Investigation of the effect of solidification processing parameters on the rod spacings and variation of microhardness with the rod spacing in the Sn-Cu hypereutectic alloy

Sn-3 wt% Cu hypereutectic alloy was prepared in a graphite crucible under the vacuum atmosphere. The samples were directionally solidified upwards under argon atmosphere with different temperature gradients (G = 4.24-8.09 K/mm) at a constant growth rate (V = 7.64 mu m/s) and with different growth rates (V = 2.24-133.33 mu m/s) at a constant temperature gradient (G = 4.24 K/mm) by using a Bridgman type directional solidification apparatus. The microstructure of directional solidified Sn-3 wt% Cu alloy seems to be rod eutectic structure. The influence of the growth rate (V) and temperature gradient (G) on the rod spacing (lambda) and undercooling (Delta T) were analysed. The values of lambda V-2, lambda(2)G, Delta T lambda, Delta TV-0.5 and Delta TG(-0.5) were determined by using the Jackson-Hunt eutectic theory. The dependence of microhardness (HV) on the rod spacing (lambda) was analyzed. According to present results, it has been found that the value of HV increases with the increasing the value of lambda.