Accession Number:

AD0446356

Title:

MICROSTRUCTURE STUDIES OF POLYCRYSTALLINE REFRACTORY OXIDES.

Descriptive Note:

Quarterly progress rept. no. 2, 28 Apr-28 Jul 64,

Corporate Author:

AVCO CORP WILMINGTON MA RESEARCH AND ADVANCED DEVELOPMENT DIV

Report Date:

1964-08-27

Pagination or Media Count:

47.0

Abstract:

Very fine grained, highly dense, pure alumina prepared by higher pressure sintering in graphite dies shows strengths which are less than would be predicted on the basis of decreasing grain size. Such structures appear to be densely packed but with weakly bonded grains, as evidenced by predominantly intergranular fractures. Preliminary results show strengths in excess of 90,000 to 110,000 psi for pure alumina prepared by ceramic die pressure sintering, even with 3 porosity. Creep studies of dense, pure, fine grained alumina revealed a transition in strain rate - stress dependence at about 2000 psi from a linear to a square dependence. An activation energy of 167 k calsmol was found. Calculated diffusion coefficients were several orders of magnitude higher than self-diffusion values. An additional vacancy creation creep mechanism was suggested which would be independent of and supplement creep due to self-diffusion, to explain the high coefficients and high activation energy.

Subject Categories:

Distribution Statement:

APPROVED FOR PUBLIC RELEASE