| The structures, the mechanical properties, the high temperature oxidation and sulfidation behavior of the unidirectionally solidified Ni₃Al (γ`)-Ni₃Nb(δ) eutectic alloy were investigated. Casted eutectic alloy round bar was directionally solidified with rates (R) between 0.6㎝/ hr and 12㎝/hr at induction furnace maintaining the thermal gradient (G) at solidliquid interface, 130℃/㎝. The eutectic microstructure was varied according to the growth condition (G/R ratio). When G/R ratio was larger than 130℃·hr/㎠ the lamellar structure was formed, and the colony structure was formed, when G/R ratio was smaller than 130℃·hr/㎠. It was found that the interlamellar spacing (λ) was dependent on the growth rate (R) through the relationship, λ²·R=8.4×10^(-13) ㎤/sec. The results also indicated that high temperature strength in tension to the growth direction of Ni₃Al-Ni₃Nb eutectic alloy was better than that of the known conventionally tasted nickel base superalloy B-1900. The microhardness of this eutectic alloy increased with the growth rate increase. The high temperature oxidation in static air of this eutectic alloy was occurred paraborically. The activation energy of parabolic process was 21 ㎉/㏖. High temperature oxidation was accelerated by the presence of Na₂SO₄. |
|
