Accession Number:

ADA128823

Title:

Vacuum Pyrolysis Coatings for Ceramic Alloys.

Descriptive Note:

Final rept. 27 Jan 81-26 Jun 82,

Corporate Author:

MARTIN MARIETTA LABS BALTIMORE MD

Report Date:

1982-08-01

Pagination or Media Count:

22.0

Abstract:

The effectiveness of vacuum pyrolysis coatings in improving oxidation resistance and mechanical properties of sintered SIALON substrates was investigated. The substrates were prepared at Martin Marietta Laboratories and the vacuum pyrolysis was performed at NADC by reacting nitrogen gas and hexamethyldisilizane on substrates heated to temperatures between 590 deg C and 710 deg C. No coating was produced at the low temperature. Characterization and mechanical testing of the substrates was performed at Martin Laboratories. The high resolution SEM mode of the STEM was used to determine coating thickness and morphology. The coatings contain silicon, carbon, nitrogen, and oxygen. X-ray diffraction of the coatings revealed no peaks other than those from the substrate, indicating that the coatings may be amorphous. Biaxial flexure testing was performed on coated and uncoated SIALON on samples at two temperatures. In samples exposed to 1400 deg C in air, both coated and uncoated samples show a new X-ray diffraction peak at d 4.07 A, which corresponds to the 101 peak for low, or alpha, cristobalite a form of Si02. The relative intensity of this peak is higher for the uncoated samples than the coated samples by a factor of 1.7, indicating that the coatings do impart some oxidation resistance.

Subject Categories:

  • Physical Chemistry
  • Ceramics, Refractories and Glass
  • Coatings, Colorants and Finishes
  • Properties of Metals and Alloys
  • Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE