Microstructural characterization of early Twentieth‐Century British period Indian copper coins

Abstract

This investigation deals with the characterization of chemical composition, microstructural, and corrosion behavior of the Indian copper alloy coins belonging to the period of different British emperors (Edward VII, King George V & King George VI). Elemental analysis showed that coins were mainly made up of copper and tin, and other elements such as iron, zinc, nickel, and lead were present in traces. The reddish‐brown layer formed on all coins was identified as cuprite by XRD, and this layer provided protection to the coins. The microstructure consists of an equiaxed grain structure along with annealing twins, which indicate that coins were subjected to annealing heat treatment. The average grain size was measured using the linear intercept method, and the variation in the average grain size of the different coins may be due to the difference in the soaking temperature/time of annealing treatment. TEM study also confirms the formation of twins by showing the double spots in SAD. The higher value of hardness in the coin belonging to the Edward VII period may be attributed to higher tin and zinc content. The corrosion product of globular morphology was observed on the surface of coins. Optical microscopy of the cross‐section of the coins showed the intergranular corrosion phenomena.