Mechanical alloying via high-pressure torsion of the immiscible Cu50Ta50 system

Ibrahim N., Peterlechner M., Emeis F., Wegner M., Divinski S., Wilde G.

Abstract

Mechanical alloying via high pressure torsion (HPT) is studied for the immiscible Cu-Ta system. Stacks of alternating 25 µm thick sheets of pure Cu and Ta were subjected to HPT processing at a pressure of 4 GPa for 10, 30, 50, 100 and 150 revolutions, respectively. The effect of subsequent heat treatment on the phase composition and microstructure evolution of Cu/Ta and pure Cu or pure Ta foil stacks is examined by X-ray diffraction, scanning and transmission electron microscopy and microhardness measurements. The HPT processing of the Cu/Ta assembly by 150 revolutions is shown to produce a mixture of ultrafine grains corresponding to a Cu-16% Ta solid solution with embedded nano-scaled Ta-rich particles and almost pure Ta grains. The microstructure reveals a superior thermal stability and remains fine-grained even after annealing at 1000 °C for 1 h. HPT deformation of pure Cu stacks results in formation of a mixture of pure Cu and CuO, presumably due to availability of numerous interfaces in the assembly, with the existence of the copper mono-oxide being verified by X-ray measurements.