INFLUENCE OF SECONDARY PHASE PARTICLES ON ZR-ALLOY PLASTIC-FLOW STABILITY AND FRACTURE

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-1.3Sn-0.4Fe alloys was studied by the methods of acoustic emiss ion (AE). Based on measurements of maximum (peak) values of AE amplitu des depending on secondary phase size and distribution two alternative mechanisms were established of loss of now stability in alloys under tension: geometrical loss of strength for uniform fine particle distri bution, and microcracking at the stage of uniform strain for coarse pa rticle aggregates or fine particle stringers. Ways of increasing the f racture toughness resistance of alloys were suggested by increasing th e stability of local now at a crack tip through optimization of matrix deformation ability, secondary phase size and distribution within mat rix. Analysis is given to quantitative relationships between fracture toughness and microstructure characteristics of alloys. Original devic es and techniques were developed to quantitatively analyze local proce sses of strain and fracture based on AE measurements which allows asse ssment of unstable now zones and measurement of microcrack 5 mu m and more in size.