EFFECTS OF WELDING PARAMETERS ON PERCENTAGE DILUTION AND MECHANICAL PROPERTIES IN WELDED JOINTS OF ULTRA-HIGH HARDNESS ARMOUR STEELS Charles Hudson Martins de Vasconcelos, Naiara Vieira, Le Sénéchal, Cristhian Ricardo Loayza Loayza, Ademir Ângelo Castro Filho, de Eduardo Magalhaes Braga, Andersan Paula, Ricardo Weber Journal of Mining and Metallurgy Section B Metallurgy, 2025 This study investigates the effects of Gas Metal Arc Welding (GMAW) parameters?specifically welding speed and stickout? on the dilution and mechanical properties of welded joints composed of ultra-high hardness quenched and tempered (UHH-Q&T) armor steel and austenitic stainless steel filler metal. An optimization methodology was used to set constant parameters, including wire diameter, gas flow rate, welding voltage, and wire feed speed, based on equipment capabilities. Experimental trials varied welding speed and electrode stick-out while maintaining a constant current through inductance control. Although the welding parameters affected the melted base and filler metal areas, the dilution percentage remained unaffected. The correlation between dilution and welding current was validated. Microstructural and mechanical analyses confirmed the consistent behavior of the welded joints under the tested conditions.
Aluminum Nanocomposites with Nickel and Carbon Nanotubes Via Gravity Die Casting Igor Alexsander Barbosa Magno, Cristhian Ricardo Loayza Loayza, Mateus José Araújo de Souza, Emerson Prazeres Rodrigues, Mário Edson Santos de Sousa, Eduardo de Magalhães Braga, Marcos Allan Leite dos Reis Materials Research, 2025 Aluminum-based nanocomposites exhibit enhanced mechanical properties along with improved thermal and electrical conductivity. However, incorporating carbon nanotubes (CNTs) into aluminum via gravity die casting remains a challenge. This study investigates the fabrication of aluminum nanocomposites via traditional casting, integrating nickel powder and multi-walled carbon nanotubes (MWCNTs) pre-treated with isopropyl alcohol and hydrogen peroxide to improve particle adhesion to the matrix. The nanostructured compounds were then incorporated into the aluminum matrix via gravity die casting. The results showed that the addition of nickel powder and CNTs refined the grains and promoted significant improvements in electrical and mechanical properties, with increases of 18% and 7%, respectively, for 0.2 wt.% Ni and 0.075 wt.% MWCNTs, when compared with commercial electroconductive aluminum. Consistent increases in hardness and ultimate tensile strength were observed, along with gains in elongation in most compositions. However, occasional reductions in yield strength and elongation indicate that the effects are not universal but depend on composition and CNT dispersion. Overall, the developed nanostructured alloys exhibited superior performance compared with commercial electroconductive aluminum, combining improved electrical and mechanical properties.
EFFECTS OF WELDING PARAMETERS ON THERMAL CHARACTERISTICS IN WELDED JOINTS OF ULTRA-HIGH HARDNESS ARMOUR STEELS Proceedings 34th International Symposium on Ballistics Ballistics 2025, 2025
Study of the corrosion resistance of high chromium white cast iron welds in the presence of NaOH (30% w/w) R.S.G. Dos Santos, T.S. Cabral, L.A.S. Rodrigues, C.R.L. Loayza, R.N.J.F. Silva, E.M. Braga Journal of Materials Research and Technology, 2024 – In the mining industry, specifically in bauxite processing, adverse working conditions demand high mechanical and chemical resistance. For such conditions, the choice of potentially resistant materials, such as high chromium white cast iron (HCr-CWI), is necessary. However, presently, there is no effective recovery of equipment made with HCr-CWI, primarily due to the machining difficulties encountered during the repair process. An alternative recovery method is being developed by the Laboratory of Metallic Materials Characterization at UFPA – LCAM, using electric arc welding with two filler metals: the ER307L stainless steel wire andsa high Mn value wire. Within this context, this study aims to investigate the corrosion resistance of the welded joint obtained with these two filler metals. The base metal (HCr-CWI) was analysed as a reference, alongside the metals generated by the welded joints, ER307L and high Mn. The samples underwent tests involving optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electrochemical tests for corrosion potential, polarization, and impedance. It was observed that the samples exhibited a similar matrix-carbide structure but with different organization and volumes. However, the electrochemical behaviour in terms of corrosion potential, polarization, and impedance was similar, with very close resultant values: 50 V; 3.53 μA; 0.18 kOhms, respectively. This was supported by the corrosion rate of 0.4mmpy and explained by calculations of Cr and Ni volume, which showed inverse concentration magnitudes among the samples.
Stainless steel-CNT composite manufactured via electric arc welding C.R. Loayza, D.C.S. Cardoso, D.J.A. Borges, A.A.F. Castro, A.C. Bozzi, M.A.L. Dos Reis, E.M. Braga Materials and Design, 2022 Stainless-steel (SS) matrix composites reinforced by multi-walled carbon nanotubes (MWCNT) were successfully prepared by arc welding. A tubular rod was used as additional material. It was filled with a nanostructured flux-cored formed by 304L SS particles and MWCNT chemically treated with H2O2. The Raman spectra of the nanostructured flux-cored revealed an ID/IG rate drop from 1.12 to 0.68 and the amorphous carbon degree diminished from 76.5 % to 17 % after the chemical treatment. EBSD graphs demonstrated that the SS composite had a grain refinement of 64 % induced by the nanotubes in the matrix, acting as nano-structured reinforcement. Compared with the 304L SS fabricated sample, the composite increased its microhardness by 45 % (305 ± 15 HV0.3) and reduced its average erosion rate by 64 % (0.53 ± 0.07 mg/h). The austenitic γ(1 1 1) phase grows up after the vibratory cavitation test. Here, it was observed for the first time that the MWCNT influences the cavitation erosion strength in SS and that it is viable economically for large-scale industry.
Stainless steel weld metal enhanced with carbon nanotubes D. J. A. Borges, D. C. S. Cardoso, E. M. Braga, A. A. F. Castro, M. A. L. Dos Reis, C. R. L. Loayza Scientific Reports, 2020 This paper aims to establish the most indicated route to manufacture a nanostructured powder composed of 5 wt% Multi-walled Carbon Nanotubes and 304LSS powder. Four specimens were prepared using Mechanical Alloying and Chemical Treatment (CT) with Hydrogen Peroxide ($${\\mathrm{H}}_{2}{\\mathrm{O}}_{2}$$H2O2) as the main processes. A thermal treatment post-processing was used in half of the samples to remove the remaining amorphous carbon and to evaluate its effects. Regarding the powder analysis, attachment, amorphous carbon degree, crystallinity, and doping of the CNT throughout the metal matrix were investigated. The nanostructured powders were then inserted as a core in a 304LSS tubular rod to perform the arc welding process. The CT route eliminated the amorphous carbon and generated more refiner grains, which provided a cross-section hardness gain of more than 40% regarding the 304LSS joint. In summary, the CT route, combined with the GTAW process, provided a new method for nanocomposite manufacturing by combining shorter preparation steps, obtaining an improvement in the microstructural and hardness performance.
