The formation of precipitates and its effect on grain structure in V-4Cr-4Ti alloys with yttrium addition

The formation of precipitates and its effect on the grain structure in V-4Cr-4Ti alloys with and without yttrium addition have been investigated. As-cast and recrystallized grain structure and the secondphase particles were studied via OM (Optical Microscopy), SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), and EBSD (Electron Back-scattering Diffraction). It was found that yttrium oxides inclusions with size of micrometer level existed in all yttriumcontaining V-4Cr-4Ti alloys including as-cast, rolled, annealed and forged states. It was revealed that fine yttrium-enriched particles, less than 200 nm in size, were frequently observed in V-4Cr-4Ti-0.3Y alloys annealed or forged above 1000 °C. Yttrium addition was observed to have refining effect on the as-cast grains and homogenization effect on the annealed grain structure of rolled sheets. Yttrium addition mitigated the inhomogeneity of recrystallized grain structure in rolled V-4Cr-4Ti sheets due to the enormous reduction of nonuniform Ti(C, N, O) particles, and inhibited the abnormal growth of grains at relatively high annealing temperatures because of the formation of the finer yttrium-enriched precipitates.