Rogerio Moraes Oliveira

This study aims to optimize the process parameters for manufacturing stainless steel AISI 316L (SS316L) components using Laser Powder Bed Fusion (LPBF) with a Laser-Adapted Powder Deposition System. The influence of volumetric energy density (VED), laser intensity, and interaction time on the topography, defect formation, and hardness of the manufactured parts was investigated. The LPBF process parameters were systematically varied, including laser power (50–250 W) and scanning speed (15–250 mm/s). This resulted in VED values ranging from 55.6 to 647.5 J/mm³. The optimization process revealed ideal process conditions at VED values of 170.9, 256.4, and 641.0 J/mm³, with a minimum laser intensity of 11.8 kW/mm² and interaction times ranging from 0.36 to 2.70 ms. Microstructural analysis revealed a predominantly austenitic phase with residual stresses associated with the LPBF process’s high cooling rates. Mechanical testing showed that parts manufactured under optimized conditions exhibited superior hardness (234–244 HV) compared to conventionally processed SS316L (170–220 HV). It was demonstrated that the laser-adapted powder deposition system can effectively fabricate high-precision components by understanding the interdependencies of parameters in LPBF. This approach contributes to optimizing manufacturing strategies for SS316L components.

Metallic tubes are widely used in industrial applications. However, the internal smoothness and chemical resistance of metallic tubes are often major concerns. In contrast to the widely studied large-diameter metallic tubes (typically > 4 cm internal diameter) commonly investigated for surface modifications in industrial applications, we have focused on modifying the internal sur-faces of much smaller SS304 tubes (0.6 cm internal diameter) using nitrogen and argon PIII, as well as acetylene PIII&D. This study demonstrated that high-quality internal surface modifica-tions can be achieved with a straightforward setup and appropriate analysis techniques, even in tubes of industrial relevance with such small dimensions. In addition to gaining insights into the characteristics of hollow cathode (HC) and dielectric barrier (DB) discharges in small-diameter tubes, we found that Ar-PIII can partially mitigate the poor surface quality of as-received tubes. The addition of an N-PIII step further enhanced the internal surface, resulting in a smoother fin-ish with fewer trapped impurities. Moreover, acetylene PIII&D enabled the rapid deposition of a thick (>300 μm) Glassy Carbon film. These findings highlight the potential of these techniques for various plasma-related applications and industrial processes, offering promising avenues for future development.

Ti-6Al-4V alloy is ideal for use in the aeronautical and aerospace industries because of its excellent strength/weight ratio and corrosion resistance. However, its applications at high temperatures are vulnerable due to its high affinity for interstitial elements, such as nitrogen and oxygen. The plasma immersion ion implantation (PIII) technique, performed at high temperature, allows formation of modified layers that can improve the mechanical and tribological properties without compromising the corrosion resistance, which is a characteristic of this alloy. In this work, the samples were treated by PIII at three different temperatures (700, 800, and 900 °C) for 120 min of exposure to evaluate PIII on the mechanical behavior of Ti-6Al-4V alloy compared to data already available in the literature. The aim of this process is to improve surface mechanical properties of the Ti-6Al-4V alloy. The techniques used in this work were x-ray diffraction microhardness, glow discharge optical emission spectrometer, and wear testing in a ball-on-disk tribometer. The results indicate a significantly increased material resistance, with a reduced wear for all treated samples and a reduced friction coefficient for samples treated at 800 and 900 °C. The best results were for alloy treated at 800 and 900 °C, because they maintain the low coefficient throughout the test, which indicates better wear resistance.

The objectives of this study were to characterize titanium (Ti) surfaces treated by ion implantation by immersion in oxygen plasma (O-PIII) at different temperatures, correlating these implanted layers with therapeutic effects and with osteogenesis, as well as the formation of monotypic biofilms microbial. The groups were divided into: a) Ti (pre-treatment) b) Ti O-PIII at 400 ° C. c) Ti O-PIII at 500 ° C. d) Ti O-PIII at 600 ° C. The properties and surface characteristics were evaluated according to the roughness, texture, corrosion resistance, formation of new phases and the identification of chemical compounds present. Cellular analyzes investigated cell interaction, viability, total protein content, alkaline phosphatase and quantification of mineralized nodules using MG-63 cells. The formation of monotypic microbial biofilms, including P. aeruginosa, S. aureus, S. mutans and C. albicans were evaluated. The increase in surface roughness, corrosion resistance and oxygen content, leading to the formation of TiO2-rutile with more intense peaks and in greater numbers according to the increase in the substrate temperature, ionic implanted Ti samples was observed. There was also a significant increase in cell viability, total protein production, alkaline phosphatase activity and formation of mineralization nodules for the group treated with O-PIII at 600ºC compared to other groups, in addition to a reduction of microorganisms in the groups treated with O- PIII. Therefore, treatment with O-PIII at 600ºC in Ti grade IV showed favorable results for its use.

High Temperature Nitrogen Plasma Based Ion Implantation (HT-NPBII) has been used to treat the surface of niobium superconducting reentrant cavities, which are part of parametric transducers in a resonant-mass gravitational wave detector. The aim is to enhance the corresponding electrical quality factors (Q-factors) which are closely related with the increase of the sensitivity of the system. In this experiment, the cavities are immersed in plasma and bombarded by energetic nitrogen ions, which are implanted into the surfaces of these heated substrates. The heating temperature of the cavities is controlled during the treatment and its level directly affects the N implantation depth profile due to the diffusion process. Additional tailoring of the nitrogen doping can be performed by the adjustment of the intensity and the duty cycle of the high negative voltage pulses used for ion implantation. For implantations performed at 5 kV /20 µs /300 Hz/ 700 °C, nitrogen atoms occupy interstitial spaces in the crystal lattice of niobium. The treatment of niobium superconducting cavities under these parameters caused the enhancement of two orders of magnitude of respective Q-factors. A set of characterization techniques was performed herein in order to help with the understanding of the underlying mechanism behind this phenomenon.

This research studied Ti-6Al-4V alloy behavior with two (2) different microstructure subjected to nitrogen addition by PIII treatment, with and without sample heating, under cyclic load. PIII conditions, at 390 °C, were DC voltage of 9.5 kV, frequency of 1.5 kHz and pulse of 40 μs. PIII conditions, with sample heating at 800 °C, were 7 kV, 0.4 kHz and 30 μs. Axial fatigue tests were performed on untreated and treated samples for resistance to fatigue comparison. The untreated Ti-6Al-4V had an annealed microstructure, PIII treatment at 390 °C resulted in a microstructure that has no nitride layer or diffusion zone. In the PIII treatment at 800 °C, the microstructure presented nitride layer and diffusion zone. Resistance to fatigue decreased with PIII treatments in both temperatures. At 390 °C, the treatment created deformation regions and cracks on surface due to nitrogen implantation that formed solid solution with titanium and imposed lattice strains on the crystal lattice. At 800 °C, bulk ductility decrease, increasing of αTi proportion in microstructure due to α case formation and the presence of a ceramic layer dropped fatigue resistance of Ti-6A-4V alloy.

A common phenomenon in the dissimilar joints is the presence of brittle compounds in the joining interface region. The brittle phases can decrease by introduction of interlayers in the joining interface, such as silicon, that inhibits the formation of Al₃Ti and AlTi₃ phases in joining process between titanium and aluminium alloys. In the present work, the joining of titanium and aluminium alloys have been carried out using a Yb:fiber laser, considering the prior silicon film deposited on titanium alloy interface by DC magnetron sputtering. Butt joint conditions were maintained constant: laser average power, process speed and beam positioning along the interface joining toward aluminium alloy (1200 W, 3.0 m/min and 0.3 mm, respectively). Metallographic analyses were carried out on the cross-section joint by optical and electronic microscopies. When the melted aluminium alloy wet the solid-state titanium alloy, a more restrict compound layer was formed in the joining interface. EDS line scanning in the joining interface showed a reduction of compound layer thickness, considering the silicon as interlayer, reaching the mean value of 3 µm, i.e., up to five times thinner if compared to joining without silicon during the process.