Observations of grain boundary structure in submicrometer-grained Cu and Ni using high-resolution electron microscopy
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Observations of grain boundary structure in submicrometergrained Cu and Ni using high-resolution electron microscopy Zenji Horita Department of Materials Science and Engineering, Faculty of Engineering 36, Kyushu University, Fukuoka 812-81, Japan
David J. Smith Center for Solid State Science and Department of Physics and Astronomy, Arizona State University, Tempe, Arizona 85287
Minoru Nemoto Department of Materials Science and Engineering, Faculty of Engineering 36, Kyushu University, Fukuoka 812-81, Japan
Ruslan Z. Valiev Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, Ufa 450000, Russia
Terence G. Langdon Departments of Materials Science and Mechanical Engineering, University of Southern California, Los Angeles, California 90089-1453 (Received 19 March 1997; accepted 29 September 1997)
Submicrometer-grained (SMG) structures were produced in Cu and Ni using an intense plastic straining technique, and the grain boundaries and their vicinities were observed by high-resolution electron microscopy. The grain boundaries exhibited zigzag configurations with irregular arrangements of facets and steps, and thus they were found to be in a high-energy nonequilibrium state. A similar conclusion was reached earlier for SMG Al–Mg solid solution alloys which have much lower melting points than Cu and Ni, suggesting that nonequilibrium grain boundaries are a typical feature of metals processed by intense plastic straining. I. INTRODUCTION
It is possible to achieve grain size refinement in metals using an intense plastic straining technique where plastic strain of the order of several hundreds of percent is imposed under a quasi-hydrostatic pressure.1–4 With this technique, grain sizes below 1 mm may be obtained. The importance of this technique is that submicrometergrained (SMG) materials may be produced in the form of large bulk samples without introducing any residual porosity. Transmission electron microscopy studies have shown that the microstructures of SMG Al–Mg solid solution alloys5,6 are generally characterized by highly deformed grains and poorly defined grain boundaries. When observed at higher magnification, most of the grain boundaries are found to be wavy or curved.7 Lattice image observations using high-resolution electron microscopy (HREM) revealed that many of the grain boundaries exhibit regular or irregular arrangements of facets and steps.7 There are also regions near the grain boundaries containing large distortions of the lattice fringes.7,8 All of these features indicate that the grain boundaries of SMG materials produced by the intense plastic straining technique are in a high-energy and nonequilibrium state. 446
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 2, Feb 1998
Downloaded: 30 May 2014
It was demonstrated that the grain boundary structures of SMG Al–Mg solid solution alloys evolved into more stable configurations as a result of irradiation by high-energy electrons during the HREM observations.7
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