Analysis of creep behavior of SiC/Al metal matrix composites based on a generalized shear-lag model (original) (raw)
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AN INFLUENCE OF SiC CONTENT AT Al (AlMg) MATRIX COMPOSITES ON CREEP CHARACTERISTICS
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Journal of the American Ceramic Society, 2006
Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated silicon were subjected to creep at 13151C at three different stress conditions. For the specimens that did not rupture after 100 h of tensile creep, fast-fracture experiments were performed immediately following the creep test at the creep temperature (13151C) or after cooling to room temperature. All specimens demonstrated excellent creep resistance and compared well to the creep behavior published in the literature on similar composite systems. Tensile results on the after-creep specimens showed that the matrix cracking stress actually increased, which is attributed to stress redistribution between composite constituents during tensile creep.
Creep deformation of alumina-SiC composites
Materials Science and Engineering: A, 1990
Composites of alumina reinforced with SiC whiskers have been creep tested in bending and in compression at 1200-1400 °C in an air ambient. The flexural creep data follow a power law constitutive relation with two distinct stress exponents that depend on the level of applied stress. Crept specimens were examined by transmission electron microscopy to determine the mechanisms of creep deformation and microstructural damage. The primary mechanism of creep deformation under these conditions is grain boundary and interface sliding resulting from diffusion. At high stress levels, the sliding is often unaccommodated, resulting in cavitation at grain boundary-interface junctions. Cavitation is associated with an increase in the stress exponent for flexural creep.
The effect of matrix creep property on the consolidation process of SiC/Ti–6Al–4V composite
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The consolidation process was discussed by using finite element analysis (FEA) in SCS-6SiC/Ti-6Al-4V composite fabricated by means of fiber coating method. With consolidation time and temperature changing, the effect of Ti-6Al-4V creep property on the matrix stress distribution was analyzed. The results indicated that the magnitude of matrix stress decreased remarkably and should be more close to the practical consolidation process when taking the effect of matrix creep property into account. In addition, the more time and the higher temperature the consolidation process took, the more obvious the effect of matrix creep property on the consolidation was. The selection of consolidation parameter such as time and temperature could be based on the simulation results.
Compression creep of PM aluminum matrix composites reinforced with SiC short fibres
Materials Science and Engineering: A, 2006
The compression creep behaviour of Al-SiC fiber metal matrix composites (MMC), made by hot-pressing (HP), was evaluated at various temperatures and over several orders of magnitude of strain rates. The interpretation of metal flow-patterns during the whole deformation cycle was complex owing to the fact that the short-fibre distribution in the composites was roughly planar. However, every specimen showed a well-defined flow stress or plateau (σ p true ) up to the end of the tests that were associated with nearly 50% linear compression strains. Such stresses clearly increased with the volume fraction (f) of fibres and strain rates, and decreased with increasing temperatures. Cross-examination of the creep curves [log strain rate (γ) versus log shear stress (τ)] for both the HP Al matrix and composites show an apparent stress exponent n ap = [δ(lnγ)/δ(ln τ)] clearly increasing while decreasing τ. This anomalous behaviour can be attributed to the existence of a finite threshold stress (τ 0 ) for every composition. This threshold stress appears to be related to the oxide contamination (judged from TEM observations) of the matrix, as a result of the use of powder metallurgy (PM) synthesis method. Following certain approximations during deformation behaviour of PM specimens reinforced with ceramic particles, the present data, for short-fibre reinforced MMC, seems to be consistent with the mechanism of dislocation climb that is characterized by an stress exponent of around five, and an activation energy close to that for self-diffusion in pure aluminum (143.2 kJ mol −1 ). (C.J.R.G. Oliver). features: the apparent n ap exponents [slope of the log (strain rate)-log (stress) plots] and apparent activation energies Q a for creep were higher [1-12] than those expected for the unreinforced matrix metal. By incorporating a threshold stress (σ 0 ) into the normal power law creep (PLC) expression, the apparent n values became lower, and more reasonable values for the activation energy were obtained. It is therefore relevant to consider [20] the fine oxide film from powder manufacture to be dispersed as fine particles during the PM process, playing an important role as a barrier to matrix deformation at high temperatures, also probably controlling the above threshold stresses.
Effect of a solid solution on the steady-state creep behavior of an aluminum matrix composite
Metallurgical and Materials Transactions A, 1996
The effect of an alloying element, 4 wt pct Mg, on the steady-state creep behavior of an AI-10 vol pct SiCp composite has been studied. The A1-4 wt pct Mg-10 vol pct SiC, composite has been tested under compression creep in the temperature range 573 to 673 K. The steady-state creep data of the composite show a transition in the creep behavior (regions I and II) depending on the applied stress at 623 and 673 K. The low stress range data (region I) exhibit a stress exponent of about 7 and an activation energy of 76.5 kJ mol-L These values conform to the dislocation-climb-controlled creep model with pipe diffusion as a rate-controlling mechanism. The intermediate stress range data (region II) exhibit high and variable apparent stress exponents, 18 to 48, and activation energy, 266 kJ mol-~, at a constant stress, cr = 50 MPa, for creep of this composite. This behavior can be rationalized using a substructure-invariant model with a stress exponent of 8 and an activation energy close to the lattice self-diffusion of aluminum together with a threshold stress. The creep data of the AI-Mg-A1203r composite reported by Dragone and Nix also conform to the substructure-invariant model. The threshold stress and the creep strength of the A1-Mg-SiC e composite are compared with those of the A1-Mg-AIzO3/and 6061 AI-SiCe.w composites and discussed in terms of the load-transfer mechanism. Magnesium has been found to be very effective in improving the creep resistance of the AI-SiC, composite.
Ceramics International, 2014
Al 2 O 3 /SiC composites containing different volume fractions (3, 5, 10, 15, and 20 vol%) of SiC particles have been fabricated by mixing alumina and silicon carbide powders, followed by hot pressing at the temperature 1740 1C for 1 h under the pressure of 30 MPa and in the atmosphere of Ar. The effect of the volume fraction of SiC on the microstructure and creep behavior of the composites was investigated and possible creep mechanisms were discussed. The creep behavior of the composites at temperatures up to 1350 1C, and mechanical load up to 200 MPa, i.e. under conditions which were more severe than those reported previously, was studied, and compared to the monolithic Al 2 O 3 reference. The microstructure and creep behavior of the Al 2 O 3 /SiC microcomposites was significantly influenced by the volume fraction of SiC particles and the average size of the alumina matrix grains. When compared to monolithic Al 2 O 3 , the creep resistance of the Al 2 O 3 /SiC composites was markedly improved, especially in the materials with 10 vol% of SiC. Long loading time before mechanical failure suggested grain boundary sliding and cavitation controlled creep behavior. The enhanced creep resistance was attributed to grain boundary pinning by the intergranular SiC nanoparticles.
Room Temperature Creep of Sic\Sic Composites
Ceramic Engineering and Science Proceedings
During a recent experimental study, time dependent deformation was observed for a damaged Hi-Nicalon TM reinforced, BN interphase, chemically vapor infiltrated SiC matrix composites subjected to static loading at room temperature. The static load curves resembled primary creep curves. In addition, acoustic emission was monitored during the test and significant AE activity was recorded while maintaining a constant load, which suggested matrix cracking or interfacial sliding. For similar composites with carbon interphases, little or no time del_ndent deformation was observed. Evidently, exposure of the BN interphase to the ambient environment resulted in a reduction in the inteffacial mechanical properties, i.e. interfacial shear strength and/or debond energy. These results were in qualitative agreement with observations made by Eldridge of a reduction in interracial shear stress with time at room temperature as measured by fiber push-in experiments.
Metallurgical and Materials Transactions A, 2009
The tensile creep behavior of powder metallurgy (P/M)-processed and hot-rolled commercially pure Al and Al-5 or Al-10 vol pct SiC particulate composites has been evaluated after subjecting to 0, 2, and 8 thermal cycles between 500°C and 0°C with rapid quenching. The images of microstructures obtained using scanning and transmission electron microscopy as well as changes in the electrical resistivity, Young's modulus, and microhardness have been examined in the samples subjected to thermal cycling, in order to compare the effects of structural damage and strengthening by dislocation generation. The damage is caused by voids formed by vacancy coalescence, and is more severe in pure Al than in Al-SiC p composites, because the particlematrix interfaces in the composites act as effective sinks for vacancies. Creep tests have shown that the application of 2 thermal cycles lowers the creep strain rates in both pure Al and Al-SiC p composites. However, the creep resistance of pure Al gets significantly deteriorated, unlike the mild deterioration in the Al-5 SiC p composite, while the time to rupture for the Al-10 SiC p composite is increased. The dislocation structure and subgrain sizes in the Al and in the matrices of the Al-SiC p composites in the as-rolled condition, after thermal cycling, and after creep tests, have been compared and related to the creep behavior. The dimple sizes of the crept fracture surfaces appear to be dependent on the void density, tertiary component of strain, and time to rupture.
Composites Science and Technology, 2008
An understanding of the elevated temperature tensile creep, fatigue, rupture, and retained properties of ceramic matrix composites (CMC) envisioned for use in gas turbine engine applications are essential for component design and life-prediction. In order to quantify the effect of stress, time, temperature, and oxidation for a state-of-the-art composite system, a wide variety of tensile creep, dwell fatigue, and cyclic fatigue experiments were performed in air at 1204oC for the SiC/SiC CMC system consisting of Sylramic-iBN SiC fibers, BN fiber interphase coating, and slurry-cast melt-infiltrated (MI) SiC-based matrix. Tests were either taken to failure or interrupted. Interrupted tests were then mechanically tested at room temperature to determine the residual properties. The retained properties of most of the composites subjected to tensile creep or fatigue were usually within 20% of the as-produced strength and 10% of the as-produced elastic modulus. It was observed that during creep, residual stresses in the composite are altered to some extent which results in an increased compressive stress in the matrix upon cooling and a subsequent increased stress required to form matrix cracks. Microscopy of polished sections and the fracture surfaces of specimens which failed during stressed-oxidation or after the room-temperature retained property test was performed on some of the specimens in order to quantify the nature and extent of damage accumulation that occurred during the test. It was discovered that the distribution of stress-dependent matrix cracking at 1204oC was similar to the as-produced composites at room temperature; however, matrix crack growth occurred over time and typically did not appear to propagate through thickness except at final failure crack. Failure of the composites was due to either oxidation-induced unbridged crack growth, which dominated the higher stress regime (> 179 MPa) or controlled by degradation of the fibers, probably caused by intrinsic creep-induced flaw growth of the fibers or internal attack of the fibers via Si diffusion through the CVI SiC and/or microcracks at the lower stress regime (< 165 MPa).