Thermodynamic study on the formation of order-disorder structure of the NiAl intermetallic compound by semi-empirical model

In this study, the mixture of nickel and aluminum powders has been mechanically milled for different times in a planetary mill and its thermodynamics were investigated. Phase and structural changes of the mixture powders have been investigated by XRD and SEM analysis. The prediction of a stable phase of the milling process was carried out using the Miedema's semi-empirical method. The results showed that Ni(55)A(l)(45) intermetallic was more stable than a solid solution and amorphous phase after the mechanical milling process. In order to determine the mechanism of forming an intermetallic mixture of milled and unmilled powders, they have been subjected to DTA thermal analysis and were compared the experimental and the theoretical results. The results of the thermal analysis have been showed that the intermetallic formation reaction was completed in four steps, with the formation of the middle phases of Ni3Al and Al2Ni3. The grain size and lattice strain changes have been calculated using the Williamson-Hall equation during mechanical alloying.