COMPOSITION DEPENDENCE OF AGING KINETICS IN SOME CU-ZN-AL SHAPE MEMORY ALLOYS

Isothermal and nonisothermal aging behaviors of five Cu/(13 to 28)Zn/(3 to 9)A1 (weight percent) shape memory alloys have been investigated. The electrical resistivity during isothermal aging from 180 °C to 340 °C increases with aging time at each aging temperature. The time to reach a constant fraction transformed during the isothermal aging increases with increasing Al content or decreasing Zn content in the Cu-Zn-Al alloys, except alloy D (Cu-18.2Zn-7.2Al). This alloy exhibits a double aging behavior by the earlier formation of the α1 bainite and the subsequent formation of the cubic γ2 phase from the β1 matrix phase. The apparent activation energy of alloy D varies with the fraction transformed by the double aging behavior. However, other alloys A, B, C, and E exhibit isokinetic behavior. The apparent activation energies estimated in the nonisothermal aging from 100 °C to 500 °C are found to be about equal to those obtained in the isothermal aging. © 1990 The Metallurgical of Society of AIME.