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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]

In this study thermophysical properties of alloy 617 have been measured as a function of temperature using various thermal analysis techniques and complemented by structural and microstructural characterization. The enthalpy increment (H T −H 298 ) has been measured using static calorimetry in the temperature range of 300–1523 K. It is found that (H T −H 298 ) increases monotonically with temperature up to about 1000 K. However, above this temperature two distinct inflections are detected at about 1030 K and 1205 K respectively. A critical comparison of these inflections with Thermo-Calc simulations and dynamic calorimetry measurements indicates that they are associated with dissolution of M 23 C 6 , and γ′-Ni 3 Al phases respectively. The enthalpy data has been numerically fitted using non-linear regression analysis to obtain the temperature dependence of heat capacity. Further, the thermal diffusivity and thermal expansivity of alloy 617 have been measured using the laser flash method and thermo-mechanical analyzer in the temperature range of 300–1523 K. Finally, with the knowledge of heat capacity, density and thermal diffusivity data, thermal conductivity has also been estimated in the temperature range of 300–1523 K. The measured properties for alloy 617 have been compared with Thermo-Calc, JMatPro simulation and other literature data, which clearly establishes the role of precipitates dissolution. The various properties measured in the present study are original and new addition to the database for alloy 617, which can serve as new input for Thermo-calc based optimization. This paper also provides the insight into the temperature and composition dependence of thermal conductivity of alloy 617. [ABSTRACT FROM AUTHOR]

Present study demonstrates by experiments and computation that a fully martensitic microstructure does not form in 9 Cr steels containing 1.9 wt% W (P92). The presence of a magnetic transition prior to the martensitic transformation during fast cooling supports the co-existence of ferrite and martensite. The formation of diffusional ferrite at high cooling rates is precluded by a systematic variation of three parameters namely cooling rate, austenitising temperature and hold times. However, complete martensite formation has not been experimentally feasible in P92 steel at all for all cooling rates (1–90 K min −1 in DSC and water quenching) employed from austenitisation temperatures (950–1150 °C), unlike in P91 steel where complete martensite forms during cooling at the rate of 30 K min −1 or higher. The experimental results have been substantiated by Thermo Calc simulation for varying W contents in P91 and P92 steels. Thermo Calc simulation revealed that P91 steel remains in the single phase γ domain during austenitisation at 950–1150 °C (1223–1423 K). It is observed that γ phase field gets shifted towards the right with addition of W in P91. P92 steel remains in the three phase domain of α + γ +MX region at 950–1150 °C (1223–1423 K), which explains the presence of ferrite above Ac 3 temperatures. [ABSTRACT FROM AUTHOR]

Abstract: An α+β Ti–5Ta–1.8Nb alloy was solutionized in the β phase field and cooled at different rates from 20 to 99K/min. Detailed microstructural characterization of the products of β→α transformation after continuous cooling from the β phase field has been carried out, to understand the effect of cooling rate on the transformation mechanisms. An increase in cooling rate causes a suppression of the β→α transformation temperature domain, resulting in composition variation of α and β phases. Such a variation in the composition of β phase was observed to induce different secondary transformations, which are sensitive to the cooling rate. [Copyright &y& Elsevier]

This paper presents the results of an experimental and computational study on interdiffusion and related structure-property changes in 304 L stainless steel/Ti–5Ta–2Nb system. Diffusion annealing treatments were carried out in the temperature range of 873–1173 K, above and below the β transus temperature of Ti. The formation of σ, FeTi and Fe 2 Ti phases at the interface as well as stabilization of α-Fe and β-Ti in 304 L SS and TiTaNb respectively has been unambiguously established in this study. Growth kinetics of the reaction zones has been determined and effective interdiffusion coefficients in various phases were calculated using Wagner's approach. Temperature dependant variations in the mechanical property of the base materials and diffusion couples have also been predicted using JMatPro® and compared with literature. Finally, the evolution of microstructure at the interface and diffusion path in the diffusion couples were compared with SS/Ti based diffusion bonded joints and explosive clads to understand the interdiffusion behavior under equilibrium and non-equilibrium conditions. • Interdiffusion studies carried out in 304L SS/Ti–5Ta–2Nb system for the first time. • Diffusion studies carried out above and below β transus temperature of Ti alloy. • Formation of σ, FeTi, Fe 2 Ti & Stabilization of α-Fe and β-Ti confirmed in reaction zone. • Temperature dependant variation in properties predicted & compared with literature. • Interface microstructure, diffusion path compared with explosive clads & diffusion bonds. [ABSTRACT FROM AUTHOR]