Optimization of high pressure torsion processing for fabrication of the Al-Nb hybrid system

Abstract

A hybrid composite material fabricated from the Al-Nb system using high-pressure torsion (HPT) up to 30 turns has been studied in the present work. To fabricate the composite, deformation of a three-layer Al-Nb-Al package was carried out at room temperature on Bridgman anvils with grooves under a pressure of 5 GPa at N=10, 25 and 30 revolutions, at a strain rate of ω=1 and 2 rpm. Initial disc diameters from pure metals and HPT conditions were experimentally optimized to obtain monolithic and defect-free composite samples. The most intensive fragmentation and stirring of niobium in the aluminium matrix was observed if diameter of aluminium discs was 10 mm and deformation conditions N=25 and 30 revolutions and ω=2 rpm were applied. Three microstructural zones were observed after HPT under optimal conditions: the central zone with wide curved layers of niobium in aluminium, the mid-radius zone with finely dispersed layered structure, and periphery with a uniform distribution of niobium in the aluminium matrix. It was shown that HPT led to occurrence of strain-induced ageing resulting in formation of the intermetallic Al3Nb phase. The microhardness measured along the diameter of the obtained composite materials changed nonmonotonically depending on the produced structure (microstructural zone).