Effect of overaging and particle size on tensile deformation and fracture of particle-reinforced aluminum matrix composites

Abstract

The effect of reinforcement particle size and overaging treatment on the tensile behavior and fracture morphology of a 2080/SiC/20 p composite was investigated. Tensile behavior was profoundly influenced by particle size and matrix strength. The composite strength increased with a decrease in particle size, while overaging greatly reduced the strength of the composite, independent of particle size. Almost all particles on the fracture plane were fractured, and the amount of particle fracture in the composites was insensitive to overaging and particle size, due to the excellent bonding between SiC particles and the Al matrix. Fractography showed that void nucleation in the matrix of peak-aged composites took place primarily at very fine SiC particles, which were much smaller than the average SiC particle size. Subsequent failure took place by the tearing topography surface (TTS) mechanism. In the overaged composite, composites failed by a more conventional void nucleation and growth process, where void nucleation took place at coarsened S precipitate particles, resulting in smaller and more elongated voids.

Effects of particle size and distribution on the mechanical properties of SiC reinforced Al–Cu alloy composites

“…3 also shows that the composites reinforced with small SiC particles (4.7 m) exhibited significantly higher yield strength and ultimate tensile strength, while the composites reinforced with large SiC particles (77 m) possess a higher elongation to fracture. For a composite undergoing elastic loading, a significant fraction of the stress is initially borne by the reinforcements, and the composite undergoes microplastic yielding [27]. Microplasticity in the composites takes place locally with high stress concentrations, normally along the poles of the reinforcements or at sharp corners of the reinforcements [28,29].…”

“…Meanwhile, the nucleated voids are unable to coalesce so easily because the smaller inter-particle spacing (directly related to the particle size) imposed higher plastic constraint [32]. The formation of dislocation tangles around the particles due to plastic incompatibility between the reinforcement and matrix, and the formation of a dislocation cell structure with a cell size inversely proportional to the inter-particle spacing could also contribute to the increase in the strength with decreasing the SiC particle size [27,33]. The effect of particle size on the tensile behavior indicates an increase in the ductility with increasing the particle size.…”

Effect of reinforcement-particle-orientation anisotropy on the tensile and fatigue behavior of metal-matrix composites

“…A strong mechanical bond between the particle and matrix is highly desirable in strengthening of MMCs, because it maximizes the degree of load transfer from the matrix to the particle and, thus, increases the chance that a given particle will be loaded to its fracture stress. [25] The microstructure of precipitates within the grains was revealed by TEM. Thermal-expansion mismatch in these materials induces thermal-misfit dislocations at the particle/ matrix interface.…”

“…When the matrix is significantly work hardened, the matrix is placed under great constraint, with an inability for strain relaxation to take place. [25,37] This causes the onset of void nucleation and propagation, which takes place at a lower far-field applied strain than that observed in the unreinforced material, resulting in a lower macroscopic ductility.…”

“…This fracture morphology has also been observed by other investigators. [1,8,10,25] Notice that the particle/matrix interface remained intact, indicating that the shear strength at the interface was higher than the particle fracture strength. The high shear strength can be attributed to the strong mechanical bond formed during extrusion.…”