Implication of peritectic composition in historical high-tin bronze metallurgy

Bronze alloys of varying tin contents from 0% to 28% were cast and then heated at elevated temperatures followed by quenching to examine the variation of microstructure, hardness and fracture characteristics. The results show that hardness increases with tin content and almost reaches the upper limit at 22% tin. Evidence has been found that the small-scale α dendrites spanning across the former β grains that were transformed to martensite serve as interlocking micro-bridges and thereby substantially reinforce the boundary strength to enhance fracture toughness. This effect is extremely sensitive to the α fraction and can best be obtained in alloys of near 22% tin. This specific composition, termed peritectic, seems optimal for sufficient strength without serious brittleness, and allows objects for a similar purpose to be made with less material. The choice of near peritectic composition in historical high-tin bronze metallurgy constitutes an excellent example of human adaptation to harsh environments where access to tin was limited and material cost had to be minimized.