Advanced Metallurgy-Ni Based Alloys at EPFL - EPF Lausanne | Flashcards & Summaries

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TESTE DEIN WISSEN
Advantages of Ni alloys for high T applications
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TESTE DEIN WISSEN
- fcc lattice with low diff coeff up to melting point
- can be alloyed with Al and Cr --> protective layer
- no toger metallic based element can be strengthened by alloying for high T applications
- Young modulus similar to Fe and Co
Lösung ausblenden
TESTE DEIN WISSEN
Ni for high T applications, disadvantages
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TESTE DEIN WISSEN
- Lower melting point
Operate at high homologous T which lead to diffusion controlled processes
- high CTE and low thermal conductivity 
Lösung ausblenden
TESTE DEIN WISSEN
Strengthening mechanisms in Ni alloys
Lösung anzeigen
TESTE DEIN WISSEN
-solid solution strengthening 
-particle strengthening

Lösung ausblenden
TESTE DEIN WISSEN
Effect of alloying elements 
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TESTE DEIN WISSEN
- depends on the size of the substitutional atom and solubility in Ni
- weak : Fe, Co, Cr
- mild : V, Ti
- Strong : W, Mo, Al, Ta, Nb
Lösung ausblenden
TESTE DEIN WISSEN
The y' - Ni3Al phase, strengthening
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TESTE DEIN WISSEN
Because of the ordered nature of Ni3Al, cutting by one single dislocation will create an anti-phase boundary. A second dislocation is needed to remove the anti-phase boudary. 
--> Anti-phase boundary represents a barrier which must be overcome if particle cutting occurs
Lösung ausblenden
TESTE DEIN WISSEN
Why are TCP phases undesired ?
Lösung anzeigen
TESTE DEIN WISSEN
- incoherent interfaces for rapid diffusion leading to accelerated coarsening
- Absorb Cr, Mo and W --> effect on solution strengthening 
Lösung ausblenden
TESTE DEIN WISSEN
Why are η-phases: Ni3Ti (hcp) undesired ?
Lösung anzeigen
TESTE DEIN WISSEN
- precipitates as platelets on the (111) planes of γ matrix
- Platelets shape indicates that growth is much easier in direction of high interface energy 
Lösung ausblenden
TESTE DEIN WISSEN
Why are δ-phase : Ni3Nb undesired ?
Lösung anzeigen
TESTE DEIN WISSEN
- it is the incoherent coarsened ecolution of the very small sizes coherent γ'' Ni3Nb 
- Ecolution is very similar to θ'',θ' and θ in Al-Cu alloys
Lösung ausblenden
TESTE DEIN WISSEN
What are the undesired IM phases ? (3)
Lösung anzeigen
TESTE DEIN WISSEN
- TCP phases (σ, μ, Χ, laves)
-η-phase: Ni3Ti (hcp) (semi coherent)
- δ-phase : Ni3Nb (incoherent orthorhombic)
Lösung ausblenden
TESTE DEIN WISSEN
Effects of 4d and 5d transition metals
Lösung anzeigen
TESTE DEIN WISSEN
-effect on the self-diffusion coefficient 
- will present a obstacle to γ' coarsenig, they partition to the γ matrix
Lösung ausblenden
TESTE DEIN WISSEN
What is the influence of STE in Ni alloys ?
Lösung anzeigen
TESTE DEIN WISSEN
- creep rate decrease with decreasing SFE 
- Re, Mo, Ru, Cr have the strongest effect on SFE but they promote formation of TCP pahses
- addition of Co 
Lösung ausblenden
TESTE DEIN WISSEN
What is the orientation of single crystalline Ni parts ?
Lösung anzeigen
TESTE DEIN WISSEN
<111>
Lösung ausblenden
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Q:
Advantages of Ni alloys for high T applications
A:
- fcc lattice with low diff coeff up to melting point
- can be alloyed with Al and Cr --> protective layer
- no toger metallic based element can be strengthened by alloying for high T applications
- Young modulus similar to Fe and Co
Q:
Ni for high T applications, disadvantages
A:
- Lower melting point
Operate at high homologous T which lead to diffusion controlled processes
- high CTE and low thermal conductivity 
Q:
Strengthening mechanisms in Ni alloys
A:
-solid solution strengthening 
-particle strengthening

Q:
Effect of alloying elements 
A:
- depends on the size of the substitutional atom and solubility in Ni
- weak : Fe, Co, Cr
- mild : V, Ti
- Strong : W, Mo, Al, Ta, Nb
Q:
The y' - Ni3Al phase, strengthening
A:
Because of the ordered nature of Ni3Al, cutting by one single dislocation will create an anti-phase boundary. A second dislocation is needed to remove the anti-phase boudary. 
--> Anti-phase boundary represents a barrier which must be overcome if particle cutting occurs
Mehr Karteikarten anzeigen
Q:
Why are TCP phases undesired ?
A:
- incoherent interfaces for rapid diffusion leading to accelerated coarsening
- Absorb Cr, Mo and W --> effect on solution strengthening 
Q:
Why are η-phases: Ni3Ti (hcp) undesired ?
A:
- precipitates as platelets on the (111) planes of γ matrix
- Platelets shape indicates that growth is much easier in direction of high interface energy 
Q:
Why are δ-phase : Ni3Nb undesired ?
A:
- it is the incoherent coarsened ecolution of the very small sizes coherent γ'' Ni3Nb 
- Ecolution is very similar to θ'',θ' and θ in Al-Cu alloys
Q:
What are the undesired IM phases ? (3)
A:
- TCP phases (σ, μ, Χ, laves)
-η-phase: Ni3Ti (hcp) (semi coherent)
- δ-phase : Ni3Nb (incoherent orthorhombic)
Q:
Effects of 4d and 5d transition metals
A:
-effect on the self-diffusion coefficient 
- will present a obstacle to γ' coarsenig, they partition to the γ matrix
Q:
What is the influence of STE in Ni alloys ?
A:
- creep rate decrease with decreasing SFE 
- Re, Mo, Ru, Cr have the strongest effect on SFE but they promote formation of TCP pahses
- addition of Co 
Q:
What is the orientation of single crystalline Ni parts ?
A:
<111>
Advanced Metallurgy-Ni based alloys

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