Nanoscale Alumina-Reinforced Aluminum Matrix Composites: Microstructure and Mechanical Properties |
| Journal |
Key Engineering Materials (Volume 395) |
| Volume |
Progress in High Temperature Ceramics |
| Edited by |
Yashwant Mahajan & J. A. Sekhar |
| Pages |
157-178 |
| DOI |
10.4028/www.scientific.net/KEM.395.157 |
| Online since |
October, 2008 |
| Authors |
Ji Xiong Han,
Yong Ching Chen,
Vijay K. Vasudevan
|
| Keywords |
Aluminum Matrix Composite, Electron Microscopy, Fracture, Mechanical Property, Microstructure, Nanoscale Al2O3, Strengthening Mechanisms |
| Abstract |
Studies were carried out on microstructure evolution and mechanical behavior of an Al
matrix–nanoscale Al2O3 particulate-reinforced composite. The thermal stability of the composite,
evaluated by heat treating specimens at temperatures from 300 to 600 °C for times varying from 1
to 100 hours, revealed that the nano-sized (30-100 nm) Al2O3 particles present in the as-received/ascast
material coalesced into larger particles, but with sizes still in the 100 to 500 nm range. Despite
the coarsening of the particles, high hardness was retained. The tensile properties of both the as-cast
DSC material and those thermally soaked for 500 hours at a number of temperatures were
evaluated. The results showed that the yield strength was quite high (283 MPa) at room temperature
and decreased nearly linearly with temperature, though values as high as 110 MPa were obtained at
400oC. Thermal soaking did not have a detrimental effect on strength. Although the macroscopic
ductility of both unsoaked and soaked materials remained quite low over the entire temperature
range, SEM observations of the fracture surfaces provided substantial evidence for high localized
plasticity as manifested by stretching, tearing and void formation in the Al matrix around the oxide
particles. Possible strengthening mechanisms, including grain size reduction, Orowan bypass and
forest hardening, were considered and modeled. Good agreement between the calculated and
experimental strengths was obtained, and majority of the strengthening at room temperature was
found to come from forest hardening (i.e, increase in dislocation density caused by the thermal
expansion mismatch between Al and Al2O3), with secondary contributions from the Orowan
mechanism. TEM observations provided confirmatory evidence for these mechanisms. The
decrease in strength at higher temperatures was attributed to a diminishing contribution from forest
hardening due to recovery processes. |
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