Dynamic abnormal grain growth in tantalum

Abstract

Dynamic abnormal grain growth (DAGG) is a phenomenon that produces one or more very large, abnormal grains during plastic deformation of polycrystalline material at high temperatures. DAGG was previously observed in commercial-purity molybdenum (Mo) and was used to produce large Mo single crystals of centimeters in length. The present investigation is the first to demonstrate DAGG in commercial-purity tantalum (Ta) sheet, another body-centered-cubic refractory metal. DAGG occurs in Ta at temperatures from 1450–1850°C across strain rates from 3×10−5 to 5×10−4s−1. Grain boundary migration rates during DAGG in Ta are on the order of 10mm/min. DAGG produces large abnormal grains preferentially oriented with the 〈101〉 direction approximately parallel to the tensile axis. A unique observation of this investigation is a preponderance of Σ3 special boundary character along the boundaries of large abnormal grains produced in Ta through DAGG. The propensity toward this special boundary character is a result of a relatively large grain size and strong texture in the polycrystalline material prior to DAGG and the typically low energy of Σ3 boundaries, which suppress boundary migration.