Hi,

How about hardening due to dislocation movement creating a new stable crystallographic structure ?

Regards,

The following links could help you:

Article Formation of crystallographic texture during severe plastic ...

Article Plastic deformation and crystallographic texture evolution i...

Hi Qiao Li,

During plastic deformation, the dislocation density is increased introducing the system instability. When dislocations are accumulated on the grain boundary, the misorientation between two grains adjacent is increased introducing the change in the initial grain orientation. This process takes place in a random way and the resulting texture depends on the deformation process itself, and on the material of course.

Regards

The main plastic deformation mechanism in metals is the dislocation slip. It proceeds in peculiar, low-indexed crystallographic systems, specific for each structure. So the deformation proceeds in the systems which are preferentially oriented, while the rest can reorientate, to become more susceptible to deformation. Thus, e.g. in austenite with the fcc structure the main deformation system is {111} so the main deformation texture components are those belonging to the α=||ND (normal direction) fibre, usually extending from the Goss orientation {110} to the brass-type orientation {110} and to the β-fibre extending from the brass {110} trough the S-type orientation {123} to the copper-type orientation {112}. Please note that the angle between the (111) and (110) crystallographic planes is 35.3° so the {111} planes are not oriented directly in the rolling direction.

Please refer also to my article https://www.researchgate.net/publication/259759898_Microstructure_and_Texture_Evolution_in_a_ColdRolled_High_Mn_Steel_with_Microadditions_of_Ti_and_Nb?_sg=emEmKew2bx3TcXjMgSWKk_Vh4bokGcHw-oOKQWxciK2i_lqVqL8D_Z6KVvaTIQfbY72lytrT807DVOvtuN_DnTMH7NQ2H-_lSSdHv0mw.hUnPAQF8wMcC-r9nKTy4YluV2UcrPPdMP5uLh9xYhuyQ28-GbwsN37EaKhyViesI87wV0Zkx11KOprn3w5hvmA

When as cast metallic materials are deformed ,all as cast grains are broken and fresh grains are formed by process of recovery, recrystallization and grain growth .By plastic deformation dislocations are piled up and creates instability in the microstructure.Please refer Mechanical Metallurgy by Dieter.

Regards

Shivraj Singh Kasana

Dear Prof. Dierk Raabe

Thank you for your comprehensive answer. I enjoy reading it. It is very good starting point to further the understanding of this problem. Thank you very much.

Best regards,

Qiao

This is how I understood with respect to the mechanics view point :

Short answer is due to Constraint and Anisotropy.

Imagine a single crystal with a single slip system . Dislocation glide at the atomic level causes plastic deformation at the macro-scale. You can roughly imagine a deck of cards sliding over one another. However, one card cannot just freely slide over the others and fall off from the pack, you have surrounding constraints. To accommodate the load and because of the constraints, the planes in the crystal both slide and rotate.

Next, imagine a single crystal with multiple slip systems, it adds one degree of complexity in motion of dislocations . here additional constraints come because of multiple slip systems (plastic anisotropy).

In real systems, we have poly-crystals (elastic anisotropy) with multiple slip systems. For each grain , we have surrounding grains which causes a constraint. As we already know, within each grain we have multiple slip systems . So more constraints. Motion at the atomic level would be super complicated.. The external load here would accommodated by a combination of slip ( plastic deformation) as well as grain rotation !

Thanks,

Prithivi

Hi

Refer to the link:

https://en.wikipedia.org/wiki/Texture_(crystalline)

Crystallographic orientation changes as plastic deformation takes place. The deformation mechanism strongly depends on the stacking fault energy (SFE) of the material and temperature of deformation. If SFE is high the material will deform by gliding (slip) of dislocations and if it is low then dislocation motion (cross-slip) will be restricted owing to larger separation between the partials of a dislocation. In those cases, material deforms by the formation of deformation twins. In a polycrystalline material, only those grains facilitate slip deformation in which the shear stress on the slip plane along the slip direction exceeds the threshold value called critical resolved shear stress. In order to make it possible the grains must rotate maintaining the integrity of the material under deformation. New dislocations (geometrically necessary dislocations) along the grain boundary start to form on both sides of the boundary. Plastic deformation of any type imposes a stress state which dictates the plastic flow of the material. A polycrystalline material deforms in such a way in which the plastic flow of the material is most feasible. In rolling, forging, drawing, extrusion the material plastically flow along the deformation axis and results in certain crystallographic orientation. In contrast, the nucleation and growth process during annealing treatment is likely to produce random texture with no preferred orientation.