Chamberlain, A. (1994) Novel silicate matrix composites. PhD thesis, University of Warwick.

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Abstract

Within this study, a novel matrix selection principle, within the MAS glass ceramic system, has been developed with emphasis placed on the use of this matrix in a ceramic fibre reinforced composite. Matrix selection was applied in order to develop a diphasic microstructure to allow tailoring of the matrix thermal expansion coefficient via a phase mixture. The phases selected were a-cordierite and enstatite, with a Nicalon fibre reinforcement. Initial studies centred on the use of chopped fibre systems in order to develop a processing methodology giving the correct phase structure, microstructure and interface development between the matrix and the fibre. It was found that variations in process route including the use of window I and window II pressing regimes (below and above the maximum crystallisation rate) caused large differences in the matrix microstructure. During this part of the study the effects of added nucleants were investigated (P2O5 at 2wt%, and Ti02 at 10wt%), the results indicating that, with the use of glass frit, the added nucleant was not necessary. Initial studies upon composite fabrication indicated the criticality of pressure application during processing indicated by a fall in the elastic modulus of the composite from the rule of mixtures calculation.

A pre-preg methodology was developed to produce high quality green state composite, including a T-piece traverse head arrangement for the fibre tow infill, 'walls' on the winding cage and rollering the pre-preg sheets. Following this, a refined process route for hot pressing was developed with application of pressure during heating in a 'process-window' identified using DTA. Composites were fabricated using the NL-607 fibre type with optimised properties reaching a matrix microcracking stress of cmm = 665±75MPa, ultimate flexure strength of oUBS = 1168±41MPa and E = 157±12GPa (within the rule of mixtures calculation). TEM analysis indicated an interface width of 25-70nm. with carbon enrichment occurring. Measurement of the micromechanical properties of the interface used an indentation technique giving the interfacial debond energy 2T = 12.4±5.4Jnv2, and shear sliding resistance T = 48±15MPa. Tensile studies indicated that two regions could be identified associated with microcracking in the 90° and 0° plies by a modulus drop and acoustic emission.

Thermal aging in air (lOOhrs) indicated that channelled oxidation via fibre / matrix interfaces was occurring at intermediate temperatures (450° - 700°C) and partial silica bridging of the interface at higher temperatures in this interval. Micromechanical property measurements indicated that for 450°C aging 2T = 13.6±4.4Jnr2 with T = 108±54 MPa, whereas for 700°C aging 2T = 35.6±29.2Jnr2 with T = 248±120MPa. At higher temperatures (1000°C), rapid silica bridging of the interface caused plugging to occur and the retention of as-fabricated mechanical properties for the bulk material. Fibres in the bulk of the composite had micromechanical properties similar to as fabricated materials, whereas fibres ~ 30pm from the edge of the sample had very high micromechanical properties indicative of fully silica bridged interfaces. Above 1000°C microstructural degradation was observed with the formation of a surface layer on the composites (60-80pm at 1000°C, 80- 140pm at 1200°C).

Tensile creep studies indicated, for the conditions utilised within this work ( 1000°-1150°C and 50-90MPa), that fibre creep properties dominated, with the observed creep rate being - 1.6 x 10 8-s1. For all the creep studies conducted, nonsteady state creep was observed, with a continuously decreasing creep rate with time.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry T Technology > TA Engineering (General). Civil engineering (General)
Library of Congress Subject Headings (LCSH):	Silicates, Silicate fibers
Official Date:	1994
Dates:	Date Event 1994 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Lewis, M. H. (Mike H.)
Sponsors:	Science and Engineering Research Council (Great Britain) ; Rolls-Royce Ltd.
Extent:	xvi, 189 leaves : charts
Language:	eng

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