Thermal stability of the nanostructure of mechanically milled Cu–5 vol% Al₂O₃ nanocomposite powder particles

Abstract

Isothermal annealing in the temperature range of 300-600°C, microstructural characterization, and analysis of the grain growth kinetics during annealing were carried out for Cu-5 vol% Al 2 O 3 nanocomposite powder particles produced by high energy mechanical milling. When the annealing temperature was 400°C or lower, only reduction in dislocation density occurred during annealing. When the annealing temperature was 500°C or higher, reduction in dislocation density, abnormal grain growth of the nanocrystalline Cu matrix, and coarsening of the Al 2 O 3 nanoparticles occurred. It has been found that the microstructure of the nanocrystalline Cu matrix of the nanocomposite exhibits a far higher thermal stability than that of monolithic nanocrystalline Cu, even though the apparent activation energy of the grain growth of the former is similar to that of the latter over the temperature range of 400-600°C, showing the dramatic drag effects of finely distributed Al 2 O 3 nanoparticles and Al 31 /O 2À clusters on the grain boundary motion.

Grain and nanoparticle coarsening of an ultrafine structured Cu–5vol.%Al2O3 nanocomposite during isochronal annealing

“…In contrast, significant grain growth from 150 nm to 1-3 lm was observed by both Č ížek et al [20] and Jiang et al [21] during annealing ultrafine structured Cu at 500°C for 1 h. Similarly, Zhilyaev et al [22] reported that after 1 h annealing at 500°C an ultrafine grained Ni sample made by ECAP completely lost its ultrafine structure and the average grain size reached 33 lm. This demonstrate that Al 2 O 3 nanoparticles significantly retard the coarsening of ultrafine Cu grains, in agreement with the observation made in previous studies [13,[23][24][25][26].…”

“…This means that the actual volume fraction of the Al 2 O 3 nanoparticles ($4%) was clearly lower than the volume fraction of Al 2 O 3 nanoparticles added to the starting powder (5%). This is likely because that most of the added gamma Al 2 O 3 nanoparticles were dissolved during HEMM [13,19] and most of the Al 2 O 3 nanoparticles observed in the microstructure of the asextruded sample formed during heating and hot extrusion in the process of powder consolidation. As shown in Fig.…”

“…The details of the process used to produce the powder can be found in reference [13]. The as-milled powder was die-pressed at room temperature into a cylindrical compact with a diameter of 25 mm, a height of approximately 28 mm and a relative density of $96%.…”

“…A study conducted by Ď urišin et al [12] showed that the recrystallization of an ultrafine structured Cu-3 vol.%MgO nanocomposite also occurred at a low temperature of $300°C, and abnormal growth of Cu grains occurred at temperatures above 500°C. Recently, we [13] investigated the microstructural stability of mechanically milled nanostructured Cu-5 vol.%Al 2 O 3 powder particles during annealing in the temperature range of 300-600°C, and found that the nanostructured Cu matrix can still maintain their nanometer sized grains after annealing at 600°C for 5 h due to the retardation of Al 2 O 3 nanoparticles on grain growth. Interestingly, Motlagh et al [14] recently reported that annealing of a nanostructured Cu-2.4 vol.%Al 2 O 3 nanocomposite sample produced by ECAP at 1000°C for 5 min causes recrystallization leading to a decrease of the average Cu grain size from 70 to 38 nm.…”

Aluminum-based nanocomposites with hybrid reinforcements prepared by mechanical alloying and selective laser melting consolidation

“…It had been found that the microstructure of the nanocrystalline Cu matrix exhibits a good thermal stability, due to the dramatic drag effects of finely distributed Al 2 O 3 nanoparticles and Al 31 /O 2À clusters on the grain boundary motion. 8 El-Eskandarany used high-energy ball milling to achieve SiC reinforced Al-based nanocomposites. It was further found that the increasing volume fractions of the SiC reinforcement led to an increase of the density, hardness, and elasticity modulus of the composite samples.…”