The effects of nanocrystalline matrix powder produced by mechanical alloying on microstructure and mechanical properties of metal matrix composites

In this thesis, it has been investigated change of matrix grain size in the nano system by means of mechanical alloying and reinforcement particles and effective strength mechanisms in a composite system. For this purpose, different weight ratio of nano size powder ZrO2 was added to pure Al powder and subjected to mechanical alloying for various hours. The alloying process was carried out. After mechanical alloying, metal matrix nanocomposites were formed by hot press sintering. Grain size analysis, microstructure imaging, hardness, density measurement and compression test were performed on the obtained samples. According to the results, through mechanical alloying and increasing alloying time grain size decreased and obtained nanocrystalline matrix powder. Smaller garin size and reinforcement particles caused different strenght mechanism such as Hall-Petch, Orowan, load bearing effect, incerasing dislocation density so the strenght, density and hardness of Al-ZrO2 composites were improved. On the other hand, uniform dispersion of reinforcement into the matrix was not achieved due to the tendency of nano reinforcement to clustering and agglomerate. This case adversly affected the strengt, density and hardness of composites. Key words: Hall-petch, grain boundary, grain size, mechanical alloying, strength mechanisms, nanocomposite, ,nanocrystalline Aluminium, Orowan, triple junction,