The Role of Interphase Boundaries in the Deformation Behaviour of Fine-Grained Sn-38wt.%Pb Eutectics

The mechanical properties of binary Sn-38wt.%Pb eutectic alloys in the deformed and annealed states were investigated at room temperature using tensile, micro- and nano-indentation tests. The softening and high plasticity of a deformed Sn-Pb eutectic are explained as a result of grain boundary sliding (GBS) and fast diffusion-driven processes developing along the Sn-Pb interphase boundaries (IBs). From the results of micro- and nano-hardness measurements it follows that the Sn and Pb phases in the annealed eutectic are strengthened, and the relaxation processes occur mainly at the IB. Such IBs in the annealed Sn-Pb eutectic act as barriers to the motion of a dislocation ensemble when the size of the plastic zone is comparable with the grain size, lowering the hardness values due to the development of GBS when more grains are involved in the process of deformation. The nanohardness and elastic modulus values obtained evidence that an IB in the Sn-Pb eutectic is to be considered as a separate phase with its own mechanical properties.