Arcam AB fka AMAVF

[Tom Joad]

Quality control of EB produced products appears to be a mix of science and art so the job ads are very likely showing use of Arcam machines. That's what I get after finally reading what appears to be very close to, if not, Arcam's "white paper." It takes a while to read even if you know a thing or two. They refer to first rate researchers and research facilities. These are names I was running into when I did my thesis some years ago, among them, individuals that had to be communicating with each other for anyone to come up with the first mathematical model of twinning. Do a search on "twinning metal" and find the source that best describes it to you if you want, but it's not important in understanding the "white paper" but it's discussed a little.

I get from it that you obtain Arcam's advertised mechanical properties for TiAl alloys if and only if one follows a tightly controlled set of procedures when using the EB machine and the conditioning that follows, HIP treatment for example. That's certainly better than not being able to produce products with the desired mechanical properties and the refinements in quality control go well beyond what is possible using other methods such as casting, however, these machines are not plug and play, put in a CAD file and go to sleep type things. One has to understand the process and apply quality control procedures, hence the job postings for those educated in those matters.

Arcam EBM-built Materials

There are clear limits for Ti-Al applications! Ti-Al cannot be used in all applications where nickel based superalloys are currently being used! So speculation about turbine stage use is just that unless experiment backs up its use. And then high levels of confidence that the EBM part is what's best mechanically and financially are not justified until there's been plenty of testing. The quoted sections below are from "?-Titanium Aluminide Manufactured by Electron Beam Melting, An Investigation of Microstructural Behavior and Related Mechanical Properties for Aerospace Applications", Sanna Fager Franzén and Joakim Karlsson 2010. The link for the "white paper" is below after the quoted material.

"At elevated temperatures the deformation behavior becomes more dependent of the rate the material is deformed. This is an important feature that severely limits the creep resistance of TiAl and is a major design issue when it comes to replacing nickel-based superalloys with TiAl (2)." -p. 22,

On the other hand-

"?-TiAl alloys has some appropriate and suitable thermal properties for aerospace applications and especially jet engines. The properties are a combination of low thermal expansion and high thermal conductivity (25). The thermal expansion of TiAl is lower than for Ni-based superalloys and that gives TiAl some advantages compared to traditionally used superalloys for applications as turbine blades. The lower thermal expansion makes the control of the expansion of the blade easier and the clearance between the blade tip and the shroud is not as critical (25)." -p. 24

In what follows they make clear what some of the limitations are for Ti-Al alloys-

"Creep properties are not the most favorable for TiAl, however they are important as many of the applications involve excessive temperature stresses (25). In many ways the creep resistance is much inferior to the nickel-based superalloys (2). As for other properties, the microstructure is important, but also the morphology of each phase is important (23)." -p. 31

"The oxidation resistance of TiAl is considered sufficient up to a temperature of about 800°C (25)." -p. 32

EBM compares very well with other manufacturing methods when we restrict what we are looking at to Ti-Al.

"Different manufacturing methods are investigated and applied to TiAl in order to make it commercial. Due to the material’s low ductility and fracture toughness processing of the material is hard and conventional manufacturing methods are difficult to apply (6). Conventional manufacturing methods have been applied, like casting, forging or powder processing, but they are all accompanied with difficulties that must be overcome. The difficulties in producing the material are said to be one reason for the limited use of TiAl today. Especially the automotive industry is sensitive to the end cost of the material and for TiAl, being so hard to process; the main cost of the product is the manufacturing cost (10). -p. 35

"Different problems must be handled when casting TiAl, the firsts being the reactivity of the molten material. TiAl reacts with all ceramics and is therefore extremely hard to contain. The problem is solved by using a cold-wall furnace; however that creates problem when the mold is being filled. With cold-wall furnace the superheating of TiAl can only be 600°C, which makes it hard to fill the mold properly. Further problem is that Al is easily vaporized from the melt when molten in vacuum. To solve that problem the melting is done in argon, which can in turn be trapped in the melt due to the low superheating and thereby the fast mold filling. The high reactivity of TiAl also causes trouble finding a good and cost efficient material for the mold. Another problem involves the microstructure that can be rough, with large grains and coarse lamellar structure." -p. 35

I'm very confident that EBM is the method to use for: some Ti-Al parts in aerospace, some auto, and many orthopedic and dental uses. The following describes quality control advantages of EBM over casting. That's all for awhile.

"The coarse microstructure and segregation obtained in casting could be avoided by using powder metallurgy with rapid solidification. The solidification microstructure can be refined and homogenous and comparable to wrought material (8). Investigation made on ?-TiAl produced by Electron Beam Melting shows that an ordered microstructure with extremely fine grains is obtained. The fine grains are expected since the melt pool is small and the cooling rate is high. By appropriate subsequent HIP and heat treatment a fine-grained duplex microstructure can be obtained (11). The manufacturing technique is built on additive manufacturing, adding layer by layer of material; despite that complete interlayer fusion is achieved (12)." p. 36

?-Titanium Aluminide Manufactured by Electron Beam Melting