An Investigation of the CNTD Mechanism and Its Effect on Microstructural Properties.
Abstract
The purpose of this research was to investigate the CNTD (Controlled Nucleation Thermochemical Deposition) process developed at Chemetal as it applies to the microstructural properties of silicon carbide. A general parametric study was conducted of the silicon carbide chemical vapor deposition system with emphasis on parameters which might influence directly the mechanism of CNTD. An iterative approach was employed which related deposition conditions to room temperature tensile strength and microstructure. It was hypothesized that conditions which effected minimum grain size with a probable minimum flaw population in deposits would result in increased strength. CNTD silicon carbide deposits with average grain sizes of 500-1000A were obtained. Room temperature flexural strengths in excess of 3000 MPa (435 kpsi) were recorded on wire samples. Strength was found to be strongly dependent upon microstructure and probably on composition of the deposit. Unexpectedly high fracture toughnesses were observed and were associated with the presence of chlorine during preliminary studies. Widely varying strengths were observed in furnace deposited bend bar samples indicating that the deposition conditions for CNTD SiC on directly heated wire substrates require significant changes when deposition is done in a hot wall furnace. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1979
- Accession Number
- ADA070018
Entities
People
- Robert A. Holzl