Accession Number : ADA267304


Title :   Transformation Toughening of Composite Ceramics


Descriptive Note : Final rept. 1 Mar 1989-30 Sep 1992


Corporate Author : ILLINOIS UNIV AT URBANA DEPT OF MATERIALS SCIENCE AND ENGINEERING


Personal Author(s) : Kriven, Waltraud M


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a267304.pdf


Report Date : 31 Dec 1992


Pagination or Media Count : 269


Abstract : A systematic investigation into some possible transformation tougheners alternative to zirconia (ZrO2) has been conducted. Three systems have been focussed upon: dicalcium silicate (Ca2S104), dysprosia (DY203) and nickel sulfide (NiS). Composites of Ca2SiO4 in calcium zirconate (CaZrO3) or magnesia (MgO) or fine grained, single phase pure, and Ba-doped Ca2S 04 were fabricated, microstructurally characterized and mechanically evaluated. Although surface grinding was able to stress-induce the transformation in Ca2SiO4, a crack tip propagating in the bulk was not. A comprehensive crystallographic study of the transformation mechanisms implied that compressive shear, rather than tensile stresses were required. The mechanism could not controllably be nucleated by a propagating crack. Spontaneous thermal transformation of Ca2Si04 was too powerful for a confining matrix and tended to cause dusting. The kinetics and mechanism of the transformation in single phase DY203 were studied and revealed that it only operated above 600 deg C. No transformation toughening in HIPPED siC-DY203 composites could be detected at room temperature. Microstructural studies of industrial NiS in glass composites found a correlation between transformed NiS and deleterious fracture.


Descriptors :   *MECHANICAL PROPERTIES , *TOUGHNESS , *CERAMIC MATERIALS , STRESSES , CALCIUM , PROCESSING , GLASS , NICKEL , KINETICS , FINES , DYSPROSIUM , TRANSFORMATIONS , CRYSTALLOGRAPHY , GRINDING , SULFIDES , ZIRCONATES , SILICATES , DOPING , CRACK PROPAGATION , PHASE , CRACKS , TENSILE STRESS , MICROSTRUCTURE , TEMPERATURE


Subject Categories : Ceramics, Refractories and Glass
      Laminates and Composite Materials


Distribution Statement : APPROVED FOR PUBLIC RELEASE