Materials Science and Engineering A 392 (2005) 209–221 Recrystallization of oligocrystalline tantalum deformed by cold rolling H.R.Z. Sandim a,∗ , J.P. Martins a , A.L. Pinto b , A.F. Padilha c a Departamento de Engenharia de Materiais, FAENQUIL, P.O. Box 116, Lorena, SP 12600-970, Brazil b Instituto Militar de Engenharia, IME, Rio de Janeiro 22290-270, Brazil c Departamento de Engenharia Metal´ urgica e de Materiais, Escola Polit´ ecnica, USP, S˜ ao Paulo 05508-900, Brazil Received 29 October 2003; received in revised form 10 September 2004; accepted 15 September 2004 Abstract The recrystallization behavior of coarse-grained tantalum deformed at large strains is strongly dependent on its deformation microstructure. In this regard, a longitudinal section of a high-purity coarse-grained tantalum ingot obtained by double electron-beam melting (EBM) was straight cold rolled to thickness reductions varying from 70 to 92% followed by annealing in vacuum at 900 and 1200 ◦ C for 1 h. Microstructural characterization was performed in cold rolled and annealed specimens using scanning electron microscopy (SEM) in the backscattered mode (BSE), electron backscattered diffraction (EBSD), and microhardness testing. The recrystallization of individual grains is strongly dependent on their initial orientation. Recrystallization kinetics varies noticeably from one grain to another. Even after annealing at 1200 ◦ C for 1 h, the microstructure of tantalum sections deformed to 92% predominantly consists of alternating bands of recrystallized grains with distinct size distributions and a few elongated areas marking the presence of individual grains softened by recovery. Results also show inhomogeneous in-grain and grain-to-grain spatial distributions of textures in the rolling plane. © 2004 Elsevier B.V. All rights reserved. Keywords: Tantalum; Oligocrystals; Recrystallization; Recovery; Texture; EBSD 1. Introduction Tantalum has a body-centered cubic (b.c.c.) crystal struc- ture and displays an unique combination of physical and chemical properties like a very high melting point (2998 ◦ C), outstanding corrosion resistance, and high ductility even at cryogenic temperatures. Tantalum and its alloys have many applications including the manufacture of equipments for chemical processing plants, and devices for electronic, aerospace and military industries [1]. Electron-beam melting (EBM) is the most suitable tech- nique to produce high-purity tantalum because of its en- hanced refining capability. Interstitial impurities such as oxy- gen and nitrogen must be minimized (O <150 wt-ppm and N <100 wt-ppm) 1 to ensure high ductility and avoiding embrit- tlement in tantalum. Electron-beam melting provides these requirements. The microstructure of high-purity tantalum ∗ Corresponding author. Tel.: +55 12 3159 9916; fax: +55 12 3153 3006. E-mail address: hsandim@demar.faenquil.br (H.R.Z. Sandim). 1 Chemical requirements specified in ASTM B-364-92. EBM ingots consists of a few coarse columnar grains whose grain boundaries are almost parallel to the longitudinal ingot axis. The grain size of electron-beam melted tantalum ingots is commonly in the cm-range. A similar grain structure is found in VAR (vacuum arc remelting) ingots. Following EBM, conventional deformation processes like rolling and swaging are carried out to get tantalum plates, sheets, rods, and other semi-finished products. Cold working is the preferred fabrication method to produce semi-finished products because of tantalum’s poor oxidation resistance and high affinity for interstitials at elevated temperatures. There are several reasons to use high-purity tantalum oligocrystals to investigate orientation effects on recrystal- lization. First, because of its high purity, solute drag effects on boundary migration during annealing are minimized. Sec- ond, individual grains can be traced during deformation and further static annealing easing the comparison of their behav- iors. Third, the identification of the initial grains nucleated at deformation heterogeneities and grain boundary regions is easier in oligocrystals especially when annealing is per- formed at low homologous temperatures (e.g. 700–900 ◦ C). 0921-5093/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2004.09.032