Samuel Filgueiras Rodrigues

This study investigates the microstructural evolution and mechanical response of premium rail steel subjected to heat‐affected zone (HAZ) thermal cycles representative of flash butt welding (FBW). Dilatometry experiments were performed using a Gleeble thermomechanical simulator. Samples were austenitized at 1100 °C (100 °C/s, 60 s dwell) and cooled at 1–8 °C/s. Cooling rates of 1–3 °C/s produced predominantly pearlitic microstructures, whereas higher rates promoted bainite and martensite formation. HAZ physical simulations were then conducted at peak temperatures of 1200, 1060, 900, and 750 °C. Fully pearlitic microstructures developed at 1060 and 900 °C, while 750 °C produced spheroidized pearlite. The spheroidized condition exhibited the lowest tensile strength (737 MPa) and hardness (296 HV), whereas 1060 °C yielded the highest values (864 MPa and 418 HV). Optical microscopy, scanning electron microscopy, and electron backscatter diffraction revealed systematic changes in colony morphology, grain structure, and crystallographic characteristics. The 750 °C condition showed the lowest hardness and highest wear rate, while 1200 °C exhibited the highest nanohardness and wear resistance, but greater microstructural heterogeneity and reduced ductility. These findings demonstrate the strong influence of HAZ thermal history on phase transformation and mechanical performance, providing guidance for optimizing FBW parameters in rail steels.

Additive Manufacturing (AM) has become increasingly prominent in the transition from rapid prototyping to the production of end-use components, particularly in metal manufacturing, due to its ability to fabricate geometrically complex parts with high dimensional precision. Among the most widely adopted AM technologies are Powder Bed Fusion (PBF) and Directed Energy Deposition (DED), with Wire Arc Additive Manufacturing (WAAM) emerging as a promising approach because of its high deposition rate and suitability for large-scale component fabrication. Nevertheless, defects such as porosity and lack of fusion still compromise part quality, making toolpath planning a critical aspect of process optimization. In this study, the operational efficiency and metallurgical performance of the WAAM process were evaluated using two toolpath strategies, namely Basic Pixel and Interleaved Pixel. Operational efficiency was assessed in terms of printing time, travel distance, and number of stops, whereas metallurgical and geometric performance were analyzed based on microhardness, microstructure, surface quality, and dimensional conformity. The results showed that both strategies exhibited similar operational efficiency, with differences of less than 0.2%. However, the Basic Pixel strategy demonstrated superior overall performance, providing higher dimensional accuracy, improved surface quality, and lower defect incidence. In contrast, the Interleaved Pixel strategy promoted greater microstructural homogeneity and lower microhardness variation, although it exhibited higher sensitivity to thermal fluctuations. Overall, despite the microstructural advantages associated with the Interleaved Pixel strategy, the Basic Pixel strategy proved to be the most robust approach, combining improved mechanical performance, structural integrity, and geometric accuracy.

The demand for sustainable food preservation has driven the development of biodegradable alternatives to conventional, petroleum-based plastics. This study developed and evaluated bioactive starch-based films incorporated with citrus peel essential oils (lemon, orange, and tangerine) at concentrations ranging from 0.5% to 2% (w/w). The physical, chemical, mechanical, and antimicrobial properties of all film formulations containing 0.5–2% (w/w) essential oils were evaluated. Based on the experimental design, only the selected formulations containing 1 and 2% essential oils were subjected to structural and thermal characterization (XRD, SEM, FTIR, and TGA/DTG), transparency measurements, soil biodegradation, and phytotoxicity assays. FTIR spectroscopy revealed that oil incorporation did not alter the characteristic chemical bands of starch, indicating predominantly physical interactions. The essential oils modulated the physical and mechanical performance of the films. The films containing lemon and tangerine essential oils exhibited superior antimicrobial activity against foodborne pathogens. Furthermore, soil biodegradation was concentration-dependent, with mass loss exceeding 50% within 15 days, while phytotoxicity tests confirmed the environmental safety of the degraded residues. These findings demonstrate that the developed citrus-infused starch films hold great promise as active biodegradable packaging to extend the shelf life of bakery products and mitigate plastic waste.

In this study, the use of açaí ( Euterpe oleracea Mart.) briquettes, with gelatinized cassava starch binder, applied at a pressure of 25 MPa, at a temperature of 25°C, serves as a sustainable alternative for renewable energy generation. Global energy demand, combined with anthropogenic emissions and the physical depletion of finite fossil reserves, accelerates the need to transition toward sustainable, renewable energy alternatives. The agro‐industrial processing of fruit generates a massive volume of waste, as the fruit seeds account for 80% of its total weight. In processing methodology, the biomass from raw açaí seeds was washed, dried, ground to a standardized particle size of 0.841 mm (20 Mesh), and blended in a 100 g to 40 g ratio with a liquid solution of cassava starch activated via gelatinization at 65°C. Comprehensive physical, mechanical, chemical, and thermal characterization is being conducted using bulk density profiling, universal axial compression testing, ultimate and proximate elemental analyses, as well as Scanning Electron Microscopy (SEM), X‐ray Diffractometry (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Thermogravimetric Analysis (TGA/DTG). The engineered bio‐briquettes achieved a stabilized bulk density of 985.6 kg.m ⁻³ , reflecting a 62.22% volume reduction and densification increase relative to the raw seeds' 601.9 kg.m ⁻³ . Ultimate analysis revealed an elemental profile comprising 48.15% carbon, 9.90% hydrogen, and an environmentally low sulfur content of 0.68%, delivering a higher heating value (HHV) of 19.75 MJ.kg ⁻¹ and a lower calorific value (LCV) of 17.55 MJ.kg ⁻¹ . Mechanical durability testing confirmed a peak load capacity, withstanding a progressive force of 3.08 kN and registering an axial compressive strength of 2.00 MPa, a value that significantly outperforms standard commercial thresholds and warm‐pressed alternatives.

This study compares the microstructure, texture evolution, and mechanical behavior of Maraging 300 steel produced by selective laser melting (SLM) and conventional manufacturing (CM), subjected to solid solution treatment, cold rolling (up to 89.4% reduction), and aging. Results showed that while both routes achieved similar hardness, AM maintained stable hardness at extreme deformations, whereas CM peaked at 80.7% reduction. Tensile tests at ~80% reduction revealed that CM achieved higher ultimate tensile strength (2105 MPa) than AM (1807 MPa), but AM demonstrated superior ductility (16.7% vs. 10.8%). Electron Backscatter Diffraction (EBSD) analyses indicated that the AM material accommodated strain more homogeneously due to its initial fine cellular substructure, leading to greater crystallographic fragmentation, whereas CM exhibited pronounced strain localization. In conclusion, the initial microstructural state dictated by the manufacturing route fundamentally governs the deformation mechanisms, explaining the distinct strength–ductility balance observed between additively and conventionally processed Maraging 300 steel.

The high-Mn steel with the composition of Fe-27Mn-1Si-0.027C (wt.%) was selected. Two samples with different grain sizes were prepared by hot rolling followed by annealing: one was annealed at 1100°C for 90 minutes after 60% hot rolling, and the other was annealed at 1100°C for 60 minutes after 80% hot rolling. The study focused on the relationship between the microstructural evolution of the low-C high-Mn steel and its tensile and impact properties influenced by the stacking fault energy (SFE) at room and cryogenic temperatures. Through SEM and SEM-EBSD experimental techniques, ε-martensite phase was observed, and its mechanical response was compared under room and cryogenic temperatures. In consequence, the low-C high-Mn steel did not present the TWIP effect, but the TRIP effect (i.e., dislocation slip deformation) was detected due to the presence of ε-martensite formed by mechanical straining, increasing its volumetric fraction as the testing temperature decreased. Even with the negative presence of the ε-manartensite phase, the mechanical properties of the low-C high-Mn steel (i.e., strength, ductility and toughness) at the cryogenic temperature testing were similar to those of commercial cryogenic alloys currently used for low temperature combustible storage applications.

This work investigates the fatigue failure mode of a shaft used in a conveyor system for mining applications through visual inspection, metallographic examination, fracture analysis, and mechanical testing. It was observed that a misalignment of about 5° between the shaft and the conveyor drum system promoted intensive contact with the parts. The combination of misalignment and overload was the leading cause of the localized plastic deformation, which resulted in the shaft fracture. A metallurgical examination revealed ferritic and pearlitic microstructures for an AISI 4140 grade steel. This suggested that the heat treatment on the steel was not adequate for the application. Therefore, it can be inferred that no preventive or corrective maintenance inspections were performed during the shaft's operational production period.

In the manufacturing of metal alloys, different processing methods are used to achieve desired mechanical properties. Thermomechanical processes involve phenomena such as work hardening (WH), dynamic recovery (DRV), and dynamic recrystallization (DRX), which influence the properties of the materials. However, replicating these processes on a laboratory scale is challenging due to the differences in conditions compared to the industrial scale and the high costs involved. Hot torsion machines are essential tools in simulating these processes, allowing for the study of microstructural evolution and parameter measurements. This article aims to physically simulate thermomechanical processing by hot torsion considering a strain rate of 1.0 s⁻¹ and five testing temperatures. The analytical methods proposed by Poliak-Jonas and Uesugi et al. were used to determine characteristic points of the flow curves and the occurrence of metallurgical phenomena. The alloy used was austenitic stainless-steel ISO 5832-9, which is utilized for orthopedic implants. Results show that temperature has a considerable influence on the shape of the curves, as well as on the DRV and DRX phenomena, which, in turn, are influenced by the stacking fault energy.