Essay On Slip In Nb

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h. Active Slip Systems in Nb
Slip during plastic deformation is the underlying mechanism that accounts for many of the phenomena previously discussed. This section will cover fundamental studies on slip in Nb, along with general theories on deformation in bcc metals.
In the cavity fabrication process, crystal orientations, active slip systems, dislocation sub-structure, and recrystallization during annealing are interrelated from the metallurgical point of view [20] – slip behavior depends on how crystals are oriented with respect to the applied stress; slip and interactions of slip systems result in a certain dislocation substructure; the dislocation substructure determines how recovery and recrystallization proceed during heat …show more content…

Since the motion of screw dislocations is thermally activated, it will likely occur by nucleation of kink pairs on well-defined atomic planes [70]. The kink pair nucleation mechanism gives rise to the temperature and strain rate dependence of flow stresses in bcc metals [70].
The low mobility of bcc screw dislocations can be partly explained by the core relaxation theory [48, 72-76]. A bcc screw dislocation core tends to spread onto three symmetric {110} or {112} planes, which results in a non-planar core structure and hinders the movement of screw dislocations [70]. Consequently, screw dislocation mobility is affected by non-glide shear stresses, which is a violation of the Schmid law. The relaxation also adds to the waviness of slip traces, as cross slip can occur on two alternating {110} or {112} planes to roughly follow a slip plane with a high resolved shear stress. Thus, long and drawn-out screw dislocations are usually left behind during plastic deformation and are observable [48].
There has been no consensus thus far regarding the core structure of screw dislocations in Nb, but it is generally agreed that the core relaxation depends on both the temperature and purity [70, 77-79]. Seeger argued that fundamental slip planes change from {110} at low temperatures ( slip systems could leave behind sessile dislocations with the resulting Burgers vector on a

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