No abstract

Incoloy(1) nickel-iron-chromium Alloy 825 can become sensitive to intergranular attack by exposure to temperatures in the 1200–1400 F (649–760 C) range. Sensitivity to intergranular attack (as measured by the Huey test) can be correlated to the presence of a chromium-depleted area adjacent to the grain boundary. This area is caused by the cellular precipitation of chromium-rich M23C6 during sensitizing treatments. The chromium-depleted region is between the M23C6 cells, but because the carbides grow by boundary migration the depletion is not in the plane of the grain boundary. Incoloy Alloy 825 can be stablized against intergranular attack by eliminating the chromium-depleted area. The degree of stabiization is related to the amount of carbon remaining in solution after the stablizing treatment. The titanium content of the alloy helps to effect stabtization. Because it has a greater affinity for carbon than does chromium, the titanium reacts to form stable carbides and thus reduces chromium depletion. Maximum stabtization of Incoloy Alloy 825 cannot be obtained if titanium carbide is used as the sole stablizing mechanism. The principal mechanism of stablization for this alloy is that of precipitating the M23C5 at a temperature where the diffusion of chromium is sufficiently rapid to prevent chromium depletion. This occurs at temperatures in the 1700–1800 F (927–982 C) range.

No abstract

An intermediate heat treatment at 1550°F used to improve the rupture ductility of INCONELY: alloy 706 had a varied effect on room-temperature yield strength of the alloy. The effect seemed to depend on very small differences in aluminum content. A laboratory investigation was conducted to determine the effects of variations in aluminum content and heat treatment on the yield strength of alloy 706. Samples having aluminum contents from 0.033% to 0.90% were studied after being subjected to four different heat treatments. The investigation produced an explanation of the variations in yield strength in terms of changes in structure of gamma prime, gamma prime/ lattice mismatch, and changes in modulus of elasticity. It was found that material age-hardened without the intermediate treatment is in a slightly underaged condition, and that yield strength of such material is a function of gamma prime particle properties. It was also found that material given the 1550°F intermediate treatment and then age-hardened is slightly overaged. The yield strength of overaged material is not a function of gamma prime properties but depends instead on matrix shear modulus and interparticle spacing of the gamma prime.

Alloy 718 has been utilized in gas turbine engines for almost 30 years because of its extremely good mechanical properties."30ver the years the property levels attained with the alloy have been increased by altering the thermomechanical history as discussed by LoriaP The chemical composition range for the alloy has remained relatively stable over the years, although there has been a tightening of the columbium range along with tighter control of minor elements such as magnesium and sulfur. Recently there has been interest in the stabilizing of Y" by adjustments of aluminum, titanium, and columbium.