23 research outputs found
Development of wear resistant spray-formed supermartensitic stainless steel for "risers" application
The oil exploitation and production in the pre-salt layers in safe, efficient and economically viable way depend on the development of materials that bear the severe conditions found in their applications during their whole life cycle. The pipes used in the oil exploitation and production such as drilling risers are subjected to severe work conditions. The stainless steel grades, such as the supermartensitic, duplex and superduplex, present the corrosion resistance and mechanical properties suit to the application in pipes used the oil exploitation, however, these materials present low wear resistance. Recent studies performed in the Materials Engineering Department at the Federal University of São Carlos (DEMa-UFSCar) have shown that the boron addition in stainless steel grades composition promotes borides formation, which increases the wear resistance of these materials. In this context, this protect aims the study of the wear resistance of spray-formed supermartensitic stainless steel with small additions of boron in its composition. This process allows the attainment of deposits with refined and homogeneous microstructure and with uniformly distributed precipitates directly from the liquid metal. The materials produced were characterized trough the techniques of X-ray diffraction (XRD), Optical microscopy (OM), scanning electron microscopy (SEM) and chemical microanalysis by energy dispersive spectroscopy (EDS). The materials wear resistance was evaluated trough the dry sand against rubber wheel test (ASTM G65-04) and trough a developed test that simulate one of the wear conditions that can occur in oil drilling risers. The results showed that the boron addition in supermartensitic stainless and the boride formation act differently in the materials wear resistance depending on the type of wear mechanism observed.Universidade Federal de Minas GeraisA exploração e produção de petróleo em camadas do pré-sal de modo seguro, eficaz e economicamente viável dependem do desenvolvimento de materiais que suportem as condições severas encontradas em suas aplicações durante todo seu ciclo de vida. Os tubos utilizados na exploração e produção de petróleo como, por exemplo, os risers de perfuração, são submetidos a condições severas de trabalho. Os aços inoxidáveis, como o supermartensÃtico, o duplex e o superduplex, por exemplo, apresentam resistência à corrosão e propriedades mecânicas adequadas para a aplicação em tubos utilizados na exploração de petróleo, contudo, estes materiais apresentam baixa resistência ao desgaste. Trabalhos recentes realizados no DEMa-UFSCar tem mostrado que a adição de boro na composição dos aços inoxidáveis promove a formação de boretos que aumentam a resistência ao desgaste desses materiais. Neste contexto, este projeto visa o estudo da resistência ao desgaste do aço inoxidável supermartensÃtico com pequenas adições de boro processado por conformação por spray. Este processo permite a obtenção de depósitos com microestrutura homogênea, refinada e com precipitados uniformemente distribuÃdos, diretamente do metal lÃquido. Os materiais produzidos foram caracterizados através das técnicas de difração de raios-X (DRX), microscopia ótica (MO), microscopia eletrônica de varredura (MEV) e microanálise quÃmica por espectroscopia por energia dispersiva (EDS). A resistência ao desgaste dos materiais foi avaliada através do ensaio de areia seca contra roda de borracha (ASTM G65-04) e através de um ensaio desenvolvido que simula de maneira mais próxima uma condição de desgaste que pode ocorrer em risers de perfuração de petróleo. Os resultados mostraram que a adição de boro no aço inoxidável supermartensÃtico e a formação dos boretos atuam de modo diferente na resistência ao desgaste do material dependendo do tipo de mecanismo de desgaste observado
Conformação por spray de tubos bimetálicos resistentes ao desgaste e à corrosão : da concepção das ligas ao processamento semi-industrial
The oil exploitation and production at the pre-salt fields in a safety and efficient
way depends on the development of materials that withstand the severe work
conditions found in these fields. For instance, pipes, such as drilling risers and
casings, are often subjected to severe wear and corrosion conditions. This thesis
is dedicated to evaluate the technical feasibility to produce wear and corrosion
resistant bimetallic pipes by spray forming. The processing-microstructure-properties relationship of the spray-formed boron-modified supermartensitic
stainless steel (SMSS) grades was comprehensively studied. Deposits of SMSS
with boron contents ranging from 0.3 %wt. to 1.0 %wt. were processed by spray
forming. The spray-formed boron-modified SMSS deposits had the wear
resistance evaluated through different wear tests and their corrosion resistances
by means of electrochemical techniques. It was demonstrated that the wear
resistance of the spray-formed boron-modified SMSS is determined by the presence of the eutectic network of M 2B-type borides resulted from the spray
forming process. On the other hand, the corrosion resistance of the spray-formed
boron-modified SMSS is controlled by the chemical composition of the martensitic matrix. Furthermore, spray-formed bimetallic pipes composed of
boron-modified SMSS and conventional SMSS were produced in the unique
semi-industrial scale spray-forming plant of the Foundation Institute of Materials
Science (IWT-University of Bremen, Germany). The relationship between the
process parameters and the metallurgical quality of the pipes was addressed. It
was shown that the key to produce a spray-formed bimetallic pipe with good
metallurgical quality is adjusting the process parameters in such a way that the
deposition zone’s temperature is kept within the alloy’s solidification temperature
range during the whole deposition process. Moreover, solidification and grain size
evolution models in spray forming were proposed. Finally, the mechanical
properties of one of the spray-formed bimetallic pipes in the as-spray formed
condition and after heat treatments were evaluated.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)A exploração e produção de petróleo nos poços do pré-sal de modo seguro e
eficiente dependem do desenvolvimento de ligas que suportem severas
condições de trabalho. Por exemplo, tubos como risers de perfuração e casings
são frequentemente submetidos à severas condições de desgaste e corrosão.
Esta tese se dedica a avaliar a viabilidade técnica de produzir tubos bimetálicos
resistentes à corrosão e ao desgaste conformados por spray. A relação
processamento-microestrutura-propriedade do aço inoxidável supermartensÃtico
(AISM) modificado com boro e conformado por spray foi estudada de forma
abrangente. Depósitos de AISM com teores de boro variando de 0,3%p. a 1,0%p.
foram processados por conformação por spray. Os depósitos tiveram a
resistência ao desgaste avaliada através de diferentes ensaios e a resistência Ã
corrosão por meio de técnicas eletroquÃmicas. Demonstrou-se que a resistência
ao desgaste das ligas modificadas com boro é determinada pela presença de
boretos eutéticos, do tipo M2B, oriunda do processo de conformação por spray.
Por outro lado, a resistência à corrosão das ligas modificadas com boro é
controlada pela composição quÃmica da matriz. Além disso, tubos bimetálicos
compostos de AISM modificado com boro e AISM convencional foram
produzidos em escala semi-industrial na planta de conformação por spray do
Instituto de Ciência dos Materiais (IWT-Universidade de Bremen). A relação
entre os parâmetros de processo e a qualidade metalúrgica dos tubos foi tratada.
Mostrou-se que a chave para produzir tubos bimetálicos conformados por spray
com boa qualidade metalúrgica é o ajustar os parâmetros do processo de tal
modo que a temperatura da zona de deposição permaneça dentro do intervalo
de solidificação da liga durante todo processo. Além disso, modelos de
solidificação e evolução de tamanho de grão em conformação por spray foram
propostos. Finalmente, avaliou-se as propriedades mecânicas de um dos tubos
bimetálicos conformado por spray, com e sem tratamentos térmicos.FAPESP: 12/25352-
Johnson-Mehl-Avrami-Kolmogorov model applied to describe the site blocking effect in interstitial solid solution
Interstitial solid solutions, such as carbon in steels or hydrogen in metal and alloys, are important materials for many applications. Thermodynamic models that accurately predict the behavior of interstitial solid solution are essential for designing new materials and to improve computational materials tools. In this work, we revisited the problem of calculating the configurational entropy of interstitial solid solutions when site blocking effect occurs. Using an unprecedented approach, we propose a new site blocking model that uses the Johson-Mehl-Avrami-Kolmogorov (JMAK) equation to calculate the fraction of blocked sites. The proposed model (to be called JMAK model) allows to estimate the number of blocked sites considering the site blocking overlapping phenomenon in a simple and direct way. The JMAK model was validated by comparing the calculated values of configurational entropy
with both numerical simulation and experimental data
Pulsed Laser Activation Method for Hydrogen Storage Alloys
The activation procedures of metals and alloys for hydrogen absorption might be a considerable challenge for large-scale applications of metal hydrides. In this work, the Pulsed Laser Activation (PLA) method for hydrogen storage alloys is introduced for the first time. We show that the hydrogen storage ability of an aged (air-exposed for 30 days) Ti11V30Nb28Cr31 body-centered cubic alloy is restored by scanning the sample with a nanosecond pulsed laser for only three minutes. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS) analyses were performed to investigate structural features that changed in the Ti11V30Nb28Cr31 samples after ageing and after the PLA treatment. Surface remelting, oxide layers and crack formation seem to be factors that affect the hydrogen storage ability of the Ti11V30Nb28Cr31 alloy activated via PLA. Although the mechanisms involved in the PLA are not clear yet, this procedure opens a new path for the development of activation methods based on laser-metal interactions which can be easily applied in alloys and metals for hydrogen storage systems
Thermodynamic Modelling of Hydrogen-Multicomponent Alloy Systems: Calculating Pressure-Composition-Temperature Diagrams
The applicability of an alloy as a hydrogen storage media
mostly relies on its pressure-composition-temperature (PCT) diagram. Since the
PCT diagram is composition-dependent, the vast compositional filed of high
entropy alloys, complex concentrated alloys or multicomponent alloys can be
explored to design alloys with optimized properties for each application. In
this work, we present a thermodynamic model to calculate PCT diagrams of body-centered
(BCC) multicomponent alloys. The entropy of the phases is described using the
ideal configurational entropy for interstitial solid solutions with site
blocking effect. As a first approximation, it is assumed that the H partial
molar enthalpy of a phase is constant, so the enthalpy of H mixing varies
linearly with the H concentration. Moreover, the H partial enthalpy of a phase
for a multicomponent alloy was approximated by a simple ideal mixture law of
this quantity for the alloy’s components with the same structure. Experimental
data and DFT calculations were used for parametrization of the enthalpy terms
of eight elements (Ti, V, Cr, Ni, Zr, Nb, Hf, and Ta), which are the components
of the alloys tested in this work. Experimental PCTs of six BCC multicomponent
alloys of four different systems were compared against the calculated ones and
the agreement was remarkable. The model and parameters presented here can be
regarded as a basis for developing powerful alloy design tools for different
hydrogen storage applications.</p
Hydrogen storage in MgAlTiFeNi high entropy alloy
International audienceIn this study, the MgAlTiFeNi high entropy alloy was processed by high-energy ball milling under both argon and hydrogen atmospheres. It is shown that this alloy forms a body-centered cubic (BCC) structure when milled under an argon atmosphere (mechanical alloying-MA) and a combination of BCC, FCC, and Mg2FeH6 when milled under hydrogen pressure (reactive milling-RM). The hydrogen storage behavior of the RM-MgAlTiFeNi samples was evaluated by a combination of thermal analyses and manometric measurements in a Sieverts apparatus. The RM-MgAlTiFeNi alloy presented an initial functional hydrogen storage capacity of 0.87 wt%, which increased to 0.94 wt% after the second absorption. Also, it exhibited a high hydrogen absorption and desorption kinetics at temperatures 100 °C lower than the one for the desorption temperature of the commercial MgH2. Electrochemical discharge of RM-MgAlTiFeNi samples showed precisely the same hydrogen content as that obtained in the gas desorption. Electrochemical charging/discharging experiments were also performed in the MA-MgAlTiFeNi samples, which presented lower electrochemical storage capacity, a behavior probably resulting from the instability of the alloy in the alkaline solution with the formation of a hydroxide layer on its surface that hinders the electrochemical reaction
Thermodynamic modelling of hydrogen-multicomponent alloy systems: Calculating pressure-composition-temperature diagrams
International audienceThe applicability of an alloy as a hydrogen storage media mostly relies on its pressurecomposition-temperature (PCT) diagram. Since the PCT diagram is compositiondependent, the vast compositional field of high entropy alloys, complex concentrated alloys or multicomponent alloys can be explored to design alloys with optimized properties for each application. In this work, we present a thermodynamic model to calculate PCT diagrams of body-centered (BCC) multicomponent alloys. The entropy of the phases is described using the ideal configurational entropy for interstitial solid solutions with site blocking effect. As a first approximation, it is assumed that the hydrogen partial molar enthalpy of a phase is constant, so the enthalpy of hydrogen mixing varies linearly with the hydrogen concentration. Moreover, the hydrogen partial enthalpy of a phase for a multicomponent alloy was approximated by a simple ideal mixture law of this quantity for the alloy's components with the same structure. Experimental data and DFT calculations were used for parametrization of the enthalpy terms of eight elements (Ti, V, Cr, Ni, Zr, Nb, Hf, and Ta), which are the components of the alloys tested in this work. Experimental PCTs of six BCC multicomponent alloys of four different systems were compared against the calculated ones and the agreement was remarkable. The model and parameters presented here can be regarded as a basis for developing powerful alloy design tools for different hydrogen storage applications
Hydrogen absorption/desorption reactions of the (TiVNb)85Cr15 multicomponent alloy
International audienceTi-V-Nb-Cr alloys have been reported as potential candidates for hydrogen storage applications. Investigating the processes of absorption and desorption is paramount to understand the hydrogen storage properties of these novel alloys and to develop more efficient hydrogen storage materials. In this work, we investigated the hydrogen absorption/desorption reactions of the (TiVNb)85Cr15 BCC multicomponent alloy by laboratory and synchrotron X-ray diffraction, Pair Distribution Function (PDF) analyses, Transmission Electron Microscopy (TEM) and thermo-desorption analyses (TDS). Hydrogen absorption behavior was studied by pressure-composition-isotherm (PCI) at room temperature, which demonstrated levels of absorption around 2 H/M (H/M = hydrogen-to-metal ratio) with low equilibrium pressure. The results showed a multi-step hydrogenation process: alloy ↔ BCC solid solution ↔ BCC intermediate hydride ↔ FCC dihydride. PDF analyses showed that the partially hydrogenated alloy at different levels of H/M and the fully hydrogenated alloy can be reasonably described by models with phases presenting random atomic distribution in the metal crystallographic sites. Moreover, the partially hydrogenated sample prior to the complete formation of the intermediate hydride showed evidence of two co-existing BCC phases
Hydrogen Sorption Properties of a Novel Refractory Ti-V-Zr-Nb-Mo High Entropy Alloy
International audienceHigh entropy alloys belong to a new and promising class of functional materials for solid-state hydrogen storage. In this context, a novel single-phase body centered cubic (bcc) high entropy alloy Ti0.30V0.25Zr0.10Nb0.25Mo0.10 was prepared. The physicochemical and hydrogen sorption properties have been determined by both laboratory and large-scale facilities. This alloy can quickly absorb hydrogen up to 2.0 H/M (2.8 wt.%) at room temperature and forms a face centered cubic (fcc) hydride, as proven by synchrotron X-ray diffraction. The Pressure–Composition Isotherm and in situ neutron diffraction during hydrogen/deuterium desorption reaction suggest that the alloy experiences a reversible single step phase transition (bcc↔fcc). PDF analysis from X-ray total scattering data points out that the hydride phase possesses an average fcc structure with random atoms distribution and small lattice distortion. Despite an initial small fading of the capacity, the alloy withstands 20 absorption/desorption cycling without phase decomposition, as demonstrated by kinetic measurements coupled with X-ray diffraction and microstructural study by SEM-EDS. Moreover, the complete hydrogen absorption occurs in less than 30 s at room temperature and the kinetic improves during cyclin