Effect of Zr on Microstructure and Properties of Cu-15Cr Alloy

Cu-15Cr and Cu-15Cr-0.24Zr alloys were prepared by vacuum medium frequency induction melting technique. The effects of Zr on microstructure of as-cast Cu-15Cr alloy and microstructure after annealing at different temperatures was studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The tensile deformation test of the two kinds of alloys was carried out, and the thermal stability of the alloy under the final deformation was studied. The results show that the addition of Zr results in the formation of flaky CuZr intermetallics in the as -cast microstructure of the alloy, which inhibit the formation of eutectic Cr phase and make the eutectic Cr content much lower than that of Cu-15Cr alloy. The size of dendritic Cr is refined as well. The addition of Zr significantly improves the thermal stability of the alloy and increases its tensile strength by 100 MPa after annealed at 550 degrees C for 1 h. Through the calculation of Gibbs free energy (Delta G(mix)) in the solidification process of the alloy, it is proved that the addition of Zr reduces the liquid phase separation temperature and decreases the dynamic nucleation driving force of the Cu-15Cr alloy in the process of solidification, which inhibits the formation of eutectic Cr and is consistent with the experimental results of the as-cast microstructure.