Jg. Rao et Sk. Varma, THE EFFECT OF GRAIN-SIZE AND STRAIN-RATE ON THE SUBSTRUCTURES AND MECHANICAL-PROPERTIES IN NICKEL 200, Metallurgical transactions. A, Physical metallurgy and materials science, 24(11), 1993, pp. 2559-2568
The substructural developments taking place in nickel 200 with grain d
iameters of 47, 108, 141, and 274 mum have been studied at four differ
ent strain rates of 0.01, 0.25, 2.5, and 5/min during tensile testing
at room temperature. The percent strain necessary to develop well-defi
ned cell boundaries increases with an increase in grain size at a give
n strain rate. The cell size refinement takes place throughout the ent
ire range of percent strains (up to 30 pct) in tension for the nickel
samples with grain diameters of 47, 108, and 141 mum at all four strai
n rates used in this article. However, nickel, with the largest grain
diameter of 274 mum, shows refinement and then saturation for tensile
strains greater than 25 pct. The cell size strengthening described by
the modified Hall-Petch (MHP) equation at the selected four strain rat
es of this article indicates that the flow stress is higher for smalle
r grain size samples at a given cell size. The effect of strain rate o
n the slope from the MHP plots is such that even though it does not ch
ange with an increase in strain rate up to 0.25/min for the four grain
sizes, the actual value of the slope decreases with an increase in gr
ain size at a given strain rate. Beyond this strain rate, even though
an increase in the slope value as a function of strain rate has been o
bserved for all four grain diameter samples, the influence of grain si
ze on the slope of the MHP plots is so small that it can be assumed th
at they may become grain size independent at extremely high strain rat
es.