Hamilton Ferreira Gomes de Abreu’s research while affiliated with Federal University of Para and other places

Maraging steels are high strength alloys used in applications that require both high mechanical strength and toughness. To achieve these properties, one of the heat treatments applied is solution treatment, although it can reduce toughness. This study compares the effect of two solution treatment temperatures, 910°C and 1100°C, on the microstructure and mechanical properties of a niobium‐containing maraging steel. Microstructural analysis was performed using X‐ray diffraction (XRD), electron backscatter diffraction (EBSD), light optical microscopy (LOM), and scanning electron microscopy (SEM). XRD analysis showed that dislocation density was higher for the sample treated at 1100°C. The XRD data were analyzed using the Williamson‐Hall method to estimate dislocation densities, and the Scherrer equation was applied to calculate crystallite sizes. EBSD revealed that solution treatment at 1100°C resulted in larger grain sizes and greater dissolution of Mo, Nb‐rich precipitates. Vickers hardness and Charpy impact tests were used to evaluate the mechanical properties. The Vickers hardness was slightly higher for the sample treated at 910°C due to the higher amount of precipitates present. In contrast, Charpy toughness increased with solution treatment temperature, reaching 98 J for the 1100°C condition, indicating greater impact energy absorption. Fractography showed predominantly ductile fractures in both conditions.

SnxSb(1−x) coatings were electrodeposited from 1ChCl:2EG on copper. The corrosion resistance of the electrodeposits was evaluated in 0.1 mol dm-3 of NaCl. The characterization was performed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Voltammetric profiles showed that the electrodeposition potential shifted towards less positive values with increasing Sb3+ concentration. SEM images revealed that the coatings exhibited grains and clusters. EDS analyses showed that the Sb content increased with the Sb3+ concentration. XRD results indicated the formation of the SbSn phases such as Cu2Sb, Cu6Sn5, and Cu6(Sn,Sb)5. The potentiodynamic polarization (PP) curves showed that Sn and Sn77Sb23 presented a passive potential region, while Sn37Sb63 had an active dissolution in the electrolyte. Immersion tests were performed for 24 h and XRD results revealed Cu, Sn, SnO, SbSn and Sb2O4 phases. Considering 48 h, Cu, CuSn, SnO2 and SnSb phases were identified. The polarization resistance values of 4.60, 14.69 and 1.81 kΩ cm2 were achieved for Sn, Sn77Sb23, and Sn37Sb63, respectively. The EIS results suggested that adding Sb3+ improves corrosion resistance for SnSb samples with higher Sn content. For Sn77Sb23, the charge transfer resistance was 10.5 kΩ cm2, for Sn and Sn37Sb63 1.15 and 1.46 kΩ cm2, respectively.

This study investigates the microstructural and crystallographic changes in a novel Nb-enhanced, Ti-reduced maraging steel. The hot-rolled steel was solution annealed at two different temperatures followed by aging. The Electron Backscatter Diffraction (EBSD) analysis of hot-rolled sample revealed a predominant {112}//RP texture, reoriented to {110}//RP during aging to minimize internal energy and stress. Solution annealing at 820oC followed by aging favored a {111} orientation, resulting in minimal crystallographic defects and grain distortion. In contrast, higher solution annealing temperatures promoted the formation of {001} cleavage planes, increasing brittleness and crystal defects, thereby impacting the material's suitability for high-performance applications.

The promising routes of metallic additive manufacturing favor the fabrication of refined functional components. Nonetheless, dealing with the Laser Powder Bed Fusion (L-PBF) parameters and costs for making the most of this technology is still an issue. The challenge gets bigger when considering less explored parameters, such as the process atmosphere and build location. So, this study aimed to address the main differences in microstructure, crystallography, mechanical properties, and surface finishing of maraging steel components manufactured under two different atmospheres (N2 and a mixture of 75%Ar-25%He atmospheres) and three build locations arranged along the gas flow direction. Based on experimental characterizations, the porosity fraction, microstructural constituents and metallurgical flaws, phase composition and martensite matrix crystallographic parameters, macrotexture, mechanical properties, roughness, and surface residual stress were investigated and compared for the different manufacturing conditions. The porosity fraction had the most expressive changes with the gas type and the build location, reaching a 53% overall reduction under N2 and a 112 to 302% rise for the front located sample compared to the others. The underlying mechanisms involved in the observed results, mainly related to process by-products behavior, were discussed. Broadly, the N2 atmosphere stands out over the analyzed properties. These findings underscore the role of atmospheric selection in the LPBF process, considering the overall quality and performance of the fabricated material and the possibility of cost reduction.

In-situ synchrotron X-ray diffraction experiments were conducted on the pearlitic steel sample with a carbon content of 0.74% by weight. Specimens were subjected to uniaxial loading that induced shear deformation and two-dimensional diffraction patterns were acquired. The evolution of the lattice microstrain and the strain-resolved crystallographic texture development of both ferrite (α-BCC) and cementite (θ-orthorhombic) phases were followed. The analysis revealed that the texture changed from {110}<113>α to {113}<121>α component and then, stabilized at {013} α orientations. The θ phase exhibited a weak texture in the {100, 010, and 001}θ family planes. Additionally, it was revealed that the nucleation of interfacial defects at the α/θ interface promotes the amorphization of cementite and the activation of slip systems in less densely packed {310}α planes. The influence of microstructural changes on mechanical properties is discussed.