On the grain size softening in nanocrystalline materials

摘要: Materials Science and Engineering Department, North Carolina State University,Raleigh, NC 27695-7907, USA(Received December 17, 1999)(Accepted 29, 1999)Keywords: Grain boundaries; Thermally activated; Hardness; AtomicIntroductionNanocrystalline materials with grain sizes in the range of 1–100 nm have been found to exhibit noveland often improved physical properties [1–4]. They are thus considerable interest from bothscientific technological viewpoints. In present paper we consider influence size onthe flow stress (or corresponding hardness) nanocrystalline materials, focus on sizesoftening (i.e., so-called negative or inverse Hall-Petch effect) which has observed at grainsizes ,;50 [5–12].The effect hardness reported theform shown schematically Fig. 1 [5–15]. At larger increases withdecrease according well-known relation (with possibility that theHall-Petch constant k