Abstract

Deformation behavior of pure iridium has been studied during thermal compression testing with the help of Gleeble-1500D in the temperature range of 1200 °C~1500 °C and strain rate range of 10−1 s−1~10−2 s−1. Resistance to deformation, microstructural evolution and hot workability of pure iridium have been used to analyze in detail. Frictional coefficient has been used to modify the experimental stress–strain curve of thermal compression test, and it has been found effective in reducing the influence of friction during thermo–mechanical testing. The hyperbolic sine constitutive equation of pure iridium has been established to give a material processing model for numerical simulation. A very high value of activation energy for iridium, 573 KJ/mol, clearly indicates that it is very hard to deform this material. The deformation mechanism of pure iridium is dependent upon temperature as well as strain rate. At low temperature and strain rate (temperature range of 1200 °C~1300 °C and strain rate range of 10−1 s−1~10−2 s−1), dynamic recovery is active while dynamic recrystallization becomes operative as temperature and stain rate are increased. On further increase in temperature and decrease in strain rate (temperature range of 1400 °C~1500 °C and strain rates of 10−2 s−1~10−3 s−1), abnormal grain growth takes place. On the basis of a constitutive model and processing map, suitable forming process parameters (temperature range of 1400 °C~1500 °C and strain rate range of 0.1 s−1~0.05 s−1) for pure iridium have been worked out.

Highlights

  • Iridium is a precious metal which belongs to the platinum group

  • The deformation characteristics of pure iridium have been studied on a Gleeble-1500D hot simulator, in the temperature range of 1200 ◦ C~1500 ◦ C and strain rate range of 10−1 s−1 ~10−2 s−1

  • The properties of stress–strain curves for pure iridium have been analyzed in detail and its hot workability has been studied through Dynamic Material Models

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Summary

Introduction

Iridium is a precious metal which belongs to the platinum group. It has a high melting point (2443 ◦ C) and density (22.56 g/cm ). There are few studies that can explain the deformation behavior, microstructural changes, mechanical properties evolved and energy consumed during plastic deformation under compression of polycrystalline iridium. Deformation resistance under compression of polycrystalline iridium has been investigated in temperature range of 900 ◦ C~1400 ◦ C and strain rates of ε = 0.2 s–1 ~20 s–1 [4], microstructural changes and mechanical properties during these studies have seldom been reported. The deformation properties of pure iridium have been examined through hot compression tests in the temperature range of 1200 ◦ C~1500 ◦ C and strain rate range of 10−3 s−1 ~10−1 s−1. Effect of deformation parameters like temperature and strain rate on plastic deformation, evolution of microstructure and mechanical properties has been analyzed quantitatively. This scientific work provides a reference to design and optimize the forming process of pure iridium

Preparation of Compression Specimen
Hot Compression Test
Microstructure Characterization
Modification of Flow Stress Curves
Constitutive Equations of Flow Stress for Pure Iridium
Constitutive Equations with Compensation for Strain
The Theory of Processing Map
Analysis of Processing Map
Microstructure Evolution of Pure Iridium
Conclusions
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