Deformation behavior of tantalum and a tantalum tungsten alloy Sia Nemat-Nasser *, Rajeev Kapoor 1 Center of Excellence for Advanced Materials, University of California, San Diego, La Jolla, CA 92093-0416, USA Received in ®nal revised form 11 January 2000 Abstract A comparative study of the deformation behavior of tantalum and a tantalum 2.5 wt.% tungsten alloy is carried out. High strain-rate experimental data are used to develop phe- nomenological constitutive relations. The temperature and the strain-rate sensitivity of the ¯ow stresses are compared. It is observed that although the ¯ow stress for the Ta±2.5%W alloy is greater than that of Ta, the corresponding temperature and strain-rate sensitivity is less pronounced. Ta±2.5%W experiences a solid-solution softening, wherein the athermal stress component has increased, while the thermal component has decreased by the alloying. # 2001 Elsevier Science Ltd. All rights reserved. 1. Introduction The addition of solute atoms in small quantities can sometimes result in a decrease of the yield stress, commonly referred to as solid-solution softening Mitchell and Rao, 1967; Das and Arsenault, 1968; Smialek et al., 1970; Christian, 1983). In the case where the ¯ow stress is considered as a sum of a thermal and an athermal component, the solute atoms can have a dierent eect on each component. The athermal component generally increases with alloying. It is the thermal component which actually experiences the softening eect. In the case where only the thermal component decreases with solute addition, the softening is referred to as pseudo- softening. A prerequisite for pseudo-softening is that the temperature sensitivity of the ¯ow stress decreases with alloying Pink and Arsenault, 1978). Ta±W Das and Arsenault, 1968; Gourdin et al., 1994), and Ta±Re Mitchell and Rao, 1967), and Ta±Nb Arsenault, 1966) alloys do show such substitutional alloy softening. Das International Journal of Plasticity 17 2001) 1351±1366 www.elsevier.com/locate/ijplas 0749-6419/00/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0749-641900)00088-7 * Corresponding author. Tel.: +1-858-534-4914; fax: +1-858-534-2727. E-mail address: sia@shiba.ucsd.edu S. Nemat-Nasser). 1 Formally with the Center of Excellence for Advanced Materials, University of California, San Diego, presently as scientist at Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400085, India.