This alloy is sometimes referred to as "half 6-4". It offers 20 to 50 per cent higher strength than C.P. grades, but is more formable and weldable than Ti6Al4V. It is principally used as tubing in aircraft and engine hydraulic systems, for high strength corrosion resisting applications such as pipes and vessels and as foil for honey-comb applications. It is also used in a variety of recreational applications such as golf club shafts, tennis racquets, bicycle frames, etc.
Grade 18 is identical to Grade 9 with the exception of the addition of palladium to increase its corrosion resistance. Mechanical and physical properties, specifications and forms are all identical to those of Grade 9.
The alloy composition differs by the addition of 0.04-0.08% Pd.
Composition
Physical Data
Mechanical Data
Fabrication Information
| C | < 0.05 % |
| Fe | < 0.3 % |
| N2 | < 0.02 % |
| O2 | < 0.12% |
| Al | 2.5 - 3.5 % |
| V | 2.0 - 3.0 % |
| H2 (sheet) | < 0.015 % |
| H2 (bar) | < 0.0125 % |
| Ti = | Rem |
| Minimum | Typical | |
| Density g/cm3 (lb/cu.in) | 4.48 (0.161) | |
| Melting Range °C+/-15°C (°F) | 1704 (3099) | |
| Volume Electrical Resistivity µohm.cm (µohm.in) | 124 (49) | |
| Thermal Conductivity W/mK(Btu/ft h°F) | 7.6 (53) | |
| *Mean Thermal Exp. Coeff. 0-300°C/°C | 7.9 x 10 -6 | 9.2 x 10 -6 |
| Beta Transus °C+/-15°C(°F) | 935 (1715) |
| Minimum | Typical | |
| Tensile Strength MPa(ksi) | 621 (90) | 740 (107) |
| 0.2% Proof Stress MPa(ksi) | 483 (70) | 607 (88) |
| Elongation over 2 Inches % | 15 | 17 |
| Elastic Modulus GPa(Msi) | 91 (13) | |
| Hardness Rockwell C | 15 | |
| Specified Bend Radius <0.070" x Thickness | 2.5 | |
| Charpy, V-Notch Impact (L direction-pipe) J(ft Ibf) | 48(35) | |
| Charpy, V-Notch Impact J(ft Ibf) | 48 (35) | |
| Short Term Creep, 1.0% Strain (1000h @ 250°C) MPa (ksi) | 400 (58) | |
| Stress Rupture (1000h @ 250°C) MPa | 421 |
| Weldability | Good |
| Forging | Rough 871-899°C(1600-1650°F), finish 843-871°C (1550-1600°F) |
| Annealing | 593-760°C(1100-1400°F), 1-3 hr, AC |
| Solution Treating | 871-927°C (1600-1700°F) 15-20 min, WQ |
| Ageing | 482-510°C (900-950°F) 2-8 hr, AC |
| Stress Relief Annealing | 316-649°C (600-1200°F), <<-3hr, AC |