PREBAINITIC TRANSFORMATION IN A Cu-Zn-Al ALLOY

The change in internal friction and frequency associated with the bainitic transformation in a Cu-25.83Zn-3.96Al(by wt-%)alloy was conducted by a new type of instrument under isothermalholding with 0.7 Hz. Results show that the internal friction exists a maximum value Q_(max)~(-1) within the incubation period. Q_(max)~(-1) increases with the raise of the isothermal temperature, and the time up to Q_(max)~(-1) decreases with the increment of the holding temperature. The frequency value is lowest at the initial time until it reaches a stable value. While the specimen is measured under a tension of 8×10~5Pa, Q_(max)~(-1) is far larger, the time up to Q_(max)~(-1) is shorter and the initial frequency value decreases more abruptly than that under the above unloading condition. The bainitie transfromation of the alloy exists a lattice softening phenomenon somewhat similar to that in thermal elastic martensitic transformation. The prebainitic transformation within the incubation period of the bainitic transformation occurs basically with the nucleation pro cess. Based upon the theory of phase transformation and the theory of local softening mode, a rule of the change in isothermal internal friction can be interpreted through the change of the nucleation rate within the incubation period.