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This paper presents the results of a study on grain boundary characteristics in cold deformed and annealed 304HCu grade austenitic stainless steel (SS 304HCu) using electron backscatter diffraction. The microstructure exhibited an increasing fraction of Σ1 to 29 coincidence site lattice boundaries with annealing temperature, resulting up to ~60 pct at 1573 K with 92 pct contribution from Σ3-type twin boundary. However, the twin boundary interaction at the triple points with a network of Σ3-Σ3-Σ9 was found to decrease from 4 to 0.5 pct with annealing temperature. To understand the resultant boundary advancement of the Σ3n (n = 1, 2, 3) boundaries, their migration was traced in the annealed specimen. However, in the specimen with extended annealing Σ3 boundary fraction was found to be higher with a concomitant decrease in the boundary fraction generated by the Σ3 interactions. In this study, a procedure to analyze the coherency of Σ3 boundaries and its interfaces that form due to Σ3 interactions has been evolved based on single-section analysis using the pole concentration across the grains. Further, a crystallographic description of the two planes meeting at the interface of Σ3-type boundary has been provided by adopting serial sectioning methods, which help to understand the morphological changes. The quantitative deviation from exact coherent Σ3 has been estimated to be within ~6 deg in this study. [ABSTRACT FROM AUTHOR]

This study presents an extensive experimental characterization of high temperature phase stability and phase transformation kinetics of intermetallic sigma and alpha phases of Fe 55 Cr 45 alloy carried out by dynamic calorimetry. Sigma phase was synthesized from its parent alpha phase of Fe 55 Cr 45 alloy by annealing at 973 K for 360 h in vacuum. A comparative thermal study of sigma and alpha phase alloy was performed from 373 to 1400 K by Differential Scanning Calorimeter. Single inflection of ferro to para magnetic transition (T c ) was observed in DSC upto melting at 831 K for alpha phase. For sigma phase, the sigma to alpha decomposition temperature was measured as 1122 K. It was observed that sigma phase decomposition temperature is nearly 30 K higher than the presently reported 1093 K. Kinetics study of sigma to alpha phase transformation has been carried out by employing various heating rates from 1 to 50 K min −1 in DSC. The non isothermal KJMA model has been adopted to model the fraction transformed to determine the order and kinetics parameters. The activation energy for sigma to alpha phase transformation was obtained 240–260 kJ mol −1 by employing KJMA model. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The present investigation deals with the efforts to form a defect free bonded interface between mild steel (MS) and titanium (Ti) using the rotation friction welding process. The conditions were optimized based on several trials by varying friction welding parameters like frictional force, upset force, burn-off length and rotational speed. It has been established that only fine FeTi particles formed in isolated regions at the interface of 'as welded' MS/Ti joints. The evolution of interface microstructure has been studied by diffusion annealing heat treatments in the temperature range of 500-800 °C for a duration of 100 h. Plastic deformation during friction welding reduced the recrystallisation temperature of MS. The variation in microchemistry was measured across the weld interface, which was used as input to predict the formation of various phases and the consequent change in the mechanical properties using the JMatPro® software. Intermetallics were present only as fine isolated particles in bcc-Fe matrix at the interface even after heat treatment at 800 °C for 100 h. The growth kinetics was found to be much slower in friction welded joints as compared to diffusion bonded and explosive clad joints. [ABSTRACT FROM AUTHOR]