Microstructure Development and Ductility of Ultra-Fine Grained Mg-Gd Alloy Prepared by High Pressure Torsion
Abstract
Lattice defects and thermal stability of ultra fine grained (UFG) Mg-Gd alloy prepared by high-pressure torsion (HPT) were investigated. Positron annihilation spectroscopy (PAS) was combined with TEM, XRD, microhardness (HV) and deformation tensile tests.
HPT deformed Mg-Gd alloy exhibits UFG structure with mean grain size of 100 nm and a dense network of dislocations distributed uniformly throughout the whole sample. Recovery of dislocations takes place at relatively low temperatures, but it is not accompanied by grain growth up to 300 °C.
Tensile tests performed at elevated temperatures showed that HPT-deformed alloy exhibits a superplastic behavior at 400 °C. Moreover, it was found that the precipitation sequence in HPT-deformed alloy differs from that in conventional coarse-grained material.