Effects of Zr addition on the liquid phase separation and the microstructures of Cu-Cr ribbons with 18-22 at.% Cr

Cu77Cr23-XZrX (X = 1, 2, 3) and Cu82-xCr18ZrX (X = 6, 10) (at.%) ribbons were prepared by melt spinning in order to obtain finer Cr particles in Cu-Cr contact materials. Microstructural analyses reveal that the Cr particles from liquid phase separation can be refined to 50 nut when Cr content is in a range of 18-22 at.% and Zr addition is more than 3%. Meanwhile, Cu5Zr precipitations in nano-scale were observed in the ribbons. The thermodynamic analyses indicate that Zr addition has reduced the large positive mixing heat between Cu and Cr, which resulted in the liquid phase separation occurring at a lower temperature and a smaller nucleation driving force. Therefore, Zr addition can partly restrain the liquid phase separation of Cu-Cr alloy during rapid cooling and then Cr particles have been refined. (c) 2007 Elsevier B.V. All rights reserved.