Dependence of thermal residual stress on temperature in a SiC particle-reinforced 6061Al alloy
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I.
INTRODUCTION
Metal matrix composites (MMCs) are generally reinforced by ceramic fibers, whiskers, or particles, which have considerably different chemical and physical properties from those of the matrix. Such differences in the properties not only make the materials difficult to manufacture but may also influence the performance of these materials in severe environment, such as repeated heating and cooling. For example, under a variable temperature, the possible difference in the coefficients of thermal expansion (CTEs) between the two phases can generate changes in internal stresses as well as cyclic plastic deformation, which are believed to have a controlling influence on the mechanical behavior and the lifetime of MMCs.[1,2,3] In recent years, MMCs have been considered for engineering applications over a wide range of temperatures, and the thermal cycling is of particular interest in these materials.[1,4–8] It has been reported that thermal cycling could result in several forms of damage and change in sample dimensions.[2,9–11] Mechanisms proposed to account for damage and dimensional changes, including whisker debonding, crack bridging, whisker pullout, and shear at the matrix-fiber interface, are related to the residual stress state in the constituent phases. In order to understand the effects of residual stresses in MMCs during heating and cooling, it is important to know how the thermal stresses (TS) vary with temperature. In Reference 12, thermal stress behavior of bonded SiC/6061Al layered material during thermal cycling was studied. In the work presented subsequently, the thermal stress variation in the matrix of SiCp/6061Al composite during thermal cycling was determined by X-ray diffraction; meanwhile, the thermal stress variation and the residual stress distribution (RSD) in the composite were calculated by finite element modeling (FEM), and the results were discussed. H. LI, Assistant Professor, and D.Z. WANG, Professor, are with the Department of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China. J.B. LI and Z.G. WANG, Professors, and C.R. CHEN, Assistant Professor, are with the State Key Laboratory for Fatigue and Fracture of Materials, Institute of Metal Research, Academia Sinica, Shenyang 110015, People’s Republic of China. Manuscript submitted September 6, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
II.
METHODS
A. X-Ray Stress Measurement The material used in the present study was 6061Al alloy reinforced with 20 vol pct SiC particles (average size 3.5 mm), which was produced by a powder metallurgical procedure. The disk-shaped sample was machined to a dimension of 10 mm in diameter and 3 mm in thickness. The sample together with 6061Al powder was solutionized at 520 7C for 1.5 hours followed by a peak-aged treatment at 170 7C for 4 and 8 hours, respectively, and then cooled in air. Pretest results indicated that the lattice parameter of 6061Al power remained unchanged within the range of 4 to 8 hours for aging treatment. Th
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