Plastic-strain cyclic response of SiC particulate reinforced aluminum composites

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Abstract

The cyclic stress response characteristics of several SiC particulate reinforced aluminum composites and their unreinforced counterpart at room temperature were investigated. The as-extruded specimens were cyclically deformed with fully-reversed loading under a range of constant plastic-strain amplitudes. The test results showed that the cyclic response characteristics of the reinforced and unreinforced materials were different. During most of the fatigue life, the unreinforced aluminum mainly exhibited cyclic hardening, while the composites showed gradual softening. The dislocation substructure developed during cyclic deformation was analyzed using transmission electron microscopy. The discrepency between the dislocation substructure obtained from processing compared to its development during cyclic strain loading is thought to give rise to the observed cyclic stress response behavior.

Introduction

Metal matrix composites (MMCs) reinforced by discontinuous reinforcement exhibit some advantages over the unreinforced matrix materials, such as high specific strength and high specific modules [1]. Applications of these composites in the aerospace, automobile and recreational industries have grown rapidly during past years [2]. With the engineering applications of MMCs, the fatigue behavior will become critical in design, life-prediction and reliability analysis of the components made of these materials. Therefore, significant effort has been made to understand the fatigue behavior of these materials [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. However, few investigations appear in the literature on MMCs where changes in mechanical behavior during cyclic deformation and the resultant dislocation substructure have been studied simultaneously. A similar cyclic stress response behavior between ceramic-particulate reinforced age-hardened aluminum alloys and their unreinforced materials was observed by several researchers [16], [17]. Potentially, the effects of the ceramic reinforcement on composite cyclic stress response are masked by the precipitates in aluminum alloy matrices. Therefore, the present study is to investigate the differences in plastic-strain cyclic deformation behavior of SiC particulate reinforced aluminum composites and their unreinforced counterpart at ambient temperature. Since the cyclic deformation behavior is highly sensitive to matrix microstructure, commercially pure aluminum was selected as a matrix material with the object to correlate changes in macroscopic mechanical behavior with evaluating dislocation structure conveniently and to eliminate precipitates and other factors that usually existed in aluminum alloys.

Section snippets

Materials and experimental procedures

The SiCp/Al composites respective containing 13, 20 or 25 volume-percent SiC particulate were made by a powder metallurgy method. The SiC particulate, with an average size of 10 μm, were mechanically mixed with the 14 μm aluminum powder. The mixture was then hot compacted and subsequently extruded by 20:1 at 693 K into a rod of 16 mm in diameter. The unreinforced matrix aluminum was produced in the same process. The chemical compositions of the matrix aluminum are given in Table 1. The

Results and discussion

The cyclic stress response curves, which were determined by monitoring the peak stresses during cyclic straining, provided useful information pertaining to the mechanical stability and damage evolution of the material. The cyclic stress response curves of the unreinforced aluminum and the SiCp/Al composites under different plastic strain amplitudes at room temperature are shown in Fig. 2a–d. Unlike the results reported for aluminum alloy matrix [16], [17], the cyclic response of reinforced

Conclusions

Based on investigations of cyclic stress response of SiC particulate reinforced aluminum composites and their unreinforced matrix, the following conclusions could be reached:

1. The cyclic stress response characteristics of the SiCp/Al composites were different from those of their unreinforced aluminum during constant plastic strain fatigue at room temperature. The unreinforced aluminum revealed initial cyclic hardening, cyclic stability and second hardening. In contrast, in spite of initial

References (22)

  • T. Christman et al.

    Mater. Sci. Eng.

    (1988)
  • Z. Wang et al.

    Acta Metall. Mater.

    (1994)
  • R.J. Arsenault et al.

    Progress Mater. Sci.

    (1994)
  • N.L. Han et al.

    Scripta Metall. Mater.

    (1995)
  • N.L. Han et al.

    Scripta Metall. Mater.

    (1995)
  • N.L. Han et al.

    Composites Sci. Tech.

    (1997)
  • N.L. Han et al.

    Scripta Mater.

    (2000)
  • N.L. Han et al.

    Composites Sci. Tech.

    (1999)
  • R.J. Arsenault et al.

    Mater. Sci. Eng.

    (1986)
  • Z.M. Sun et al.

    Acta Metall. Mater.

    (1992)
  • M. Taya et al.

    Metal Matrix Composite Thermomechanical Behavior

    (1989)
  • Cited by (0)

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