ISSN:
1013-9826
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Studies were carried out on microstructure evolution and mechanical behavior of an Almatrix–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 1to 100 hours, revealed that the nano-sized (30-100 nm) Al2O3 particles present in the as-received/ascastmaterial coalesced into larger particles, but with sizes still in the 100 to 500 nm range. Despitethe coarsening of the particles, high hardness was retained. The tensile properties of both the as-castDSC material and those thermally soaked for 500 hours at a number of temperatures wereevaluated. The results showed that the yield strength was quite high (283 MPa) at room temperatureand decreased nearly linearly with temperature, though values as high as 110 MPa were obtained at400oC. Thermal soaking did not have a detrimental effect on strength. Although the macroscopicductility of both unsoaked and soaked materials remained quite low over the entire temperaturerange, SEM observations of the fracture surfaces provided substantial evidence for high localizedplasticity as manifested by stretching, tearing and void formation in the Al matrix around the oxideparticles. Possible strengthening mechanisms, including grain size reduction, Orowan bypass andforest hardening, were considered and modeled. Good agreement between the calculated andexperimental strengths was obtained, and majority of the strengthening at room temperature wasfound to come from forest hardening (i.e, increase in dislocation density caused by the thermalexpansion mismatch between Al and Al2O3), with secondary contributions from the Orowanmechanism. TEM observations provided confirmatory evidence for these mechanisms. Thedecrease in strength at higher temperatures was attributed to a diminishing contribution from foresthardening due to recovery processes
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/01/57/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.395.157.pdf
Permalink
