Microstructural and thermal characterization of nano-structured Al-Cu-Ni-Si alloy powders produced by mechanical alloying

In this thesis, AlCuNiSi medium entropy alloys with equal atomic ratio were produced as nanostructured powder by mechanical alloying technique at different milling times. Microstructural characterization of the produced mid-entropy nanostructured powders was performed by X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray (SEM/EDX) analyzes, and also thermal characterization was performed by differential thermal analysis (DTA). XRD results showed that as a result of mechanical alloying, intermetallic Al2Cu, AlNi, AlNi3 and fcc structure Cu based solid solution phases were formed during milling for 50-140 h. In addition, according to the XRD results, as the milling time increased, the particle size of the alloy powders decreased. After 140 h of mechanical milling, it was found that the crystallite size was approximately 3nm, the lattice strain was 1.15%, and the discollation density was 0.11x1018/m2. SEM/EDX analyzes showed that as the milling time increased, fragmentation, breakage, aggregation and cold-welds occurred in the alloy powders, and accordingly the particle size decreased and a more homogeneous structure was formed. DTA results showed a series of endothermic peaks indicating phase transformation and crystallization during continuous heating at a temperature range of 750-800 oC. According to the results obtained, it was understood that the microstructural properties of the AlCuNiSi alloy produced by milling for 140 h were superior to the microstructural properties of all other alloys produced in this study.