Nabarro-Herring creep

The most intriguing aspect of nanostructured metals and, especially, ceramics such as titania is that the very small grain size encourages Herring-Nabarro creep which, in turn is the precondition of superplastic forming under stress. The essential facts concerning this process are laid out in Section 4.2.5, Nanostructured ceramics can be plastically formed, in spite of extreme resistance to dislocation motion, and this has been plentifully documented in many studies. Examples are set out in Gleiter s own (1996) overview of nanostructured materials. The ability to form nano-ceramics to near net shapes looks to have very promising industrial potential.  [c.400]

In polycrystaUine ceiamics, in which cieep occuis by dislocation motions contioUed by the late of diffusion of atoms thiough the lattice, a lattice cieep mechanism is said to operate. Far more common to polycrystaUine ceramics is diffusional creep, in which deformation occurs by diffusional flow of atoms to and from grain boundaries, either by diffusion through the lattice (Nabarro-Herring creep), or along the grain boundaries (Coble creep) (38,39). Creep can also occur by grain boundary sliding in materials with and without Hquid grain boundary phases. Diffusional creep and creep by grain boundary sliding are categorized as boundary creep mechanisms. Detailed information on creep mechanisms can be found in the Hterature (38,40).  [c.323]

One useful technique for the measurement of tire average surface energy of a metal is to find the condition where a metal wire of radius, r, and length, I, just fails to elongate under sU ess from an applied weight at constant teiuperamre, over a long period of time. The process of creep, which would lead to tlris extension, increases the surface area of the wire, and thus the limiting weight occurs when the work to extend the wire by the weight is just counter-balanced by the work of surface extension. If the sample consists of U ansverse grains, the vacancies which are removed from the surface during creep migrate to the grain boundaries, as in Nabarro-Herring creep. The total superficial energy of the system. Eg, is given by  [c.196]

See pages that mention the term Nabarro-Herring creep : [c.180]    [c.201]   
The coming of materials science (2003) -- [ c.180 , c.400 ]