Abstract Usually, scraps of X22CrMoV12-1 alloy are obtained through machining of steam turbine blades and recycled through casting. However, this process is considered too costly. The viability of recycling X22CrMoV12-1 scraps with addition of vanadium carbide (VC) through powder metallurgy was analyzed in this study. Scraps of X22CrMoV12-1 alloy with VC were milled in a planetary ball mill during 10, 30 and 60 hours. The granulometry of the powder was determined through laser granulometry. The evolution in particles morphology and amorphization was conducted using scanning electron microscope (SEM) and x-ray diffraction (DRX) techniques. Stress-strain curves were obtained through compressive strength test. The results indicated that the best milling condition found was 60 hours. Also, the X22CrMoV12-1 alloy with VC addition produced by powder metallurgy showed good mechanical strength. Thus, this route was considered promising to reshape this material with smaller energy involved in the process.

Vanadis®8 is a high-value tool steel, that undergoes gas atomization and hot isostatic pressing during production , resulting in costly waste. Repurposing this waste material through powder metallurgy (PM) offers a cost-effective solution. This study explores the PM process applied to Vanadis®8 steel scraps, involving high energy ball milling, uniaxial pressing, and sintering. The final product and the as-received steel underwent heat treatments, including quenching and tempering. Microstructural evaluation employed X-ray diffraction and scanning electron microscopy, while physical evaluation entailed Archimedes density measurements. Mechanical analysis was carried out through microhardness and compression strength tests. Results revealed that optimal milling conditions were achieved at 30 hours with 400 rpm (s-1). Vanadis®8 steel produced through PM attained 85% densification compared to the as-received material (6.31 g/cm3). MC-type carbides were present in all evaluated conditions. Heat treatments improved mechanical values for all conditions, suggesting that PM-produced Vanadis®8 steel, subjected to quenching and tempering, presents a viable reuse option.

Abstract The purpose of circular economy is to maximize resources efficiency. With the increase in consumption of raw materials, energy and waste generation, recycling is necessary for environmental and industrial reasons. Thus, the powder metallurgy, together with mechanical milling, stands as a new method for scraps recycling. This study aimed to produce UNS S31803 duplex stainless steel powders, with vanadium carbide (VC) addition as reinforcement, through mechanical milling. Different uniaxial compaction pressures (700, 800 and 900 MPa) were used, as well as sintering temperatures (1200, 1240 and 1280 °C) and times (1, 1.5 and 2 hours), in order to determine the best conditions. Particle size analysis, scanning electron microscopy and x-ray diffraction were used to characterize the powders. It was observed that the use of VC increased the comminution during the milling process, being obtained an average particle size of 42 μm. The highest density obtained was of 82% and hardness of 72%, in comparison with the steel from the manufacturing process. According to the analysis, it was verified that this method is viable, becoming an alternative route to reuse UNS S31803 duplex stainless steel scraps.

Abstract In this paper, Fe-15at.%Nb alloys were produced from high purity Fe (min. 99.8%) and Nb (min. 99.8%) powders via a mechanical alloying process. The effects of different Process Control Agents (i.e., methanol, hexane, and stearic acid) were investigated with powder morphologies, particle size distribution, and phase formation, and were sampled after up to 80 milling hours at 350 rpm. The powder morphologies and particle sizes were evaluated using scanning electron microscopy and laser diffraction analysis, respectively, and phases were identified via X-ray powder diffractometry. The results demonstrate for all conditions that, in the early stages, there was significant particle agglomeration due to the ductile-ductile feature of Fe and Nb powders, and latter an amorphization trend up to 80 milling hours. Methanol was the most efficient Process Control Agent in terms of avoiding cold welding, reducing of agglomeration, particle size distribution, reducing contamination and crystallinity reduction rate.

Abstract Nodular cast iron is a fundamental material used in engineering. It has unique properties and is one of the most produced materials in the world nowadays. The production of nodular cast iron involves melting of raw materials such as steel scrap, pig iron, machining returns and alloy irons. With the development of increasingly technological steels through the addition of chemical elements to meet a specific application, there is an increasing difficulty in acquiring steel scrap content low alloy for the production of nodular cast iron. The chemical elements present in the steel scrap favor the appearance of unwanted phases and particles. The present study evaluated the effect of the addition of the elements copper, chromium, molybdenum and nickel in levels between 0.50% w and 1.0% w in the formation of nodular cast iron microstructure. While nickel and copper were evenly distributed in the matrix, chromium and molybdenum formed carbides. In addition, chromium strongly favored the formation of perlite in nodular cast iron and molybdenum, the martensite.

Abstract One of the major health security challenges of the 21st century is the occurrence of microbial infections and bacterial complications that could affect 10 million people by 2050. On the biomaterial field, implant metallic currently replaces partial or total body parts and can fail to be integrated into the body due to infections. This study performs two combined surface modifications on Ti-30Ta alloy, in order to obtain an infection-resistance and osseointegration surface on metallic implants to be tested within bacterial biofilm. The Group 1 investigated surface modifications by the anodization process in the electrolyte glycerol + NH4F 0.25% at 30V- 9 hours and annealed in 530°C (5°C/min). The Group 2 underwent the same process as Group 1 and, additionally, the samples were immersed in 0.3 M CaCl2 and 0.5 M Na2HPO4 solutions for hydroxyapatite growth. The substrate was characterized using scanning electron microscopy (SEM), X-ray diffractometer (XRD) and dynamic contact angle. S. epidermidis bacterial adhesion and biofilm formation. The results indicated that the Group 1 shows a higher antimicrobial activity, hydrophilic behavior and potential to be used for metallic implant applications. The Group 2 with the hydroxyapatite film coating did not have an improvement in the antimicrobial response.

RESUMO A cerâmica à base de fosfato de cálcio hidroxiapatita (Hap) é muito utilizada para reparos ósseos por ser um biomaterial biocompatível e apresentar propriedades osteocondutoras e osteoindutoras. No entanto, a baixa resistência mecânica da Hap pode limitar sua aplicabilidade. Assim, o presente trabalho tem como objetivo melhorar as propriedades mecânicas da Hap, associando-a à alumina (Al2O3), pela técnica de metalurgia do pó, que consiste na moagem dos pós precursores em moinho planetário, prensagem uniaxial e sinterização. A microestrutura e a resistência mecânica das amostras sinterizadas foram avaliadas através dos testes de densidade, microdureza, resistência à compressão e molhabilidade. Concluiu-se que o uso de Al2O3 no compósito melhora as propriedades mecânicas da Hap, enquanto diminui seu potencial hidrofílico. Assim, a composição com 40% de Hap / 60% de Al2O3 foi considerada a melhor para aplicações biomédicas.

ABSTRACT The hydroxyapatite calcium phosphate based ceramic (Hap) is widely used for bone repair, as it is a biocompatible biomaterial and because it has osteoconductive and osteoinductive properties. However, the low mechanical strength of Hap may limit its applicability. Thus, the present work aims to improve the mechanical properties of Hap, associating it with alumina (Al2O3), using the powder metallurgy technique, which consists in the milling of the precursor powders in a planetary ball mill, uniaxial pressing and sintering. The microstructure and mechanical strength of the sintered samples were evaluated using density, microhardness, compressive strength and wettability tests. It was concluded that the use of Al2O3 in the composite improves the mechanical properties of Hap, while decreases its hydrophilic potential. Thus, the composition with 40% Hap / 60% Al2O3 was considered the best for biomedical applications.

Abstract The Vanadis® 8 is a tool steel used in the manufacture of dies, punches and tools. It has a high carbon content combined with chromium, molybdenum and vanadium, and presents good performance in its mechanical properties. Usually, its chips obtained by machining are sold to companies that use remelting. However, this technique is considered expensive and harmful to the environment. Therefore, this work aimed to analyze the efficiency of the addition of vanadium carbide (VC) and molybdenum carbide (Mo2C) in the high energy ball milling of the Vanadis® 8 steel. Microstructural analysis were performed in the pure steel and with 3% of VC and Mo2C additions. The milling parameters used were: speed of 350 rpm, ball-to-powder weight ratio of 15:1 and times of 4, 8 and 12 hours. The results indicated that the Vanadis® 8 steel milled with VC presented the best microstructural results in all of the conducted tests.

Several studies have been carried out to develop new materials for biomedical applications. Material surfaces that present biomimetic morphology like nanotubes or nanofibers that provides nanoscale architectures have been shown to alter cell/biomaterial interactions. The coated surface biomaterial with biocompatible polymers and nanotubes of TiO2 is an alternative to improve osseointegration. The anodization process was performed to obtain nanotubes of TiO2 covering the Ti-30Ta alloy surface and the electrospinning process has been used for producing polymer fibers. Characterization techniques such as scanning electron microscopy (SEM - FEG), X-ray diffraction analysis (X-rays), thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC) and contact angle were used for samples analyses. Adult human adipose-derived stem cells (ADSCs) were used to investigate the cellular response and S. aureus antimicrobial activity on these coated surfaces. The results indicated that both surface modification treatment showed a favorable micro-environment for cells growth and proliferation such as adhesion, viability and morphology which is a desire property for an implant. In addition, the antimicrobial activity study presented both materials with similar growth of S. aureus. So, it can conclude nanotubes and nanofibers can be used at biomedical field and both present similar cell evaluation and antimicrobial activity results.

Abstract The Al4.5wt%Cu is an aeronautical and automobile alloy with extensive use in industry for structural purposes. The aim of this work was to evaluate two different solidification processes of the Al4.5wt%Cu alloy, conventional and unidirectional, as well as its recrystallization process. Firstly, the Al4.5wt%Cu alloy was deformed by cold rotary forging and then heat treated at temperatures that varied from 250 to 450 °C. The samples for analysis were obtained after 54, 76 and 91% of reductions in area. Tests of optical microscopy, scanning electron microscopy and Vickers microhardness were performed to evaluate the recrystallization process. The results indicated that the recrystallization started at 350 ºC, being that the conventional samples presented full recrystallization after 5 minutes, while the unidirectional samples presented only partial recrystallization. In general, both solidification processes presented similar results for all of the analysis performed.

Abstract The coating formation by Fe-Cr-Si codeposition was done in a single step via Halide Activated Pack Cementation (HAPC) on Nb-Si alloy with the aim of improving the oxidation resistance. The activator salt and temperature selections for HAPC process were obtained by thermodynamic analysis. The isothermal oxidation test results for the coated alloy at 1200 °C for 62 h showed good oxidation resistance. The mass gain was 17.5 mg/cm2. Furthermore, no cracks and spallation on the oxide layers were observed for the coated alloy after the oxidation test, being that the oxidative kinetics curve is in accordance with the parabolic rate law. On the other hand, total oxidation was observed for the uncoated alloy after 12 h at 1200 °C in the isothermal oxidation test. The mass gain was 49.27 mg/cm2 and several cracks and spallation on the oxide layers led to a severe oxidation process.

Abstract Aluminum bronze alloy is applied in environments that require materials of high mechanical resistance and wear, such as marine, oil & gas and aerospace ones. This study analyzes the densification of composites based on aluminum bronze with additions of the vanadium (VC) and niobium (NbC) carbides, and the influence of these carbides in the milling efficiency and improvement of the diffusion process between particles to obtain better results for density and porosity. The composites were produced by powder metallurgy from aluminum bronze powders obtained from the mechanical milling process of discarded scraps. The efficiency of the sintering process depends on parameters, such as the time and temperature of sintering, together with the size of the particles obtained from the milling process. This study aimed to obtain and characterize the composites produced by the powder metallurgy route, with NbC and VC addition and to analyze physical properties, such as density and porosity. The powder morphologies, particle sizes and samples sintered were performed by scanning electron microscopy (SEM), X ray diffraction (XRD), laser diffraction analysis and optical microscopy (OM). The results indicate that addition of VC improves the milling efficiency, when compared to NbC addition, since it promotes a greater reduction of the particle size, directly favoring the sintering process. In this case, to achieve similar particle size, twice the milling time was required when NbC was used. The density values achieve ~ 73% of reference material for VC addition and ~ 68% for NbC and porosities varying between 27% and 38%.

Abstract The 316L stainless steel (316L SS) is one of the most used metallic materials for implants, due to its high mechanical properties and low cost. However, it is bioinert. One possibility to improve its biocompatibility is the production of a composite with b-tricalcium phosphate (β-TCP) addition. This study investigated the mechanical behavior of 316L SS/β-TCP composites through powder metallurgy. For this, used were 3 compositions, with 0 %, 5 % and 20 % of β-TCP. The compositions with 5% and 20% were milled during 10 hours with a mass/sphere ratio of 1:10 and 350 rpm. All compositions were uniaxially pressed with 619 MPa and sintered during 1 hour at 1100ºC. The microstructural and mechanical evaluations were performed through scanning electron microscopy, density and compressive strength. The results indicated that, by increasing the percentage of β-TCP in the compositions, the mechanical resistance decreases, as a consequence of its low load support.

Abstract This study aims to analyze the efficiency of niobium and vanadium carbides in the high energy mechanical milling of aluminum bronze alloy. Two series of experiments were made following the same steps for both niobium carbide (NbC) and vanadium carbide (VC) additions: 30 g of chips were weighed and placed in a stainless steel jar with 3 % of carbide and 1 % of stearic acid for a mass/sphere relationship of 1:10. The milling was realized using a planetary ball mill for 10, 30 and 50 hours in an inert argon atmosphere at 300 rpm. Results shown in laser diffraction indicate a great reduction in the particle sizes of powders when VC is used. For 30 hours milling, D50 values ranged from 1580 µm with NbC to 182.3 µm with VC addition. The D50 values ranged from 251.5 µm with NbC to 52.26 µm with VC addition, for 50 hours milling. The scanning electron microscopy showed that in 10 hours of milling, the energy was not sufficient to achieve the shear of chips in both cases. For 30 hours, it's possible to observe particles with sizes between 100 µm and 800 µm with NbC addition while for the same milling time, with VC it's possible to see particles with different sizes, but with many shapes of fine particulates. For 50 hours milling, particles achieved the smaller sizes between 50 and 200 µm with NbC and ranging from 5 until 50 µm with VC addition.

Resumo Os aços inoxidáveis ferríticos vêm ganhando cada vez mais espaço na indústria, devido principalmente a sua grande durabilidade e aplicabilidade. Nos últimos anos, o crescente avanço tecnológico da indústria metal mecânica, possibilitou o desenvolvimento de novas ligas e processos de soldagem deste metal. Em meio a estes processos, a soldagem por resistência tem sido muito utilizada por possibilitar rapidez com custo baixo. Muito embora existam poucas informações disponíveis na literatura, é reconhecido que a união pela mescla da atuação simultânea de calor e deformação, presentes no processo de soldagem por resistência, podem interferir diretamente nas propriedades magnéticas e mecânicas dos aços inoxidáveis ferríticos. Assim, uma avaliação destas características em produtos manufaturados torna-se importante em determinados setores industriais, notadamente nos de equipamentos eletrônicos e metrológicos. O objetivo desse artigo é a observação das tensões residuais e propriedades magnéticas em diferentes níveis de energia de soldagem e deformação no processo de soldagem a ponto por resistência elétrica em chapas de aço AISI 444. Os resultados mostraram que a energia de soldagem e deformação afetam as propriedades magnéticas, por outro lado não existe influência substancial na tensão residual.

Abstract Ferritic stainless steel has been gaining space in the industry, due mainly to its durability and applicability. In recent years, the growing technological advances of the metalworking industry, enabled the development of new alloys and welding processes of this metal. In the midst of these processes, resistance spot welding has been largely used due to the very short process time with low cost. Although there is a lack of available information in the literature, the union of materials by the mixture of the simultaneous action of heat and deformation, present in the resistance spot welding, can affects the mechanical and magnetic properties directly of ferritic stainless steels. Thus, an evaluation of these characteristics in manufactured products becomes important in certain industrial sectors, especially in electronic and metrological equipment. The main objective of this article is the observation of residual stresses and magnetic properties at different levels of welding energy and deformation in the resistance spot welding process steel AISI 444. The results showed that welding and deformation energy affect magnetic properties, on the other hand there is no substantial influence on the residual stress.