Grade 21 Ti 15Mo 2.7Nb 3Al 0.25Si Alloy (UNS R58210)

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).

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