Chapter 11-1triangle.kaist.ac.kr/lectures/MS371/2017 spring/Chap 11 … · · 2017-05-23Nickel-copper alloy Copper products Froth flotation Copper ... form age-hardening precipitates

/MS371/ Structure and Properties of Engineering Alloys

Chapter 11-1

Nickel and Cobalt Alloys

/MS371/ Structure and Properties of Engineering Alloys/MS371/ Structure and Properties of Engineering Alloys

Production of Ni

• Properties of Ni

– FCC: tough,

– High- and low-temp

– High oxidation resistance

– Good resistance for most environments

– High cost

• Ni deposits

– Ni-Cu (Canada)

– Ni silicates (New Caledonia)

– Ni laterites (tropical and subtropical regions)


Production of Nickel

Iron-ore

recovery

plantBessemer matte

Nickel

concentrate

Copper

concentrate

Iron sulfide

concentrate

(pyrrhotite)

Ni-Cu-Fe sulfide Froth flotation

Nickel and Copper sulfide

Nickel-copper alloy

Copper

products

Froth flotation

Copper

sulfide

Nickel sulfideNickel oxidePure nickel


Commercially Pure Nickel

Chemical Composition

Typical Application


Commercially Pure Nickel

• Nickel 200 alloy

– An solid solution

– Good properties

– Excellent resistance to many corrosive environment

– High strength at elevated temperatures

– Tough and ductile at low temperature


– Low-carbon contents (limited to %)

– Low work-hardening rate, increased

– Adaptable for spinning and cold-working operations


– High- (99.98 % Ni)

– Excellent thermal conductivity, high ductility

– Heavy cold deformation without annealing

Fig 11Microstructures


Nickel-Copper Alloys (Monels)

– Cu-Ni: completely

– : about 67% Ni and 33% Cu

Chem Comp and Typical Applications


Nickel-Copper Alloys (Monels)

• Monel 400

– High , weldability, excellent

resistance, toughness over

a wide range of temp

– under high-velocity

conditions

• Monel R-405

– addition to improve the

machining characteristics.

• Monel K-500

– Addition of 3.0% Al and 0.6% Ti to

form age-hardening precipitates of

Microstructure


Nickel-Chromium Alloys

Cr: An important alloying element for many corrosion-

resistant and high-temp- Ni base alloys

Phase Diagram




• Microstructure and Properties

– 600

• Standard engineering alloy for use in some

severely corrosive environments at elevated

temp

• 15.5% Cr and 8% : high strength and

workability

• Strengthened by (not heat-

treatable)

Fig 11

Fig 11



– Inconel 601

• 23% Cr, 14% Fe, 1.4% Al: heat and corrosion

resistance

• A protective film formation on the metal

surface during high-temp exposure

– Inconel 625

• 22% Cr, 5% Fe, 9% Mo, 3.6% Nb

• High strength (solid-solution strengthening effect of

Mo and Nb)

• High corrosion resistance to (Cr and Mo)

• Weldability (niobium carbide)


Nickel-Base Superalloys

• Superalloys

– High strength at high

– Good and resistance

– Superior resistance to and at elevated temp

– Nickel base, nickel-iron base, and cobalt base




• Major phases present in nickel-base superalloys

– γ (gamma) phase: continuous matrix of

– γ’ (gamma prime) phase: major phase

– Carbides: mainly and

Microstructure



• Problems

– Cellular M23C6 carbides: shortened rupture (elimination via heat treatment)

– σ (sigma) phase: low-temp , shortened rupture life

(overcome by changing the alloy chemistry)



• γ phase

– Strengthened by of solid-solution elements (atomic factor)

– Electron hole number of elements Nv ↑ ↓ slip to occur difficult

– Slow-diffusing element (Mo, W) high-temp creep ↓

• γ’ phase

– FCC A3B-type precipitate (A = Ni, Co, Fe while B = Al, Ti, Nb)

– Homogeneous nucleation with low energy (0.1% mismatch)

– Extraordinary long-term

– Antiphase boundary (APB) in γ- γ’

alloys by dislocation interaction

– Temperature ↑ degree of in Ni3(Al,Ti)

increase in

– Morphology: sphere (small , 0.05%),

cube, semicoherent plates (above 1.25%)

Microstructure



• Role of carbides in nickel-base heat-resistant alloys

– Carbon contents: wrought alloys (0.02 ~ 0.2%), cast alloys (0.6%)

– No carbides along the grain boundaries (GB) GB

– Continuous chains of carbides along the GB fracture

• Types of carbides

– carbides: M = Ti, Ta, Nb, W

• very stable

• restricting grain growth

• temp range where solidification begins

– carbides: M = Cr, Fe, W, Mo, Co

• complex cubic structure

• to precipitate along GB

• 760 ~ 980C

– M6C carbides: M = Mo, W

• complex cubic structure

• 815 ~ 980C



• Topologically closed-packed (TCP) phases: σ, μ, Laves, χ– Thin parallel to the {111}γ rupture strengths, loss in rupture

– Changing chemical balance by removing refractory elements such as Cr, Mo, W

reduced solid-solution strengthening, γ/γ’ mismatch

Fig 11



• Microstructure of Inconel

– Precipitation- Ni-base superalloy

– Corrosion and oxidation

– High-temp strength (up to about 760~ °C)

– 4 types of heat treatment

• Solutionizing + air cooling → γ’ + (carbides)

• Solutionizing + air cooling + double-aging treatment

→ dense γ’ particles, stabilized GB carbides

• Solutionizing + air cooling + single-aging treatment

→ discontinuous carbides precipitates at GB

• Solutionizing + air cooling + overaging

→ coarse γ’ particles (undesirable)

Documents

Chapter 11-1triangle.kaist.ac.kr/lectures/MS371/2017 spring/Chap 11 … · · 2017-05-23Nickel-copper alloy Copper products Froth flotation Copper ... form age-hardening precipitates