Titanium, one of the most common metals found on Earth, has excellent mechanical properties and allows the creation of very light components and structures with excellent corrosion resistance. Additive manufacturing is increasingly used for the production of titanium elements and structures, which can therefore also benefit from complex shapes and internal channels obtainable only with this manufacturing method.
Discovered in 1791, titanium is a rather widespread chemical element found on Earth's crust, yet rather difficult to extract: since it readily combines with oxygen, nitrogen, carbon and hydrogen, obtaining the pure metal is only possible by carrying out complicated production processes, which require considerable energy.
Titanium is a metal that is light, resistant, ductile and malleable and with excellent corrosion resistance, for this reason it is used more and more in a range of industrial sectors. It is also biocompatible and can therefore be used in the field of medicine and dentistry.
If one compares the characteristics of titanium with those of other metals, it is possible to notice how, in respect to iron, aluminium or steel, titanium has higher specific properties: therefore, titanium alloys offer excellent performance and allow the creation of lighter and more resistant manufactured products.
Titanium is usually alloyed with small percentages of other elements such as nickel, vanadium, and aluminium creating alloys with high mechanical and fatigue resistance, high hardness and excellent corrosion resistance. However, it also allows the creation of very light components and structures.
Based on the presence of alloy elements and/or interstitial elements, titanium is commonly classified in "grades"; in the industrial field the most commonly used grades are 1, 2, 5 and 23. In addition to these more usual grades, other alloys have been developed over the years, with improved mechanical properties, which are classified according to their chemical composition. Examples of these materials are Ti-6Al-2Sn-4Zr-2Mo (Ti-6242), Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) and Ti–6Al–2Zr–1Mo–1V (TA 15).
Grades 1 and 2 fall into the category of commercially pure (CP) and have low mechanical properties, but very high corrosion resistance thanks to the layer of titanium oxide that is created on the surface and which is very resistant to corrosive agents. This type of titanium titanium is widely used in the chemical and oil & gas sectors, in particular for pipes.
Amongst the grades offering the best performance, the most commonly used are 5 and 23. Also known as Ti6Al4V, grade 5 titanium is composed of 6% aluminium, 4% vanadium, and the rest titanium (with a maximum 0.25% of iron and a maximum 0.2% of oxygen), it has excellent corrosion resistance, good mechanical properties and high toughness.
Grade 23, also known as Ti-6Al-4V-ELI also has excellent properties: ELI is an acronym for Extra Low Interstitial, indicating that this alloy has a very low amount of interstitial elements (carbon, oxygen, nitrogen, hydrogen). The interstitial elements are inserted in the crystalline lattice of the material making the structure more fragile and reducing elongation at break; however, they also result in an increase in the mechanical properties, for this reason, it is preferable to vary the amount according to the alloy's intended use.
If an extremely ductile and tough material is required, the interstitial elements should be reduced as much as possible, just as it was done for grade 23 titanium which contains 6% aluminium, 4% vanadium, 0.13% (maximum) of oxygen and the rest titanium.
Grades 5 and 23 are in the number of high-performance grades and possess excellent mechanical properties and excellent corrosion resistance; they are perfect for making structures lighter, even those mechanically loaded and heavily stressed, and are used in sectors such as aerospace, motorsport, oil&gas and biomedical.
When the excellent mechanical properties of grades 5 and 23 are not enough, there are the alloys Ti-6Al-2Sn-4Zr-2Mo, Ti-6Al-2Sn-4Zr-6Mo and Ti–6Al–2Zr–1Mo–1V (TA 15). These alloys are formed with aluminium and vanadium, like grades 5 and 23, but also with other elements such as zirconium, tin and molybdenum, which bestow greater mechanical strength, especially in hot applications (T>350°C, which is the maximum continuous use temperature of grades 5 and 23).
These alloys are actually used in various high-tech sectors such as motorsport and aerospace, for the production of highly stressed parts of racing engines, frames and blades for compressors and impellers for turbines.
Titanium, additive manufacturing, subtractive, vacuum casting
Mechanically machining titanium is not a straightforward procedure and, in addition to the processing difficulties, there is the production of particularly troublesome waste material.
The vacuum-assisted investment-casting process, typical of reactive materials, usually also requires long processing times due to the complexity and the number of phases, as well as the drawback of there not being so many companies that can perform this delicate task.
Additive manufacturing is increasingly used for the production of titanium elements and structures, which can therefore also benefit from complex shapes and internal channels obtainable only with additive production.
In this regard, however, a specific design approach is required for additive manufacturing: a co-design that sees collaboration between the designer and technician specialised in additive manufacturing in order to optimise the design and avoid massive structures and wall thicknesses that are too great and which may generate excessive residual tension during printing.
Titanium lends itself to a wide range of heat treatments that allow the improvement of many properties: once subjected to these treatments, the product made of titanium using additive manufacturing has mechanical properties identical or superior to those of products obtained with machining from solid block.
Heat treatments and analysis laboratory
The in-house analysis laboratory plays a key role here by validating and developing the heat treatments that determine the mechanical properties of the finished component and ensuring that the performances are maintained for each job carried out, all this with reduced lead times and absolute confidentiality; in the same way, the quality control department periodically checks the mechanical properties of the titanium powder, which being very similar to oxygen could decay, to guarantee constant performance and properties.
Titanium is used for wing structures, nacelle parts and in general for highly stressed parts of aircraft, for turbines, compressor blades, for components used in motorsport, where it can also replace parts in composite materials, for prostheses in the biomedical sector and in all those applications where lightness, mechanical and corrosion resistance are required.