The goal of this study is to characterize the hardness distribution and texture evolution in a friction stir welded oxide dispersion strengthened (ODS) ferritic steel. Hardness profiles were plotted by collecting data on the transverse cross section of the joint. The texture evolution and microstructure characteristics were studied by electron backscattering diffraction (EBSD). Results showed that regions near the bottom of the stir zone were the weak points in hardness, as those regions comprise coarser grains compared with the adjacent regions. EBSD results showed that the grain characterization (size, shape, and aspect ratio) varied within different regions and provided important insight into the material flow within the stir zone. EBSD results also revealed that textures within different regions presented some features of rotating coincidence. By suitable rotations of the poles figures, textures within different regions could superpose with each other almost exactly.

The effect of adding minor elements, such as Ti, Mg, Zr, Ca or Hf, on the size of oxide particles was investigated in Ni-based ODS alloy, Ni-0.5 mass%Al-1 mass%Y 2 O 3 . Among these elements, Hf is the most effective at refining the oxide particles, particularly at a concentration of 0.8 mass% Hf, as verified by TEM observation and hardness measurement. X-ray diffraction measurements indicate that the formation of Y 2 Hf 2 O 7 is responsible for the refinement of oxide particles. The Hf is also effective for a commercial superalloy of PM1000.

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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.