Accession Number : ADA305720

Title :   Microstructure and Reliability of Ceramics.

Descriptive Note : Final technical rept. 1 Nov 91-31 Mar 95,

Corporate Author : CARNEGIE-MELLON UNIV PITTSBURGH PA

Personal Author(s) : Readey, Michael J.

PDF Url : ADA305720

Report Date : JAN 1996

Pagination or Media Count : 191

Abstract : The aim of this program was to investigate the role of microstructure on the reliability of ceramics, in particular those ceramics having pronounced R-curve behavior and thus the property of flaw tolerance, where the failure stress is minimally affected by processing defects or by damage accumulated in service. Hence, flaw-tolerant ceramics should show decreased strength variability and thus exhibit higher structural reliability. The program examined the effect of increasing R-curve behavior on the strength variability of ceramics toughened by phase transformation or grain bridging. The principal result of this work is that high reliability will only result in materials having both a strongly rising R-curve and a narrow intrinsic flaw population. The strong R-curve allows for stable crack extension under in-service conditions, and the narrow flaw population ensures that strength variability will be minimized in as-processed materials. These criteria are readily satisfied in zirconia ceramics by careful control of processing contaminants and heat-treatment schedules. In monolithic ceramics such as alumina, achieving a rapidly rising R-curve is more complex, involving tailoring the grain shape and grain boundary toughness through the use of additives. jg p1

Descriptors :   *MICROSTRUCTURE, *CERAMIC MATERIALS, *RELIABILITY, STRESSES, STABILITY, PHASE TRANSFORMATIONS, STRUCTURAL PROPERTIES, PROCESSING, CRACKS, TOUGHNESS, HEAT TREATMENT, DEFECTS(MATERIALS), ALUMINUM OXIDES, STRENGTH(GENERAL), TOLERANCE, CONTAMINANTS, ADDITIVES, MONOLITHIC STRUCTURES(ELECTRONICS), FAILURE(MECHANICS), GRAIN BOUNDARIES, HIGH RELIABILITY, ZIRCONIUM OXIDES.

Subject Categories : Ceramics, Refractories and Glass
      Inorganic Chemistry
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE