Evaluation of the thermodynamic possibility of in-situ composites fabrication in aluminum-metal and aluminum-metal oxide systems through friction stir processing

Abstract

Thermodynamic evaluations of the possibility of the interaction reaction of aluminum with powders of Ti, Ni, Fe, TiO2, NiO and Fe2O3 leading to the formation of intermetallics and aluminum oxide Al2O3 during friction stir processing (FSP) were carried out. The Gibbs energy was considered as a determining parameter since its change resulted from chemical transformations makes it possible to establish the fundamental possibility of a chemical reaction proceeding under certain conditions. The change in the Gibbs free energy with temperature was calculated, and the Ellingham diagrams were plotted for the reactions observed experimentally during FSP in the systems Al+Ti, Al+TiO2, Al+Ni, Al+NiO, Al+Fe and Al+Fe2O3. The evaluations were performed for 1 mole of aluminum. The selected temperature range was 620 – 720 K because during FSP of aluminum and its alloys the peak temperatures usually fall into this temperature range. It was shown that all considered reactions of aluminum interaction with both pure metals (Ti, Ni, Fe) and oxides (TiO2, NiO, Fe2O3) were thermodynamically possible. However, chemical reactions involving aluminum interaction with TiO2, NiO and Fe2O3 gave higher absolute values of ΔG than those with Ti, Ni, and Fe. In the systems Al+NiO and Al+Fe2O3 in reactions involving the formation of intermetallics of MeAl3 type and oxide Al2O3 the absolute values of ΔG were approximately the same and in two times higher than that for the system Al+TiO2. It was concluded that for manufacturing of the in-situ Al-based composites by FSP the use of nickel and iron oxides (NiO and Fe2O3) is preferable to the pure metals (Ti, Ni, Fe) and the titanium oxide (TiO2).