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.

Application of Thermodynamic Modeling for Optimization of the Composition of Nanostructured Low-Alloyed Hafnium Bronzes by High-Pressure Torsion

“…Therefore, it can be concluded that for the Cu-Hf system, the grain size formed by SPD is the determining factor that affects the hardening of these alloys. But the fact that the microhardness figures after SPD for the annealed composition [20] are higher than those obtained for the alloy after prequenching [1] indicates that increasing the Hf concentration in the copper matrix is not always determinative for a more dispersed structure during SPD and, therefore, for higher strength characteristics. Materials Engineering and Technologies for Production and Processing VII This can be explained by differences in the deformation scheme.…”

“…[1]; 3 -Cu -0.35 at. % Hf, annealing at 800 °C [20]; R 2 -Reliability of approximation by a linear function Fig. 3.…”

“…Materials Engineering and Technologies for Production and Processing VII This can be explained by differences in the deformation scheme. For instance, in [1] a scheme with a pressure of 4 HPa is used, while in [20] the pressure during SPD was 6 HPa. That means that the SPD conditions are the limiting factor in obtaining higher characteristics of the system in question and the minimum concentration of Hf in copper matrix (about 0.01 at.%, determined from alloy conductivity dependences [1]) obtained during annealing treatment is sufficient for the structure to be stable during further heating).…”