded joint after postweld heat treatment (PWHT) at 600 °C for 3, 6, and 12 days. The results showed that the welded joint was appropriately formed, with fractures occurring in the copper substrate. The average tensile strength of the welded joint was 240 MPa. The copper and nickel dissolved into each other, forming a Cu_0.81Ni_0.19 strengthening phase. A columnar crystal diffusion layer formed at the interface between the Ni-Cr alloy and the fusion zone after welding. Grain boundary migration promoted the continuous growth in the columnar crystals as the PWHT duration increased, eliminating the microdefects and inhomogeneities caused by welding. The microhardness progressively decreased from the Ni-Cr alloy side to the copper side. However, the nanoindentation results at the Ni-Cr fusion line initially decreased and then increased with increasing PWHT duration, which contrasted the overall hardness trend observed across the joint after PWHT. Full article

This study aimed to compare the flexural strength, surface roughness, and microhardness of a resin for three-dimensional (3D) printing and a conventional composite resin and to evaluate whether the printing orientation influences these properties. To evaluate the flexural resistance, test specimens were produced and divided into four groups: three groups of resins for 3D printing with inclinations of 0°, 45°, and 90° and one group of conventional composite resin. Forty discs were produced and subjected to a sandpaper-polishing sequence, and the surface roughness was measured using a roughness meter. The Vickers microhardness (HV) test was performed at three different points, and the average was obtained. The results were subjected to ANOVA statistical analysis and Tukey’s test. There were statistical differences in the flexural strength and microhardness between the conventional resin and the resin used for 3D printing. No statistical difference in surface roughness was observed. The resin for 3D printing exhibited lower flexural strength and microhardness than conventional composite resins. We concluded that the resin for 3D printing had lower flexural strength and HV than the conventional composite resin but similar surface roughness. The printing orientation did not affect the flexural strength, whereas the hardness increased as the printing angle increased. Full article

This study examines the effect of gallium doping on the phase transformation, transmission, and hardness of commercial multispectral-grade ZnS specimens exposed to Ga₂S₃ vapor. Using secondary ion mass spectrometry, we show that Ga diffusion extends into the subsurface down to several tens of microns. X-ray diffraction patterns reveal minimal to no precipitation of wurtzite, resulting in limited infrared transmission loss after treatment. We report a monotonic increase in Vickers surface microhardness with increasing Ga concentration, reaching values more than double those of untreated windows. Future work will focus on optimizing this process and evaluating its effectiveness in enhancing the durability of ZnS windows under harsh environmental conditions. Full article

In recent years, metal chip powders obtained from solid-state processes have shown great potential as a sustainable raw material for powder technologies. The material and fragmentation process of the chips has a significant role in the final characteristics of the powder particles, such as size and particle size distribution, shape, surface, and structure, which are essential parameters to consider when converting chips to powder for applications. However, tool steel chips as a powder raw material have not yet been significantly studied. In this study, the steel chips were from machining AISI H13 steel and the milling process used a ball mill, and the challenge was to obtain powder particle sizes of around 20 µm with suitable properties from the application of envisaged material extrusion (MEX). A comparison study with the commercial raw material for MEX, such as powder metal filament extrusion, was performed. This study highlights the behaviors of chip powders during all steps of MEX, namely, feedstock and filament production, 3D object shaping, thermal de-binding, and sintering. A comparison of the mixture based on powder from chips and commercial powders for MEX was performed after evaluating the mixing torque of the powder and the system of binders and additives suitable for the rheological characteristics required for an extrusion mixture, and optimizing the binder removal and the sintering conditions. The 3D objects resulting from chip powders had a refined microstructure, showing an increase of 15% in the microhardness when compared with the those resulting from commercial powders. Full article

An investigation was conducted on electron beam-welded and additively manufactured joints on a thick-walled titanium alloy utilizing in situ laser beam deposition and electron beam welding techniques. The surface morphology, microstructural characteristics, and mechanical properties of both joint types were comprehensively analyzed using stereomicroscopy, scanning electron microscopy (SEM), microhardness and tensile strength testing, and electron backscatter diffraction (EBSD) techniques. The electron-beam-welded joint exhibited distinct fusion and heat-affected zones, whereas the laser-beam-deposited joint exhibited a smoother surface that was free from excess spatter. Both joints featured a sharp microstructural boundary with a pronounced hardness gradient across the interface, lacking a gradual transition area. During tensile testing, both joint types demonstrated a mixed brittle-ductile fracture mode; however, the electron beam-welded joints surpassed the laser-beam-deposited joints in terms of tensile strength, achieving over 1183 MPa with an elongation of more than 7.3%, compared to 1123 MPa and 5.9% elongation, respectively. Full article

The utilization of 20CrNiMo/Incoloy 825 composite materials as high-pressure pipe manifold steel can not only improve the strength and hardness of the steel, but also improve its corrosion resistance. However, research on the heat treatment of 20CrNiMo/Incoloy 825 composite materials is still scarce. Thus, the aim of this study was to investigate the influence of solid solution treatment on the microstructure and properties of 20CrNiMo/Incoloy 825 composite materials. Firstly, the composite materials were subjected to solid solution treatment at temperatures ranging from 850 to 1100 °C with varied holding times of 1 h, 4 h, and 6 h. Microstructural analysis revealed that the solid solution treatment temperature had a more pronounced effect than the treatment time on the interface decarburization layer, carburization layer, and grain size. It was observed that the carburized layer thickness decreased while the decarburized layer thickness increased with an increase in the solid solution treatment temperature, oil cooling was found to enhance the hardness of the base layer of the composite materials, and the size of the original austenite grains of 20CrNiMo steel and Incoloy 825 increased with an increase in the solid solution treatment temperature. Secondly, the tensile properties, microhardness, and fracture morphology were evaluated after the composite materials underwent solid solution treatment at temperatures between 950 °C and 1100 °C for 1 h. The results indicated that increasing the solution temperature initially led to an increase in tensile strength and elongation after fracture, followed by a decrease; furthermore, the hardness of Incoloy 825 exhibited a declining trend, while the hardness of 20CrNiMo first decreased then increased. Thirdly, the shear properties and interfacial element diffusion of the composite materials were analyzed following solid solution treatment in a temperature range of 950 °C to 1100 °C for 1 h. The findings demonstrated that higher solid solution treatment temperatures induced full diffusion of Cr, Ni, and Fe atoms at the interface and softened the matrix, leading to an increase in the thickness of the diffusion layer and toughening of the composite interface. Therefore, the shear strength increased with an increase in the solid solution treatment temperature. Finally, the optimal solid solution treatment process for 20CrNiMo/Incoloy 825 composite materials was determined to be 1050 °C/1 h oil cooling, following which the composite materials had good comprehensive mechanical properties. Full article

Objectives: Hybrid implants commonly exhibit decreased corrosion resistance and fatigue due to differences in compressive residual stresses between the smooth and rough surfaces. The main objective of this study was to investigate the influence of an annealing heat treatment to reduce the residual stresses in hybrid implants. Methodology: Commercially pure titanium (CpTi) bars were heat-treated at 800 °C and different annealing times. Optical microscopy was used to analyze the resulting grain growth kinetics. Diffractometry was used to measure residual stress after heat treatment, corrosion resistance by open circuit potential (E_OCP), corrosion potentials (E_CORR), and corrosion currents (I_CORR) of heat-treated samples, as well as fatigue behavior by creep testing. The von Mises distribution and the resulting microstrains in heat-treated hybrid implants and in cortical and trabecular bone were assessed by finite element analysis. The results of treated hybrid implants were compared to those of untreated hybrid implants and hybrid implants with a rough surface (shot-blasted). Results: The proposed heat treatment (800 °C for 30 min, followed by quenching in water at 20 °C) could successfully homogenize the residual stress difference between the two surfaces of the hybrid implant (−20.2 MPa). It provides better fatigue behavior and corrosion resistance (p ˂ 0.05, ANOVA). Stress distribution was significantly improved in the trabecular bone. Heat-treated hybrid implants performed worse than implants with a rough surface. Clinical significance: Annealing heat treatment can be used to improve the mechanical properties and corrosion resistance of hybrid surface implants by homogenizing residual stresses. Full article

(1) Background: This study investigates the effects of curing light intensity, exposure time, and distance on the Vickers microhardness (VMH), hardness bottom-to-top ratio (HR), and temperature rise (TR) of conventional dental resin-based composite (RBC). (2) Materials and Methods: Specimens of one conventional RBC (Tetric EvoCeram, Ivoclar Vivadent) were cured with 12 different curing protocols (CPs), created with three different light intensities (Quartz Tungsten Halogen 300 mW/cm², LED 650 mW/cm², LED 1100 mW/cm²), two exposure times (20 and 40 s), and two distances of curing tip (0 and 8 mm). The VMH of top (VMH-T) and bottom (VMH-B) surfaces was measured. The hardness bottom-to-top ratio (HR) was calculated from VMH-B and VMH-T. The HR below 80% was rated as inadequate polymerization. The TR at the depth of 2 mm within the RBC was measured using a K-type thermocouple. Data were analyzed using Levene’s test and the multivariate analysis of variance (MANOVA). The level of significance was set at p < 0.05. (3) Results: Exposure time and distance significantly influenced VMH-B and HR. Increased distance significantly reduced VMH-B, HR, and TR. CPs 300 mW/cm²/8 mm/20 s and 650 mW/cm²/8 mm/20 s produced inadequate polymerization (HR < 80%). Prolonged exposure time produced higher values of VMH-B and HR. The TR was significantly influenced by light intensity and distance. (4) Conclusions: Suboptimal light intensity (<800 mW/cm²) can produce inadequate polymerization at the lower side of the composite layer when used from a distance. Prolonged irradiation can improve the polymerization to a certain extent. Clinicians are advised to monitor the intensity of the LCUs in order to optimize the photopolymerization process. Caution is required when polymerizing with high-intensity curing light in direct contact with the RBC with longer exposure times than recommended. Full article

The positive effect of plasma electrolytic treatment on CrWMn tool steel to increase the wear resistance of its surface is shown. The effect of plasma electrolytic nitriding and subsequent polishing on the structure, phase and elemental composition, microhardness of the surface layer, and surface morphology is established. Steel nitriding leads to the formation of a modified surface layer including Fe_2–3N iron nitride and nitrogen martensite, below which hardening martensite is formed, reaching a microhardness value of 1200 HV. Subsequent polishing leads to a decrease in surface roughness by 42–68%. Tribological tests were carried out according to the shaft-bushing scheme. A decrease in the friction coefficient and weight wear of up to 2.6 and 30.1 times, respectively, is shown. The formed structure of the surface layer compensates for the effect of the counter body and determines the destruction of friction bonds by plastic displacement. The wear mechanism has been established and is defined as fatigue wear under dry friction and plastic contact. Full article

In this paper, the butt joint of unequal thickness 410 ferritic stainless steel and RCL540 low-carbon alloy steel sheets are realized by laser welding. The effects of different laser powers on weld formability, mechanical properties, and residual stress in the welding process are investigated. It is observed that with increasing laser power, the heat accumulates at the bottom of the molten pool and weld metal, causing the ratios of upper and lower melt widths to decrease. The tensile test results show that all specimens fractured in the weak zone of the base metal on the stainless steel side at 10 mm from the weld seam. The residual stress distributions of the specimens are calculated using ABAQUS 2022 software and compared with the measurements of the blind-hole method. It is found that the stainless steel side produces tensile stresses, with the power increase offset by compressive stresses in the base metal. When the laser power is 1200 W, the welded joint has the best weld formability and mechanical properties and the least residual stress. The upper and lower melt width ratio is 1.17, the maximum microhardness of the weld metal is 374.7 HV, the maximum test force and tensile strength are 5617.5 N and 468.12 MPa, respectively, and the minimum values of the transverse and longitudinal stresses are −45.8 MPa and −106.4 MPa, respectively. Full article

In order to gain insight into the unique characteristics of manufacturing large-scale products with intricate geometries, experimental nozzle-shaped samples were created using wire-feed electron beam additive technology. Bimetal samples were fabricated from nickel-based alloy and copper. Two distinct approaches were employed, utilizing varying substrate thicknesses and differing fabrication parameters. The two approaches were the subject of analysis and comparison through the examination of the surface morphology of the samples using optical microscopy, scanning electron microscopy, and X-ray diffraction analysis. It has been demonstrated that the variation in heat flux distributions resulting from varying the substrate thicknesses gives rise to the development of disparate angles of grain boundary orientation relative to the substrate. Furthermore, it is demonstrated that suboptimal choice of the fabrication parameters results in large disparities in the crystallization times, both at the level of sample as a whole and within the same material volume. For example, for the sample manufacturing by Mode I, the macrostructure of the layers is distinguished by the presence of non-uniformity in their geometric dimensions and the presence of unmelted wire fragments. In order to characterize the experimental nozzle-shaped samples, microhardness was measured, uniaxial tensile tests were performed, and thermal diffusivity was determined. The microhardness profiles and the mechanical properties exhibit a higher degree of strength than those observed in pure copper samples and a lower degree of strength than those observed in Inconel 625 samples obtained through the same methodology. The thermal diffusivity values of the samples are sufficiently close to one another and align with the properties of the corresponding materials in their state after casting or rolling. The data discussed above indicate that Mode II yields the optimal mechanical properties of the sample due to the high cooling rate, which influences the structural and phase state of the resulting products. It was thus concluded that the experimental samples grown by Mode II on a thinner substrate exhibited the best formability. Full article

The paper deals with the evaluation of the quality of Cu-Al-AlMg3 structural transition joints (STJ) made by explosion welding proposed for the renovation of galvanizer hangers. The three-layer joint consisted of electrolytic copper with a thickness of 25 mm, 2 mm of aluminium represented by the AW1050 alloy, and 25 mm of the EN AW 575 aluminium alloy. Light microscopy analysis confirmed the wavy pattern of both interfaces of the welded joint and significant plastic deformation in close proximity to the waves. Microhardness measurement revealed a partial strain hardening of the AW5754 copper-aluminium alloy near the interface and a significant increase in microhardness in the vortex zone of waves, reaching a value of up to 863 HV 0.025. Microcracks were also observed in these places. The intermetallic phase Al₂Cu was identified in the vortex zones by XRD analysis. As a continuous layer of intermetallic phase was not observed in the interface of the welded joint, it is possible to consider the used welding parameters as appropriate. A semi-quantitative EDX analysis revealed a diversity of chemical composition in the vortex zones, which does not correspond to the phase composition based on the equilibrium binary Al-Cu diagram due to non-equilibrium conditions in the formation of the welded joint interface. The bond strength of three-layer welded joint evaluated by the strength test ranged from 151 to 171 MPa, which represented approximately a two-fold increase in comparison to the ultimate tensile strength of alloy AW1050, while the failure occurred in all samples at the AW1050-AW5754 alloy interface. Full article

Hard bone disease is a clinical problem affecting more than 20 million people annually worldwide, with significant health, social, and economic consequences. For successful integration of any implant, the key aspects are bone regeneration, osseointegration at the bone–implant interface, and the mitigation of inflammation. The purpose of this research work is to demonstrate an innovative material system and method of biomaterial preparation for regenerative medicine. A number of studies were carried out for both hydroxyapatite powder and composites. Wet-precipitated synthesized hydroxyapatite was compared to commercial products through accurate physicochemical studies that confirmed the high purity of the obtained calcium phosphate without any impurities. Ti/HAp composites before and after sintering were compared by XRF, XRD, SEM, EDS, PSA, and roughness measurements, and the Vickers microhardness was analyzed. The fabrication of the biomaterial was based on a bottom-up approach, which involved fabricating HAp particles with specific morphologies using powder metallurgy (PM) to sinter Ti composites. The resulting gradient structures consisting of two compositions (5%HAp%5CMC and 10%HAp10%CMC) mimic the structure of bone tissue. The created pores of 10–100 µm in size will allow bone cells to penetrate the implant and regenerate bone. In turn, the introduction of hydroxyapatite into the material reduces the microhardness of the composite and introduces properties such as bioactivity. The developed composite material contains a combination of Ti alloy and hydroxyapatite (HAp), creating an excellent biomaterial that promotes bone growth and eliminates the problem of implant loosening by integrating it into the bone. This material requires further research, especially biological research. However, it shows promising potential for further experiments. Full article

Traditionally, structural wire is characterized by a homogeneous microstructure, where the average grain size in different parts of the wire is uniform. According to the classical Hall–Petch relationship, a homogeneous polycrystalline metal can be strengthened by decreasing the average grain size since an increase in the volume fraction of grain boundaries will further impede the motion of dislocations. However, a decrease in the grain size inevitably leads to a decrease in the ductility and deformability of the material due to limited dislocation mobility. Putting a gradient microstructure into the wire has promising potential for overcoming the compromise between strength and ductility. This is proposed a new combined technology in this paper in order to obtain a gradient microstructure. This technology consists of deforming the wire in a rotating equal-channel step die and subsequent traditional drawing. Deformation of copper wire with a diameter of 6.5 mm to a diameter of 5.0 mm was carried out in three passes at room temperature. As a result of such processing, a gradient microstructure with a surface nanostructured layer (grain size ~400 nm) with a gradual increase in grain size towards the center of the wire was obtained. As a result, the microhardness in the surface zone was 1150 MPa, 770 Mpa in the neutral zone, and 685 MPa in the central zone of the wire. Such a symmetrical spread of microhardness, observed over the entire cross-section of the rod, is a direct confirmation of the presence of a gradient microstructure in deformed materials. The strength characteristics of the wire were doubled: the tensile strength increased from 335 MPa to 675 MPa, and the yield strength from 230 MPa to 445 MPa. At the same time, the relative elongation decreased from 20% to 16%, and the relative contraction from 28% to 23%. Despite the fact that the ductility of copper is decreased after cyclic deformation, its values remain at a fairly high level. The validity of all results is confirmed by numerous experiments using a complex of traditional and modern research methods, which include optical, scanning, and transmission microscopy; determination of mechanical properties under tension; and measurement of hardness and electrical resistance. These methods allow reliable interpretation of the fine microstructure of the wire and provide information on its strength, plastic, and electrical properties. Full article