Liquid Phase Separation Of Cu-Cr Alloys

In this paper, Cu-Cr ribbons with 2-30wt.%Cr were prepared by single roller melting spinning. The ribbons solidified at different cooling rates were obtained by controlling the thickness of samples. The effects of compositions, cooling method and aging on the nonequilibrium solidification and the microstructures of Cu-Cr alloys were studied in detail by use of X-ray diffractmeter, scanning and transmission electron microscopy. Meanwhile, elements Ni and Ti were added into Cu-25wt.%Cr melts, the effects of alloying on the microstructures of Cu-25wt.%Cr alloys were studied and the effect mechanisms were analyzed by the thermodynamics calculations. The main results are shown as following:Liquid phase separation occurs in some Cu-Cr alloys with a higher Cr content when the melts cooled in rapid solidification. The size of primary Cr particles in the microstructure of Cu-Cr alloys is larger from liquid phase separation. The main work of refining the microstructure of Cu-Cr alloys is to decrease size of primary Cr particles. Comparing with the samples prepared by melt-casting, arc remelting, sintering-seeping and et al, the microstructures of melt-spun Cu-Cr ribbons are sharply refined by high cooling rates although the liquid phase separation has taken place during rapid cooling. Adding alloying elements into Cu-25wt.%Cr ribbons could partly restrain the liquid phase separation of Cu-25wt.%Cr alloys. As a result, the Cr particle from liquid phase separation is refined. The effect of adding Ti is better than of Ni, the size of Cr particle in melt-spun Cu-25wt.%Cr could be refined to smaller than 100 nm. The nano-sized Cr particles can be obtained in Cu-Cr alloys. The Cr particle from liquid phase separation in Cu-Cr-based alloys ribbons did not grow up obviously during aging. The Cr particles did not grow up evidently with increasing the aging temperatures and durations.The thermodynamic analyses show that the rapid solidification can provide a large supercooling, which can drive Cu-Cr melts into miscibility gap and so the liquid phase separation occurs. Higher cooling rates results in the liquid phase separation occuring at a lower temperature and an increase of the nucleation rate of Cr-rich melts and then the microstructure can be refined. Alloying can decrease the driving force of the liquid phase separation, the liquid phase separation can be partly restrained, the microstructures of melt-spun Cu-Cr-based alloys can be refined.