Article ID Journal Published Year Pages File Type
9796406 Materials Science and Engineering: A 2005 14 Pages PDF
Abstract
Room temperature fatigue crack growth (FCG) testing was conducted after thermal aging for 500 and 5000 h at 823 K and for 500 h at 923 K, on 9%Cr-1%Mo steel normalized at 1323 K and tempered at 1053 K. Though crack growth behavior in Paris regime is not much affected by aging, stress intensity factor range for threshold (ΔKth) is found to increase monotonically. Acoustic emission signal analysis indicates identical crack propagation mechanisms in both threshold and Paris regimes. But SEM fractography reveals micro-voiding in the Paris regime only. Also, theoretical analysis of plastic zone size and inter-particle spacing (λm) predicts microcleavage in the threshold regime. This indicates FCG occurs as a two-step mechanism, but each regime has a different dominant step viz. initial micro-void nucleation and growth at precipitates, followed by eventual micro-cleavage of inter-particle ligaments. Aging induces solid solution dilution, precipitate coarsening and increases λm. In threshold regime, due to a tougher matrix, and a smaller cyclic crack increment (δaN) than λm, an increase in ΔKth values is observed. Conversely, Paris regime δaN is greater than λm, making it rather insensitive to aging.
Related Topics
Physical Sciences and Engineering Materials Science Materials Science (General)
Authors
, , , , ,