Effects of cold rolling and annealing on the structure of γ″ precipitates in a Ni-18Cr-16Fe-5Nb-3Mo alloy |
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Authors: | Kiyoshi Kusabiraki Shigeoki Saji Tomoya Tsutsumi |
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Affiliation: | (1) Department of Intelligent Information Engineering, Toyama University, 930-8555 Toyama, Japan;(2) Department of System Engineering of Materials and Life Science, Toyama University, 930-8555 Toyama, Japan;(3) Present address: Department of Materials Science and Engineering, Toyama University, Japan;(4) Metallurgical Engineer, Somic Ishikawa Co. Ltd., 435-8560 Hamamatsu, Japan |
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Abstract: | A Ni-18Cr-16Fe-5Nb-3Mo alloy (a modified alloy 718, referred to herein as 718M), in which the γ″ phase is the only precipitation-strengthening phase, was made by substituting most of the aluminum and titanium in INCONEL
718 with niobium. The specimens of alloy 718M were solid-solution heat treated, aged at 1033 to 1073 K for up to 360 ks, and
cold rolled to a reduction of 10 to 15 pct at room temperature. After subsequent annealing heat treatments, at the same temperatures
used for aging, the morphological and structural changes of the γ″ precipitates were investigated by transmission electron microscopic observation using carbon extraction replicas. Although
stacking faults were not noticed in the γ″ precipitates extracted from the aged 718M alloy, stacking faults introduced in the {112}
γ″
planes by cold rolling of the samples were confirmed. The stripelike contrast due to the stacking faults becomes less clear
with increasing annealing time. With longer annealing times, necking occurs between the stripes, which eventually separate
into plural particles. The selected-area electron diffraction (SAED) patterns of the cold-rolled and annealed particles show
that the metastable γ″ precipitates with stacking faults are transformed gradually into a stable δ phase. In this article, we discuss the basis of morphological and structural changes in detail.
INCONEL is a trademark of INCO Alloys International, Inc., Huntington, WV. |
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