Influence of Secondary Phase Particles on Zr-Alloy Plastic Flow Stability and Fracture

Abstract
The influence of intermetallic particles and hydrides on the total and local ductility as well as on the fracture mechanism in Zr-2.5Nb and Zr-1Nb-l.3Sn-0.4Fe alloys was studied by the methods of acoustic emission (AE). Based on measurements of maximum (peak) values of AE amplitudes depending on secondary phase size and distribution two alternative mechanisms were established of loss of flow stability in alloys under tension : geometrical loss of strength for uniform fine particle distribution, and microcracking at the stage of uniform strain for coarse particle aggregates or fine particle stringers. Ways of increasing the fracture toughness resistance of alloys were suggested by increasing the stability of local flow at a crack tip through optimization of matrix deformation ability, secondary phase size and distribution within matrix. Analysis is given to quantitative relationships between fracture toughness and microstructure characteristics of alloys. Original devices and techniques were developed to quantitatively analyze local processes of strain and fracture based on AE measurements which allows assessment of unstable flow zones and measurement of microcrack 5 µm and more in size.