Moisture-Induced Delayed Alumina Scale Spallation on a Ni(pt)Al Coating

By: Nasa, National Aeronautics and Space Adm

Delayed interfacial scale failure takes place after cooling for samples of a Ni(Pt)Al-coated CMSX4 single crystal superalloy, cycled at 1150 C for up to 2000 hr. One sample exhibited premature coating grain boundary wrinkling, alumina scale spallation to bare metal, and a final weight loss of 3.3 mg/cm2 . Spallation under ambient conditions was monitored with time after cooldown and was found to continue for 24 hr. This produced up to 0.05 mg/cm2 additional loss for each hold, accumulating 0.7 mg/cm 2 (20 percent of the total) over the course of the test. After test termination, water immersion produced an additional 0.15 mg/cm2 loss. (A duplicate sample produced much less wrinkling and time dependent spalling, maintaining a net weight gain.) The results are consistent with the general phenomena of moisture-induced delayed spallation (MIDS) of mature, distressed alumina scales formed on oxidation resistant M-Al alloys. Relative ambient humidity is discussed as the factor controlling adsorbed moisture, reaction with the substrate, and hydrogen effects on interface strength. Smialek, James L. Glenn Research Center WBS: 984754.02.07.03.16.02

• Format: Paperback
• Language: English
• ISBN: 1793915865
• ISBN13: 9781793915863
• Release Date: January 1
• Publisher: Independently Published
• Length: 26 Pages
• Weight: 0.19 lbs.
• Dimensions: 0.1" x 8.5" x 11.0"