The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Tatiana Lebedkina - One of the best experts on this subject based on the ideXlab platform.
-
micromechanical modeling of hardening mechanisms in commercially pure α titanium in tensile condition
International Journal of Plasticity, 2016Co-Authors: Kékéli Eva K. Amouzou, Thiebaud Richeton, Amandine Roth, Mikhail Lebyodkin, Tatiana LebedkinaAbstract:Tensile tests on commercially pure α-titanium show a three-stage behavior giving rise to a well on the Strain dependence of the work hardening. An opposite Strain Rate effect on the well depth is found whether specimens are elongated along the rolling or the transverse direction. Slip lines analysis reveals an initial predominance of prismatic slip, particularly pronounced in specimens Strained along the rolling direction. The relative activity of prismatic slip is then observed to decrease with the samples deformation. These results provide grounds for elaboration of an elasto-viscoplastic self-consistent model based on the translated field method and an affine linearization of the viscoplastic flow rule, and capable of explaining such peculiar work hardening behavior. The model considers crystal plasticity and deals sepaRately with mobile dislocation density and dislocation velocity. It assumes Lower Strain Rate sensitivity as well as higher dislocation multiplication Rate for prismatic systems. Based on these assumptions, the model reproduces correctly the stress–Strain curves and gives sound estimates of Lankford coefficients, prismatic slip activity and textures evolution. Most importantly, the opposite effect of Strain Rate on the well depth with regard to the orientation of the tensile axis is qualitatively retrieved, which allows putting forward an explanation of the observed phenomena.
-
Multifractality and randomness in the unstable plastic flow near the Lower Strain-Rate boundary of instability.
Physical Review E, 2008Co-Authors: Mikhail Lebyodkin, Tatiana LebedkinaAbstract:The unstable plastic flow of an AlMg alloy, associated with the Portevin-Le Chatelier effect, was studied near the Lower Strain-Rate boundary of instability using multifractal analysis. Self-similarity of deformation curves, indicating long-range time correlations of stress serrations, was detected within the Strain-Rate range where serrations are commonly ascribed to the occurrence of uncorrelated deformation bands. The deformation curves display a wide range of shapes that are characterized by different groupings of serrations. Multifractal analysis provides a method to quantify the observed complexity and compare it to known Portevin-Le Chatelier effect regimes. The measurement noise effect on the multifractal spectra determined from experimental data was mimicked by superposing multifractal Cantor sets with random noise. Such tests using standard multifractal data sets justify the separation of self-similar and random components of the serRated deformation curves. Furthermore, these results shed light on the general problem of the effect of experimental noise on the apparent multifractal properties of physical fractals.
Xusheng Yang - One of the best experts on this subject based on the ideXlab platform.
-
texture evolution and microstructural thermal stability of as extruded aa2099 during hot deformation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: Xusheng Yang, Linjiang Chai, Weijiu Huang, Zhenhao ZhangAbstract:Abstract Two thermal-mechanical regimes were selected to investigate the recrystallization process of an as-extruded AA2099 alloy. Specimens were deformed to Strains of 0.4, 0.7 and 0.9 at 520 °C and Strain Rates of 0.001 s −1 and 0.1 s −1 , respectively. Electron backscatter diffraction (EBSD) and electron channeling contrast (ECC) imaging were performed for all specimens to characterize their textures and microstructures. The texture evolution is reflected by variation of deviation angle between and extrusion directions, which appears to progressively approach ~35° ( //ED) due to lattice rotation in both regimes before e =0.7. The reconstruction maps indicate that the nucleation of recrystallization is related to Strain incompatibility near grain boundaries. The textures of specimens deformed to Strain of 0.9 exhibit significant difference between the two regimes, i.e the //ED fiber texture is comparatively weakened by recrystallization nuclei growth at the Lower Strain Rate (0.001 s −1 ). ECC images for specimen deformed at 0.001 s −1 reveal significant differences in size and volume fraction of Al 3 Zr particles between recrystallized and unrecrystallized regions, suggesting remarkable influence of boundary migration on the thermal stability of Al 3 Zr particles.
Gobbi, Vagner João - One of the best experts on this subject based on the ideXlab platform.
-
Comportamento em fluência e caracterização microestrutural das superligas VAT 36, VAT 32 e NIMONIC 80A
2014Co-Authors: Gobbi, Vagner JoãoAbstract:Materiais com comportamento adequado em temperaturas elevadas tornaram-se uma necessidade nos dias atuais. Superligas são conhecidas desde a década de 1930 e utilizadas, principalmente, em aplicações aeroespaciais e automobilísticas. Com as novas regulamentações para redução das emissões atmosféricas e aumento da eficiência, surgiram projetos que submetem certos componentes de motores como válvulas, a temperaturas e pressões mais elevadas. Assim, exige-se que as ligas utilizadas na fabricação desses componentes possuam maior resistência à alta temperatura, a exemplo da NIMONIC 80A. Esta é uma liga de custo elevado devido à alta quantidade de níquel (70 a 80% em peso) além de possuir tratamento térmico extenso. Uma alternativa é a utilização de ligas com menor teor de níquel (30 a 40% em peso) e tratamento térmico reduzido. Neste contexto a Villares Metals desenvolveu duas novas superligas, as VATS 32 e 36. Essas ligas são concebidas para válvulas de motores de combustão interna, porém podem ser utilizadas nos casos que necessitem de resistência mecânica a quente, resistência à fluência, corrosão a quente, especialmente por gases sulfurosos, e resistência a fadiga substituindo às ligas NIMONIC 80A em diversas aplicações. A Empresa Villares Metals fez algumas caracterizações à quente das ligas VAT 32 e VAT 36 porém, não foram realizados ensaios por fluência medindo a deformação com o tempo. Portanto, este trabalho tem como objetivo fazer um estudo do comportamento em fluência, em termos de taxa de deformação secundária e tempo de fratura, das superligas VAT 36, VAT 32 e NIMONIC 80A. As ligas são submetidas a ensaios de fluência na modalidade de carga constante, na faixa de temperatura de 675 a 750 ºC e na faixa de tensão de 500 a 600 MPa definidas de acordo com suas aplicações. Os ensaios de fluência são realizados conforme a norma ASTM E139. Obtem-se um conjunto de curvas de deformação verdadeira pelo tempo como função das tensões e temperaturas aplicadas. Foi avaliado a ductilidade, a taxa de fluência estacionária e o tempo de vida. Complementou-se o trabalho com caracterização microestrutural das superligas através das técnicas de microscopia ótica, microscopia eletrônica de varredura, microscopia eletrônica de transmissão, difração de raios X, refinamento de Rietveld e ensaios de dureza. Os resultados mostram que a liga VAT 32 apresenta maior resistência à fluência (menor taxa de deformação secundária e maior tempo de fratura) em relação à VAT 36 e NIMONIC 80A. Isto se deve além do efeito benéfico dos compostos intermetálicos γ' (Ni 3(Al,Ti)), ao maior tamanho de grão e a maior fração de carbonetos ligados MC encontrado na VAT 32. Estes precipitados ricos em titânio e nióbio são estáveis a temperaturas elevadas, aumentam a resistência ao movimento de discordâncias e retardam processos difusionais associados à deformação por fluência. Ancoram os contornos de grãos dificultando o deslizamento relativo entre eles afetando a facilidade com que as vacâncias possam ser geradas nestas mesmas regiões. Por meio da análise dos expoentes de tensão, energias de ativação e imagens obtidas por microscopia eletrônica de transmissão após fluência o mecanismo de deformação dominante no estado secundário de fluência das ligas VAT 32, VAT 36 e NIMONIC 80A é movimento de discordâncias envolvendo provavelmente processo de Orowan loops e cisalhamento de precipitados pelas discordâncias, além da presença de deformação por twinning para as ligas VATS e escorregamento e escalagem de discordâncias para a NIMONIC 80A. ______________________________________________________________________________ ABSTRACTMaterials with appropriate behavior at elevated temperatures have become a necessity nowadays. Superalloys have been known since the 1930 and used primarily in automotive and aerospace applications. With the new regulations to reduce air emissions and increased efficiency projects emerged that submit certain engine components such as valves, temperatures and higher pressures. Thus, it is required that the alloys which are used in manufacturing these components have high temperature resistance, such as the NIMONIC 80A. This alloy has high cost due to the high amount of nickel (70 to 80% wt) and extensive heat treatment. An alternative is to use alloys with Lower nickel content (30 to 40% wt) and reduced heat treatment. In this context, Villares Metals has developed two new superalloys, the VATS 32 and 36. These alloys are designed for valves internal combustion engines, but can be used in cases requiring mechanical strength hot, strength creep and corrosion, substitute alloy NIMONIC 80A in various applications. Villares Metals Company made some characterizations of the hot alloy VAT 32 and VAT 36 however, no tests were performed measuring creep deformation with time. The objective of this paper is to make a study of the behavior in creep in terms of secondary Strain Rate and rupture time of the superalloys VAT 36, VAT 32 and NIMONIC 80A. The alloys are subjected for creep tests in constant load mode, of the temperature range 675-750°C and stress range 500-600 MPa defined according to their applications. The creep tests are performed according to ASTM E139. Is obtained a set of curves of deformation real by the time in function of the applied stress and temperatures. Are evaluated ductility, the stationary creep Rate and life time. Work is complemented with icrostructural characterization of superalloys through the techniques of optical microscopy, SEM, TEM, X-ray diffraction, Rietveld refinement and hardness tests. The results show that the alloy VAT 32 has a higher creep resistance (Lower Strain Rate secondary and higher fracture time) from the VAT 36 and NIMONIC 80A. This is due to the beneficial effect of the intermetallic compounds γ' (Ni3 (Al, Ti)), the largest grain size and the largest fraction of MC carbides found in the VAT 32. These precipitates rich in titanium and niobium are stable at elevated temperatures, increased resistance to movement of dislocations and retard diffusional processes associated with creep deformation. Anchor the grain boundaries impairing the relative sliding between them affect the ease with which the vacancies may be geneRated in these same regions. Through analyzing the stress exponents, activation energies and images obtained by transmission electron microscopy after the creep deformation mechanism dominant in state secondary creep alloys VAT 32, VAT 36 and NIMONIC 80A is movement of dislocations probably involving process Orowan loops and shearing of precipitates by dislocations and the presence of deformation twinning for alloys VATS and slip of dislocations and climb for NIMONIC 80A
-
Comportamento em fluência e caracterização microestrutural das superligas VAT 36, VAT 32 e NIMONIC 80A
2013Co-Authors: Gobbi, Vagner JoãoAbstract:Tese (doutorado)-Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2013.Materiais com comportamento adequado em temperaturas elevadas tornaram-se uma necessidade nos dias atuais. Superligas são conhecidas desde a década de 1930 e utilizadas, principalmente, em aplicações aeroespaciais e automobilísticas. Com as novas regulamentações para redução das emissões atmosféricas e aumento da eficiência, surgiram projetos que submetem certos componentes de motores como válvulas, a temperaturas e pressões mais elevadas. Assim, exige-se que as ligas utilizadas na fabricação desses componentes possuam maior resistência à alta temperatura, a exemplo da NIMONIC 80A. Esta é uma liga de custo elevado devido à alta quantidade de níquel (70 a 80% em peso) além de possuir tratamento térmico extenso. Uma alternativa é a utilização de ligas com menor teor de níquel (30 a 40% em peso) e tratamento térmico reduzido. Neste contexto a Villares Metals desenvolveu duas novas superligas, as VATS 32 e 36. Essas ligas são concebidas para válvulas de motores de combustão interna, porém podem ser utilizadas nos casos que necessitem de resistência mecânica a quente, resistência à fluência, corrosão a quente, especialmente por gases sulfurosos, e resistência a fadiga substituindo às ligas NIMONIC 80A em diversas aplicações. A Empresa Villares Metals fez algumas caracterizações à quente das ligas VAT 32 e VAT 36 porém, não foram realizados ensaios por fluência medindo a deformação com o tempo. Portanto, este trabalho tem como objetivo fazer um estudo do comportamento em fluência, em termos de taxa de deformação secundária e tempo de fratura, das superligas VAT 36, VAT 32 e NIMONIC 80A. As ligas são submetidas a ensaios de fluência na modalidade de carga constante, na faixa de temperatura de 675 a 750 ºC e na faixa de tensão de 500 a 600 MPa definidas de acordo com suas aplicações. Os ensaios de fluência são realizados conforme a norma ASTM E139. Obtem-se um conjunto de curvas de deformação verdadeira pelo tempo como função das tensões e temperaturas aplicadas. Foi avaliado a ductilidade, a taxa de fluência estacionária e o tempo de vida. Complementou-se o trabalho com caracterização microestrutural das superligas através das técnicas de microscopia ótica, microscopia eletrônica de varredura, microscopia eletrônica de transmissão, difração de raios X, refinamento de Rietveld e ensaios de dureza. Os resultados mostram que a liga VAT 32 apresenta maior resistência à fluência (menor taxa de deformação secundária e maior tempo de fratura) em relação à VAT 36 e NIMONIC 80A. Isto se deve além do efeito benéfico dos compostos intermetálicos γ' (Ni 3(Al,Ti)), ao maior tamanho de grão e a maior fração de carbonetos ligados MC encontrado na VAT 32. Estes precipitados ricos em titânio e nióbio são estáveis a temperaturas elevadas, aumentam a resistência ao movimento de discordâncias e retardam processos difusionais associados à deformação por fluência. Ancoram os contornos de grãos dificultando o deslizamento relativo entre eles afetando a facilidade com que as vacâncias possam ser geradas nestas mesmas regiões. Por meio da análise dos expoentes de tensão, energias de ativação e imagens obtidas por microscopia eletrônica de transmissão após fluência o mecanismo de deformação dominante no estado secundário de fluência das ligas VAT 32, VAT 36 e NIMONIC 80A é movimento de discordâncias envolvendo provavelmente processo de Orowan loops e cisalhamento de precipitados pelas discordâncias, além da presença de deformação por twinning para as ligas VATS e escorregamento e escalagem de discordâncias para a NIMONIC 80A. ______________________________________________________________________________ ABSTRACTMaterials with appropriate behavior at elevated temperatures have become a necessity nowadays. Superalloys have been known since the 1930 and used primarily in automotive and aerospace applications. With the new regulations to reduce air emissions and increased efficiency projects emerged that submit certain engine components such as valves, temperatures and higher pressures. Thus, it is required that the alloys which are used in manufacturing these components have high temperature resistance, such as the NIMONIC 80A. This alloy has high cost due to the high amount of nickel (70 to 80% wt) and extensive heat treatment. An alternative is to use alloys with Lower nickel content (30 to 40% wt) and reduced heat treatment. In this context, Villares Metals has developed two new superalloys, the VATS 32 and 36. These alloys are designed for valves internal combustion engines, but can be used in cases requiring mechanical strength hot, strength creep and corrosion, substitute alloy NIMONIC 80A in various applications. Villares Metals Company made some characterizations of the hot alloy VAT 32 and VAT 36 however, no tests were performed measuring creep deformation with time. The objective of this paper is to make a study of the behavior in creep in terms of secondary Strain Rate and rupture time of the superalloys VAT 36, VAT 32 and NIMONIC 80A. The alloys are subjected for creep tests in constant load mode, of the temperature range 675-750°C and stress range 500-600 MPa defined according to their applications. The creep tests are performed according to ASTM E139. Is obtained a set of curves of deformation real by the time in function of the applied stress and temperatures. Are evaluated ductility, the stationary creep Rate and life time. Work is complemented with icrostructural characterization of superalloys through the techniques of optical microscopy, SEM, TEM, X-ray diffraction, Rietveld refinement and hardness tests. The results show that the alloy VAT 32 has a higher creep resistance (Lower Strain Rate secondary and higher fracture time) from the VAT 36 and NIMONIC 80A. This is due to the beneficial effect of the intermetallic compounds γ' (Ni3 (Al, Ti)), the largest grain size and the largest fraction of MC carbides found in the VAT 32. These precipitates rich in titanium and niobium are stable at elevated temperatures, increased resistance to movement of dislocations and retard diffusional processes associated with creep deformation. Anchor the grain boundaries impairing the relative sliding between them affect the ease with which the vacancies may be geneRated in these same regions. Through analyzing the stress exponents, activation energies and images obtained by transmission electron microscopy after the creep deformation mechanism dominant in state secondary creep alloys VAT 32, VAT 36 and NIMONIC 80A is movement of dislocations probably involving process Orowan loops and shearing of precipitates by dislocations and the presence of deformation twinning for alloys VATS and slip of dislocations and climb for NIMONIC 80A
Mikhail Lebyodkin - One of the best experts on this subject based on the ideXlab platform.
-
micromechanical modeling of hardening mechanisms in commercially pure α titanium in tensile condition
International Journal of Plasticity, 2016Co-Authors: Kékéli Eva K. Amouzou, Thiebaud Richeton, Amandine Roth, Mikhail Lebyodkin, Tatiana LebedkinaAbstract:Tensile tests on commercially pure α-titanium show a three-stage behavior giving rise to a well on the Strain dependence of the work hardening. An opposite Strain Rate effect on the well depth is found whether specimens are elongated along the rolling or the transverse direction. Slip lines analysis reveals an initial predominance of prismatic slip, particularly pronounced in specimens Strained along the rolling direction. The relative activity of prismatic slip is then observed to decrease with the samples deformation. These results provide grounds for elaboration of an elasto-viscoplastic self-consistent model based on the translated field method and an affine linearization of the viscoplastic flow rule, and capable of explaining such peculiar work hardening behavior. The model considers crystal plasticity and deals sepaRately with mobile dislocation density and dislocation velocity. It assumes Lower Strain Rate sensitivity as well as higher dislocation multiplication Rate for prismatic systems. Based on these assumptions, the model reproduces correctly the stress–Strain curves and gives sound estimates of Lankford coefficients, prismatic slip activity and textures evolution. Most importantly, the opposite effect of Strain Rate on the well depth with regard to the orientation of the tensile axis is qualitatively retrieved, which allows putting forward an explanation of the observed phenomena.
-
Multifractality and randomness in the unstable plastic flow near the Lower Strain-Rate boundary of instability.
Physical Review E, 2008Co-Authors: Mikhail Lebyodkin, Tatiana LebedkinaAbstract:The unstable plastic flow of an AlMg alloy, associated with the Portevin-Le Chatelier effect, was studied near the Lower Strain-Rate boundary of instability using multifractal analysis. Self-similarity of deformation curves, indicating long-range time correlations of stress serrations, was detected within the Strain-Rate range where serrations are commonly ascribed to the occurrence of uncorrelated deformation bands. The deformation curves display a wide range of shapes that are characterized by different groupings of serrations. Multifractal analysis provides a method to quantify the observed complexity and compare it to known Portevin-Le Chatelier effect regimes. The measurement noise effect on the multifractal spectra determined from experimental data was mimicked by superposing multifractal Cantor sets with random noise. Such tests using standard multifractal data sets justify the separation of self-similar and random components of the serRated deformation curves. Furthermore, these results shed light on the general problem of the effect of experimental noise on the apparent multifractal properties of physical fractals.
Satyam Suwas - One of the best experts on this subject based on the ideXlab platform.
-
investigation of stress Strain response microstructure and texture of hot deformed pure molybdenum
International Journal of Refractory Metals & Hard Materials, 2018Co-Authors: Atanu Chaudhuri, Apu Sarkar, Satyam SuwasAbstract:Abstract The deformation behavior of pure molybdenum (Mo) was studied in very high temperature range (1400–1700 °C) by carrying out uniaxial compression tests at four different Strain Rates (0.01–10 s−1). Three types of stress-Strain curves including work hardening, steady state and softening behavior were observed depending upon the deformation condition. The Strain Rate sensitivity (m) map geneRated from the flow stress data revealed two domains of high m values - one at about 1400 °C and 10−1 s−1 and the second one at ~1700 °C and Strain Rate of 10−2–1 s−1. The kinetic analysis of the deformation data yielded the apparent activation energy as 390 kJ mol−1, the stress exponent as 8.5, and the activation volume about 100–600 b3 for pure Mo. Microstructures of the deformed samples were investigated using the electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM). The appearance of smaller Strain-free grains along the boundaries of deformed grains indicated the occurrence of dynamic recrystallization (DRX) in the samples deformed at conditions corresponding to the high m values. Grain growth was significant at higher temperature and Lower Strain Rate deformation. Bulk texture measurements of the hot deformed samples indicated strengthening of 〈001〉 fiber texture during occurrence of the DRX.
