Search Results (190)

This article provides a comprehensive overview of recent studies concerning laser heat treatment (LHT) of structural and tool steels, with particular attention to the 21NiCrMo2 steel used for carburized gear wheels. Analysis includes the influence of critical laser processing conditions—including power output, motion speed, spot size, and focusing distance—on surface microhardness, hardening depth, and microstructure development. The findings indicate that the energy density is the dominant factor that affects the outcomes of LHT. Optimal results, in the form of a high surface microhardness and a sufficient depth of hardening, were achieved within the energy density range of 80–130 J/mm², allowing for martensitic transformation while avoiding defects such as melting or cracking. At densities below 50 J/mm², incomplete hardening occurred with minimal microhardness improvement. On the contrary, densities exceeding 150–180 J/mm² caused surface overheating and degradation. For carburized 21NiCrMo2 steel, the most effective parameters included 450–1050 W laser power, 1.7–2.5 mm/s scanning speed, and 2.0–2.3 mm beam diameter. The review confirms that process control through energy-based parameters allows for reliable prediction and optimization of LHT for industrial applications, particularly in components exposed to cyclic loads. Full article

In this study, the effect of aging heat treatment on the superelastic properties and microstructure of [001]-oriented Fe₄₁Ni₂₈Co₁₇Al_11.5Ti_1.25Nb_1.25 (at.%) single crystals was investigated using the cyclic superelastic strain test and a transmission electron microscope (TEM). The TEM results reveal that the average precipitate size is around 3–5 nm in the 600 °C/24 h samples, 6–8 nm in the 600 °C/48 h samples, and 10–12 nm in the 600 °C/72 h samples. The results indicate that precipitate size increases as aging time increases from 24 to 72 h. EDS analysis results show decreased Fe and increased Ni when the analyzed line crosses the precipitate region. The diffraction pattern results show that the precipitate has an L1₂ crystal structure. The thermo-magnetization curves of single crystals under the three aging conditions (600 °C/24 h, 600 °C/48 h, and 600 °C/72 h) show that the values of the transformation temperatures increased from 24 to 72 h. Magnetization was saturated at 140 emu/g under the magnetic field of 7 Tesla. When increasing the magnetic field from 0.05 to 7 Tesla, the transformation temperatures rose. The results indicate that magnetic fields can activate martensitic transformation. From the results of the superelasticity test at room temperature, [001]-oriented FeNiCoAlTiNb single crystals aged at 600 °C for 24, 48, and 72 h presented recoverable strains of 3%, 5.1%, and 2.6%, respectively. Digital image correlation (DIC) results of the aged samples show that two martensite variants were activated during the superelasticity test. The two variants form corresponding variant pairs (CVPs) and improve the recoverable strain of superelasticity. Although maximum recoverable strain was obtained for the 600 °C/48 h samples, the samples show poor cyclic stability at room temperature after applying the 6% strain. According to the DIC results, the retained martensite, which is pinned by dislocations, was observed after the test. The irrecoverable strain was attributed to the residual martensite. For the 600 °C/72 h samples, the large size of the precipitates poses an obstacle to dislocation transformation and formation. The dislocations increase the stress hysteresis width and stabilize the martensite, causing poor recoverability. Full article

A surrogate artificial neural network (ANN) model trained on the data generated from a computational finite element-based (FE-based) model is developed. The developed ANN model enables the estimation of the fatigue life (number of load cycles to failure) of component-like specimens with stress concentrators. Using the developed model, the component-specific S-N curves can be generated with an accuracy comparable to that of the computational FE-based model. The investigation covered through- and surface-hardened steel components with different numbers and types of stress concentrators. The basis for data generation is the parametrized computational FE-based model, which enables the determination of the stress–strain response and the calculation of the fatigue life of examined components under cyclic loading conditions. The computational FE-based model can be adjusted to include components with different geometries and heat treatment conditions. The computational FE-based model incorporates nonlinear material behavior to provide a more accurate representation of the component’s behavior, which results in higher computational costs. In contrast, the developed ANN model provides a quicker and more efficient way to assess the fatigue life of both through- and surface-hardened components, overcoming these limitations. Full article

This paper presents the biodegradation and cavitational erosion behavior of new zinc alloys in the ZnMgFe system. The alloys were heat-treated through homogenization at 300 °C and 400 °C, with maintenance times of 5 and 10 h each. The experimental research consisted of characterizing the structure and mechanical properties of the newly made alloys in different structural states, as well as determining their biodegradation and cavitation behavior. Biodegradability was achieved using laboratory tests in SBF, with different immersion durations (3, 7, 14, 21, or 35 days). The cavitation behavior was assessed by performing tests on a piezoceramic crystal vibrator in compliance with ASTM G32-2016, thus constructing the curves of the erosion velocity MDER(t) and the cumulative average erosion depth MDE(t). The analyses performed on the mechanical properties, microscopic images, and the cavitation parameters MDER and MDEmax (results at the end of the cavitation attack) showed the effect of the heat treatments on the structure and structural resistance to cyclic loadings of the cavitation. The double alloying of zinc with magnesium and iron may increase either the mechanical properties or the corrosion resistance to cavitation and can control the biodegradability of the resulting ZnMgFe alloy. The best heat treatment for improving these properties is homogenization at 400 °C/10 h, which may increase the cavitation erosion of zinc by up to seven times. The experimental results demonstrate that the new alloys from the ZnMgFe system are a good option for manufacturing biodegradable implants with functional in vitro properties. Full article

Today, 3D printing is no longer only used for rapid prototyping, but also for the production of customized objects, spare parts, etc. However, printed parts often exhibit mechanical and thermal inadequacies. Here, we investigate novel filaments for fused deposition modeling (FDM) with and without fibrous fillers before and after cyclic temperature variations between −40 °C and +80 °C, similar to the situation of a microsatellite in the low Earth orbit (LEO). Maximum bending forces, deflection at maximum force, and tensile strengths remained nearly unchanged for most materials after heat treatment, suggesting that most materials investigated here can be used in environments with strongly varying temperatures. Full article

Background and Objectives: Nickel–titanium (Niti) instruments have enhanced root canal cleaning in primary teeth, but file fractures are still common. Materials and Methods: This study evaluated the cyclic fatigue resistance of 120 Niti files from four different systems, A: Kedo SG (n = 30); B: Neoendo Pedoflex (n = 30); C: Pedoflex Waldent files (n = 30); and D: Vortex Blue files (n = 30). All the files had similar tip diameters (0.25 mm) and tapers (0.4%) and underwent heat treatment during manufacturing. Cyclic fatigue tests showed notable variations in cycles to fracture (NCF) across groups. All fracture surfaces of the files were assessed through scanning electron microscopy. Results: The mean values achieved in the experimental groups (A, B, C) were less than those in the control Group D (976.90 ± 1085.19). Files in Group A demonstrated the highest NCF (697.01 ± 420.09), while Pedoflex files in Group C showed the lowest values (203.88 ± 155.46). Statistical analysis using the Mann–Whitney test revealed significant differences between Group C and Groups A, B, and D and no differences among Groups A, B, and D. Conclusions: These findings suggest that Kedo SG and Neoendo Pedoflex files offer comparable cyclic fatigue resistance to Vortex Blue files. In contrast, Pedoflex Waldent files exhibit lower resistance to fracture. Full article

This experimental study analyses the extent of chemo-mineralogical changes that occur when a building stone encounters a cycling isothermal treatment at 600 °C. Four carbonate and two silicate European building stones were analysed in their fresh quarried and thermally treated conditions by means of colour measurements, in situ X-ray diffraction (XRD), and optical microscopy. Furthermore, powdered samples were characterised by Fourier-transform infrared spectroscopy, simultaneous thermal analysis, and cycling thermogravimetry (TG). The in situ XRD spectra revealed a surface-limited phase transformation of solid calcite and dolomite under isothermal conditions during the first 10 min at 600 °C and 500 °C, respectively. The onset of thermal decomposition and extent of phase transformation were governed by the microstructure of the solid samples. Inter- and intragranular microcracks are induced to varying degrees, and their incidence depended on the stone’s microstructure. Discolouration indicated a transformation of minor elements across the entire analysed sample volumes. Kaolinite was preserved even after three hours of thermal treatment at its dehydroxylation temperature due to its sheltering in confined pore spaces. Mass loss was more pronounced when cyclic treatment was employed compared to a non-periodic treatment, as determined by a TG analysis performed at same time intervals. Examining the chemo-mineralogical and microstructural changes caused by heat treatment allows us to study how and if regaining mechanical strength and restoring physical properties are possible for purposes of heritage restoration after fire damage. Full article

The metal injection molding (MIM) manufacturing process has made relevant advances for applications in components with complex geometries, small dimensions, and high production volumes. New technologies such as hot isostatic pressing (HIP), uniform polymer extraction, and sintering with reduced temperature variations improve metallurgical and mechanical properties. However, there are still knowledge gaps in understanding these technologies and the behavior of catalytic low-alloy steels obtained by the MIM process and cyclic applications. This study aims to analyze the behavior of Catamold 100Cr6 steel subjected to quenching and tempering heat treatment in different microhardness ranges and the effect of compressive stresses on the samples obtained by polishing using ceramic microchips. The samples were characterized using optical microscopy, scanning electron microscopy, an EDS microprobe, and X-ray diffraction and subjected to elastic return cycling and an experimental device developed to apply a 19° bending angle. The findings show a significant increase in fatigue life due to the compressive stresses (up to—430 MPa) generated by the reduction in retained austenite and surface plastic microdeformation, indicating the effectiveness of 100Cr6 Catamold steel in cyclic applications. Full article

Selective laser melting (SLM) is an advanced additive manufacturing technique that enables the fabrication of complex metal components with high precision. However, inadequate parameter optimization can lead to defects that compromise the corrosion resistance of fabricated parts. Therefore, optimizing both SLM and heat treatment parameters is essential for enhancing electrochemical properties. The present work aims to determine the effect of the SLM process and heat treatment parameters on the corrosion resistance of SLM-made 17-4 PH stainless steel. A set of SLM and heat treatment parameters (laser power, scanning speed, aging time, and aging temperature) was determined by employed Taguchi method and a set of cyclic potentiodynamic polarization and electrochemical impedance experiments was performed in 3.5 wt% NaCl solution to generate corrosion data. The Taguchi method and statistical analysis of variance reveal the effect of laser power, scanning speed, aging time, and aging temperature on corrosion current density and passive film resistance of the SLM-made 17-4 PH samples. Laser power and aging temperature had the most significant effects, with lower laser power and higher aging temperature leading to decreased corrosion resistance, as indicated by higher corrosion current density and lower passive film resistance. Additionally, this study proposes empirical predictive models to estimate the electrochemical properties of SLM-made 17-4 PH stainless steel. Full article

This study aimed to analyze the effect of 1% sodium hypochlorite (NaOCl) solution at different temperatures on endodontic file resistance to cyclic fatigue. A total of 90 files, Reciproc NiTi M-Wire^® (REC) (n = 30), WaveOne Gold^® (WOG) (n = 30), and Reciproc Blue^® (RB) (n = 30) were activated under constant irrigation with 1% NaOCl at 5, 37, and 60 °C in a stainless-steel artificial canal (curvature angle = 60°; radius = 5 mm). The time to the fracture and the maximum and minimum load were recorded for each instrument, and data were subjected to statistical analysis. A higher number of cycles to fracture at 5 °C was observed between WOG and RB compared to the REC system (p < 0.05). The RB files were more resistant to cyclic fatigue fracture at 60 °C than WOG and REC (p < 0.05). No statistically significant differences were found between the mean values of the three file types used at 37 °C. The high temperature of NaOCl significantly affects the lifespan of endodontic files, making them more prone to fractures due to cyclic fatigue. The files manufactured with heat treatment showed a longer life than M-wire reciproc files. Full article

Objectives: This study aimed to evaluate the effectiveness of gonadotropin-releasing hormone-loaded chitosan–TPP nanoparticles (GnRH-CNPs) and prostaglandin F_2α-loaded chitosan–TPP nanoparticles (PGF_2α-CNPs) within the Ovsynch protocol for enhancing reproductive performance in heat-stressed dairy cows. Methods: Thirty-six cyclic purebred Friesian cows not detected in standing heat for more than 90 days postpartum were randomly allocated to three treatment groups. The control group (OVS, n = 12) followed the standard Ovsynch protocol with conventional doses. The ½ OVS group (n = 12) received 5 µg GnRH-CNPs on days 0 and 9, along with 250 µg PGF_2α-CNPs on day 7. While the ¼ OVS group (n = 12) was administered 2.5 µg GnRH-CNPs on days 0 and 9, with 125 µg PGF_2α-CNPs on day 7. Ovarian follicular dynamics and corpus luteum (CL) development were monitored on days 0, 4, 7, and 9 of the protocol. Serum progesterone (P₄) concentrations were measured throughout the synchronization period and on days 15 and 30 post-AI. Pregnancy was diagnosed on day 30 post-AI. Results: The ¼ OVS protocol achieved a significantly greater follicular response (p < 0.05) than other protocols. On day 4, following the first GnRH administration, the OVS group exhibited a higher number of subordinate follicles (p < 0.05) and a greater diameter of the dominant follicles (DFs), whereas the ¼ OVS group showed a greater subordinate follicle diameter (p < 0.05) and a higher number of DFs. On day 9, after PGF_2α administration, the ¼ OVS group maintained an elevated number of subordinate follicles, while larger subordinate follicle diameters were observed in the ½ OVS and OVS groups. No significant differences in DF numbers and diameters were observed among groups. P₄ concentrations remained similar across groups during treatments. Compared to control, a significantly higher value of P₄ concentration (p < 0.05) was recorded on day 15 post-AI in the ½ OVS group and on day 30 post-AI in the ¼ OVS group. These findings correlated with a higher pregnancy rate in the ¼ OVS group (65%) compared to the ½ OVS and OVS groups (40% in each). Conclusions: Nanofabrication reduced GnRH and PGF_2α dosage by 50% and 75% without impairing ovarian response and pregnancy rates. The ¼ OVS protocol notably enhanced the ovarian activity and fertility, highlighting the use of GnRH-CNPs and PGF_2α-CNPs as promising and practical approaches to enhance the fertility in dairy cattle under heat stress (HS). Full article

This study is focused on the sorption properties and the changes in the structure and state of Ti-25Al-25Nb (at.%) system alloys under thermal cyclic loading. These samples were produced by combining high-energy processing methods through mechanization and spark plasma sintering in the temperature range of 1100–1300 °C, followed by two-stage heat treatment at temperatures of 800 °C and 1250 °C. Thermal cyclic experiments on hydrogen sorption/desorption with samples of the Ti-25Al-25Nb (at.%) system were conducted at the VIKA experimental installation at a saturation temperature of about 500 °C and a degassing temperature of 610 °C. It took about 41 min to reach pressure equilibrium at 500 °C. The hydrogen diffusion coefficient was calculated based on the Barrer formula and was 9.1 × 10⁻⁵ cm²/s at 500 °C. The maximum hydrogen content was recorded after the first sorption/desorption cycle and was 1.91 wt%. Due to the multiple thermal cyclic effects in the hydrogen medium, the predominantly two-phase (O + B2) alloy structure underwent transformation to form a new structure (O-AlNbTi₂). In the phase composition of the Ti-25Al-25Nb (at.%) alloy, the formation of hydrides in the form of independent phases as a result of thermal cycling was not detected. Hydrogen absorption is most likely to be associated with the formation of an interstitial solution based on existing crystalline phases. Full article

The quality, reproducibility, and reliability of additive-manufactured parts strongly depend on optimizing printing parameters and post-processing treatments. This study evaluates the effects on the microstructure and corrosion resistance properties of solution annealing and aging heat treatments performed on 17-4 PH stainless steel samples fabricated with different build-up orientations using a material extrusion technology: the Bound Metal Deposition^TM. The chemical composition and microstructures were determined using X-ray diffraction, chemical etching, optical microscopy, and scanning electron microscopy. The corrosion resistance properties in neutral sodium chloride electrolytes were investigated through cyclic potentiodynamic polarization and open circuit potential monitoring and analysis. The findings demonstrated that the solution annealing heat treatment remarkably enhanced the overall corrosion resistance properties of the samples. The improvement was attributed to the growth of the ferritic phase along the grain boundaries of the martensitic matrix and a finer dispersion of copper precipitates. The aging heat treatment performed after solution annealing enhanced the ferritic phase development, resulting in a further improvement of the localized corrosion resistance properties. Full article

Cyclic failure problems in layered ductile iron are evident in a wide range of elements in transportation and mining equipment and depend on production technology and operating conditions. The aim of this study was to analyze the effect of residual stresses on the behavior of cyclic and static failure. The stress intensity factor, crack initiation, propagation patterns, static tension diagrams, and fracture behavior of compact tension (CT) specimens were determined. The samples used in this study were made from base cast iron, some of which were subjected to a special localized heat treatment. Experimental and analytical methods were used to conduct this study. The experiments were performed using original testing methods that adhered to the American Society for Testing and Materials (ASTM) regulations. The deformations of the partially heat-treated specimens due to residual stresses were determined using the grid method. The limiting stress intensity coefficient and the failure threshold under cyclic loading were determined in accordance with ASTM recommendations for various crack depths and openings. The results show that the heat treatment process readily produces residual stresses of different magnitudes, stress redistribution, different structures, and layer positions. Residual stresses affect the crack initiation and propagation. The stress intensity factor depends on the depth of the crack, the position of the layers, and the magnitude of the residual stresses. Full article

The article addresses stress formation in the structural 3D-printed elements of a high-pressure die casting die mould used for production of aluminum castings. The 3D-printed elements with conformal cooling are manufactured of 18Ni300 powder. Initial numerical calculations were performed on a test die mould made of standard steel X40CrMoV5 to determine temperature distribution and stress state, providing a baseline for comparing 3D-printed 18Ni300 parts. A database for 18Ni300 material was developed, including optimal heat treatment parameters: aged at 560 °C for 8 h. The resulting tensile strength of approximately ~1600 MPa, yield strength 1550 MPa, and elongation 6–7%, with properties temperature-dependent from 20 °C to 600 °C. Results show that conformal cooling increases stress gradients, highlighting the demands on fatigue strength at elevated temperatures. The study revealed that the heat treatment significantly influences the final properties, with tensile strengths of 1400–2000 MPa and elongation from 1 to 8%. While the heat treatment has a greater impact on the mechanical properties than the printing parameters, optimizing the printing settings remains crucial for ensuring density and quality in the die moulds under cyclic loads. Full article