THERMO-MECHANICAL PROCESSING OF Zr-Nb ALLOY AND ITS CHARACTERIZATION

Abstract

Bulk deformation processes are usually carried out at high temperature, above 0.5 Tm, where Tm is the absolute melting point of the material. Generally these processes involve large amount of strain and high speed of deformation, beneficial to achieve good production rate. The high temperature process allows achieving large strain in a single step without any failure, so final product can be produced in fewer steps. Material behavior in bulk metalworking is described by word 'workability'. Workability is defined as how easily a material can be shaped by plastic deformation. The microstructure of material is changed significantly due to hot working and it contributes one part of workability generally referred as intrinsic workability, which is responsive to initial condition of material. In present work hot working characteristics of Zr-2.5Nb alloy is studied in the temperature range of 700-925°C and constant true strain rate range of 0.01-10s1. Compression tests are carried out on Gleeble®3800 Thermo-mechanical Simulator for this purpose. Processing maps are developed using Dynamic Materials Model (DMM) for three different strains (0.2, 0.4, and 0.6). Processing map for 0.4 strain is developed using modified DMM and compared with DMM. It is found that higher efficiency domains of power• dissipation are nearly same. The efficiency of power dissipation z is calculated and plotted as function of temperature and strain rate to develop processing map. Instability maps. are drawn for three different strains (0.2, 0.4, and 0.6) using instability parameter(). Instability map for 0.4 strain is developed using k < 0 as function of temperature and strain rate and compared with Optical microscopy and EBSD technique is used correlate the microstructural evolution.