High temperatures liquid metal-ceramic systems and joining processes

REFERENTS:
MARIA LUIGIA MUOLO
FABRIZIO VALENZA

UNITS:
GENOA

Studies of the physico-chemical properties of the solid-liquid interfaces at high temperatures, in particular wetting and reactivity, and of the related mechanisms.
These studies are used in the:

Design of brazing alloys and processes for the production of metal-ceramic and ceramic-ceramic joints.
Identification of non-reactive ceramics in contact with liquid metals with particular reference to investment casting processes.
Manufacture of metal-ceramic composite materials.

All these research lines are based on:
Experimental studies and physico-chemical interpretation of the interfacial reactivity in solid-liquid systems using the sessile drop method at high temperatures.
Design and construction of equipments and tensiometric techniques for the measurement of interfacial tension and wettability.
Use of phase diagrams, computed by the CALPHAD method, for the optimization of brazing processes (in cooperation with DCCI, Unige).
Modelling, at the molecular level (DFT), of metal-ceramic interfaces (in collaboration with EMPA-Zurich).
Design, development and execution of interface properties measurements in immiscible metallic systems in microgravity.

HfB₂-HfB₂ joint, brazing alloy: Ni-B 50at%.
NiB-ZrB₂ system: microstructure of cross-sectioned samples after wetting tests and their relation with the B-Ni-Zr phase diagram computed by CALPHAD.
Wetting test of liquid Ni-Ta ALLOY ON SiC: wetting kinetics and sample after test.
Ti6Al4V-ZrB₂ joint, brazing alloy: Ag-Ti

Altogether these activities lead to the following applications and possible developments:

Design of brazed metal-ceramic and/or ceramic-ceramic joints for use in thermally and/or mechanically highly stressed parts. Examples of joints:
- Ultra High-Temperature borides (e.g. ZrB₂, HfB₂) to themselves or to Ti alloys (e.g. thermal shields in aerospace);
- SiC and SiC composites to TiAlV (e.g. in aerospace, nuclear industry);
- Refractory oxides-steel (e.g. heat shields in combustion chamber);
- YAG-TiAlV (e.g. ceramic transparent windows for sensors).
Production of innovative metal matrix composites (High Entropy Alloys) and advanced ceramic fibers (long bundles).
Brazing repair of gas turbine blades.
Optimization of ceramic materials used as castable refractories.

Wetting test - Ag on sapphire

Wetting test

YAG/AgCu/Ti6Al4V joint

Brazed optical window YAG/Ti6Al4V - prototypes

KEYWORDS:

physico-chemistry of surfaces surface energy wetting reactivity brazing composites UHTC aerospace

RECENT PUBLICATIONS:
- Gambaro S., Muolo M.L.,Valenza F., Cacciamani G.,Esposito L., Passerone A.
  Wettability of transparent YAG (Y3Al5O12) by molten Ag-Cu-Ti alloys
  Journal of the European Ceramic Society 35, (2015), pp. 2895-2906
- Artini C., Muolo M.L., Passerone A., Valenza F., Manfrinetti P., Cacciamani G.
  Experimental investigations and thermodynamic modeling in the ZrB2-Ni section of the B-Ni-Zr system
  Journal of alloys and compounds, Vol. 592C, (2014), pp. 115-120
- Valenza F., Artini C., Passerone A., Muolo M.L.
  Joining of ZrB2 ceramics to Ti6Al4V by Ni-based interlayers
  Journal of Materials Science, Vol. 47, Issue 24, (2012), pp.8439-8449
- Valenza F., Muolo M.L., Passerone A., Glaeser A.M.
  Wetting and Interfacial Phenomena in relation to Joining of Alumina via Co/Nb/Co Interlayers
  Journal of European Ceramic Society, Vol. 33, (2013), pp. 539-547
- Passerone A., Valenza F., Muolo M.L.
  A review of transition metals diborides: from wettability studies to joining
  Journal of Materials Science, Vol. 47, Issue 24, (2012), pp. 8275-8289
- Liu G. W., Muolo M. L., Valenza F., Passerone A.
  Survey on wetting of SiC by molten metals
  Ceramics International, Vol. 36 (4), (2010) pp. 1177–1188, 2010.

PROJECTS:
- FIRB "MITGEA- "Study of new materials for gas turbines of very high efficiency and reduced environmental impact", 2008-2011
- CARIPLO "Advanced joints between metals and UHT ceramic materials for high temperature applications. JOINHT", 2011-2012
- RITMARE "Advanced aerospace materials for applications in marine conditions", 2012-2016
- FP7-2013-NMP-ICT-FOF (RTD) G.A.609188 "ADMACOM-Advanced manufacturing routes for metal/composite components for Aerospace", 2013-2016.