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Third generation γ‐TiAl alloys with a high niobium content, Ti–(47–48)Al–2Cr–8Nb, were processed by electron beam melting (EBM). This near‐net‐shape additive manufacturing process produces complex parts according to a CAD design. The starting powder is deposited layer by layer on the building table and selectively melted to progressively form the massive part. The EBM parameters such as layer thickness, melting temperature, scanning speed, or building strategy were set up to minimize porosity. The chemical composition of the built material is similar to the composition of the base powder despite a slight evaporation of aluminum and reveals a neglectable oxygen pick‐up. The very fine equiaxed microstructure resulting after EBM can be then set up by heat treatment (HT). According to the HT temperature in particular, an equiaxed microstructure, a duplex microstructure with different lamellar ratio and a fully lamellar microstructure is obtained. Not only test bars have been produced but also complex parts such as demo low pressure turbine blades.

Titanium aluminide alloys are good candidates for structural applications thanks to their low density and good balance of properties up to relatively high temperatures. However, their application is still limited by significant oxidation. Four c-TiAl alloys with different content of aluminum and niobium were produced by electron beam melting: Ti-45Al-2Cr-2Nb, Ti-48Al-2Cr-2Nb, Ti-45Al-2Cr-8Nb, and Ti-46Al-2Cr-8Nb. The behavior of these alloys in response to oxidation in air during constant heating up to 1000°C and isothermal oxidation for 10 h at 850 and 950°C were studied by thermogravimetric analysis. The mass gain due to oxidation of the low Nb-containing alloys was always at least twice that of the high Nbcontaining alloys. Both low and high Nb-containing alloys exhibited on their surface oxidation products of the same nature: oxides TiO 2 and Al 2 O 3 , and nitrides TiN and Ti 2 AlN. Niobium addition up to 8 at.% did not suppress the growth of rutile and promote the formation of a protective alumina layer. However, it efficiently reduced the formation of rutile, mainly responsible for the mass gain due to oxidation of c-TiAl alloys and with tendency to spallation.

Alloys displaying positive enthalpy of mixing demix below a critical temperature. In Co-Cu and related ternaries the miscibility gap is metastable, i.e. it occurs at temperatures lower than the liquidus. In order to study the liquid phase separation high melt undercooling is necessary. This was obtained via rapid solidification techniques using melt spinning and casting in moulding devices, as well as high temperature DSC experiments with samples embedded in a flux. Results are given for Co-Cu, Co-Cu-Fe and Co-Cu-Ni systems. Phase diagrams were optimised using the DSC data. The mechanism of phase separation was investigated by comparing samples produced under different cooling conditions. The hierarchy of microstructures obtained was interpreted accounting for the processing technique and the phase diagram. They constitute a database useful for the interpretation of the thermal history of samples processed in microgravity.

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