Em. Lehockey et G. Palumbo, ON THE CREEP-BEHAVIOR OF GRAIN-BOUNDARY ENGINEERED NICKEL, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 237(2), 1997, pp. 168-172
Grain boundaries described by low-Sigma CSL relationships (i.e. Sigma
less than or equal to 29) have previously been shown to be resistant t
o grain boundary sliding, cavitation and fracture. The present work re
ports on efforts to reduce creep rates in conventional polycrystalline
nickel by increasing the frequency with which these 'special' interfa
ces occur in the microstructure. Suitable thermomechanical processing
was employed to enhance the frequency of 'special' grain boundaries (S
igma less than or equal to 29) in 99.99% Ni from 13 to 66%, resulting
mostly from the formation of twins (Sigma 3) and crystallographically-
related Sigma 9 and Sigma 27 boundaries. This 53% increase in the frac
tion of low-Sigma boundaries produced reductions of 16-fold in the ste
ady-state creep rate and six-fold in the primary creep strain. Microst
ructures having 'special' boundary frequencies of less than 50% exhibi
ted significant cavitation almost exclusively along 'random' boundarie
s (i.e. Sigma > 29) at or near triple points. No gross cavitation was
evident in microstructures containing 'special' boundary fractions of
66%. Such improvements in creep properties provide considerable promis
e for the application of a 'grain boundary engineering' approach to de
veloping interfacial materials for structural applications. (C) 1997 E
lsevier Science S.A.