Thermal evolution of Fe - ZrO2 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 ZrO2 nanocomposite powder using Differential Scanning Calorimetry, X-ray Diffraction and Electron Microscopy techniques. The formation of FeO phase from Fe and Fe3O4 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 Fe0.87O. 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 Fe0.87O phase was estimated to be similar to 195 kJ mol(-1). This phase is also found to be partially stabilizing the cubic phase of ZrO2, at high temperatures. A cubic reversible arrow tetragonal transformation of ZrO2 was identified at 1140 K. A rather broad peak was observed for Fe alpha -> gamma transformation in the Calorimetry thermograms as the Fe grains were nanocrystalline which became sharper as the crystallites grew in size.