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Abstract This paper presents the results of an experimental study on evolution of the nanocrystalline microstructure in a mechanically alloyed Oxide dispersion strengthened (ODS) 18Cr ferritic steel powder during densification by spark plasma sintering (SPS) in the temperature range of 1273 K (1000 °C) to 1423 K (1150 °C). Systematic Electron Back-Scatter Diffraction analysis has been carried out to study the grain size distribution and texture as a function of consolidation temperatures. Based on the kinetics of the densification process and resultant microstructure/microtexture, a sintering temperature slightly above 1323 K (1050 °C) within a range of 50 K was found to be optimum. The 18Cr-ferritic steel powder consolidated at 1323 K (1050 °C) was also studied to understand the role of dispersoids on microstructure. The dispersoids exerted a profound influence on the strength as well as toughness of the steel by restricting the grain growth at high temperatures. Further, a signature of (1 1 0) grain cluster is observed during consolidation and its preferential growth with increase in sintering temperature is noticed which lead to the alignment of the (1 1 0) plane in the direction of applied pressure. The minimum creep rate of the consolidated steel under a load of 300 MPa was found to be 5E-7 h−1 and 1E-4 h−1 at 873 and 973 K (600 and 700 °C) respectively. The apparent activation energy for creep deformation was estimated as ~ 402 kJ/mol, which is typical of lattice diffusion assisted general climb mechanism of dislocations over the barriers such as present dispersoids. [ABSTRACT FROM AUTHOR]

HCF-creep interaction in type 316LN stainless steel is investigated at 923 K by conducting HCF tests well below the endurance limit with high mean stress (high R- ratio). High mean stress inflicts creep damage at 923 K, which when imposed on a small alternating stress, leads to significant HCF-creep interaction. Depending on the magnitude of mean stress (R -ratio), three distinct regimes are identified, viz. (a) HCF regime (b) HCF-creep interaction regime and (c) creep regime. Detailed fractographic investigation revealed distinct fracture characteristics pertaining to each of the three regimes. HCF-creep interaction regime is marked by significant intergranularity at low values of mean stress which changes to predominantly dimpled fracture with increasing mean stress. The above observations are corroborated through detailed EBSD investigations which bring out the underlying deformation mechanisms responsible for failure under HCF-creep interaction. [ABSTRACT FROM AUTHOR]