材料期刊网

使用微机自动控制相变内耗仪,以0.7Hz频率测量Cu-25.83wt-％Zn-3.96wt-％Al合金在贝氏体相变温区等温过程中的内耗和频率随时间的变化,实验结果显示,在孕育期内随时间出现内耗峰值Q_(max)~(-1)且Q_(max)~(-1)随等温温度升高(孕育期缩短)而升高,达到Q_(max)~(-1)所需时间却随等温温度升高而缩短.在等温初期频率最低,随时间延长逐渐上升至稳定值.在施加8×10~5Pa拉应力的条件下,重复上述等温测量表明,Q_(max)~(-1)升高,达到Q_(max)~(-1)所需的时间缩短,且初期频率下降更为显著. 本文揭示:Cu-Zn-Al合金贝氏体相变存在类似于热弹性马氏体相变的点阵软化现象。在贝氏体相变孕育期内存在预相变的主要过程为形核。等温内耗的变化规律可根据相变理论和局部软化理论,通过孕育期内形核率J~*的变化作出解释。

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.