The effect of alloying with hafnium on the thermal stability of chromium bronze after severe plastic deformation

The effect of alloying with 0.9 wt% hafnium on the thermal stability of the Cu-0.7%Cr alloy after severe plastic deformation by high pressure torsion has been studied by microhardness and resistivity measurements, optical microscopy, and transmission electron microscopy. The data obtained were used to construct the curves of the temperature dependences of microhardness and resistivity for the alloy samples in a temperature range of 50–550 °C and the curves of the microhardness distribution over the sample diameter. The effect of preliminary heat treatment on the stability of the structure formed upon deformation is considered. It is shown that alloying with hafnium decreases the grain size from 250 to 120 nm, increases the strength, and elevates the temperature of the beginning of alloy softening upon heating. In addition, the introduction of hafnium to the alloy results in the occurrence of aging upon heating, and the strength reaches maximum (3177 MPa) at a temperature of 450 °C.