Journal of Mechanical Science and Technology 35 (8) 2021 DOI 10.1007/s12206-021-0710-1 3369 Journal of Mechanical Science and Technology 35 (8) 2021 Original Article DOI 10.1007/s12206-021-0710-1 Keywords: · High temperature · Kocks - Mecking · Tensile test · Work hardening · Zr-2.5Nb Correspondence to: Saptarshi Dutta d.saptarshi@iitg.ac.in Citation: Dutta, S., Robi, P. S. (2021). Analysis of tensile flow and work hardening behavior of Zr-2.5Nb alloy in the framework of Kocks - Mecking approach. Journal of Mechanical Science and Technology 35 (8) (2021) 3369~3374. http://doi.org/10.1007/s12206-021-0710-1 Received December 9th, 2020 Revised April 20th, 2021 Accepted May 9th, 2021 † Recommended by Editor Chongdu Cho Analysis of tensile flow and work hardening behavior of Zr-2.5Nb alloy in the framework of Kocks - Mecking approach Saptarshi Dutta and P. S. Robi Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Assam 781039, India Abstract High-temperature tensile tests were carried out on Zr-2.5Nb alloy in the temperature range of 298-873 K for both longitudinal and transverse specimen directions. Kocks-Mecking (K-M) approach was used to analyze the tensile flow and work-hardening nature of this alloy. The graph of instantaneous work hardening rate (θ = dσ/dε, where true stress is denoted by σ and true plastic strain by ε) with stress exhibited two-stage strain hardening behavior at all temperatures. The graph of θ vs σ and the variation in the parameters of strain hardening displayed three temperature zones, with a plateau region in 473-573 K. A fairly good correlation was achieved between the strain hardening parameters measured with the K-M method and the Voce equation at the above-mentioned temperature range. 1. Introduction Zr-2.5Nb alloys are the primary option for manufacturing pressure tubes (P.T.) in pressurized heavy water reactors (PHWR) [1-3]. Zirconium alloys have low neutron absorption cross- section, sufficient creep resistance, outstanding tolerance to corrosion under aqueous condi- tions and good microstructural and irradiation stability [4-6]. In the case of a hypothesized de- sign accident such as loss of coolant accident (LOCA), heat from the core is not absorbed by the primary coolant, resulting in very high temperatures [7, 8]. These adverse conditions may lead to the sagging and ballooning of the horizontal P.T.s, which may eventually allow radioac- tivity to leak into the atmosphere. Thus, it is imperative to have a detailed knowledge of the work hardening behavior of Zr-2.5Nb at elevated temperature. The approach of Kocks-Mecking (K-M) is being widely used to analyze and model the strain hardening nature of metals and alloys [9, 10]. This approach offers a sound explanation of the physical significance of the Voce relationship [9-11]. The Voce relationship, which relates the true stress (σ) with the plastic part of strain (ε) [12, 13], is given as ( ) ( ) exp ⎡ ⎤ − = − − − ⎢ ⎥ ⎢ ⎥ ⎣ ⎦ I S S I C ε ε σ σ σ σ ε , (1) in which saturation stress is denoted by σ S , true stress by σ I , true plastic strain is given by ε I and ε C is a constant. Eq. (1) becomes ( ) exp( ) = − − S S I v n σ σ σ σ ε , (2) when I ε = 0, with σ S , σ I and V n as the constants where 1/ = − V C n ε . The behavior of instan- taneous work hardening rate ( / = d d θ σ ε ) with flow stress σ, by K-M method exhibits three stages of strain hardening. Stage I of work hardening is exhibited by single crystals where de- © The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature 2021