Phase Equilibria in the Nb -Si-B SystemPhase Equilibria in the Nb -Si-B System

Carlos Angelo Nunes(1), Dário Moreira Pinto Júnior( 1), Gilberto Carvalho Coelho(1,2), Paulo Atsushi Suzuki(1), Antonio Augusto Araújo Pin to da Silva(1), Rafael Bogado Tomasiello(1)

1 Universidade de São Paulo (USP), Escola de Engenh aria de Lorena (EEL), Polo Urbo-Industrial Gleba AI -6, Caixa postal 116, 12602-810, Lorena, SP, Brazil

2 UniFoa – Centro Universitário de Volta Redonda, Nú cleo de Pesquisa, Campus Três Poços, Avenida Paulo Erlei Alves Abrantes, 1325 – Bairro três Poços, 27240-560, Volta Redonda, Rio de Janeiro, Brazil.

Introduction

Objectives of the Nb-Si-B Project

Outline

Literature

Experimental Procedure

Results and Discussion

Summary

� Need to develop materials to work under aggressive conditions

(oxidant atmosphere; dynamic loading) at T > 1200 oC;

� Ni-base superalloys limitationl: T service ≅≅≅≅ 0.85 x Tmelting. ≅≅≅≅ 1150oC;

Introduction

� High melting point material;� Microstructure: intermetallic phase(s) containing e lements for good oxidation resistance in thermodynamic equilibrium w ith a ductile metallic phase (solid solution) => Me-Si-B systems;� Possible solution should involve a multicomponent M e-Si-B system => need for phase stability information.

Introduction

� Two-phase field Moss+Mo5SiB2 (T2)

(T2 - Cr5B3 prototype)

Mo-Si-B Isothermal Section at 1600ºC.H. Nowotny et al., Monatsh. Chem. 88 (1957) 180-192.

Objectives of the Nb-Si-B Project

Reevaluation of the Nb-B system;

Determination of Liquidus projection (Nb-rich regio n);

Determination of the isothermal section at 1700 oC (Nb-

NbSi 2-NbB2) region;

Thermodynamic modeling of the Nb-Si-B system.

Literature

Nb-B SystemNb-B System

Nb-B Phase Diagram [1990Mas]. Nb-B Phase Diagram [1969Rud].

?

Nb-Si SystemNb-Si System

1765oC [1980Koc]

Literature

T1

Nb-Si Phase Diagram [1993Sch].

1670oC [1991Men]

T2

B-Si SystemB-Si System

Literature

B-Si Phase Diagram [1990Mas]

Nb

B

Si

Literature

Nb-Si-B SystemNb-Si-B System

a

a

(b)

a

c

(c)

(a)

Isothermal Section of the Nb-Si-B system at1600oC [1960Now]

Nb5SiB2 crystal structure

Nb-Si-B SystemNb-Si-B System

Literature

Sub-Solidus projection of the Nb-Si-B system in the Nb-Nb5Si3-NbB region

(1) single-phase; (2) two-phase; (3) three-phases.

Literature

Nb-Si-B SystemNb-Si-B System

Vertical section connecting Nb 99Si1 to Nb 5Si2B

Experimental Procedure

Alloys processing:

Arc Melting

Alloys processing:

Arc MeltingArc MeltingHeat-treatment (1500 – 1800 oC)

* Some samples also processed via powder metallurgy

Arc MeltingHeat-treatment (1500 – 1800 oC)

* Some samples also processed via powder metallurgy

Experimental Procedure

Microstructural Characterization

XRD : powder, room temperature, filtered Cu-K αααα radiation; 40kV; 30 mA; (2 θθθθ) from 10 o to 90o; 0.05º angular step; 2 s/point;

Microstructural Characterization

XRD : powder, room temperature, filtered Cu-K αααα radiation; 40kV; 30 mA; (2 θθθθ) from 10 o to 90o; 0.05º angular step; 2 s/point;from 10 o to 90o; 0.05º angular step; 2 s/point;

SEM: Back-scaterred electrons image.

Microanalysis via WDS – PET (Nb), TAP (Si), LSM200 ( B)

from 10 o to 90o; 0.05º angular step; 2 s/point;

SEM: Back-scaterred electrons image.

Microanalysis via WDS – PET (Nb), TAP (Si), LSM200 ( B)

Results : Nb-B System

OK!

b

a

Nb5B6 + NbB

Results : Nb-B System

L+Nb3B4����Nb5B6

L����NbB+Nb 5B6

L+Nb3B4����Nb5B6

L����NbB+Nb 5B6

SEM/BSE micrographs of as-cast Nb-B alloys:(a) 48Nb-52B; (b) 45,45Nb-54,55B

b

Nb3B4

NbB + Nb 5B6

L����NbB+Nb 5B6L����NbB+Nb 5B6

Results : Nb-B System

Lattice parameters of NbB 2-phase as a function of Bcontents

12%

Results : Nb-B System

Tridimensional view of the NbB 2 crystalstructure

5%

Results : Nb-B System

Results : Nb-B System

Nbss

Nbss primary

Results: Liquidus Projection

T2

SEM/BSE micrograph of as-cast84Nb-8Si-8B alloy

Nbss + T2

NbB

T

NbB primary

Results: Liquidus Projection

T2

SEM/BSE micrograph of as-cast70Nb-10Si-20B alloy

Nbss + T2

T2

T2 primary

Results: Liquidus Projection

SEM/BSE micrograph of as-cast70Nb-20Si-10B alloy

Nbss + T2

D88

D88 primary

Results: Liquidus Projection

T2

SEM/BSE micrograph of as-cast62Nb-25Si-13B alloy

Nbss + T2

T2

Results: Experimental Isothermal sections

30

60

65

Nb B3 2

NbB

Nb B43

Nb B5 6

NbB2

.

23..

..25

80

81

.

NbNb

SEM/BSE micrograph of alloy # 34(75Nb-21Si-4B) after HT at 1700 oCfor 16 h.

0

10

20

0 10 20 30 5040 60Nb Si3NbSi2T2

Nb

.12

.14

15 16. .39

.

.

.

82

8329

. ...

.

.

..

. 3032

33

3435

38

.69

76

77T2

.51

17..

T1

D8 + T + T8 2 1

Nb

NbIsothermal Section of the Nb-Si-B at 1700 oCfrom this investigation

T

Nbss

Results: Experimental Isothermal sections

30

60

65

Nb B3 2

NbB

Nb B43

Nb B5 6

NbB2

.

23..

..25

80

81

.

NbNb

SEM/BSE micrograph of alloy #33(80Nb-19Si-1B) after HT at 1700 oCfor 64 h.

T2

0

10

20

0 10 20 30 5040 60Nb Si3NbSi2T2

Nb

.12

.14

15 16. .39

.

.

.

82

8329

. ...

.

.

..

. 3032

33

3435

38

.69

76

77T2

.51

17..

T1

D8 + T + T8 2 1

Nb

Nb

Isothermal Section of the Nb-Si-B at 1700 oCfrom this investigation

30

60

65

Nb B3 2

NbB

Nb B3 4

Nb B5 6

NbB2

23..

..25

80

NbNb

Results: Experimental Isothermal sections

60

65

NbB

Nb B43

Nb B5 6

NbB2

NbNb

T = 1500oCT = 1500oC

T = 1600; 1700; 1800oCT = 1600; 1700; 1800oC

0

10

20

30

0 10 20 30 5040 60 70Nb Si3NbSi2T2

Nb

.12

.14

15 16. .39

.

.

.

81

82

8329

. ...

.

.

..

. 3032

33

3435

38

.69

76

77T2

.51

17..

T1

D8 +T +T8 2 1

Nb

NbNb0

10

20

30

0 10 20 30 5040 60

Nb B3 2

Nb Si3NbSi2T2

Nb

.12

.14

15 16. .39

23..

.

.

..25

80

81

82

8329

. ...

.

.

..

. 3032

33

3435

38

.69

76

77T2

.51

17..

T1

D8 + T + T8 2 1

Nb

Nb

Results: Experimental Isothermal sections

60

65

Nb B3 2

NbB

Nb B43

Nb B5 6

NbB2

23..

..25

80

NbNbT = 1600; 1700; 1800oCT = 1600; 1700; 1800oC

0

10

20

30

0 10 20 30 5040 60Nb Si3NbSi2T2

Nb

.12

.14

15 16. .39

.

.

.

81

82

8329

. ...

.

.

..

. 3032

33

3435

38

.69

76

77T2

.51

17..

T1

D8 + T + T8 2 1

Nb

Nb

Results: Calculated Liquidus Projection

L���� D88+Nb3B4+NbSi2L���� D88+Nb3B4+NbSi2

L���� D88+NbB2+NbSi2L���� D88+NbB2+NbSi2

Results: Calculated Isothermal Section at 1600oC

Calculated Isothermal section at 1600oC

Isothermal Section of the Nb-Si-Bsystem at 1600 oC [1960Now]

Summary

Experimental Part

- Nb-B System: Confirmed results from Rudy et al. + insertion of the Nb 5B6-phase

forming from the liquid;

- Liquidus Projection for the Nb-rich region was det ermined: Observation of primary

solidification regions of T 2 and D88 phases in addition to those expected from 2 8

the binary systems;

- Isothermal sections: Confirmed the general phase e quilibria reported by Nowotny

et al. (isothermal sections at 1600 oC) and Katrych et al.; additional work needed

for the Nb 3B4-NbB2-NbSi2-D88 region based on the experiments carried out at

1500, 1700 and 1800oC.

Thermodynamic Modelling Part

- Good description for the Nb-B; Nb-Si and Nb-Si-B s ystem; additional work needed

to correct the Nb 3B4-NbB2-NbSi2-D88 region.

Acknowledgements

THANK YOU FOR YOUR ATTENTION!!THANK YOU FOR YOUR ATTENTION!!