Jul 5 2013
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Fabrication and Heat Treatment
Welding
Annealing
Applications
Introduction
Grade 21 Ti 15Mo 2.7Nb 3Al 0.25Si alloy has improved oxidation resistance and creep strength. This alloy is resistant to aircraft hydraulic fluids at all temperatures, thus it is ideal for use in aerospace engines and parts. It is also ideal for metal matrix composites as it can be economically rolled to foil, and is compatible with most fibers.
The following sections will discuss in detail about grade 21 Ti 15Mo 2.7Nb 3Al 0.25Si alloy.
Chemical Composition
The chemical composition of grade 21 Ti 15Mo 2.7Nb 3Al 0.25Si alloy is outlined in the following table.
|
Element |
Content (%) |
|
Titanium, Ti |
76 - 80.8 |
|
Molybdenum, Mo |
14 - 16 |
|
Aluminum, Al |
2.5 - 3.5 |
|
Niobium, Nb |
2.4 - 3.2 |
|
Iron, Fe |
≤ 0.40 |
|
Silicon, Si |
0.15 - 0.25 |
|
Oxygen, O |
0.11 - 0.17 |
|
Carbon, C |
≤ 0.050 |
|
Nitrogen, N |
≤ 0.050 |
|
Hydrogen, H |
≤ 0.015 |
Physical Properties
The physical properties of grade 21 Ti 15Mo 2.7Nb 3Al 0.25Si alloy are tabulated below.
|
Properties |
Metric |
Imperial |
|
Density |
4.94 g/cm3 |
0.178 lb/in3 |
Mechanical Properties
The following table shows mechanical properties of grade 21 Ti 15Mo 2.7Nb 3Al 0.25Si alloy.
|
Properties |
Metric |
Imperial |
|
Tensile strength |
930 MPa |
135000 psi |
|
Yield strength |
860 MPa |
125000 psi |
|
Elastic modulus |
96.0 - 103 GPa |
13900 - 14900 ksi |
|
Elongation at break |
14% |
14% |
|
Hardness, (HV) |
360-420 |
360-420 |
Thermal Properties
The thermal properties of grade 21 Ti 15Mo 2.7Nb 3Al 0.25Si alloy are tabulated below.
|
Properties |
Metric |
Imperial |
|
Thermal expansion co-efficient (@38°C/100°F) |
7.07 µm/m°C |
3.93 µin/in°F |
|
Thermal conductivity |
7.60 W/mK |
52.7 BTU in/hr.ft².°F |
Fabrication and Heat Treatment
Welding
Weldability of grade 21 Ti 15Mo 2.7Nb 3Al 0.25Si is rated as fair.
Annealing
Annealing of this material can be performed by heating to 815-845 °C (1499-1553°F) for 3-30 min and then air cooled. In case of stress relieving, the material is held at 510-650 °C (950-1202°F) for 8-16 h.
Applications
Grade 21 Ti 15Mo 2.7Nb 3Al 0.25Si alloy is applied in the following:
-
Warm airframes of engine structures
-
Engine exhaust plug and nozzle assemblies in aerospace applications
-
Honeycomb, fasteners, metal matrix composites
-
In applications where the temperature ranges from 230°C to 600°C (446-1112°F).