Effects of heat treatment on the structure of BrNKHK bronze

Nickel-chromium-silicon bronze BrNKhK is a moderately dispersion-hardened alloy used for contacts and hardened by cold plastic deformation of the alloy in a hardened state and with subsequent ageing. However, articles made of bronze BrNKhK often do not possess sufficient stability of the contact separating force. The paper presents results of the research of the structure of bronze BrNKhK in a hardened and deformed state, and also after various ageing modes. It was found that immediately after hardening particles of different shapes and sizes on the basis of chromium and silicon are observed in a solid solution with different contents of copper and nickel. Ageing at 500 °C increases the size of separated coarse particles and enriches fine particles with nickel. It is shown that two-stage ageing increases stress relaxation resistance of bronze BrNKhK in both deformed and non-deformed states as compared to one-stage ageing due to changes of the chemical composition, the nature and dispersion of precipitated phases.