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

A hybrid composite material fabricated from the Al – Nb system using severe plastic deformation by 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 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).