Effect of thermal and cryogenic conditioning on flexural behavior of thermally shocked Cu-Al2O3 micro- and nano-composites

Abstract

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.