Mechanical characterization of alumina and carbon nanotube reinforced Al-4Cu nanocomposites produced by powder metallurgy

In this study, alumina particle (80 nm in size) and multi-wall carbon nanotube (MWCNT) with 9.5 nm in diameter reinforced Al-4Cu alloy matrix nanocomposite was produced by powder metallurgy method. While the MWCNT reinforcement ratio was kept constant as 1.5 vol. %, alumina was used in different proportions between 4.5-13.5 vol. %. In addition, the unreinforced alloy was also produced for comparison. After a premixing of 30 min, the mechanical alloying was applied to the mixed powders at a rotational speed of 250 rpm for 5 hours in an argon gas environment and 5 wt. % ethanol was used as a process control agent. After the mechanical alloying, the samples were produced by applying the cold compaction at 800 MPa and then the microwave sintering. Nanocomposites were sintered at 615 °C for 1 h in an argon gas environment. Two different heat treatments were applied to the produced samples. One of the heat treatments applied is the annealing process at 400 °C for 2 hours. The other heat treatment is the artificial aging process for 11 hours at 200 °C after a solutionizing at 550 °C for 70 min and subsequent rapid cooling. In addition, the aging curves were determined by applying the artificial aging to all samples at 170, 180 and 200 °C for up to 100 hours, individually. After the production, the microstructures of the samples were examined by means of X-ray diffraction, scanning electron microscope and light microscope. Besides that, the mechanical properties were determined by macro hardness, microhardness, nanoindentation and compression tests. In addition, the wear behavior was investigated by performing a pin on disc test. According to the experimental results, an increase in the macro hardness, microhardness and nano hardness values of the samples together with the reinforcement ratio was observed. Moreover, while the compression strength and ductility decreased with the reinforcement, the yield strength increased. In addition, the incorporation of 15% hybrid reinforcement into the alloy increased the elastic modulus by 60% in comparison to the unreinforced alloy. Furthermore, the wear resistance and friction coefficient increased with the reinforcement content.