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The alloy composition limits for transformation of the ordered bcc β1 Cu–Sn phase to the β1′ and γ1′ martensites during quenching to 20°C and subsequent cooling to −196°C have been determined by optical metallography. It is shown that the limits are imposed by the variation with composition of the initial β1 phase of the Ms and MF temperatures for the transformations. In duplex structures the transformation behaviour changes with quenching temperature probably as a consequence of the temperature dependence of the Sn concentration in the β1 phase.An additional product, termed β′, formed in all alloys quenched from above some minimum temperature and was identified as martensite from relief effects which accompanied the transformation.
Kennon et al. (Sat,) studied this question.