Alloying-Element Loss During High-Temperature Processing of a Nickel-Base Superalloy

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 45; no. 2; pp. 962 - 979
• Main Authors: Semiatin, S. L., Shank, J. M., Saurber, W. M., Pilchak, A. L., Ballard, D. L., Zhang, F., Gleeson, B.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01-02-2014; Springer; Springer Nature B.V
• Subjects: Alloys; Aluminum; Applied sciences; Argon; Characterization and Evaluation of Materials; Chemical elements; Chemistry and Materials Science; Chromium; Exact sciences and technology; Heat treatment; High temperature; Materials Science; Metallic Materials; Metals. Metallurgy; Nanotechnology; Nickel alloys; Nickel base alloys; Quartz; Structural Materials; Superalloys; Surface chemistry; Surfaces and Interfaces; Thin Films; Heat Treatment Time; Vacuum Furnace; Follow Heat Treatment; Free Surface; Sample Heat; Nickel base alloys; Superalloy; Temperature; High temperature; Alloying element
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-013-2005-3

The effect of exposure at temperatures commonly used for wrought processing/heat treatment of nickel-base superalloys on the loss of alloying elements at the free surface has been determined. For this purpose, LSHR superalloy samples were exposed at 1408 K (1135 °C) for 0.25 to 4 hours in a vacuum or air furnace. Samples heat treated in the air furnace were either bare or enclosed in quartz capsules that had been evacuated or backfilled with argon. Following heat treatment, the alloy composition as a function of depth below the surface was determined by wavelength dispersive spectroscopy. Samples that had been heat treated in the vacuum furnace exhibited significant depletion of only chromium, a behavior explained on the basis of its high activity in nickel solid solution and corresponding rapid rate of evaporation. By contrast, samples heat treated in air exhibited an irregular scale at the surface and an underlying grain-coarsened, gamma-prime-depleted metal layer lean in aluminum, titanium, and chromium. A yet different behavior characterized primarily by aluminum loss at the surface was noted for samples that had been heat treated in evacuated or argon-backfilled capsules. These observations were interpreted in the context of a reaction between the quartz capsule and the aluminum evaporant.