INVESTIGATION OF HIGH TEMPERATURE DEFORMATION BEHAVIOUR IN P/M ODS ALLOYS

Abstract

The Oxide dispersion strengthened steels have been the popular materials among the researchers because of their high creep strength at elevated temperatures. The particle dispersions although improves the creep strength but degrades their workability. In order to investigate the effect of oxide particle dispersions on the workability of these materials, two alloy compositions are selected, with and without yittria. The alloys are thermomechanically processed on GLEEBLE 3800 where, hot compression tests are carried out in the temperature range of 950 ֯ C to 1150 ֯ C with the step of 100 ֯ C, at the strain rates of 0.1 s-1, 1 s-1 and 10 s-1. The obtained flow stress data is used to establish constitutive equations of flow and to develop the processing map based on dynamic material modelling. The differences in the processing maps of both the alloys suggests that on addition of yittria, the instability in deformation is introduced in high temperature and high strain rates regime. The activation energy for alloy with yittria is found to be 428 kJ/mol and the stress exponent is calculated as 3.4, which suggests that the deformation is dislocation creep controlled. The processing maps reveals that the alloy with yittria is not able to withstand high deformation speeds, the success rate of deformation at 10 s-1 is about 10%. The stable regions for alloy without yittria is found to be in the range of 1050 ֯ C to 1150 ֯ C at 1 s-1. While for the alloy with yittria, the stable flow is found for 1050 ֯ C, 0.1 s-1 and 950 ֯ C, 1 s-1.