Evolution of the structure of annealed hafnium bronze nanostructured by high pressure torsion

The effect of severe plastic deformation by 1, 3 and 5 revolutions of high pressure torsion (HPT) on the structure and mechanical properties of low-alloyed hafnium bronze Cu–0.78wt%Hf is studied. In the initial annealed state, hafnium is almost completely bonded into intermetallic com-pounds. It has been found that the structure of all the investigated bronze specimens subjected to HPT is stable and that it remains unchanged after unloading and prolonged ageing at room tempera-ture. It is shown that all the specimens develop a dispersed submicrocrystalline structure gradient along the radius of the disk, with an average crystallite size of 200 nm after 1 revolution to 120 nm after 5 revolutions (at mid-radius). The structure is non-uniform even after 5 revolutions, this being confirmed by microhardness measurements. The high-pressure-torsion behavior of hafnium bronze with Hf bonded into precipitates has much in common with the behavior of pure copper. At the same time, in terms of the stability of the obtained structures at room temperature, the behavior of the alloy under study demonstrates much in common with that of low-alloyed tin bronze.