Influence of growth rate on microstructure, microhardness, and electrical resistivity of directionally solidified Al-7 wt% Ni hypo-eutectic alloy

Al-7 wt% Ni alloy was directionally solidified upwards with different growth rates, V (8.3-489.5 mu m/s) at constant temperature gradient, G (4.2 K/mm) using a Bridgman-type growth apparatus. The dependence of the dendritic microstructures such as primary dendrite arm spacing (lambda (1)) and secondary dendrite arm spacing (lambda (2)) on the growth rate were determined using a linear regression analysis. The present experimental results were also compared with similar previous experimental results. Measurements of microhardness (HV) and electrical resistivity (rho) of the directionally solidified samples were carried out. The dependence of the microhardness and electrical resistivity on the growth rate (V) was also analyzed. According to these results, it has been found that, for increasing values of V, the values of HV and rho increase. However, the values of HV and rho decrease with increasing values of lambda (1) and lambda (2).