MICROMECHANICS OF PLASTICITY OF ZR-2.5%NB ALLOY


11th International Conference on CANDU® Maintenance and Nuclear Components - 2017 Oct. 01-04

Presented at:
11th International Conference on CANDU® Maintenance and Nuclear Components
2017 Oct. 01-04
Location:
Toronto, ON Canada
Session Title:
Material Properties and Degradation

Authors:
I. Khan (University of Western Ontario)
R.J. Klassen (University of Western Ontario)
  

Abstract

In this study micromechanical testing was carried out to obtain information regarding the stress-strain response of Zr-2.5%Nb pressure tube material used in CANDU nuclear reactors. Of particular interest is how the strength and ductility of the material changes as the size of the deforming volume decrease to dimensions in the micrometer range. This project intends to obtain such data for pressure tube material in the as-received and the ion-irradiation hardened conditions. Micropillars containing single ?-phase grains and multiple grains were tested such that the effect of pillar diameter and crystal orientation on the flow stress and strain hardening coefficient could be assessed. The micropillars displayed a clear increase in flow stress with decreasing pillar diameter which reflects the length-scale dependence of the mechanical properties. Micro-compression data obtained from ion-irradiation hardened micropillars were compared with unirradiated micropillars. Irrespective of the irradiation condition, the flow stress of the single-crystal micropillars oriented along the axial direction of the pressure tube is lower than that of similar micropillars oriented along the transverse direction of the pressure tube. Micropillars were irradiated at two different temperatures (20°C and 300°C) to observe the effect of irradiation temperature on the compressive strength of the material. The obtained data clearly indicate that micropillars irradiated at 20°C display much higher compressive strength at 10% strain in comparison to the pillars irradiated at 300°C. A noticeable difference between the stress-strain curves of the pillars irradiated at different temperatures is that, for the low temperature irradiated pillars, the transition from elastic to plastic deformation is usually quite smooth whereas for the pillars irradiated at higher temperature strain jumps were observed.

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