Accession Number : ADA320605

Title :   Transformation Weakening of Ceramic Composite Interfaces.

Descriptive Note : Final rept. 1 Apr 93-30 Mar 96,

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

Personal Author(s) : Kriven, Waltraud M.

PDF Url : ADA320605

Report Date : 06 DEC 1996

Pagination or Media Count : 71

Abstract : Phase stability and transformations in some chosen ceramics was investigated and several new transformations in oxide systems were identified. To quantitatively understand the coupling of mechanical shear stress to nucleation, a constrictive double shear test was devised. It indicated that a minimum debonding shear strength of 95 MPa was needed to overcome the nucleation barrier for the proto (orthorhombic) to clino (monoclinic) transformation in enstatite (MgO.SiO2) and to give rise to 'transformational plasticity' in the polycrystalline ceramic. For comparison with transformation weakening, monazite (LaPO4) and zenotime (YPO4) fiber coatings were studied. Fiber pushout measurements indicated debonding shear strengths of 110-120 MPa were required for LaPO4 coatings, versus 95 MPa for YPO4, depending on coating thickness. A four layer, strong and damage tolerant oxide laminate was devised, based on YPO4, yttria stabilized zirconia (3 mol% Y2O3-ZrO2) and alumina (Al2O3), and having four point bend strengths of 392 MPa and work of fracture of approx. 10 KJ/sq m. Amorphous mullite (3Al2O.SiO2) and YAG (Y3Al5O12) fibers of tensile strengths 6.0 and 2.4 GPa respectively, were collaboratively fabricated and evaluated. Transformation weakening was demonstrated as a viable mechanism for interphase debonding in oxide systems. YPO4 demonstrated chemical compatibility in air with YAG (Y3Al5O12) and mullite (3Al2O3.SiO2) up to temperatures of 1600 deg C and 1500 deg C, respectively.

Descriptors :   *INTERFACES, *PHASE TRANSFORMATIONS, *COMPOSITE MATERIALS, *CERAMIC MATERIALS, *OXIDES, *TRANSFORMATIONS, YTTRIUM ALUMINUM GARNET, THICKNESS, FIBERS, MECHANICAL PROPERTIES, STABILITY, DAMAGE, CHEMICALS, LAYERS, LAMINATES, COMPATIBILITY, NUCLEATION, BENDING, STRENGTH(MECHANICS), FRACTURE(MECHANICS), PHASE, COATINGS, ALUMINUM OXIDES, SHEAR STRESSES, BARRIERS, TOLERANCE, YTTRIUM OXIDES, ZIRCONIUM OXIDES, SHEAR TESTS.

Subject Categories : Ceramics, Refractories and Glass
      Inorganic Chemistry
      Physical Chemistry
      Crystallography
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE