Distribution of plastic strain in alloys containing small particles

Tensile Fracture Behavior of 316L Austenitic Stainless Steel Manufactured by Hot Isostatic Pressing

“…In ODS steels, the oxides are often referred to as nano-oxide dispersions since typical oxide particle diameters on the order of < 100 nm. [43][44][45][46][47] Mobile dislocations interact with nanometer-sized oxide particles via mechanisms involving direct particle shearing [48,49] and/or circumventing the particle via a bypass manoeuver, such as the looping mechanism as proposed by Orowan, [50] depending on the particle-matrix coherency and degree of bonding between the particle and the matrix, the energy penalty of this bypass mechanism being proportional to the material flow stress. [51,52] However as particle size and spacing increases, their ability to hinder dislocation mobility via individual particle-dislocation interactions diminishes, and their relatively large volumes cause multiple dislocations to agglomerate in the form of dislocation forests on the surface of oxide particles.…”

A Review on Nano-Scale Precipitation in Steels

“…Precipitate shearing mechanism occurs when the precipitates are small in size so that dislocations can cut through (shearable or penetrable) the precipitates easily, while the Orowan looping mechanism takes place when the precipitates are large and impenetrable by dislocations [42][43][44][45][46][47]. In other words, precipitation strengthening depends on how dislocations interact with precipitates [46].…”

“…For Cu [33] and TiC [40] precipitates, the yield strength increment reaches its peak at a critical precipitate size of 2 to 6 nm and drops with a further increase of size. The increase in yield strength with increasing a precipitate size can be understood as the precipitates become more difficult to cut through when the precipitates become larger [46,47]. After the maximum strength increment, a further increase of precipitate size might lead to Orowan looping.…”

“…It can be generally recognized that the shearing mechanism occurs in fine dispersed shearable precipitates ,while Orowan process occurs in steels with overaged precipitates. From the past knowledge [46,47], precipitate shearing mechanism will lead to the localization of slip (large slip step) that degrades the ductility dramatically. On the other hand, overaged or Orowan precipitates will homogenize the slip distribution (small slip step) by activating more slip systems, leading to an enhanced ductility normally at the expense of yield strength.…”

“…This subsequently lowers strain accumulation and prevents crack initiation at the precipitate/matrix interface. Zhang et al [1] also suggested the local disordering of NiAl precipitates due to the deviation from the stoichiometric ratio [51], and the strong coherency between precipitate/matrix interface can allow for easier dislocation to climb or cut through with only a slight change of Burger's vector [47], resulting in the improvement of the ductility. In addition, Kapoor et al [52] also suggested that the high ductility of ferritic steels after the incorporation of fine, coherent precipitates can be due to the misfit centers (the coherent precipitates) [53] that help to form mobile kink segments, pulling a dislocation out of its Peierls energy valley.…”