A Review of Challenges to Hastelloy – C Series Weld Overlay
163
Table 3 Summary of the general effect of various alloying elements on phase stability in Ni-base
alloys [8]
Sr No. Effect
Elements
1
Gamma—solid solution strengthening
Cobalt, chromium, iron, molybdenum,
tungsten, tantalum
2
Former of gamma prime
Aluminum (Ni 3 Al), titanium (Ni 3 Ti)
3
Solid solution strengthening of gamma
prime
Chromium, molybdenum, titanium,
silicon, niobium
4
Former of gamma double prime
Niobium (Ni 3 Nb)
5
Carbide formers
Tungsten, tantalum, titanium,
molybdenum, niobium are MC and M (C,
N) formers
Chromium is M 7 C 3 former
Chromium, molybdenum, and tungsten
are M 23 C 6 former
Molybdenum and tungsten are M 6 C
former
6
Topological closed-packed phase (σ, ρ, μ,
Laves)
Titanium, vanadium, zirconium, niobium,
tantalum, aluminum and silicon are TCP
phase former
7
Surface oxide former
Chromium (Cr 2 O 3 ), aluminum (Al 2 O 3 )
Table 4 Characteristics of phases in nickel alloys [22]
Phase
Characteristics
– Face-centered cubic structure
– Gamma is a nonmagnetic phase
– Generally, a high percentage of solid solution contains
– Matrix phase in nickel-based alloy
γ
– Phase provides good creep resistance and high-temperature strength
– Al and Ti precipitate face-centered cubic γ (Ni 3 Al, Ti); other elements enter
in gamma prime are Nb, Cr, and Ta
γ
– Body-centered tetragonal phase form Ni 3 Nb
– Ni and Nb combine in the presence of Fe
– γ is unsteady at a high temperature around 650 °C
γ —G.B.
– With heat treatments and service exposure a film of γ form along the G.B.
in the stronger alloys
Phase-Carbides – Metal carbides form with C (0.02–0.2 wt%) and reactive elements like Ti,
Ta, Hf, and Nb
Phase-Borides – B segregates at grain boundaries and forms low-density boride particles
Phase-TCP
– TCP phases mean σ,μ, and Laves kind of phases
– The formation depends on composition and circumstances
– The structure is a needle or a plate type
– Brittle phases
Note γ—Gamma, γ —Gamma prime, γ —Gamma double prime, γ —Grain boundary, TCP—
Topologically close-packed phases, G.B.—Grain boundary
163
Table 3 Summary of the general effect of various alloying elements on phase stability in Ni-base
alloys [8]
Sr No. Effect
Elements
1
Gamma—solid solution strengthening
Cobalt, chromium, iron, molybdenum,
tungsten, tantalum
2
Former of gamma prime
Aluminum (Ni 3 Al), titanium (Ni 3 Ti)
3
Solid solution strengthening of gamma
prime
Chromium, molybdenum, titanium,
silicon, niobium
4
Former of gamma double prime
Niobium (Ni 3 Nb)
5
Carbide formers
Tungsten, tantalum, titanium,
molybdenum, niobium are MC and M (C,
N) formers
Chromium is M 7 C 3 former
Chromium, molybdenum, and tungsten
are M 23 C 6 former
Molybdenum and tungsten are M 6 C
former
6
Topological closed-packed phase (σ, ρ, μ,
Laves)
Titanium, vanadium, zirconium, niobium,
tantalum, aluminum and silicon are TCP
phase former
7
Surface oxide former
Chromium (Cr 2 O 3 ), aluminum (Al 2 O 3 )
Table 4 Characteristics of phases in nickel alloys [22]
Phase
Characteristics
– Face-centered cubic structure
– Gamma is a nonmagnetic phase
– Generally, a high percentage of solid solution contains
– Matrix phase in nickel-based alloy
γ
– Phase provides good creep resistance and high-temperature strength
– Al and Ti precipitate face-centered cubic γ (Ni 3 Al, Ti); other elements enter
in gamma prime are Nb, Cr, and Ta
γ
– Body-centered tetragonal phase form Ni 3 Nb
– Ni and Nb combine in the presence of Fe
– γ is unsteady at a high temperature around 650 °C
γ —G.B.
– With heat treatments and service exposure a film of γ form along the G.B.
in the stronger alloys
Phase-Carbides – Metal carbides form with C (0.02–0.2 wt%) and reactive elements like Ti,
Ta, Hf, and Nb
Phase-Borides – B segregates at grain boundaries and forms low-density boride particles
Phase-TCP
– TCP phases mean σ,μ, and Laves kind of phases
– The formation depends on composition and circumstances
– The structure is a needle or a plate type
– Brittle phases
Note γ—Gamma, γ —Gamma prime, γ —Gamma double prime, γ —Grain boundary, TCP—
Topologically close-packed phases, G.B.—Grain boundary