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PHASE EQUILIBRIA AND DIFFUSION COUPLES
IN THE Al-Co -Si SYSTEM
Beatrix Huber 1, Alexander Kodentsov 2 and Klaus W. Richter 1
1 University of Vienna, Department of Inorganic Chemistry / Materials Chemistry, Austria. bea.huber@univie.ac.atbea.huber@univie.ac.at
2 Department of Chemical Engineering and Chemistry, Materials and Interface Chemistry, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
TOFA 2010 / September 12th - 16th 2010 / Porto / Portugal
• Literature
• Isothermal sections at 1050 and 1200 °C
• Diffusion couples
• DTA measurements and vertical sections
Overview
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
• DTA measurements and vertical sections
• Reaction scheme and liquidus surface projection
Literature Richter and Tordesillas Gutièrrez, 2005
α, Co3Al3-xSi4+x: cI40, Im-3m, Ge7Ir3-type
β, Co2±xAl1+xSi2-x: hP5, P-3m1, Al3Ni2-type
γ, Co10+xAl43+ySi12-y: mC296+, C2/c
δ, Co32.5Al40.5-43Si22-24.5: mC*
ε, Co6Al11Si6: oC184, Cmc21
χ, Co4Al7+xSi2-x: mC26,C2/m
φ, Co10+xAl25-xSi7: oP168, Pmna
(AlCo): cP2, Pm-3m, CsCl-type
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
• Preparation of the alloys in the arc furnace
• 1050 °C: annealing in alumina crucibles in evacuate d quartz
glass tubes for 2 weeks
• 1200 °C: Sealed into Ta-crucible, annealing in the high
temperature furnace for 7 days
Isothermal sections / Sample preparation
temperature furnace for 7 days
• Preparation for further investigation (pulverizing and embedding)
• Optical microscopy (Polarisation Microscope)
• XRD, x-ray powder diffraction (CuKα-radiation, SolX-detector)
• EPMA, electron probe microanalysis
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
Isothermal sections / Results
Co-rich: Phase field determined by DTA
(AlCo) – ββββ: continuous transition?
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
• Due to the differences in chemical potential equilibrium is reached
Diffusion Couples / Sample preparation
• Solid – Solid:
cutreaction zone
• Due to the differences in chemical potential equilibrium is reached via diffusion
• Si / AlCo: 900 °C – 200 h – under vacuum
• AlCo / Co2Si: 1050 °C – 100 h – under vacuum
The Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
• Different layer are formed in the reaction zone
• Al / CoSi 2
Diffusion Couples / Sample preparation
20 min 680 °C �Al melts �
connection to CoSi
• quenched in cold water
• 550 °C – 5 weeks – under vacuum
connection to CoSi2
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
Diffusion couples / Results
Si / AlCo - 900 °C
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
no continuous transition from (AlCo) to β
Diffusion couples / Results
Si / AlCo - 900 °C
Diffusion Path
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
Diffusion couples / Results
Al / CoSi 2 – 550 °C
• contact formation was done at a liquid-solid interface• vague to talk about local equilibria in the diffusion zone• interpretation of the diffusion path is tentative
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
Diffusion couples / Results
Diffusion Path
Al / CoSi 2 – 500 °C
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
DTA-measurements and vertical sections
90 Samples
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
• DTA measurements: Netzsch 404 S, maximum T=1500 °C
• Al2O3 – crucibles
• Heating rate: 5 K min-1
• Ar - atmosphere
DTA-measurements and vertical sections
DTA Netzsch 404 S Al 2O3 – sample holder
• 14 vertical sections• Reaction scheme (Scheil Diagram)• Liquidus surface projection
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
Vertical sections / Results
Isopleth 26 at.% Co
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
Reaction scheme – Scheil diagram
Derived reactions based on DTA -measurements
1 eutectic reaction
19 transition reactions
7 peritectic decompositions of α, γ, δ, ε, χ, φ and Co3Si7 peritectic decompositions of α, γ, δ, ε, χ, φ and Co3Si
congruent melting point of β 1400 °C<T>1500°C
2 maxima
Complete liquidus surface projection
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
Liquidus surface projection
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
Liquidus surface projection
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
• Isothermal sections in the Co-rich part
• Diffusion couples in good agreement with isothermal sections
• DTA-measurements:
Conclusion
• DTA-measurements:Isopleths over the whole composition range
• Reaction scheme for the entire ternary system
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
Acknowledgements
FWF for financial support (project number: 19305)
D. Tordesillas Gutièrrez for DTA-measurements
F. Kiraly for support in EPMA-measurements
Colleagues from the Department of Inorganic Chemistry / Materials Chemistry
TOFA 2010 / September 12th - 16th / Porto / PortugalThe Al-Co-Si System, B. Huber , A. Kodentsov, K.W. Richter
F. Kiraly for support in EPMA-measurements
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