Paulo Roberto MeiUniversity of Campinas | UNICAMP · School of Mechanical Engineering
Paulo Roberto Mei
Ph. D. in Mechanical Engineering
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157
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Introduction
Teaching and doing research in silicon purification, structure and properties of steels and metallic alloys
Additional affiliations
January 1977 - present
July 1976 - July 1977
Publications
Publications (157)
Technical contribution to the 59th Seminário de Laminação, Conformação de Metais e Produtos, part of the ABM Week 8th edition, September 3rd-5th, 2024, São Paulo, SP, Brazil.
Global attention is increasingly focused on recycling and clean energy generation. The present study delves into both areas by examining the reuse of secondary aluminium for hydrogen generation. The aim is to investigate how the microstructural length scale influences the hydrogen production behaviour of two Al-3%Mg (wt.%) alloys, with and without...
This work aimed to characterize a new class D microalloyed forged wheel (called 7NbMo). For this purpose, the following analyses were carried out: obtaining CCT curves for the steel (cooling rates of 0.5-50 °C/s), investigating the microstructure below the rolling track (scanning electron microscopy and hardness), performing mechanical tensile and...
Although temperature is an important variable in tribosystems, its monitoring and control are constantly neglected by studies that use the twin-disc test to simulate the interactions that occur at the wheel-rail interface. In this study, a heating system was developed that allows the performance of tests with temperature control. For validation, te...
Using greases offers numerous advantages to the railroad system, which include the lifespan extension of wheels and rails, fuel consumption decrease, and the reduction of the friction coefficient and component wear. However, there is still a lack of understanding regarding the relationship between the grease formulation and its performance. This st...
Tribological testing using twin disc equipment is widely used in railway research as it allows for a simulation of the complex wheel/rail tribological system. In this study, an extensive systematic bibliographic review was carried out, seeking to understand, synthesize, organize the knowledge developed and the methodological strategies adopted in r...
Niobium is added to carbon steels in small amounts (< 0.1weight %), thus being called a microalloying element, to increase mechanical strength and toughness. When added to steel, niobium is partly soluble in the matrix and another part combines with carbon and nitrogen forming a family of Nb x C y N z precipitates (niobium carbides, nitrides or car...
The railway wheels are one of the most critical components of the train and, any problem that may arise in the wheel, can generate numerous consequences. The ability to manage friction at the wheel-rail interface currently represents one of the greatest challenges and one of the most powerful tools in railway engineering. To define the efficiency o...
Twin-disc tests were carried out between two discs of rail steel (fully pearlitic and spheroidized microstructures) to investigate the effect of the flash-butt welded rail HAZ microstructure. The spheroidized cementite micro-structure was obtained by heat-treating simulating the HAZ softer region. Ten tests were performed for each condition, consid...
Railway transport companies in Brazil and worldwide have become more productive and efficient by increasing the weight transported and using faster locomotives. These actions have caused the premature exchange of wheels and rails due to excessive wear and rapid growth of rolling contact fatigue (RCF) cracks, and both consequences have been minimize...
This research shows two new microalloyed steels with niobium (Nb) for railroad wheels (Nb1 and Nb2) applied on heavy haul transportation (load over 30 tons/axle). The steels have mixed microstructure composed of pearlite and bainite (finished wheel rim section), and another one composed of martensite with bainite (black wheel section removed on mac...
Management of wheel-rail contact is of great importance for railways. It is essential to understand the tribology of railway materials to maximize productivity and reduce maintenance. Many studies on wear and rolling contact fatigue (RCF) were performed, ranging from field and full-scale experiments to small-scale tests, such as twin-disc. However,...
Brazilian heavy-haul railway companies have drawn extensive research in the last years for developing solutions that can make the operation in this area more efficient and safer, such as friction management, the use of new mechanical assemblies, and the use of new materials for wheels and rails. Another solution implemented is increasing the weight...
As ligas a base de ferro, especialmente os aços, são materiais tão comuns e importantes na nossa civilização que, por vezes, sua existência e presença generalizada em nossas vidas é pouco percebida. A esfera da caneta do estudante, lâminas de barbear, talheres, ferramentas manuais dos mecânicos e pedreiros, carroceria, estrutura e peças dos automóv...
Superduplex stainless steel alloy exhibit high mechanical and corrosion resistance, which main industrial application is in the petrochemical industry. The manufacture and maintenance of such equipment usually involve welding processes, followed by post-welded heat treatment and it often becomes impossible to apply heat treatments. Thereby, the pur...
This article focused on the microstructure characterization and residual stress measurements of the flange from classes D and C railway wheels (called 7D and 7C steel, respectively) to contribute with the residual stress level on new forged wheels flange area. A correlation with the hardness was conducted. The residual stress was measured in three...
Wear and contact fatigue are the main problems that reduce the durability of the rail and wheels. Pearlitic and bainitic microstructures have been studied over the years to obtain steel with higher mechanical properties, minimizing the wear and fatigue defects. However, the studies have not yet consistently confirmed whether bainite is a better alt...
The Heavy-Haul railroad wheels started to use higher wear resistance steels microalloyed with niobium, vanadium, and molybdenum [1]. During continuous cooling, these elements depress the temperature of the pearlite formation, producing smaller interlamellar spacing that increases the hardness of the steel, besides to favor the precipitation hardeni...
The maximum allowed hardness for low carbon martensitic stainless steel components used in the oil and gas industry is 247 HV. Inter-critical tempering is an effective method for hardness control due to the production of stable reverted austenite. By conducting multiple-step tempering cycles, the austenite reversion kinetics can be accelerated and...
At the Brazilian Synchrotron Light Laboratory (LNLS), new double-crystal monochromators are under development for use at the new Brazilian fourth-generation synchrotron, Sirius. The soldering technique used for the double-crystal monochromators ensures the union of monocrystalline silicon with FeNi alloy, Invar36 (64Fe–36Ni) from Grupo Metal and In...
During welding of the superduplex stainless steels are exposed to thermal cycles, allowing precipitation of deleterious phases as well as unbalance as the ferrite and austenite phases. This work analyzed the microstructural changes taking place on a plate ASTM A890/A890M-grade 6A steel submitted to arc welding one welding of pass conducted on a fla...
This work addresses the fundamentals of inter-critical austenite reversion in a Ti-stabilized 12Cr-6Ni-2Mo (at.%) supermartensitic stainless steel, combining thermodynamic and experimental assessments. The calculation of the temperature and composition at which ferrite and austenite phases have the same free energy, i.e. T0 and C0(T), respectively,...
To verify the effect of 0.13 % vanadium addition (% in weight) on the wear resistance of a railroad wheel steel with 0.7 % carbon, twin-disc rolling-sliding test were performed. These two steels were named 7V and 7C. The test discs were analyzed to verify the superficial conditions and wear mechanisms using SEM (Scanning Electron Microscopy) and ro...
Upgraded metallurgical grade silicon (UMG-Si) was obtained through metallurgical methods using two steps. First, metallurgical grade silicon was purified by the vacuum degassing technique using an electron-beam system. An ingot was then produced through Czochralski (CZ) growth. This later process was also used to reduce impurities through the segre...
Heavy haul transportation (load over 30 tons/axle), as well as the axle load, has been more and more used in Brazil and worldwide. The stress generated in the wheel-rail contact with loads up to 30 tons/axle is around 760 MPa, which causes premature wear and cracks of conventional wheels (AAR (Association of American Railroads) class C). Microalloy...
The thermal cycles associated to friction stir welding and processing produce a wide range of
microstructures, resulting in different mechanical behaviors along the weld. Most research
efforts have focused on the development of welding parameters to obtain sound welds,
yet there is still an opportunity for performance improvement based on the under...
The Double Crystal Monochromator (DCM) will be developed at the Brazilian Synchrotron Light Laboratory (LNLS) to select the desired X-Ray wavelength of Sirius, the new Brazilian fourth generation synchrotron. Components of this optical instrumentation can be obtained through welding processes, such as brazing, soldering, and diffusion bonding. The...
Metastable β-type Ti alloys with non-toxic addition elements such as Mo, Zr, Sn, Ta and Nb were developed as an alternative to the widely used Ti-6Al-4V alloy for biomedical applications. These alloys possess enhanced biocompatibility and reduced elastic modulus in comparison with Ti-6Al-4V. Moreover, for orthopedic implants, low Young's modulus is...
Controlling the amount of reverted austenite at room temperature allows for tailoring of mechanical properties in supermartensitic stainless steels. The austenite reversion and stabilization occurs during inter-critical tempering through partitioning of austenite-stabilizing elements. The degree of partitioning greatly depends on the reversion temp...
The increasing in the ratio load per wagon has been a fundamental subject to reduce the
costs in railway transportation, requiring wheels with a higher strength and toughness.
One of the strategies is to add small amounts of alloys (<0,5% in weight) of niobium
and/or vanadium, wich in solid solution on austenite retards its decomposition increas...
Recent studies have focused on the development of metastable beta-type Ti alloys with non-toxic elements such as Nb, Ta, Mo and Zr for biomedical applications. These alloys present low modulus, good mechanical compatibility and good corrosion resistance. Moreover, the processing variables can be controlled to produce microstructures with specific p...
Correlative physical simulation, synchrotron x-ray diffraction and laser dilatometry were used to characterize the surface and volumetric austenite reversion kinetics and stability in a Ti-stabilized supermartensitic stainless steel. A fast heating rate of 500 °C s−1 was used to minimize any martensite to austenite reversion related to the heating...
Os aços inoxidáveis superduplex (AISD) são materiais de grande aplicação na indústria de Óleo e Gás, principalmente nas plataformas “offshore”, devido ao seu excelente desempenho mecânico e resistência à corrosão por pite em ambientes contendo íons cloreto. A fabricação de componentes de bombas centrífugas, com geometrias complexas, tais como rotor...
2013 - 1st Proceedings of FSW -- Osaka -- Page 65
DOI: 10.1533/978-1-78242-164-1.75
As ligas de titânio são bem satisfatórias para aplicações biomédicas devido a suas propriedades físicas, mecânicas e biológicas. Recentemente, houve muitas pesquisas voltadas para o desenvolvimento de ligas de Ti do tipo β, compostas de elementos não tóxicos (Nb,Mo,Ta,...), pois as vantagens destas ligas em relação as ligas do tipo alfa e alfa + βe...
Ligas de titânio do tipo beta têm sido largamente desenvolvidas para aplicações na área biomédica por apresentar uma boa combinação de propriedades, tais como, baixo módulo de elasticidade, alta resistência e boa ductilidade com excelente resistência a corrosão. Devido a isto foi desenvolvida uma nova liga do tipo beta metaestável Ti-12Mo-3Nb. Este...
Ligas de titânio do tipo beta têm sido largamente desenvolvidas para aplicações na área biomédica por apresentar uma boa combinação de propriedades, tais como, baixo módulo de elasticidade, alta resistência e boa ductilidade com excelente resistência a corrosão. Devido a isto foi desenvolvida uma nova liga do tipo beta metaestável Ti-12Mo-3Nb. Este...
As ligas de titânio são bem satisfatórias para aplicações biomédicas devido a suas propriedades físicas, mecânicas e biológicas. Recentemente, houve muitas pesquisas voltadas para o desenvolvimento de ligas de Ti do tipo β, compostas de elementos não tóxicos (Nb,Mo,Ta,...), pois as vantagens destas ligas em relação as ligas do tipo alfa e alfa + βe...
O objetivo deste trabalho foi o de determinar, de maneira sistemática, o potencial de remoção de impurezas do silício de grau metalúrgico, empregando-se a técnica de FZ (fusão zonal) em forno de feixe de elétrons, com cadinho de cobre refrigerado a água. Utilizou-se silício de grau metalúrgico (99,85% de pureza em massa ou 1.500 ppm de impurezas) p...
Super duplex stainless steels (SDSS) are widely used in many industrialapplications, such as petrochemical sector due to their excellent mechanicalproperties and corrosion resistance. Frequently, the production of theseequipments requires fusion welding to join components and to operate smallrepairs. It is known that the changes of microstructures...
Mechanical properties of metastable β-Ti alloys are highly dependent on the final microstructure, which is controlled by the thermomechanical processing. These alloys are used for biomedical applications and require a high mechanical strength as well as a low Young’s modulus to avoid stress shielding. Previous work on the development of cold swaged...
Friction stir welding with the optimum parameters offers high toughness and mechanical properties for pipeline steel applications; however, at subzero temperatures such joints have shown decreased toughness relative to room temperatures values as well as predominantly brittle behavior. This paper relates certain microstructural features to fracture...
Friction stir welding with the optimum parameters offers high toughness and mechanical properties for pipeline steel applications; however, at subzero temperatures such joints have shown decreased toughness relative to room temperatures values as well as predominantly brittle behavior. This paper relates certain microstructural features to fracture...
Friction-stir welding (FSW) is an alternative welding process for pipelines. This technology offers sound welds, good repeatability, and excellent mechanical properties. However, it is of paramount importance to determine the toughness of the welds at low temperatures in order to establish the limits of this technology. Ductile-to-brittle transitio...
Fracture mechanics approach is important for all mechanical and civil projects that might involve cracks in metallic materials, and especially for those using welding as a structural joining process. This methodology can enhance not only the design but also the service life of the structures being constructed. This paper includes detailed considera...
To understand the effect of vanadium on the austenite decomposition of a 0.7 %C steel used in railway wheels the Continuous Cooling Transformation (CCT) diagrams were obtained and the microstructures analyzed with optical, SEM, TEM and XRD techniques. Vanadium refined the austenitic grain (12 and 6 μm for 7C and 7V, respectively), what can be expla...
Beta titanium alloys were developed for biomedical applications due to the combination of its mechanical properties including low elasticity modulus, high strength, fatigue resistance, good ductility and with excellent corrosion resistance. With this perspective a metastable beta titanium alloy Ti-12Mo-13Nb was developed with the replacement of bot...
In order to verify the viability of dissimilar UNS S31603 austenitic and UNS S32750 superduplex stainless steels joined by friction stir welding, 6-mm-thick plates were welded using a PCBN-WRe tool. The welded joints were performed in position control mode at rotational speeds of 100 to 300 rpm and a feed rate of 100 mm/min. The joints performed wi...
The acoustoelastic theory states that mechanical stress relates to the wave speed. The microstructure of the materials influences the propagation of any ultrasonic wave, which is a major drawback in employing critically refracted longitudinal waves (L \(_\mathrm{CR}\) ) in field measurements. The present study investigates the effect of mean austen...
Ligas de Ti são muito utilizadas em aplicações biomédicas. Dentro desta classe, as ligas de Ti do tipo β metaestável se destacam, pois através de processamentos termomecânicos é possível obter propriedades mecânicas e em especial, um módulo de elasticidade adequados para aplicação biomédica. Estas ligas para serem usadas em aplicações ortopédicas r...
Ligas de Ti são muito utilizadas em aplicações biomédicas. Dentro desta classe, as ligas de Ti do tipo β metaestável se destacam, pois através de processamentos termomecânicos é possível obter propriedades mecânicas e em especial, um módulo de elasticidade adequados para aplicação biomédica. Estas ligas para serem usadas em aplicações ortopédicas r...
Zone refining comprises a number of techniques utilized to deal with the rearrangement of soluble impurities or phases along a bar in order to produce high-purity materials. The concentration curves can be predicted for given values of segregation partition coefficient (k), molten zone length, and a number of sequential zone passes. The combination...
Austenitic stainless steels represent a significant portion of the alloys used in the aeronautical, chemical, shipbuilding, food processing and biomechanical industries. They combine good mechanical properties with high corrosion resistance. When subjected to cold deformation, these steels exhibit a metastable phase called: strain induced martensit...
We report a combination of metallurgical routes intended to improve the purity of metallurgical grade silicon (MG-Si) for solar cell fabrication. Initially, MG-Si was submitted to vacuum degassing (VD) by means of an electron-beam to reduce the impurities represented by chemical elements with high vapour pressure. This was followed by preparing a m...
The influence of adding molybdenum and niobium on the microstructure and mechanical properties of C5 steel used in railway wheels was studied. The samples were heated to 1250°C and hot rolled in four passes, starting at 1200°C, undergoing a total reduction of 67%, followed by air cooling. After rolling between 1200 and 1120°C, it was found that add...
Resumo. Este trabalho apresenta o uso de duas técnicas metalúrgicas diferentes utilizadas para purificar silício metalúrgico nacional. O material foi submetido ao um processo de desgaseificação o vácuo com feixe de elétrons que reduz os elementos com alta pressão de vapor. O material obtido foi utilizado para crescimento Czochralski que finaliza o...
In recent years, different beta titanium alloys have been developed for biomedical applications with a combination of mechanical properties including a low Young's modulus, high strength, fatigue resistance and good ductility with excellent corrosion resistance. From this perspective, a new metastable beta titanium Ti–12Mo–3Nb alloy was developed w...
For the production of photovoltaic cells, the silicon purity can be intermediate between metallurgical grade silicon (MG-Si, 98%–99.9% pure) and electronic grade silicon (>99.9999% pure). This silicon, with intermediate purity and that still meets solar cell requirements, is called upgraded metallurgical grade silicon (UMG-Si). One method of produc...
As the silicon melting point is very high (1414 °C), the temperature in the solid fraction, near the interface solid/liquid during solidification is also high and this can provoke a solute redistribution in the solidified portion. This phenomena is called back diffusion. So, it is important to estimate the potential of back diffusion during the sol...
In this study, we aimed at systematically determining the potential of the zone melting (ZM) technique to remove impurities from Metallurgical Grade Silicon (MG- Si) in an Electron Beam Furnace (EBF), using a water-cooled copper crucible. Our focus was on obtaining solar grade silicon, with the purity between Electronic Grade Silicon (EG-Si) and MG...