EFFECT OF MICROSTRUCTURE ON FATIGUE-CRACK GROWTH IN ZR-2.5 NB ALLOY

The influence of microstructure on room temperature fatigue crack grow th (FCG) rate in Zr-2.5 Nb pressure tube material was investigated. Fo ur different microstructure, namely beta-quenched, beta-annealed, alph a+beta-annealed and as received pressure tube material were selected f or the study. FCG rate in stage II was found to be insensitive to micr ostructures. On the other hand, FCG rate in stage I was strongly micro structure sensitive. Microstructures containing aligned alpha-grains h ave better resistance for near threshold FCG. The observed FCG behavio ur of microstructures studied has been rationalized with the help of t he existing models.