Abstract: The transformation of the early stage of aging in Cu-3.2Ni-0.75Si alloy was investigated by means of transmission electron microscope and X-ray diffraction . It is shown that the supersaturated solution Cu-Ni-Si alloy first decomposes into solute-rich and solute-depleted zones by spinodal mechanism, then the solute-rich zones form Ni2Si phases which remain coherent with the matrix. Due to the significant difference in structure between the matrix and the precipitate, an Orowan type strengthening mechanism is believed to still operate. The strengthening effect of the spinodal structure aged at 450℃ for 2h is calculated to be 342MPa by using dislocation theory, and that of the Ni2Si phase precipitated in aging at 450℃ for 4h is about 405MPa, which are quite consistent with the experimental data.
Transformation and strengthening of early stage of aging in Cu-3.2Ni-0.75Si alloy
Abstract:
The transformation of the early stage of aging in Cu-3.2Ni-0.75Si alloy was investigated by means of transmission electron microscope and X-ray diffraction . It is shown that the supersaturated solution Cu-Ni-Si alloy first decomposes into solute-rich and solute-depleted zones by spinodal mechanism, then the solute-rich zones form Ni 2Si phases which remain coherent with the matrix. Due to the significant difference in structure between the matrix and the precipitate, an Orowan type strengthening mechanism is believed to still operate. The strengthening effect of the spinodal structure aged at 450 ℃ for 2 h is calculated to be 342 MPa by using dislocation theory, and that of the Ni 2Si phase precipitated in aging at 450 ℃ for 4 h is about 405 MPa, which are quite consistent with the experimental data.
Fig.2 XRD patterns of Cu-3.2Ni-0.75Si alloy aged for various time
图3 合金时效早期所形成的成分调幅组织及衍射花样
Fig.3 Microstructures of Cu-3.2Ni-0.75Si alloy aged at 450 ℃ for various time (a) —0.25 h; (b) —0.5 h; (c) —2 h; (d) —Diffraction pattern of aged for 2 h
图4 450 ℃时效4 h合金的微观组织 (a) 及其高分辨相 (b)
Fig. 4 TEM BF image (a) of Cu-3.2Ni-0.75Si alloy aged at 450 ℃ for 4 h and HREM image (b) of GP zone