Grain Boundary Deformation at High Temperature Tensile Tests in ODS Ferritic Steel

Abstract

The tensile test of the recrystallized ODS ferritic steels was performed in the loading direction for the longitudinal and 45° inclined with respect to the grains alignment. The testing temperature was 800°C and the strain rate was 10 -4 s -1 . A clear serration structure was observed at near the grain boundaries at the surface of 45° specimen ruptured. This is a clear evidence of the occurrence of the grain boundary sliding in 45° direction. For the total strain of 12% in 45° direction, grain boundary deformation induced by sliding was estimated about 9%, whereas the amounts of the transgranular strains was 2% measured by EBSD analysis. The grain-subdivision was also identified near grain boundaries by FIB analysis, which could be caused by a dynamic recrystallization during the localized grain boundary deformation.

Microstructural characterizations of 14Cr ODS ferritic steels subjected to hot torsion

“…The occurrence of the grain boundary sliding at high temperature deformation of ODS ferritic steels was also reported by Sugino et al in tensile tests at 800°C and 10 À4 s À1 [26]. It is therefore assumed that intragranular plastic strain is limited by the nano-precipitates, and that the material significantly deforms by accommodation at grain boundaries, which leads to intergranular damage unless prevented by large negative stress triaxiality.…”

Local deformation heterogeneity in cyclically deformed interstitial free steel

“…, the average misorientation of the undeformed specimen was subtracted from the misorientation values of the specimens failed at various cyclic strain amplitudes. The GND density ( ρ g ) was then calculated using the following relationship: where b is the Burgers vector and D is average grain diameter in microns.…”

“…However, these investigations are primarily restricted to monotonic deformation . Because the evolved misorientation is related with the generation of GNDs, it is possible to estimate the density of GND from a measurement of misorientation values . There have been some investigations to characterise the heterogeneity of plastic deformation and generation of GNDs during cyclic loading of different materials .…”

Microstructure and mechanical properties of γ΄ strengthened Co–Ni–Al–W-base ODS alloys

“…Moreover, the lower strain rate supplements the sufficient time for microvoids coalescence resulting in large voids and considerable softening [28]. Therefore, the high temperature deformation of Co-base ODS alloy arises from grain boundary deformation, diffusion-controlled void formation, and deformation along discontinuously formed area [29].…”