It is evident that discontinuous yielding can be produced in all the common metal structures provided the appropriate solute elements are present, and correct testing procedure adopted. The effect is particularly strong in the bcc metals and has been observed in α-iron, molybdenum, niobium, vanadium and β-brass each containing a strongly interacting interstitial solute element. The hexagonal metals (e.g. cadmium and zinc) can also show the phenomenon provided interstitial nitrogen atoms are added. The copper- and aluminium-based fcc alloys also exhibit yielding behaviour but often to a lesser degree. In this case it is substitutional atoms (e.g. zinc in α-brass and copper in aluminium alloys) which are responsible for the phenomenon

Hi, The reason for this behaviour is the presence of interstitial atoms like C and N as alloying elements. The dislocations usually pinned to these interstitial solutes and hence become immobile. So additional stress required to free the dislocation.

It is evident that discontinuous yielding can be produced in all the common metal structures provided the appropriate solute elements are present, and correct testing procedure adopted. The effect is particularly strong in the bcc metals and has been observed in α-iron, molybdenum, niobium, vanadium and β-brass each containing a strongly interacting interstitial solute element. The hexagonal metals (e.g. cadmium and zinc) can also show the phenomenon provided interstitial nitrogen atoms are added. The copper- and aluminium-based fcc alloys also exhibit yielding behaviour but often to a lesser degree. In this case it is substitutional atoms (e.g. zinc in α-brass and copper in aluminium alloys) which are responsible for the phenomenon

The characteristic feature of discontinuous yielding is that at the yield point the specimen goes from a condition where the availability of mobile dislocations is limited to one where they are in abundance, the increase in mobile density largely arising from dislocation multiplication at the high stress level. A further feature is that not all the dislocations have to be immobilized to observe a yield drop.