Nov 20 2012
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Fabrication and Heat Treatment
Machinability
Forming
Heat Treatment
Cold Working
Annealing
Applications
Introduction
Super alloys or high performance alloys have the capacity to function at very high temperatures and severe mechanical stressing, and also where high surface stability is required. They have good creep and oxidation resistance, and can be formed in different shapes. Solid-solution hardening, work hardening, and precipitation hardening processes can be performed for strengthening the super alloys. They are classified into three types such as cobalt-based, nickel-based, and iron-based alloys.
Super alloy D-979 is a nickel-chromium-molybdenum-tungsten alloy having precipitation hardening additions. The datasheet given below provides an overview of super alloy D-979.
Chemical Composition
The following table shows the chemical composition of super alloy D-979.
|
Element |
Content (%) |
|
Nickel, Ni |
42-48 |
|
Iron, Fe |
20.8 - 34.5 |
|
Chromium, Cr |
14-16 |
|
Molybdenum, Mo |
3-4.50 |
|
Tungsten, W |
3-4.50 |
|
Titanium, Ti |
2.70-3.30 |
|
Aluminum, Al |
0.750-1.30 |
|
Manganese, Mn |
0.750 |
|
Silicon, Si |
0.750 |
|
Carbon, C |
0.0800 |
|
Boron, B |
0.00800-0.0160 |
Physical Properties
The physical properties of super alloy D-979 are displayed in the following table.
|
Properties |
Metric |
Imperial |
|
Density |
8.19 g/cm³ |
0.296 lb/in³ |
|
Melting point |
1220-1390°C |
2230-2530°F |
Mechanical Properties
The mechanical properties of super alloy D-979 are outlined in the following table.
|
Properties |
Metric |
Imperial |
|
Rupture strength (@ 871°C, time 3.60e+6 sec/ 1600°F, time 1000 h) |
69 MPa |
10000 psi |
Thermal Properties
The thermal properties of super alloy D-979 are highlighted in the following table.
|
Properties |
Metric |
Imperial |
|
Thermal expansion co-efficient (@ 93°C/199°F) |
13.7 µm/m°C |
7.61 µin/in°F |
|
Thermal conductivity |
12.6 W/mK |
87.4 BTU in/hr. ft².°F |
Fabrication and Heat Treatment
Machinability
Super alloy D-979 is machined using conventional machining methods which are used for iron-based alloys. A coolant can be used for performing machining operations. Water-based coolants are generally used in high speed operations. Heavy lubricants are normally preferred for boring drilling, tapping, boring or broaching.
Forming
Super alloy D-979 can be formed using all conventional techniques. Heavy-duty lubricants are used for cold forming.
Heat Treatment
Super alloy D-979 is heat treated at 1038°C (1900°F) followed by quenching in oil.
Cold Working
Super alloy D-979 can be cold worked using standard tooling. Soft die materials are used in order to produce good finishing and reduce galling problems.
Annealing
Super alloy D-979 is annealed at 1038°C (1900°F) for 1 hr followed by quenching in oil.
Applications
Super alloy D-979 is mainly used in gas turbine hot section components.