Abstract
The combination of the materials alumina and titanium was
selected for the purpose of studying the effect of the
metal-ceramic interface structure on the mechanical
properties of the joints. The behaviour and structure of
Al2O3 - Ti interfaces are important both for direct
diffusion bonding and reactive brazing. The good
reactivity of titanium with oxide ceramics is well known
and there are several industrial applications in which
this material couple can be readily used.
The results show that various types of interfaces can be
produced in Al2O3 to metal systems where the activity of
Ti is nearly one. In a liquid state, using a Ag-Ti alloy
or Ti-Ag-Ti multilayers, the phase next to the alumina is
a-Ti(O). In the solid state, alumina is in contact with
TiAlx intermetallics, either TiAl in infinite and finite
couples or Ti3Al in equilibrated couples. The addition of
Nb to Ti, 10 and 20 at. % leads to the formation of
TiAlx(Nb) at the alumina interface. The kinetics of the
reaction layer growth and furthermore the structural
changes in the interface can be calculated by the
experimentally derived equations for the infinite and
finite diffusion couples.
The shear mode testing which was selected has proved to
be applicable for optimizing the bonding process and
material selection. The fracture mechanics testing was
introduced to measure the effect of the interface
structure on the properties of the joints. The interface
fracture energies for diffusion-bonded Al2O3 - Ti joints
were calculated on the basis of Griffith's energy
balance. From the various energy terms determined, values
for both interface types, TiAl-alumina and Ti3Al-alumina,
could be determined. The interface fracture energy of
brazed joints is found to be almost a half less than the
one for finite diffusion-bonded joints.
The measured energy, as calculated directly from Kc,
depends on the metal foil thickness and the bonding time.
Taking various energy terms into account, the interface
fracture energy is obtained. This is, unlike the measured
energy in the testing, a constant that is independent of
the metal/brazing foil thickness or the structural
kinetic parameter dx:de.
| Original language | English |
|---|---|
| Qualification | Doctor Degree |
| Awarding Institution |
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| Supervisors/Advisors |
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| Award date | 12 May 1995 |
| Place of Publication | Espoo |
| Publisher | |
| Print ISBNs | 951-38-4656-3 |
| Publication status | Published - 1995 |
| MoE publication type | G4 Doctoral dissertation (monograph) |
Keywords
- metals
- ceramics
- titanium
- aluminium oxide
- joints
- fracture properties
- interfaces
- structure
- mechanical tests
- tensile properties
- shear tests
- bend tests
- adhesion
- mechanical properties