BS in Materials Engineering
Materials Engineering Department
The microstructure of rolled rings of Incoloy 909 nickel-iron-cobalt superalloy subjected to a standard customer solution and aging treatment exhibited unacceptably large grains. Samples cut from a failed ring were mounted and polished for analysis. The samples were etched with a modified Kalling’s waterless reagent and metallographic analysis was done to identify characteristic large grain structures distributed among the desired smaller grain structures. The large grains were identified and noted for comparison to later samples. Two test rings were forged out of Incoloy 909 using revised forging procedures involving reduced soak temperatures before each forging step. Metallographic samples were cut from micro-samples of each ring and mounted. The samples from the test rings were subjected to the same grinding, polishing, and etching procedure as the samples from the failed ring. Metallographic analysis was done on samples cut from the two test rings, which confirmed that the revised forging procedures had eliminated the large grain structures present in the failed ring, exhibiting instead a relatively uniform smaller grain structure. Tensile testing was done on samples from the test rings, reporting an average yield strength of 139.5 ksi for process A and 144.8 ksi for process B, an average ultimate tensile strength of 171.8 ksi for process A and 179.3 ksi for process B, and an elongation of 9.55% for process A and 10.5% for process B. These values were under the required minimum tensile properties of Incoloy 909 at room temperature, and the forging cycles were concluded to be unsuccessful.
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