Microstructure evolution in a CuZr alloy and CP Ti processed by a novel technique of free bending in rotating rollers

Abstract

A novel technique referred to as free bending in rotating rollers was employed to refine the initial structure and to produce gradient fine-grained microstructures in the Cu0.5Zr alloy and commercially pure titanium (CP Ti). A newly designed die allowing a continuous and repetitive movement of a workpiece through a set of rollers in a channel bent by 90 degrees was employed to produce a series of billets after different numbers of passes resulting in different strains imposed on the billet. Microstructure evolution with increasing number of passes was characterized by precise measurements of microhardness (HV) distribution along the cross section of individual billets. The heterogeneous distribution of HV observed after a single pass was transformed to almost a uniform one in the whole cross section of the billets after 8 passes. EBSD analysis and TEM observations revealed a significant microstructure refinement in both materials after the final stage of processing. A homogeneous microstructure with an average grain size of about 300 nm was observed in CP Ti, whereas the microstructure of the Cu0.5Zr alloy was not fully refined and exhibited a bimodal grain size distribution. The experimental results were compared with the theoretical modelling of strain distribution by FEM.