O61-PHASE EQUILIBRIA AND DIFFUSION COUPLEStofa2010/Apresentacoes_TOFA201… · · 2010-11-03PHASE EQUILIBRIA AND DIFFUSION COUPLES ... 1 University of Vienna, Department of Inorganic

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. [email protected]@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


• 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


Isothermal sections / Results

Co-rich: Phase field determined by DTA

(AlCo) – ββββ: continuous transition?


• 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


Diffusion couples / Results

Si / AlCo - 900 °C


no continuous transition from (AlCo) to β


Si / AlCo - 900 °C

Diffusion Path



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



Diffusion Path

Al / CoSi 2 – 500 °C


DTA-measurements and vertical sections

90 Samples


• 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


Vertical sections / Results

Isopleth 26 at.% Co


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


Liquidus surface projection


Liquidus surface projection


• 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


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


F. Kiraly for support in EPMA-measurements

Vertical sections / Results

Isopleth 5 at.% Co

Onset: 574.1

E 574: L=Al+Al9Co2+Si

Al 60Co5Si35


Documents

O61-PHASE EQUILIBRIA AND DIFFUSION COUPLEStofa2010/Apresentacoes_TOFA201… · · 2010-11-03PHASE EQUILIBRIA AND DIFFUSION COUPLES ... 1 University of Vienna, Department of Inorganic