Analysis of creep behavior of SiC/Al metal matrix composites based on a generalized shear-lag model
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Kyung H. Chung College of Engineering, University of California—Davis, Davis, California 95616
Seung I. Cha and Soon H. Honga) Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejon 305-701, Korea (Received 22 July 2004; accepted 15 September 2004)
The creep behaviors of 20 vol% SiCw/2124Al, extruded with different ratios, and SiCp/2124Al, reinforced with 10–30 vol% SiC particles, were investigated to clarify the effects of aspect ratio, alignment, and volume fraction of reinforcement on creep deformation. The effective stresses on the matrix of SiC/Al composites are calculated based on the generalized shear-lag model. The minimum creep rates of SiCw/2124Al extruded with different ratios and SiCp/2124Al reinforced with different volume fractions of SiC particles are found to be similar under a same effective stress on matrix, which is calculated by the generalized shear-lag model. The subgrain sizes in matrices of crept SiC/Al composites are dependent on the effective stress on matrix but not on the applied stress on the composite. It is suggested that the role of SiC reinforcements is to increase the creep resistance of SiC/Al composite by reducing the effective stress on matrix.
I. INTRODUCTION
Metal matrix composites (MMCs) such as SiC/Al composites show improved high-temperature creep resistance compared to their monolithic matrix alloys.1,2 This improvement is achieved by an addition of high modulus ceramic reinforcement into a ductile metal matrix having low strength at elevated temperatures. The understanding and prediction of creep behavior of SiC/Al composites are highly needed for the structural application at high temperature. The high-temperature creep behavior of MMCs has been investigated by several researchers.2–16 Morimoto et al.2 found that the higher volume fraction and the larger aspect ratio of reinforcement resulted in an increased creep resistance of SiCw/2124Al composite. Nieh et al.3 found that the creep behavior of SiC/Al composite shows minimum creep rate without showing welldefined steady-state creep region. It has been found that the creep of SiC/Al composite is controlled by the lattice diffusion of Al in matrix.4,5 An overview of the creep behavior of SiC/Al composites shows that the whiskerreinforced composites generally exhibit a higher creep a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0472 J. Mater. Res., Vol. 19, No. 12, Dec 2004
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resistance than the particle reinforced composites, and the stress exponent and activation energy for creep are much higher than those observed for pure aluminum. The higher stress exponent and activation energy for creep have been attributed to the presence of threshold stress.6–8 Park et al.10 have indicated that the stress exponent and activation energy for creep increase with decreasing the applied stress. Li and Mohamed11 showed that the creep behavior of SiCp/2124Al composite fabricated
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