Accession Number : AD0619369

Title :   MECHANICAL BEHAVIOR OF POLYCRYSTALLINE MAGNESIUM OXIDE AT HIGH TEMPERATURES.

Descriptive Note : Technical rept.,

Corporate Author : HONEYWELL RESEARCH CENTER HOPKINS MINN

Personal Author(s) : Day,R. B. ; Stokes,R. J.

Report Date : JUL 1965

Pagination or Media Count : 55

Abstract : The paper describes high temperature tensile deformation of polycrystalline magnesia prepared by (a) single crystal recrystallization and (b) hot pressing. Recrystallized polycrystalline magnesia goes through a brittle-ductile transition at 1700C (strain rate 0.0001/ sec). The brittleness below 1700C is due to a lack of slip systems and grain boundary sliding. At 1700C grain boundary migration produces corrugations in the interface which interfere with sliding. About 1700C the matrix becomes sufficiently plastic through multiple slip and polygonization to accommodate any distortion. Polycrystalline specimens then neck down for completely ductile fracture. Hot pressed magnesia starts to go through a transition at 2200C, i.c., 500C higher. The increase is attributed to the presence of pores and impurity. Porosity is considered to promote grain boundary sliding by (a) providing the source for intergranular sliding, (b) decreasing the interfacial contact area, (c) preventing grain boundary migration and corrugation. These observations confirm that high temperature deformation occurs by dislocation glide and climb and grain boundary sliding and migration. (Author)

Descriptors :   (*CERAMIC MATERIALS, DEFORMATION), (*MAGNESIUM COMPOUNDS, OXIDES), (*DEFORMATION, MAGNESIUM COMPOUNDS), (*FRACTURE(MECHANICS), MAGNESIUM COMPOUNDS), CRYSTAL DEFECTS, GRAIN BOUNDARIES, CRYSTALS, POROSITY, RECRYSTALLIZATION, TRANSITION TEMPERATURE, BRITTLENESS, DUCTILITY, HIGH TEMPERATURE, TENSILE PROPERTIES, HOT WORKING

Distribution Statement : APPROVED FOR PUBLIC RELEASE