The Effect of Heat Treatment and Alloying on The Decomposition of the beta Phase of The Copper-Tin System.

The decomposition characteristics of tin bronzes have been examined by means of techniques adapted from those used to study steel transformations. The predominant method of investigation has been the use of a special end-quench test, incorporating subsequent microhardness measurement. The results of this test have been amplified by the determination of the isothermal transformation curve for a 25%Sn alloy and the correlation thereby obtained for transformation characteristics under both continuous and isothermal conditions. It has been shown that: (a) Lattice strain and supersaturation effects seem to account satisfactorily for the behaviour of alloys with different tin contents and alloying additions; (b) Metallographic evidence for the eutectoidal nature of the B-G reaction has been disproved, and a second-order reaction shown to be more likely; (c) Observed sub-boundary phenomena possess characteristics which are of importance in the assessment of the role played by polygonisation in the transformation of metals. Discrepancies observed during microhardness testing at low loads may indicate that low-load deviations are the rule rather than the exception