Hot hardness behaviour of ultrafine grained ferritic oxide dispersion strengthened alloys prepared by mechanical alloying and spark plasma sintering

The microstructure, hot hardness, and indentation creep of ultrafine grained (ufg) 9Cr-1Mo and 9Cr-1W based ferritic oxide dispersion strengthened (ODS) alloys prepared by mechanical alloying and spark plasma sintering are investigated. Studies on hot hardness revealed that the hardness of Mo-containing alloys is higher than that of W-containing alloys. This is attributed to the complete dissolution of Mo while W did not dissolve completely during mechanical alloying. Hardness of Ti containing alloys is higher compared to the base and Y2O3 containing alloys and this is attributed to the presence of Ti-Y-O based nanoprecipitates. Study of hot hardness behaviour of ufg ferritic ODS alloys revealed a sharp transition at around 700-800 K. This is possibly due to the enhanced grain boundary mediated plasticity and pronounced reduction in Hall-Petch coefficient with increase in temperature. (C) 2012 Elsevier B.V. All rights reserved.