  This investigation has used flexural test to explore the effects of thermal
treatments, i.e., high-temperature and cryogenic environments on the mechanical
property of alumina particulate-reinforced Cu metal matrix micro and
nanocomposites in ex-situ and in-situ conditions. Cu-5 vol. pct alumina micro
(10 micron)- and nanocomposites (<50 nm) fabricated by powder metallurgy route
were subjected to up-thermal shock cycle [193 K to 353 K (-80C to 80C)] and
down-thermal shock cycle [193 K to 353 K (from 80C to -80C)] for different time
periods followed by 3-point bend test. One batch of specimens (micro and
nanocomposites) was conditioned at [193 K to 353 K (from 80C to -80C)]
separately followed by 3-point flexural test. High-temperature flexural test
was performed at [373 K to 523 K (100C to 250C)] on the micro and
nanocomposites. All the fractured samples obtained after various thermal
treatments were studied under scanning electron microscope (SEM). The
development of thermal stresses quite often results in concentration of
residual stresses at the particle/matrix interface eventually weakening it.
Enhancement of flexural strength was recorded for down- as well as for
up-thermal shock in microcomposites. The high-temperature flexural strengths of
micro and nanocomposites are lower than those at ambient temperature. The
amelioration and declination in mechanical properties as a consequence of
thermal shock, thermal conditioning, and high-temperature flexural testing have
been discussed in the light of fractography.
