Peculiarities of Thermoelastic Martensitic Transformation in the Cu-Zn-Al and Cu-Zn-Al-V after Decomposition of the β-Solid Solution

Abstract
Dilatometric, metallographic, and electron-microscopic methods were used to study martensitic transformations in Cu-Zn-Al alloys that were subjected to a heat treatment to the decomposition of β solid solution at temperatures of α-phase precipitation (635-530°C) and bainite formation (300-125 °C). The partial decomposition and the accompanying redistribution of the components were shown to alter the type of martensitic transformation from nonthermoelastic to thermoelastic with a corresponding change in the martensite morphology from plate type to needle type (spear-shaped). A decrease in the temperature of isothermal anneal in the α+β range from 600 to 530°C substantially decrease the M_s temperature (by 140 °C). The temperature hysteresis of the transformation changes from 0 to 70 K.