Selective Laser Melting and Mechanical Properties of Stainless Steels.

Metal additive manufacturing (AM) has been evolving in response to industrial and social challenges. However, new materials are hindered in these technologies due to the complexity of direct additive manufacturing technologies, particularly selective laser melting (SLM). Stainless steel (SS) 316L, due to its very low carbon content, has been used as a standard powder in SLM, highlighting the role of alloying elements present in steels. However, reliable research on the chemical impact of carbon content in steel alloys has been rarely conducted, despite being the most prevalent element in steel. Considering the temperatures involved in the SLM process, the laser-powder interaction can lead to a significant carbon decrease, whatever the processing atmosphere. In the present study, four stainless steels with increasing carbon content-AISI 316L, 630 (17-4PH), 420 and 440C-were processed under the same SLM parameters. In addition to roughness and surface topography, the relationship with the microstructure (including grain size and orientation), defects and mechanical properties (hardness and tensile strength) were established, highlighting the role of carbon. It was shown that the production by SLM of stainless steels with similar packing densities and different carbon contents does not oblige the changing of processing parameters. Moreover, alterations in material response in stainless steels produced under the same volumetric energy density mainly result from microstructural evolution during the process.

The Study of New NiTi Actuators to Reinforce the Wing Movement of Aircraft Systems.

Actuators using Shape Memory Alloy (SMA) springs could operate in different mechanical systems requiring geometric flexibility and high performance. The aim of the present study is to highlight the potential of these actuators, using their dimensional variations resulting from the phase transformations of NiTi springs (SMA) to make the movements of the system's mobile components reversible. This reversibility is due to thermal-induced martensitic transformation of NiTi springs. The transformation promotes the extended and retracted of the springs as the phase changing (martensite-austenite) creates movement in part of the system. Therefore, the phase transition temperatures of NiTi, evaluated by differential scanning calorimetry (DSC), are required to control the dimensional variation of the spring. The influence of the number of springs in the system, as well as how impacts on the reaction time were evaluated. The different numbers of springs (two, four, and six) and the interspaces between them made it possible to control the time and the final angle attained in the mobile part of the system. Mechanical resistance, maximum angle, and the system's reaction time using different NiTi springs highlight the role of the actuators. Fused Deposition Modelling (FDM)/Material Extrusion (MEX) or Selective Laser Sintering (SLS) was selected for shaping the composite matrix system. A new prototype was designed and developed to conduct tests that established the relationship between the recoverable deformation of the matrix suitable for the application as well as the number and distribution of the actuators.

Searching New Solutions for NiTi Sensors through Indirect Additive Manufacturing.

Shape Memory Alloys (SMAs) can play an essential role in developing novel active sensors for self-healing, including aeronautical systems. However, the NiTi SMAs available in the market are almost limited to wires, small sheets, and coatings. This restriction is mainly due to the difficulty in processing NiTi through conventional processes. Thus, the objective of this study is to evaluate the potential of one of the most promising routes for NiTi additive manufacturing-material extrusion (MEX). Optimizing the different steps during processing is mandatory to avoid brittle secondary phases formation, such as Ni3Ti. The prime NiTi powder is prealloyed, but it also contains NiTi2 and Ni as secondary phases. The present study highlights the role of Ni and NiTi2, with the later having a melting temperature (Tm = 984 °C) lower than the NiTi sintering temperature, thus allowing a welcome liquid phase sintering (LPS). Nevertheless, the reaction of the liquid phase with the Ni phase could contribute to the formation of brittle intermetallic compounds, particularly around NiTi and NiTi2 phases, affecting the final structural properties of the 3D object. The addition of TiH2 to the virgin prealloyed NiTi powder was also studied and revealed the non-formation of Ni3Ti for a specific composition. The balancing addition of extra Ni revealed priority in the Ni3Ti appearance, emphasizing the role of Ni. Feedstocks extruded (filaments) and green strands (layers), before and after debinding & sintering, were used as homothetic of 3D objects for evaluation of defects (microtomography), microstructures, and mechanical properties. The composition of prealloyed powder with 5 wt.% TiH2 addition after sintering showed a homogeneous matrix with the NiTi2 second phase uniformly dispersed.

Joining of Ti6Al4V to Al2O3 Using Nanomultilayers.

Diffusion bonding of Ti6Al4V to Al2O3 using Ni/Ti reactive nanomultilayers as interlayer material was investigated. For this purpose, Ni/Ti multilayer thin films with 12, 25, and 60 nm modulation periods (bilayer thickness) were deposited by d.c. magnetron sputtering onto the base materials' surface. The joints were processed at 750 and 800 °C with a dwell time of 60 min and under a pressure of 5 MPa. Microstructural characterization of the interfaces was conducted by scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). The mechanical characterization of the joints was performed by nanoindentation, and hardness and reduced Young's modulus distribution maps were obtained across the interfaces. The joints processed at 800 °C using the three modulation periods were successful, showing the feasibility of using these nanolayered films to improve the diffusion bonding of dissimilar materials. Using modulation periods of 25 and 60 nm, it was also possible to reduce the bonding temperature to 750 °C and obtain a sound interface. The interfaces are mainly composed of NiTi and NiTi2 phases. The nanoindentation experiments revealed that the hardness and reduced Young's modulus at the interfaces reflect the observed microstructure.

Development of Actuators for Repairing Cracks by Coating W Wires with Reactive Multilayers.

The aim of this research work was to optimize the coating of tungsten wires with reactive multilayer thin films and promote an exothermic self-propagating reaction. The ultimate goal is to use this heat to liquify low melting temperature materials, and thus block crack propagation in metallic materials. Ni/Me (Me = Al, Ti) multilayers were deposited by a DC (direct current) magnetron sputtering onto tungsten wires with diameters of 0.05 and 0.20 mm. The depositions were carried out to obtain films with near equiatomic average chemical composition and a modulation period (bilayer thickness) between 20 and 50 nm. The cross-section of the films was analyzed using electron microscopy before and after electrical ignition. A new substrate holder was developed to improve the quality of the Al/Ni films, allowing a reduction in the defects previously observed. The Ni/Ti thin films showed no discernible defects, regardless of the substrate holder. However, after ignition, the Ni + Ti reaction occurred in a non-self-propagating mode. Passing an electric current through a wire (ϕ = 0.05 mm) coated with an Al/Ni thin film, promoted a flash of light that was associated with the start of a self-propagating reaction. The reaction product was a B2-AlNi intermetallic phase. W wires coated with reactive multilayers may contribute to crack filling, and have potential to be self-healing actuators.

Influence of Metallic Powder Characteristics on Extruded Feedstock Performance for Indirect Additive Manufacturing.

Material extrusion (MEX) of metallic powder-based filaments has shown great potential as an additive manufacturing (AM) technology. MEX provides an easy solution as an alternative to direct additive manufacturing technologies (e.g., Selective Laser Melting, Electron Beam Melting, Direct Energy Deposition) for problematic metallic powders such as copper, essential due to its reflectivity and thermal conductivity. MEX, an indirect AM technology, consists of five steps-optimisation of mixing of metal powder, binder, and additives (feedstock); filament production; shaping from strands; debinding; sintering. The great challenge in MEX is, undoubtedly, filament manufacturing for optimal green density, and consequently the best sintered properties. The filament, to be extrudable, must accomplish at optimal powder volume concentration (CPVC) with good rheological performance, flexibility, and stiffness. In this study, a feedstock composition (similar binder, additives, and CPVC; 61 vol. %) of copper powder with three different particle powder characteristics was selected in order to highlight their role in the final product. The quality of the filaments, strands, and 3D objects was analysed by micro-CT, highlighting the influence of the different powder characteristics on the homogeneity and defects of the greens; sintered quality was also analysed regarding microstructure and hardness. The filament based on particles powder with D50 close to 11 µm, and straight distribution of particles size showed the best homogeneity and the lowest defects.

From Machining Chips to Raw Material for Powder Metallurgy-A Review.

Chips are obtained by subtractive processes such as machining workpieces and until recently considered as waste. However, in recent years they are shown to have great potential as sustainable raw materials for powder technologies. Powder production from metal chips, through the application of solid-state processes, seems to be an alternative to conventional atomization from liquid cooled with different fluids. However, chip material and processing have an essential role in the characteristics of powder particles, such as particle size, shape, size distribution and structure (4S's), which are essential parameters that must be considered having in mind the powder process and the metallurgy applications. Moreover, different approaches refereed in the application of this new "powder process" are highlighted. The goal is to show how the actual research has been transforming subtractive processes from a contributor of wastes to clean technologies.

Experimental Analysis of NiTi Alloy during Strain-Controlled Low-Cycle Fatigue.

The interaction between the stress-induced martensitic transformation and resistivity behavior of superelastic NiTi shape memory alloy (SMA) was studied. Strain-controlled low-cycle fatigue up to 6% was monitored by in situ electrical resistivity measurements. The experimental results show that a great motion of martensite fronts results in a significant accumulation of defects, as evidenced by transmission electron microscopy (TEM), before and after the tensile cycles. This gives rise to an overall increase of the resistivity values up to the maximum deformation. Therefore, the research suggests that shape memory alloy wire has great potential as a stress sensor inside bulk materials.

In Search of the Optimal Conditions to Process Shape Memory Alloys (NiTi) Using Fused Filament Fabrication (FFF).

This research was performed so as to investigate the additive manufacturing of NiTi shape memory alloys, which is associated with direct processes, such as selective laser melting. In addition to its expensive production costs, NiTi readily undergoes chemical and phase modifications, mainly as a result of Ni loss during processing as a result of high temperatures. This research explores the potential usefulness of NiTi as well as its limitations using indirect additive processes, such as fused filament fabrication (FFF). The first step was to evaluate the NiTi critical powder volume content (CPVC) needed to process high-quality filaments (via extrusion). A typical 3D printer can build a selected part/system/device layer-by-layer from the filaments, followed by debinding and sintering (SDS), in order to generate a near-net-shape object. The mixing, extruding (filament), printing (shaping), debinding, and sintering steps were extensively studied in order to optimize their parameters. Moreover, for the sintering step, two main targets should be met, namely: the reduction of contamination during the process in order to avoid the formation of secondary phases, and the decrease in sintering temperature, which also contributes to reducing the production costs. This study aims to demonstrate the possibility of using FFF as an additive manufacturing technology for processing NiTi.

Living Conditions as a Driving Factor in Persistent Methicillin-resistant Staphylococcus aureus Colonization Among HIV-infected Youth.

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) colonization has been linked to HIV-related sexual and social behaviors. MRSA risk factors may be different for HIV-infected children, adolescents and young adults. We investigated the association of MRSA colonization, persistent colonization and genotypes with potential risk factors among HIV-infected youth. METHODS: For this case-control study, patients 24 years of age or younger attending 2 HIV reference centers were recruited from February to August 2012 and followed for 1 year. Nasal swabs were collected at enrollment and every 3 months. MRSA clones were characterized by staphylococcal chromosomal cassette mec typing, spa typing and multilocus sequence typing. We compared MRSA colonization and persistent colonization with patient demographic and clinical characteristics. RESULTS: Among 117 participants, MRSA colonization frequency (calculated for each collection based on the number of positive cultures per patient) was 12.8% at the first collection. The average MRSA colonization frequency was 10.4%. Our results showed 11.1% were persistent carriers (subjects with more than 1 positive culture in at least 3). Crowding was the only factor associated with MRSA colonization (P = 0.018). Persistent carriers had significantly higher (4.2 times) odds of living in a crowded household (95% confidence interval-1.1-16.2). We observed high genetic diversity among MRSA isolates, with t002/ST5 and t318/ST30 being the most frequent. CONCLUSIONS: MRSA colonization among HIV-infected youth is more closely related to living in a low-income or slum community than to HIV-related clinical factors. High genetic MRSA isolate diversity in our population suggests frequent transmission.

Determination of airborne nanoparticles from welding operations.

The aim of this study is to assess the levels of airborne ultrafine particles emitted in welding processes (tungsten inert gas [TIG], metal active gas [MAG] of carbon steel, and friction stir welding [FSW] of aluminum) in terms of deposited area in pulmonary alveolar tract using a nanoparticle surface area monitor (NSAM) analyzer. The obtained results showed the dependence of process parameters on emitted ultrafine particles and demonstrated the presence of ultrafine particles compared to background levels. Data indicated that the process that resulted in the lowest levels of alveolar deposited surface area (ADSA) was FSW, followed by TIG and MAG. However, all tested processes resulted in significant concentrations of ultrafine particles being deposited in humans lungs of exposed workers.

Photorejuvenation with topical methyl aminolevulinate and red light: a randomized, prospective, clinical, histopathologic, and morphometric study.

BACKGROUND: Photodynamic therapy (PDT) is an option for skin rejuvenation. Although many studies report clinical improvement with PDT in photodamaged skin, histologic and morphometric evidence is not documented in most cases. OBJECTIVE: To evaluate clinical and histopathologic changes induced by methyl aminolevulinate (MAL)-PDT and to morphometrically quantify collagen and elastic fibers in skin remodeling induced by MAL-PDT in photodamaged skin. METHODS AND MATERIALS: Fourteen patients were treated with two sessions of MAL-PDT. The light source was a light-emitting diode: 635 nm, 37 J/cm(2). Skin biopsies were performed before and 3 and 4 months after treatment. All fragments were stained using the hematoxylin-eosin, orcein, and picrosirius techniques. Morphometric studies were done of three samples from each patient. RESULTS: Global clinical improvement was observed in 10 of 14 patients. The histopathologic study showed increased collagen fibers 3 and 6 months after treatment. The decrease in the amount of elastic fiber was statistically significant 3 (p=.016) and 6 (p=.008) months after treatment. The increase in the amount of collagen fiber was statistically significant 6 months after treatment (p=.048). CONCLUSION: Clinical improvement with regard to texture, firmness, wrinkle depth, skin coloration, and clearance of actinic keratoses was observed. Histopathologic and morphometric studies were consistent with the clinical findings.

Coronary-subclavian steal syndrome. A case report.

Coronary-subclavian steal is an unusual clinical syndrome after successful internal mammary-coronary artery bypass grafting. Proximal subclavian artery (SA) stenosis is present and atherosclerotic disease is the underlying pathophysiologic mechanism in the majority of cases. The authors report a case of a sixty-two-year old man with angina and ventricular fibrillation soon after myocardial revascularization with left internal mammary artery (LIMA) to left anterior descending coronary (LAD). Dobutamine stress echocardiography showed ischemia in the anterior myocardial territory with patent LIMA-LAD bypass in the angiographic evaluation. This procedure showed occlusion of the proximal SA with reversal of flow in the LIMA. The best therapeutic approach was discussed and a carotid-subclavian bypass was performed with restoration of antegrade blood flow and reversal of the clinical setting.

[Factors associated with necrotizing enterocolitis]. / Fatores associados à enterocolite necrosante.

OBJECTIVE: To evaluate the features of clinical presentation of neonatal necrotizing enterocolitis and its associated factors. METHODS: Retrospective study of the cases of neonatal necrotizing enterocolitis (n = 56) diagnosed at Neonatal Intensive Care Unit Lagoa (NICU), between December 1986 and July 1992. Diagnosis and stages of the disease followed the modified Bell's criteria. Diagnosis and follow-up of all cases were evaluated. The cases of enterocolitis - degrees II and III (n = 44) - were subsequently selected and compared to a case-control group (n = 44), selected according to birthweight (+/- 250 g) and hospitalization period (+/- 2 weeks). The statistically significant analysis was considered as p < 0.05. RESULTS: Out of 2,447 newborns admitted to the NICU, 56 (2.3%) presented enterocolitis. Mean weight was 1908.5 g; mean gestational age was 35 weeks and 1 day; mean period for diagnosis was 10.7 days; 51 (91.1%) patients were fed before diagnosis; 18 (32.1%) needed urgent surgery; nine (16.9%) hemocultures were positive; 10 (17.8%) patients died. Four clinical standards were observed: fulminant, acute with pneumatosis, insidious and suspect. Comparatively to the case-control group, three factors were significantly associated with enterocolitis: apnea (p = 0.045), rapid increase of food intake (< 20 ml/kg/day) - (p = 0.048) and presence of infectious agent (p = 0.000). CONCLUSIONS: Significant factors associated with enterocolitis were occurrence of apnea, rapid increase of food intake and identification of the infectious agent.

Fatores associados à enterocolite necrosante / Factors associated with necrotizing enterocolitis

Objetivo: avaliar as formas de apresentação clínica da enterocolite necrosante neonatal e os fatores associados à doença. Métodos: estudo retrospectivo dos casos de enterocolite necrosante neonatal (ECN) (n=56) ocorridos na UTI Neonatal Lagoa, entre dezembro de 1986 e julho de 1992. O diagn6stico e o estadiamento da doença seguiram o critério de Bell modificado. Foram avaliados o diagn6stico e a evolução de todos os casos. Posteriormente, foram selecionados os casos de enterocolite grau II e III(n=44) e comparados com um grupo controle (n=44), selecionado pelo peso de nascimento (250g) e época de internação (2 semanas). Para a análise estatística, foi considerado significante p<0,05. Resultados: dos 2.447 recém-natos internados na UTI, 56 (2,3po cento ) evoluíram com enterocolite. O peso médio dos pacientes foi de 1.908,5g; a idade gestacional média, de 35 semanas e um dia; a idade média do diagn6stico foi de 10, 7 dias; 51 (91,1por cento ) pacientes foram alimentados anteriormente ao diagnóstico; 18 (32, 1por cento) necessitaram de cirurgia de urgência; em 9 (16,9por cento) as hemoculturas foram positivas; 10 (17,8) pacientes faleceram. Observaram-se quatro padrões evolutivos da doença: aguda fulminante, aguda com pneumatose, insidiosa e suspeita. Comparativamente ao grupo controle, três fatores associaram-se significativamente à enterocolite: apnéia(p=0,045), a progressão rápida da dieta (acima de 20 ml/kg/dia)(p=0,048) e a presença de agente infeccioso (p=0,000).Conclusões: os fatores associados significativamente à enterocolite foram a ocorrência de apnéia, a progressão rápida da dieta e a identificação do agente infeccioso