Cantor and Yeh [1, 2] were the first who suggested that the conventional alloying strategy has been very restrictive with respect to the whole range of possible materials, thus suggesting the new alloy concept of high entropy alloys (HEAs), which soon was extended more generally to compositional complex alloys (CCAs) and multi-principal element alloys (MPEAs) [3]. Despite of huge scientific advances, efforts to commercialize HEAs are still on a low TRL level, mainly due to restrictions in upscaling manufacturing strategies to industrial standards. One of the major challenges on the way to applications is the extensive alloy design and selection efforts due to the great variety of possible alloy compositions and its consequences for processibility and resulting material properties.

The favorable high-temperature strength of Ni-based and Co-based superalloys can be ascribed to a defined gamma/gamma’ structure consisting of a disordered fcc matrix and ordered L12 precipitates [4]. The same approach has been used to design new HEAs for high-temperature applications in the CoCrFeNi + Al + Cu/Ti alloy systems [5]. These so-called high entropy superalloys (HESAs) can offer lower density as well as higher stability and strength at higher temperatures than Ni-based superalloys.

In the current work we extended the HESA design concept, allowing, disordered bcc A2 and ordered B2 phases in additions or in substitution of the original gamma/gamma’ structure. For this, we used a high-throughput screening approach combining CALPHAD-based computational tools with in situ alloying by means of laser cladding of samples with graded composition. Based on CALPHAD simulations, a compositional field was defined as a function of Al, Ti and Cr additions, satisfying the above conditions and avoiding the formation of further phases such as sigma or eta phases fostering embrittlement.

Laser powder deposition was applied to build wall structures with gradient composition, e.g. Alx Co1.5-Cr-Fe-Ni1.5-Ti0.2 or Crx-Al0.3-Co1.5-Fe-Ni1.5-Ti0.3. For the laser powder deposition an in-house developed COAXshield powder nozzle was utilized enabling the monitoring of the whole cladding process while providing Ar gas-shielding to protect the powder and the molten material against oxidation. Both pre-alloyed powders and mixtures of element powders were used and in situ mixed to achieve the desired alloy compositions. As built, solution annealed and aged conditions were thoroughly analyzed by means of scanning electron microscopy (SEM), including advanced EDS and EBSD techniques. Furthermore, micro-hardness and tensile testing was used to evaluate the mechanical performance of the new designed alloys.

The combined modelling and experimental screening approach was demonstrated to be a powerful tool for designing new high performance AM-ready metallic materials. Based on the results process, structure and property relationships are explored and interesting compositions for future high-temperature applications are identified.

[1] B. Cantor, I.T.H. Chang, P. Knigth, A.J.B. Vincent, Mater. Sci. Eng. A 375-377 (2004), 213

[2] J.-W. Yeh, S.K. Chen, S.J. Lin, J.Y. Gan, T.S. Chin, T.T. Shun, C.H. Tsau, S.Y. Chang, Adv Eng Mater. 6 (2004), 299

[3] D.B. Miracle, O.N. Senkov, Acta Materialia 122 (2017), 448

[4] D. Hausmann, C. Solís, L. P. Freund, N. Volz, A. Heinemann, M. Göken, R. Gilles, S. Neumeier, metals 2020, 10, 321

[5] H. M. Daoud, A. M. Manzoni, N. Wanderka, U. Glatzel, JOM 2015, 67, 2271