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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 ~ 195 kJ mol− 1. This phase is also found to be partially stabilizing the cubic phase of ZrO2, at high temperatures. A cubic ⇆ tetragonal transformation of ZrO2 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.

This paper presents the results of an electron microscopy study on the formation of metastable fcc Ti phase under shock loading conditions in an explosive clad of α + β Ti–5Ta–2Nb alloy and the mechanism and kinetics of its reversion during annealing. The fcc Ti phase with a volume fraction of over 0.6 formed in hcp Ti matrix with a characteristic needle shaped morphology. The biphasic fcc + α structure when heat treated in the temperature range of 100–1100 °C showed the gradual transformation of fcc to parent α phase and the maximum reversion was observed at temperatures > 600 °C. The α phase was nucleated within the fcc as well as on the fcc/α interfaces. Orientation relationship between fcc and hcp phases has been derived using standard 1 − 12 fcc and [0001]α stereographic projections. The kinetics of the reversion process followed diffusion controlled nucleation and growth process with an effective activation energy corresponding to the self diffusion of Ti in hcp matrix.

This paper presents a detailed electron microscopy study on the microstructure of various regions of weldment fabricated by three welding methods namely tungsten inert gas welding, electron beam welding and laser beam welding in an indigenously developed 9Cr reduced activation ferritic/martensitic steel. Electron back scatter diffraction studies showed a random micro-texture in all the three welds. Microstructural changes during thermal exposures were studied and corroborated with hardness and optimized conditions for the post weld heat treatment have been identified for this steel. Hollomon–Jaffe parameter has been used to estimate the extent of tempering. The activation energy for the tempering process has been evaluated and found to be corresponding to interstitial diffusion of carbon in ferrite matrix. The type and microchemistry of secondary phases in different regions of the weldment have been identified by analytical transmission electron microscopy.

This study aims at understanding the microstructural changes due to variation of W and Ta content and heat treatment in 9Cr–W–Ta–0.2V–C reduced activation ferritic/martensitic steels, with W and Ta concentrations varied from 1 to 2 wt.% and 0.06 to 0.14 wt.% respectively. An increase in concentration of W and Ta in the steels refined prior austenite grain size and lath width, though the change was not significant beyond 1.4 wt% W. Increase in W and Ta concentrations also resulted in a decrease in size and increase in number density of carbides on tempering. Microchemical analysis of M 23 C 6 precipitates in tempered steel showed enrichment of W with increase in W content of the steel, whereas addition of Ta showed no significant change in chemistry of M 23 C 6 or MX, but only increased the number density of fine MX precipitates.

This paper presents the results of a study on the characteristics of the passive oxide film that forms on the surface of an {alpha} + {beta} Ti-5%Ta-1.8%Nb alloy, which possesses good corrosion resistance in severe oxidizing environment of boiling 11.5 M nitric acid. Through systematic structure-property studies, the microstructure with low corrosion rate (< 1 mpy) in liquid, vapor and condensate phases of nitric acid was identified. The characteristics of the passive film, which imparts corrosion resistance to the alloy, are influenced by its microstructure, temperature and concentration of the acid. The microstructure, thickness and composition of the oxide film were characterized using different techniques. TiO{sub 2}, Nb{sub 2}O{sub 5} and Ta{sub 2}O{sub 5} formed on exposure to vapor and condensate phases, while TiO{sub 2} was observed on exposure to the liquid phase. Detailed microstructural studies showed that the passive film consists of nano-crystalline phases of titanium and tantalum oxides, predominantly anatase in an amorphous matrix. Based on these studies, the mechanism of corrosion of the alloy is derived. - Research Highlights: {yields}Liquid phase corrosion results in a thicker and protective oxide film. {yields}Oxide film is a mixture of amorphous and nano-crystalline anatase. {yields}Higher amounts of Nb{sub 2}O{sub 5} andmore » Ta{sub 2}O{sub 5} form on vapor and condensate phase corrosion. {yields}High corrosion rate in condensate phase is due to selective dissolution of Ti in {alpha} phase.« less

This paper deals with the influence of direct current pulsing on the microstructure, room temperature hardness and tensile properties at four different temperatures of tungsten inert gas (TIG) weldments of Ti–6Al–4V. Autogenous full-penetration bead-on-plate TIG welds were made with and without direct current pulsing. A few coupons were subjected to a post-weld heat treatment (PWHT) at 900 °C. Room temperature hardness and tensile properties at four different temperatures (25, 150, 300 and 450 °C) of the weldments in both as-welded and PWHT conditions were studied and correlated with the microstructure. Current pulsing resulted in slight refinement of prior β grains leading to higher hardness, tensile strength and ductility of weldments in the as-welded condition. The post-weld heat treatment at 900 °C resulted in improvement in ductility and reduction in strength of weldments (both unpulsed and pulsed) owing to more coarsening of α, reduction in defect density and decomposition of martensite to equilibrium α and β. Both pulsed and unpulsed weldments after PWHT exhibited almost the same values of strength and ductility. This may be attributed to the width of the α plates being almost the same in both welds.