Fa. Mohamed et Y. Li, Creep and superplasticity in nanocrystalline materials: current understanding and future prospects, MAT SCI E A, 298(1-2), 2001, pp. 1-15
Nanocrystalline materials (nc-materials), which are characterized by a grai
n size in the range 1-100 nm, have emerged as a new class of materials with
unusual structures. In recent years, creep and superplasticity in nc-mater
ials have been the subject of a number of studies. In particular, experimen
tal studies have focused on (a) whether grain boundary diffusion creep, whi
ch is expected to be dominant in coarse-grained materials at moderate tempe
rature (0.4-0.6 T-m) and low stresses, becomes significant at low temperatu
res (for example, room temperature), and (b) whether micrograin superplasti
city, which has been observed at high temperatures (T > 0.5 T-m) and modera
te strain rates (10(-5) -10(-2) s(-1)), can be observed at low temperatures
and high strain rates. A review of these studies shows that data obtained
by different investigators are either not consistent in trend or too limite
d in scope. Various aspects characterizing these consistencies and limitati
ons are identified. It is suggested that a number of issues need to be full
y addressed in order to provide a better understanding of the deformation p
rocesses which control the behavior of nc-materials. (C) 2001 Elsevier Scie
nce B.V. All rights reserved.