Dobedoe, Richard Simon (1997) Glass-ceramics for ceramic/ceramic and ceramic/metal joining applications. PhD thesis, University of Warwick.

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Abstract

The use of sintered cordierite/enstatite glass-ceramics as interlayers for joining silicon
nitride to itself and to metals has been investigated. The role of the additives B203 and
P205, which control the dynamics of sintering and crystallisation, has been studied
using SEM, XRD and non-isothermal DTA-based measurements of activation energy.
The measured activation energies for the crystallisation of μ-cordierite, for compositions
with no additives, with B203 only, and with P205 only, did not differ significantly and
were in the range 415-460 kJ mol-1. When both B203 and P205 were present this was
increased to 503-524 kJ mol-1. The activation energy for α-cordierite formation when
no additives were present was 952 ± 57 kJ mol-1. This was substantially reduced by the
presence of B203 (540 ± 27 kJ mol-1), P205 (668 ± 41 kJ mol-1) and when both were
present (352 ± 26 kJ mol-1).
Cordierite/enstatite glass-ceramics have been successfully used to join silicon nitride to
itself. Joining at 1050-1100'C in N2 with an applied load of ~ 2.5 MPa, resulted in
joint strengths, measured in 4-pt bending, of 110-170 MPa. This is comparable to the
intrinsic strength of the glass-ceramic and sufficient for practical applications. These
strengths were obtained using an interlayer with a TCE (5.7 MK-1) greater than that of
the silicon nitride (3.0 MK-1). Suggestions for further improvements to the joint
strength are discussed.
The use of a glass-ceramic joint with graded thermal expansion to bridge a TCE
mismatch is discussed, and the geometrical restrictions on the joint, which limit possible
practical applications, are outlined.
The concept of a ceramic/metal compression joint with a glass-ceramic interlayer has
been demonstrated for joining silicon nitride to both Nimonic alloy 80A and Ti. The
requirements for continuity of electronic structure at the Nimonic 80A/glass-ceramic and
the Ti/glass-ceramic interfaces are satisfied by reaction between the glass/glass-ceramic
and, the pre-oxidised surface of the Nimonic alloy to form a MgTi205-Al2TiO5 solid
solution phase, and the Ti to form Ti5Si3. For the lower WE mismatch (Ti-silicon
nitride) the residual joining stresses generated on cooling were marginally too high and
need to be further reduced, either by a slight alteration to the joint geometry and/or a
smaller WE mismatch.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Glass-ceramics, Cordierite, Enstatite, Silicon nitride, Sintering, Crystallization, Ceramic to metal bonding
Official Date:	September 1997
Dates:	Date Event September 1997 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Holland, Diane
Sponsors:	TWI Ltd ; Engineering and Physical Sciences Research Council (EPSRC)
Extent:	xiv, 246 leaves
Language:	eng

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