Investigation of mechanical, tribological, and thermal properties of nano TiO2 and nano ZrO2 reinforced AL7075 alloy

In this thesis study, In this thesis study, cylindrical bulk specimens were produced by the powder metallurgy method through the addition of TiO₂ and ZrO₂ nanoparticles in varying proportions to the Al7075 matrix. The effects of the addition of TiO2 and ZrO2 powders, either individually or as a hybrid combination, on the hardness, microstructure, wear performance, and thermal properties of the composites were investigated. Phase analyses of the produced composites were carried out using X-ray diffraction (XRD). Thermal properties were evaluated using a Hot Disk thermal analyzer. Additionally, the microstructures of the powders were examined using optical microscopy following compaction, sintering, and etching processes. To determine the effect of reinforcement type and content on the hardness of the composites, Vickers hardness measurements were carried out on the produced samples. Furthermore, both experimental and theoretical densities of the composites were calculated, followed by pin-on-disk wear tests. In these tests, the effects of reinforcement type, applied load, sliding distance, and sliding speed on wear behavior were studied. A 3 wt.% TiO2 reinforcement resulted in a 20% increase in the hardness of the alloy. The highest hardness value, 95 Hv, was achieved in the hybrid composite reinforced with 2 wt.% TiO₂ and 3 wt.% ZrO2. It was observed that both TiO2 and ZrO2 nanoparticles improved the wear performance of the alloy and reduced the coefficient of friction. With the addition of 3% nano TiO₂ reinforcement, the coefficient of friction decreased from 0.81 to 0.62, while with 3% nano ZrO₂ reinforcement, it further decreased to 0.57. It was found that increasing the reinforcement content and sliding speed enhanced the wear resistance, while increasing the applied load reduced the wear rate. SEM examinations of the worn surfaces revealed that matrix deformation decreased and the scratch marks became shallower with increasing sliding speed. In terms of thermal properties, the lowest thermal conductivity was measured as 7.52 W/m·K in the unreinforced Al7075 alloy, whereas the highest thermal conductivity was obtained as 23.81 W/m·K in the hybrid composite reinforced with 2 wt.% TiO2 and 3 wt.% ZrO2.