2006 Volume 46 Issue 10 Pages 1427-1431
The effect of oxygen partial pressure (PO2) in different gas atmospheres on heat transfer, cast structure and secondary dendrite arm spacing in droplet solidification process has been investigated. It has been found that the PO2 of the gas affects solidification process and undercooling. As PO2 decreases, at relatively high PO2 (10−1.2–10−4) in 99.99% Ar and air atmosphere, heat flux is decreased and equiaxed zone ratio and secondary arm spacing are found to be increased. At intermediate PO2 (10−14 to 10−20) in Ar–H2 atmospheres, heat flux and equiaxed zone ratio varies only slightly and secondary arm spacing is reduced. At low PO2 (10−20–10−23) in Ar–5%H2 atmosphere, heat flux increases dramatically and the equiaxed zone ratio and secondary arm spacing are reduced. The largest equiaxed zone is found with intermediate PO2 levels in Ar–H2 gas atmospheres, whereas the finest grains are obtained in Ar–5%H2 gas in low PO2 value.