| In order to meet the requirements of marine gas turbine blade materials, a new-typed directional solidification nickel-base superalloy DZ68 alloy was developed. So DZ68 alloy should have high temperature capability and good hot corrosion resistance. On the basis of Rene' 142, DZ125L and DZ38G (IN738) alloys, DZ68 was made by ourselves with low-segregation. The segregating lightlyγ'- phase forming elements of AI and Ta are added into DZ68 for precipitation hardening, this alloy has a small amount of Ti and no Hf or Nb segregating severely elements. High contents of refractory elements such as W and Re are added for solid solution strengthening and High Cr content is added into DZ68 for hot corrosion resistance.The heat treatment of DZ68 is composed of prior homogeneous treatment, solid solution treatment and two aging treatments. The whole heat treatment as follows: 1240℃/0.5hrs+1260℃/0.5hrs+1280℃/2hrs air cool, 1120℃/4hrs+One hour cool to 1080℃+1080℃/4hrs air cool, 900℃/4hrs air cool. Mechanical properties of DZ125, DZ38G and DZ68-1 alloys after each heat treatment have been compared in this paper. The rupture conditions are in the cases of 980℃/235MPa and 980℃/245MPa. The hot corrosion resistances of DZ125L, DZ38G and DZ68-1 alloys have been compared at the conditions of 900℃and 75%Na2SO4+25%NaCl molten salt.The mechanically experimental results show that the mechanical properties of DZ68-1 are high, because theγ'-volume faction of DZ68-1 is about 50% and it contains a certain amounts of W and Re. The room temperature tensile properties of DZ68-1 are similar to DZ125, the extension strength and extensibility of DZ38G is poor. The rupture properties of DZ68-1 are equivalent to DZ125 in the experimental cases and better than that of DZ38G.The hot corrosion experimental results show that the hot corrosion resistance of DZ68-1 is equivalent to DZ38G alloy and better than that of DZ125L. In this paper, the hot corrosion mechanism of three alloys is previously proposed the basic dissolution model. The processes of their hot corrosion are different for which they have different compositions, corrosive productions and microstructures. DZ125L alloy is corroded severely after short time; DZ38G alloy is locally corroded seriously for its non-uniform microstructure; DZ68-1 alloy has a more homogeneous microstructure and uniform corrosion, so its hot corrosion resistance is equivalent to DZ38G even if the chromium content of DZ68-1 is lower than that of DZ38G. |
