Accession Number : AD0467852


Title :   MECHANISMS OF DEFORMATION IN POLYCRYSTALLINE MAGNESIUM OXIDE.


Descriptive Note : Summary technical rept., 1 Feb 64-15 Mar 65,


Corporate Author : AVCO CORP WILMINGTON MA RESEARCH AND ADVANCED DEVELOPMENT DIV


Personal Author(s) : Passmore, E M ; Duff, R ; Vasilos, T


Report Date : Jun 1965


Pagination or Media Count : 24


Abstract : Creep of polycrystalline MgO was determined using four-point transverse bending between 1380 to 1800 K and stresses from 1000 to 5000 psi. Effects of temperature, stress, and grain size on the creep rate were determined for grain sizes from 2 to 20 microns. Activation energies for creep decreased sharply with increasing grain size from 96,000 cals/mol at 2 microns to 54,100 cals/mol at 5.5 microns and then remained constant over the grain size range from 5.5 to 20 microns. Creep was attributed partly to a stress-directed diffusional mechanism controlled by extrinsic oxygen ion diffusion in the latter range of grain sizes. Calculated ionic selfdiffusion rates were higher than those predicted by the Nabarro-Herring theory; this discrepancy may be due to a defect formation mechanism, consistent with the observed formation of dislocation substructure and preferentially distributed porosity during creep, as well as with the observed decrease in creep rate with increasing creep strain. (Author)


Descriptors :   *DEFORMATION , OXIDES , MAGNESIUM COMPOUNDS , MAGNESIUM COMPOUNDS , CREEP , HIGH TEMPERATURE , SCIENTIFIC RESEARCH , HYPERBARIC CONDITIONS , SCIENTIFIC RESEARCH , GRAIN STRUCTURES(METALLURGY) , HEAT OF ACTIVATION , OXYGEN , IONS , DIFFUSION , CRYSTAL DEFECTS , POROSITY


Distribution Statement : APPROVED FOR PUBLIC RELEASE