The Structure of Annealed Hafnium Bronze Subjected to Severe Plastic Deformation by High Pressure Torsion

Abstract

The structure and mechanical properties of low-alloyed hafnium bronze (Cu-0.78 wt. % Hf) under severe plastic deformation by high-pressure torsion (HPT) by 1, 3 and 5 revolutions of anvils at room temperature have been studied by electron microscopy and microhardness measurements. In the initial annealed state Hf is practically completely bonded in intermetallic compounds. The structure of bronze specimens deformed by HPT is stable and does not undergo any changes after unloading and long room temperature ageing. Under the deformation a dispersed submicrocrystalline structure gradient along specimen radius is formed. Average crystallite size in the radius middle is 200 nm after 1 revolution and 120 nm after 5 revolutions of anvils. It is demonstrated that in all the specimens studied including those deformed by 5 revolutions the structure is not uniform which is confirmed by microhardness measurements. Such behavior of hafnium bronze with Hf bonded in precipitates has much in common with the behavior of pure copper. However, the room temperature stability of the structures obtained by HPT demonstrates similar behavior with that of low-alloyed tin bronze. © Published under licence by IOP Publishing Ltd.