MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
Effect of Nanocrystallization and Twinning on Hardness in Ni3Al Deformed by High-Pressure Torsion
Octav CiucaKoichi TsuchiyaYoshihiko YokoyamaYoshikazu TodakaMinoru Umemoto
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Volume 50 (2009) Issue 5 Pages 1123-1127

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Abstract

Samples of Ni3Al intermetallic compound were subjected to deformation by high-pressure torsion (HPT). The plastically-deformed structure revealed a bimodal character: coarse grains, retaining a degree of long-range order, surrounded by regions of nanocrystalline, disordered grains. It was inferred that the grain refinement proceeds in an inhomogeneous manner throughout the sample. Grains as large as 100 nm in size were shown to contain only a low density of perfect dislocations, but a large density of nanotwins and stacking faults. These planar defects appeared to originate from the grain boundaries, suggesting that grain boundaries are active sources for Shockley-partial dislocations. Their formation is accompanied by a deviation of the microhardness dependence on grain size from the Hall-Petch behavior, potentially suggesting the activation of a deformation mechanism different from the one acting in coarse structures. The hardness saturates at a significantly larger grain size than in the case of nanostructured pure Ni.

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© 2009 The Japan Institute of Metals and Materials
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