Ti6242: the titanium alloy for high temperature applications

In recent months, Beamit Group has parameterised the Ti6242 alloy produced via LPBF (laser powder bed fusion), a titanium alloy that maintains excellent mechanical properties even at 550°C.

Perfect for aeronautical engine components and motorsport, it is used in all applications that require lightweight components able to offer high performance even at high temperatures.

Laboratory

Titanium alloys for use at high temperatures were developed after World War II for use in new supersonic aircraft. At the time, Ti64 titanium alloys were available allowing the use at temperatures up to 400°C and parts components subject to stresses were made of steel or nickel-based alloys. The new titanium alloys are therefore developed with the aim of obtaining high performance even at high temperatures, with the further advantage of reducing the weight of the elements thus produced.

Titanium and additive manufacturing

Mechanically processing titanium is not a straightforward procedure and, in addition to the processing difficulties, there is the production of particularly troublesome waste material. Added to this is a non-optimal availability of the raw material.

For this reason, additive manufacturing is increasingly used for the production of titanium elements and structures: additive technologies allow to obtain results equal, if not better in terms of mechanical properties, to those obtainable with the same alloys and traditional technologies, with zero waste material. Last but not least, the components made in this way can benefit from the complex geometries and internal channels that can only be obtained with additive manufacturing.

In recent months, Beamit Group has parameterised the Ti6242 alloy produced via LPBF (laser powder bed fusion), a titanium alloy for applications at high temperature with excellent mechanical properties even at 550°C.

Application areas and characteristics of the Ti6242 alloy

Titanium alloys for high temperature applications have been specially developed for aircraft engine components, but are also widely used in motorsport for exhausts and mufflers and for all those applications that require lightweight components with excellent mechanical characteristics at high temperatures.

In particular, the titanium alloy Ti6242 is a near-alpha alloy with very high mechanical properties: characterised by excellent wear resistance and the ability to maintain mechanical performance over time, it performs very well up to temperatures of 550°C, allowing the production of low weight elements.

Microstructures

The Ti6242 titanium alloy is usually subjected to two heat treatments, the first by annealing, the second by ageing, to form the most suitable microstructure for the mechanical properties that characterise it; the microstructure is usually bimodal, but thanks to the treatments developed by the Beamit Group it was also possible to obtain other types of structures.

To process titanium alloys with additive laser technologies it is necessary to use argon as an inert gas, while heat treatments must be carried out with high vacuum furnaces and argon quenching.
Beamit Group carries out these treatments in furnaces with a high vacuum level fundamental to avoid contamination, Nadcap accredited and in class 2 according to AMS2750.

Mechanical properties: additive vs subtractive technologies

Ti6242 made by additive manufacturing tends, in temperature conditions above 350°C, to offer superior mechanical properties compared to the same material obtained by forging (a process traditionally used on this alloy). On the other hand, in the case of temperatures below 350°C , the performance between the two production methods will be absolutely comparable.

Ti6242s produced via AM shows tensile properties that are similar to or exceed the one reached by Ti6242 and IMI834 produced via forging

The most significant advantages of additive manufacturing, however, remain the possibility of designing complex shapes and not presenting the typical difficulties of mechanical processing of titanium as well as reducing the buy-to-fly ratio, that is to say the ratio between the quantity of material required and the amount of material the component is actually made of (a parameter which, in the case of expensive materials such as titanium alloys, is very important).

With additive technologies, only the strictly necessary raw material is used, without the waste that is inevitably produced with subtractive production or fusion: obvious advantages derive from the lower use of raw material.

LPBF technology

LPBF technology is ideal for working with Ti6242 powders thanks to the possibility of maintaining a constant process standard, geometric versatility and excellent production scalability.

Considering that the typical applications of the Ti6242 alloy are often linked to the fluid dynamics field, the greater roughness typical of other technologies would have a negative impact and it is therefore more appropriate to adopt the LPBF technology.

Research and development

The research and development activity for the Ti6242 alloy took place over a year within the thesis project of Gabriele Boari, supervised by Professor Riccardo Casati of the Politecnico di Milano.
The first phase involved an in-depth analysis of the state of the art of materials aimed at identifying which high temperature alloys were the most interesting, most easily processed and readily available. Following this analysis, the choice fell on Ti6242, a very promising material from the point of view of weldability.

Lab

Once the material was identified, the next step involved the search for the supplier of the raw material and the procurement of the first batch.
The laser process parameters were developed on the first batch of material through the design of experiment (DOE), a series of statistical techniques that allow to vary the process parameters in a controlled and optimised manner, with the aim of increasing the density of the material.

In the next phase, again through DOE, the goal was to develop the heat treatment, varying the times and temperatures of both the annealing and ageing, with the aim of improving the mechanical properties by studying the consequent variations in the microstructure of the material. After selecting the most promising microstructures, the heat treatments were applied to a larger set of specimens on which the material characterisation part was also implemented by carrying out tensile tests both at room temperature and at temperatures of 350°C, 550°C and 750°C (the latter to analyse the material beyond the applicability limit).

The highest values of YS and UTS are obtained for material annealed at 940°C

A timely response to customer requests

The Ti6242 alloy, designed and parameterised by the Beamit group, arises from the requests of customers operating in the motorsport field and is part of a consultancy and partnership service aimed at providing tailor-made solutions thanks to consolidated know-how.

Additive manufacturing is a recent production method, which requires significant research and development to be exploited in a versatile and scalable way, expanding the application possibilities.
For this reason, the Beamit Group continuously invests in this direction, using one of the largest machine parks in Europe and a large number of departments that allow complete control of all phases of the production cycle.

For the three companies of the Group, Beamit, Zare and Pres-X, producing via additive manufacturing does not simply mean printing the component, but implies the supply of a tailor-made process, with specific characteristics and parameters from the point of mechanical, aesthetic and dimensional view, and with specially designed post-process treatments. All this within a short supply chain that allows us to reduce production times, quickly obtaining pieces with high added value.