W and C co-segregation at dislocations in a γ -TiAl based alloy identified by correlative APT-TEM observations

In this work, a γ-TiAl based alloy has been designed for increased strength at high temperature using promising substitutional (W) and interstitial (C) solutes. Creep tests at 800 °C and 200 MPa show that the addition of C to a W-containing alloy leads to an increase by about two times of the creep lifetime of this alloy with a fine near lamellar microstructure. A correlative approach, combining 3D chemical reconstructions by atom probe tomography (APT), with specific dislocations characterizations by transmission electron microscopy (TEM), has therefore been developed to study the local chemical environment in the vicinity of dislocations. Because such advanced APT-TEM correlations are challenging, dislocations of marked edge character were first selected, because they seemed to exhibit higher tendency for segregation. In addition to the early stages of carbide precipitation, co-segregation effects of W and C were thus observed after creep. This effect is interpreted as resulting from the mutual chemical affinity between these two solutes. Therefore, selecting solutes of mutual chemical affinity appears as a promising dislocation engineering route suitable for the development of materials employed in high-temperature environments encountered in turbine blades of advanced aircraft engines.