Titanium Grade 5 vs Titanium Grade 2
Comparison between the alpha-beta alloy and the workhorse of commercially pure grade
Ti 6Al-4V is the most widely used of all Titanium grades. It is typically available in the annealed condition and is readily heat treatable to increase strength, for a wide range of applications. As a general-purpose alloy, Ti 6Al-4V has a broad spectrum of desirable properties at temperatures around -210°C – 400°C.
Titanium grade 5 or Ti 6Al-4V is an alpha-beta (α-β) alloy. Therefore, it may be heat treated to give medium-high strength in sections under 100 mm thick. However, hardenability is limited and sections over 25 mm may not fully develop desired properties. Ti 6Al-4V has a good weldability (with matching or ELI filler wire) and hot-formability. The degree of cold forming is, however, limited.
Titanium grade 1 is the most ductile of the commercially pure Titanium grades. As a result, the alloy is widely specified for the manufacture of plate heat exchangers.
Titanium Grade 2 or Titanium CP3 is a commercially pure alpha (α) alloy. Although not as strong as Ti 6Al-4V, Titanium grade 2 has outstanding corrosion resistance against variety of aggressive media. For example, Titanium grade 2 is virtually immune to wet chlorine at 10°C – 80°C (0-0.02 mpy or 0.001 mm/y) and thus, used to make chlorine dioxide mixers, pipework and fasteners in modern bleach plants.
Titanium grade 2 is specified based on its excellent corrosion resistance in environments which include: calcium chloride, cupric chloride, ferric chloride, various concentrations of acetic acid, high temperature seawater, most organic media and more.
However, other conditions such as temperature, pH level and flow velocity could alter its properties drastically e.g. susceptibility to stress corrosion cracking and crevice corrosion. When compared with Titanium grade 5 (Ti 6Al-4V), Titanium grade 2 is generally selected where aqueous corrosion resistance and/or formability are required.
| Properties | Ti 6Al-4V (UNS R56400) | Titanium Grade 2 (UNS R50400) |
|---|---|---|
| Metallurgy | 895 MPa | 345 MPa |
| Ultimate tensile strength | 827 MPa | 276 MPa |
| 0.2% offset yield strength | 827 MPa | 276 MPa |
| % Elongation (Ductility) | 10 | 20 |
| Corrosion resistance | Very good | Outstanding |
| Creep and stress-rupture | High | NA |
| Fatigue | High | NA |
| Service temperature | -210°C – 400°C for reliable structural integrity | Depends on environments e.g. up to 316°C for steam and seawater |
| Weldability | Weldable |
At temperatures up to 200°C in normal atmosphere, Titanium grade 2 and other commercially pure grades are also a popular choice for lining material, when corrosion resistance is needed on the surface. Often cheaper and stronger steels are used as outer assemblies. One key application is lining of chimney stacks on coal fired power stations which have been retrofitted with FGD Systems ( Flue Gas Desulphurisation plants).
