Mechanical behaviour and in situ observation of shear bands in ultrafine grained Pd and Pd–Ag alloys

An in situ tensile test with grey scale correlation has been performed to study the deformation process in ultrafine grained (UFG) Pd and Pd–x at.% Ag (x = 5 or 20) alloys produced by high-pressure torsion. Shear band nucleation and propagation was found to be an important deformation mechanism after strain localization during the tensile test. The underlying microscopic mechanism is related to cooperative grain boundary sliding. Moreover, the additional influence of stacking fault energy was found to change the nature of the deformation mechanism from localized strain in Pd to more homogeneous deformation in Pd–20% Ag. In situ analysis and the findings are new and give innovative insight into the basics of deformation in UFG face-centred cubic metals.