Effect of cooling rate on the microstructure and microhardness of the CuZrAgAl alloy

The effect of cooling rate on the microstructure and microhardness of the Cu40Zr44Ag8Al8 (at.%) alloy has been studied. The crystalline phases were characterized by X-ray diffraction, optical microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy, and identified as AlCu2Zr, Cu10Zr7 and CuZr2. The solidification sequence was established as following: the Cu10Zr7 phase forms first in the periphery of the rod, then following with AlCu2Zr phase in the rod center and finally CuZr2 crystals in Cu-depleted areas. The effect of crystals on the mechanical properties of the Cu40Zr44Ag8Al8 alloy was also estimated through the microhardness. According to the value of microhardness, inhomogeneous structure of the amorphous matrix is more easily formed for the alloy in the low cooling rate (i.e., 9 mm) as compared with the alloy with fully amorphous state in the large cooling rate (i.e., 3 mm). This inhomogeneous structure was attributed to the composition change of amorphous matrix arising from the forming of crystalline phases due to the low cooling rate.