Saint Martin Almeida, Renato
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Saint Martin Almeida, Renato
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Saint Martin Almeida, Renato
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Item type:Publication, Long-term behavior of polycrystalline oxide fibers at elevated temperatures(2017-10-27); ; 484 240 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Microstructure and properties of Cu-Ti alloy infiltrated chopped Cf reinforced ceramics compositesNovel friction composites (C/C-Cu5Si-TiC) were prepared via reactive melt infiltration (RMI) of Cu-Ti alloy into porous C/C-SiC composites. The microstructure, physical properties and tribological behaviors of the novel material were studied. Results were compared to conventional C/C-SiC composites produced by liquid silicon infiltration(LSI). The resultant composite showed the microstructure composed of Cu5Si matrix reinforced with TiC particles and intact C/C structures. Most importantly, the composite did not present traces of free Si. As a result, the C/C-Cu5Si-TiC composite showed higher flexural strength, impact toughness and thermal diffusivity in comparison to C/C-SiC composites. Tribological properties were measured using 30CrSiMoVA as a counterpart. In general, the C/C-Cu5Si-TiC composites showed lower coefficient of friction(COF), but higher wear resistance and frictional stability. The improved wear resistance of the C/C-Cu5Si-TiC composites is credited to the formation of friction films from Cu5Si matrix. Other deformation and wear mechanisms are also described considering the microstructural observations.journal articleBand:43Heft:1882 104 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Obtaining complex‐shaped oxide ceramic composites via ionotropic gelation(Wiley, 2018-08-23); ; ; In this communication, we present a new processing method for obtaining oxide ceramic composites based on the ionotropic gelation technique. Nextel 610 fiber fabrics were infiltrated by an alumina-zirconia suspension with a total solid content of 50 vol.% and alginate as the binder. Subsequently, the suspension was slowly cross-linked by adding Al3+ cations and transferred to a gel state. The gelled fabric layers could be easily cut, stacked and shaped, as well as joined to other ceramic materials and composites. Furthermore, the fiber content could be adjusted by pressing the layers together. In summary, the composites produced with this technique presented a very good fiber bundle infiltration, matrix with fine porosity and excellent mechanical properties. Nextel 610/alumina-zirconia composites sintered at 1200°C for 1 h showed bending strength of 306 MPa, interlaminar shear strength of 9.8 MPa and nominal fracture toughness of 13.6 MPa m0.5.journal articleBand:102Heft:1124 117 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Fatigue behavior and damage analysis of PIP C/SiC composite(Elsevier Science, 2022-10-01); ; ; ; In this work, we study the fatigue behavior of a C/SiC composite produced by several cycles of polymer infil- tration and pyrolysis (PIP). Fatigue tests were performed with maximum stresses corresponding to 60–90% of the tensile strength of the composite. During the fatigue tests, acoustic emission (AE) monitoring was performed and the measured AE energy was utilized to quantify the damage and distinguish possible damage mechanisms. Most of the fatigue damage in the form of matrix cracking, interface damage and fiber breakage occurs in the first cycle. As loading cycles proceeded, damage in form of matrix crack re-opening and interfacial friction constantly accumulates. Nevertheless, all samples survived the run-out of 1,000,000 cycles. After the fatigue tests, an in- crease of the tensile strength is observed. This phenomenon is associated with the relief of process-induced in- ternal thermal stresses and the weakening of the fiber-matrix interface. In general, the studied material shows very high relative fatigue limit of 90% of its tensile strengthjournal articleBand:42Heft:1371 82 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Fatigue behavior and residual strength evolution of 2.5D C/C-SiC composites(Elsevier {BV}, 2016-08-20); ; ; ; The residual tensile strength (RTS) evolution of a chemical vapor infiltration and liquid silicon infiltration based 2.5 dimensional reinforced C/C-SiC (2.5D C/C-SiC) composites after fatigue loadings has been investigated. The results show that the fatigue limit (106 cycles) of the 2.5D C/C-SiC composites reaches 58.2 MPa, which corresponds to 75% of the virgin static tensile strength (77.7 MPa). Moreover, an ultimate strength enhancement is observed after fatigue loading. The most pronounced RTS increases to 92.5 MPa when specimens are subjected to fatigue stress of 69.3 MPa for 105 cycles. The microstructural analysis indicates that RTS after cyclic loading is affected by the formation and propagation of cracks and interfacial degradation. Furthermore, a model proposed in this work can well evaluate the RTS of the composites in relation to the number of the applied fatigue cycles.journal articleBand:36Heft:16100 114 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Phase-field simulation of abnormal anisotropic grain growth in polycrystalline ceramic fibers(Elsevier {BV}, 2020-08-05); ; ; ; The present work proposes a phase-field approach to realistically simulate abnormal grain growth in polycrystalline ceramic fibers at temperatures above 1000 °C. Under these conditions, grain growth is characterized by the formation of large elongated rectangular grains in a matrix of normal grains. The multi-phase-field model is extended by mechanisms which are responsible for the abnormal anisotropic growth: anisotropic interface energy, anisotropic interface mobility and a recrystallization driving force. Two types of the mobility anisotropy are considered: anisotropy due to the misorientation between grains and anisotropy due to the dependency on inclination angles. The experimental data from heat treatments of the ceramic fiber Nextel 610 at 1200–1300 °C with different dwell times are examined by the proposed model. The comparison of the experiment and the simulation results at various times shows that the extended multi-phase-field model is able to simulate the microstructure realistically. In most model cases, abnormal grains have a rectangular shape, similar to the experiment. The best fit of the experimental grain size distribution and the grain shape is achieved by the simulation with the misotientation dependency of the interface mobility. Furthermore, it was shown that a strong decrease on the grain growth rate with time, observed in the experiment, can be reproduced by the simulations taking into account the segregation of impurities on grain boundaries that results in the decreasing grain boundary mobility.journal articleBand:185148 177 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Damage analysis of 2.5D C/C-SiC composites subjected to fatigue loadings(Elsevier {BV}, 2019-03-11); ; ; ; Damage analyses of a ceramic matrix composite during fatigue and quasi-static loads were performed by acoustic emission (A.E.) monitoring. The material studied was a 2.5D C/C-SiC composite produced by chemical vapor infiltration followed by liquid silicon infiltration. The analysis done during the first 200 cycles of a fatigue test showed that the number of A.E. hits is a good parameter for the quantification of damage. Furthermore, the A.E. hit energy was associated with the type of damage. In this sense, the damage developed during the fatigue loading was related to matrix crack initiation, propagation and re-opening, as well as fiber-matrix friction. Quasi-static tests on post-fatigue samples showed that the previous fatigue loadings increased the material`s damage threshold and hindered the development of new damage. Particular attention was given to the sample after 2,000,000 cycles as this sample showed distinct A.E. signals that could be related to fiber debonding.journal articleBand:39Heft:7110 109 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Thermal exposure effects on the long‐term behavior of a mullite fiber at high temperatureThe behavior of an oxide fiber at elevated temperatures was analyzed before and after thermal exposures. The material studied was a mullite fiber developed for high-temperature applications, CeraFib 75. Heat treatments were performed at temperatures ranging from 1200°C to 1400°C for 25 hours. Quantitative high-temperature X-ray analysis and creep tests at 1200°C were carried out to analyze the effect of previous heat treatment on the thermal stability of the fibers. The as-received fibers presented a metastable microstructure of mullite grains with traces of alumina. Starting at 1200°C, grain growth and phase transformations occurred, including the initial formation of mullite, followed by the dissociation of the previous alumina-rich mullite phase. The observed transformations are continuous and occur until the mullite phase reaches a state near the stoichiometric 3/2 mullite. Only the fibers previously heat treated at 1400°C did not show further changes when exposed again to 1200°C. Overall, the heat treatments increased the fiber stability and creep resistance but reduced the tensile strength. Changes observed in the creep strain vs. time curves of the fibers were related to the observed microstructural transformations. Based on these results, the chemical composition of the stable mullite fiber is suggested.journal articleBand:100Heft:9110 112 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Enhancing thermal stability of oxide ceramic matrix composites via matrix doping(2022-02-23); ; ; To overcome the main limitation of oxide ceramic matrix composites (Ox-CMCs) regarding thermal degradation, the use of matrix doping is analyzed. Minicomposites containing Nextel 610 fibers and alumina matrices with and without MgO doping were produced. The thermal stability of the minicomposites was evaluated considering their microstructure and mechanical behavior before and after thermal exposures to 1300 C and 1400 C for 2 h. Before heat treatment, both composite types showed very similar microstructure and tensile strength. After heat treatment, densification, grain growth and strength loss are observed. Furthermore, the MgO dopant from the matrix diffuses into the fibers. As a result, abnormal fiber grain growth is partially suppressed and MgO-doped composites show smaller fiber grains than non-doped composites. This more refined microstructure leads to higher strength retention after the heat treatments. In summary, doping the matrix can increase the overall thermal stability without impairing the room-temperature properties of Ox-CMCs.journal articleBand:42Heft:7181 437 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Mechanical behavior of LSI based C/C-SiC composites subjected to flexural loadings(Elsevier {BV}, 2017-02-14); ; ; ; In general, flexural loads result in more complicated and uneven stress distributions in specimens, compared to axial loading. This study reports the influence of flexural fatigue loads including different stress levels and cycles on the mechanical behavior of a 3D C/C-SiC composite. The cyclic tensile loads in the lower part of the specimens result in strength enhancement after short fatigue duration with the expense of decreased flexural modulus due to the fatigue damage such as cracking and interfacial degradation. Whereas the upper part of the post-fatigue specimens, which is almost free of fatigue damage under compressive stress, can still properly deflect the cracks and result in quasi-plastic failures like virgin specimens. Most notably, specimens will suffer strength decline rapidly, after 50,000 cycles with maximum stress of 95 MPa for instance, because of considerable stress concentrations and wear of fibers at 90 fiber bundles in the lower part.journal articleBand:9583 88