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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
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