Influence of alloy chemistry on carbide precipitation in a nickel base superalloy
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compositions of the alloys studied are presented in Table I, and the reported values represent the averages of three separate analyses. Alloys designated A1-4 were prepared with the intention of varying the alloys' matrix composition while maintaining constant minor element concentrations. Alloys BI-4 were prepared with variations in both major chemistry and minor chemistry in order to determine their relative effects. Table II contains calculated matrix chemistries for the alloys using assumptions similar to those involved in calculating an electron vacancy number (Nv), with the exception of the inclusion of the electron vacancy number. These assumptions include chemical partitioning considerations with regard to the y ' , M23C6, M C , and M3Bz phases; the remaining chemical constituents are assumed to partition to the matrix. The y ' partitioning coefficients employed were based upon the work on IN-100* by Kriege and Baris. z
Influence of Alloy Chemistry on Carbide Precipitation in a Nickel Base Superalloy Y.J. G A R O S S H E N
In a previous publication we reported on the formation of a continuous M23C6 carbide in a P/M nickel base superalloy. 1 The carbide phase forms in the 732 to 760 ~ temperature range and is observed to reduce the stress-rupture life of the alloy. The composition of the carbide was observed to be enriched in chromium with lesser amounts of molybdenum, cobalt, and nickel. Selected area electron diffraction analysis of the carbide indicated an fcc structure with a lattice parameter (a0) of approximately 1.063 nm. Both the composition and structure of the carbide are typical of the M23C6 carbides which form at higher temperatures in this alloy. Factors which were shown to influence the formation of the continuous carbide phase include the materials' thermal history and alloy composition. As formerly reported, the appearance of this continuous carbide phase can be reduced by decreasing the time and temperature of the 3/' precipitation ages. In addition, increased carbide stabilization (formation) at an intermediate temperature was also observed to reduce the extent of the continuous carbide reaction. In this article we report on the influence of alloy chemistry on the formation of continuous M23C6 phase. The two sets of alloys studied in this investigation were prepared from two different master heats. The compositions were altered by elemental additions to the melt prior to atomization in the Homogeneous Metals Inc., Clayville, NY, experimental vacuum atomization unit. Consolidation of the powders was performed via extrusion and isothermal forging under inert conditions as previously described.r The alloys were subjected to the following heat treatment: 1130 ~ hrs/forced air cooled, 871 ~ min/air cooled, AC, 982 ~ min/AC, 650 ~ hours/AC, 760 ~ hrs/AC. Standard tensile specimens and stressrupture combination smooth/notch specimens were machined from the heat-treated material and tested in air. The Table I.
Alloy A-1 A-2 A-3 A-4 B-I B-2 B-3 B-4
Ni bal. bal. bal. bal. bal. bal. bal. bal.
Co
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