Abstract
Thermal stability of the structure of Cu-0.8%Hf alloy subjected to severe plastic deformation by 2 passes of dynamic channel angular pressing (DCAP) has been investigated. It is demonstrated that after such deformation the microstructure of the hafnium bronze is non-uniform, where areas of cell structure are neighboring with thin-lamellar structure of twinning type. Such structure indicates the action of two deformation mechanisms, dislocation sliding and twinning. It has been revealed that doping with hafnium has considerably affected susceptibility of copper to relaxation processes under the DCAP and following annealing. It has been found that the microstructure formed under the deformation can be retained at the annealing up to 500°C without noticeable changes, and the microhardness changes only slightly in this temperature range. At the same time, at heating up to 600°C and higher the relaxation processes are developed in the structure which is accompanied with a drastic drop of microhardness.
Highlights
In the last decades materials with ultrafine-grained (UFG) structure attract great attention of the researchers due to their unique physical and mechanical properties [1, 2]
As shown by metallographic studies (Figure 1), the structure of specimens after DCAP in transverse sections is quite uniform excluding narrow areas in upper and lower parts, which is typical of specimens subjected to the dynamic channel angular pressing [6, 8, 13, 15]
According to TEM studies, the structure after 2 passes of DCAP is non-uniform, and it is seen that there are two deformation mechanisms, dislocation sliding and twinning. These mechanisms result if the formation of two types of microstructure, namely, areas of cell structure interchanging with thinlamellar structure of twinning type
Summary
In the last decades materials with ultrafine-grained (UFG) structure attract great attention of the researchers due to their unique physical and mechanical properties [1, 2]. Application of severe plastic deformation (SPD) enables obtaining bulk UFG materials demonstrating unusual mechanical behavior and a complex of unique properties which are often unachievable for coarse-grained materials. One of the new promising methods of SPD is the dynamic channel angular pressing (DCAP), which has the scheme of deformation similar to that of the ECAP, but its main difference is the high deformation rate (104 – 106 s-1). Compared to the ECAP, in case of the DCAP the rate of plastic deformation is increased, and the shock-wave impact is added, which increases the SPD influence on the structure and properties of materials. Application of the DCAP makes it possible to change the properties of metals and alloys substantially by the formation such structures in them
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