Accession Number : AD0778843

Title :   The Effect of Carbon Additions on the Grain Growth and Strength of Hot Pressed Silicon Carbide.

Descriptive Note : Technical rept. Mar 72-Sep 73,


Personal Author(s) : Crane,R. L. ; Hollenberg,G. W.

Report Date : JAN 1974

Pagination or Media Count : 23

Abstract : The growth of high aspect ratio alpha-SiC grains has been shown to seriously limit the material's load carrying capacity. It has been noted that the addition of excess carbon to hot pressed billets limits this discontinuous grain growth. A study was, therefore, undertaken to document the grain growth of SiC as a function of temperature for specimens containing 0, 1, 5, and 10 weight percent (wt %) chopped carbon fibers. The 5 and 10 wt % additions limited the discontinuous grain growth both during the initial hot pressing of specimens and during subsequent annealing studies at 2000 and 2150C. These data were interpreted using a modified Zener criterion. The fourpoint bend strength and modulus of hot pressed specimens containing 0, 5, 15, and 30 wt % carbon fibers were determined. Two groups of specimens containing different amounts of boron were examined. A strength maximum was noted for specimens that contained 5 wt % boron and 15 wt % carbon. Assuming that the fibers act as pores, a model is presented to explain the increasing and then decreasing strength of SiC as a function of increasing carbon fiber content. (Modified author abstract)

Descriptors :   *Silicon carbides, *Hot pressing, *Carbon, Additives, Density, Strength(Mechanics), Grain size, Boron, Elastic properties

Subject Categories : Ceramics, Refractories and Glass

Distribution Statement : APPROVED FOR PUBLIC RELEASE