Effect of annealing on structure and properties of a dispersion strengthened superalloy, IN-853
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Dispersion strengthened nickel-base superalloy bar has been produced by hot extrusion of mechanically alloyed powders. The fabrication methods produce an ultra-fine grained material which r e s i s t s grain growth up to a critical temperature around 1506 K (2250~ Above this temperature, a discontinuous grain growth process leads to the formation of c o a r s e elongated macrograins. The material becomes completely coarse grained in short times. Annealing below this temperature produces only slight grain coarsening, and relieves stored strain energy. Changes in properties are related to the grain growth and strain annealing processes.
IMPROVED superalloys are sought to meet the needs of advanced high temperature technology. A particular requirement is for materials which combine high creep strength at intermediate and elevated t e m p e r a tures with good high temperature corrosion resistance. A new dispersion strengthened nickel-base superalloy, designated IN-853,* combines the corrosion resistance This alloy is produced commercially by the Huntington Alloy Products Division of the International Nickel Company, Inc., as INCONEL| alloy MA-753.
and intermediate t e m p e r a t u r e strength of a conventional y' hardened nickel-base superalloy with the high temperature strength and stability c h a r a c t e r i s t i c s of a dispersion strengthened metal. 1 The alloy is made by extrusion of powder produced by the newly-developed mechanical alloying process. Mechanical alloying consists of processing a blend of raw material powders in a dry, high energy ball mill or attritor in which the charge is driven by a rotating paddle. 1 The combined processes of cold welding and comminution z which occur during mechanical alloying lead to the production of composite powder particles containing an intimate dispersion of r e f r a c t o r y oxide particles. Extruded IN-853 bar is an ultra-fine grained material which is strong at ambient temperature. Exceptional elevated temperature tensile and creep rupture strengths are developed after heat treatments designed to produce a coarse elongated grain structure in the material. This paper discusses the effects of annealing on grain growth, and mechanical properties of IN853. EXPERIMENTAL P R O C E D U R E S
oxide. The Y2Os content was 2.25 vol pct. Excess oxygen (~ 0.5 wt pct) and nitrogen (~ 0.12 wt pct) introduced into the powder during the milling process, form s e c ondary dispersoids in combination with part of the m a trix aluminum and titanium. Mechanically alloyed powder, produced from the raw materials shown in Table I, was packed in mild steel cans which were sealed by fusion welding, and extruded to bar in a 8.9 cm diameter press. A range of extrusion temperatures and ratios were used in the preparation of bar. Mechanical Tests Tensile tests at both room and elevated temperature were performed on samples of bar in the as-extruded condition and after various anneals at temperatures ranging from 1311 K (1900~ up to 1589K (2400~ 1311 K (1900~ s t r e s s rupture tests w
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