Thermal evolution of Fe - ZrO 2 nanocomposite: Insights from calorimetric and microscopy investigations

Abstract This article presents the results of an experimental study on the evolution of phases during annealing of ball milled Fe – ZrO 2 nanocomposite powder using Differential Scanning Calorimetry, X-ray Diffraction and Electron Microscopy techniques. The formation of FeO phase from Fe and Fe 3 O 4 is identified through Differential Scanning Calorimetry and confirmed using Synchrotron Diffraction and Transmission Electron Microscopy. Qualitative X-ray phase analysis showed the stoichiometry of the FeO phase as Fe 0.87 O. This phase is expected to be beneficial as it offers strengthening in the Fe matrix and is thermally stable. The activation energy of formation of the Fe 0.87 O phase was estimated to be ~ 195 kJ mol − 1 . This phase is also found to be partially stabilizing the cubic phase of ZrO 2 , at high temperatures. A cubic ⇆ tetragonal transformation of ZrO 2 was identified at 1140 K. A rather broad peak was observed for Fe α → γ transformation in the Calorimetry thermograms as the Fe grains were nanocrystalline which became sharper as the crystallites grew in size.