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TITANIUM GRADES

The common term “titanium” usually implies not only pure titanium, but also
its alloys. For the most part, industry consumes just alloys. Alloying titanium is
oriented to receiving grades with different properties and allows heat treatment TITANIUM GRADES
for some of them. Typical alloying elements for titanium are Aluminum,
Vanadium, Molybdenum, Ferrum, Chrome and others. Even small amounts
of these elements can drastically change the properties of the alloys.

Pure titanium can exist in two crystalline forms: the low-temperature α-phase with
hexagonal close-packed lattice and the higher-temperature β-phase with body-
centered cubic lattice. The alloying elements in titanium alloys lead to an increase
in α-phase or β-phase. Elements that strengthen, or stabilize a phase are called
stabilizers: α-stabilizers or β-stabilizers. For example, Aluminum, Nitrogen and
Plumbum are α-stabilizers, and Vanadium and Molybdenum are β-stabilizers. Some
elements added to titanium alloys do not strengthen either the α- or β-phase, but
are important as “neutral” elements that give certain properties to the alloy.

Based on its metallurgical characteristics, titanium is divided into the following groups:

• Commercially pure titanium (unalloyed), featuring a good
corrosion resistance but low strength.
• α-alloys (alpha-alloys), consisting of only α-phase and having a lot of
α-stabilizers, which feature strength retention at relatively high temperatures.
• Near-α-alloys (near-alpha-alloys), which are α-alloys with a small addition of β-stabilizers
and have good resistance to creep for working temperatures 450°C -550°C.
• α-β-alloys (alpha-beta-alloys), perhaps the most common group, which is a type
of mixture of both phases and contains α- and β-stabilizers. The alloys of this
group are suitable for heat treatment and aging for strength improvement.
• β-alloys (beta-alloys) include a sufficiently large number of β-stabilizers to obtain
β-phase structure after treatment or even cooling in some cases. The group is
characterized by high hardenability and, therefore, high strength. However, increasing
the amount of the alloying elements leads to higher density. In addition, increasing
strength by solution treating and aging causes a reduction in ductility.

The family of near-β-alloys (near-beta-alloys) is sometimes separated from the
group because it does not retain a fully β-phase structure after treatment.

Generally, the α-alloys have better ductility and the β-alloys have higher strength.
The α-β-alloys lay between the mentioned two (Fig. 1).

There are different code systems for designating titanium. The American
Society for Testing and Materials (ASTM), for instance, uses a grade
numbering method: Grade 1, Grade 2, … , Grade 12,…

This guide utilizes the chemical composition system, where the designation shows the
percentage of main alloying elements in an alloy. For example: “Ti6Al4V” or
“Ti-6Al-4V” means that the titanium alloy contains 6% Aluminum (Al) and 4% Vanadium
(V). The amount of the other alloying elements is small and, if necessary, can be
found in detailed specification of the grade. The remaining component is titanium.

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