Accession Number : AD0475046

Title :   EFFECT OF PROCESSING ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF POLYCRYSTALLINE CERAMICS PREPARED BY HIGH PRESSURES.

Descriptive Note : Technical rept.,

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

Personal Author(s) : Vasilos, T.

Report Date : 24 NOV 1965

Pagination or Media Count : 28

Abstract : High pressure hot forming, involving ceramic dies, has been successfully used in preparing high density, fine grain size specimens of a variety of high purity polycrystalline oxides. Besides conventional hot pressing, press forging was also used to obtain unique deformed microstructures and/or preferred orientation. Pressures up to 40,000 psi and temperatures up to 1200 C were used in preparing dense compacts. Microstructure examination, employing chiefly electron microscopy methods revealed that a large number of the hot pressed oxides investigated; e.g., NiO, MgO, Al2O3, Cr2O3, Y2O3, had average grain sizes below 1 micron. Transmission electron microscopy of nickel oxide specimens revealed no evidence of any dislocation substructure in the as hot pressed condition. Transverse bend strength measurements were performed on the fabricated oxides, and the values observed were generally among the highest yet reported. Press forging was observed to have modestly increased the fracture strength of both nickel and yttrium oxides. The high temperature strength of dense chromium oxide was found to be comparable to that of high purity, high density alumina. Microhardness measurements were also performed on all the oxides in both as pressed and thermally annealed conditions. (Author)

Descriptors :   (*CRYSTALS, MICROSTRUCTURE), (*CERAMIC MATERIALS, PROCESSING), PREPARATION, MECHANICAL PROPERTIES, CRYSTALLIZATION, DENSITY, X RAY DIFFRACTION, HIGH PRESSURE, HIGH TEMPERATURE, ELECTRON MICROSCOPY, FRACTURE(MECHANICS), NICKEL COMPOUNDS, MAGNESIUM COMPOUNDS, ALUMINUM COMPOUNDS, CHROMIUM COMPOUNDS, YTTRIUM COMPOUNDS, OXIDES, HARDNESS, CRYSTAL STRUCTURE.

Subject Categories : Crystallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE