Accession Number:

ADA275461

Title:

Superplasticity in Fine-Grained Ceramics

Descriptive Note:

Final rept. 1 Jul-31 Dec 1993

Corporate Author:

LAWRENCE LIVERMORE NATIONAL LAB CA

Personal Author(s):

Report Date:

1994-01-31

Pagination or Media Count:

44.0

Abstract:

1. The superplastic deformation behavior of fine-grained, 20aluminayttria-stabilized tetragonal zirconia 20A1203NTZP under conditions of biaxial gas-pressure deformation is described. Sheet specimens were deformed into hemispherical caps at temperatures ranging from 1450 deg C - 1600 deg C and at imposed gas pressures of 345 and 690 KPa. For the conditions examined, hemispherical caps were formed at times ranging from 1 000 s to 2.1 X 104 s. The correlation between data obtained in uniaxial tensile testing and the behavior observed during the biaxial deformation experiments is discussed. 2. The high- temperature deformation behavior of a SiC whisker-reinforced, yttria-stabilized, tetragonal zirconia polycrystalline composite containing 20 vol. SiC whiskers SiCY-TZP has also been investigated. Tensile tests were performed in vacuum at temperatures from 14500C to 16500C and at strain rates from 10-3 to 1 05 s-1. The material exhibits useful high temperature engineering properties e.g., approx. 100 MPa and 16 elongation at T 1550 deg C and at a strain rate of -10- 4 s-1. The stress exponent was determined to be n2. Scanning electron microscopy was used to characterize the grain size and morphology of the composites, both before and after deformation. Both dynamic and static grain growth were observed during deformation. The morphology of ceramic reinforcements appears to affect strongly the plastic deformation properties of Y-TZP. A comparison is made between the properties of monolithic Y-TZP, 20 wt. A1203 particulatereinforced Y-TZP A1203Y-TZP, and SiCN-TZP composites. 3. Superplasticity deformation processing of ceramics has also been performed.

Subject Categories:

  • Ceramics, Refractories and Glass
  • Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE