NADEA Nano-scale duplex high entropy alloys produced by additive manufacturing ​(M-ERA.NET-2 2018-2022)

(Nanostrukturalne stopy o wysokiej entropii konfiguracyjnej otrzymywane metodą druku 3D)

Project results

In NADEA a new family of duplex materials was developed starting from cobalt-free high entropy alloys AlxCrFe2Ni2 with further specific alloying additions, e.g., Mo. Focus was placed on the development of dual-phase, duplex-type microstructures along the additive manufacturing routes LMD (laser metal deposition) and L-PBF (laser powder bed fusion) including heat treatment steps. Casting processes were upgraded in parallel as conventional reference processes. The R&D tasks were aligned along the entire value chain(s), with the aim of bringing the technological maturity level from TRL2 to TRL4. The research was targeted in particular on alloy development, powder production and process engineering as to achieve well equilibrated dual-phase microstructures and assess the material properties, here including mechanical properties as well as functional properties like corrosion and wear resistance.

The starting point at the beginning of the project was the quaternary alloy AlCrFe2Ni2, which was described by Dong et al. in a short article and which showed a good balance between strength and ductility in the as-cast state. Due to the high chromium content, good corrosion properties were also expected, such that the development was targeted at applications for high-performance pumps.

The joint research effort on alloy design was targeted to further develop the alloy composition following the demands and limitations from particular process conditions: For L-PBF processing with no baseplate preheating the alloy Al0.8CrFe2Ni2 was developed as best-performer. For LMD processing with baseplate preheating an alloy close to AlCrFe2Ni2 was identified as best-performer. For casting processes, the alloy composition is not that critical, and Al0.8CrFe2Ni2, AlCrFe2Ni2 as well as AlCrFe2Ni2Mo0.1 were successfully cast into either sand molds or ceramic shell molds.

As a highlight research result, the consortium developed a deep understanding of microstructure formation in this type of alloys, especially during the solid-state BCC–FCC phase transformation. This phase transformation depends on the spinodal decomposition of the parent BCC phase, giving rise to a variety of morphological features of the resulting FCC phase. The resulting FCC displays (i) Widmanstätten plates, (ii) a novel vermicular morphology or (iii) micro-platelets. All microstructures were characterized by SEM/EBSD and TEM/HRTEM in depth. The vermicular microstructure shows a characteristic new orientation relationship between the two phases FCC and BCC, which was previously unknown.

All investigated materials show remarkably good mechanical properties with a pronounced strain hardening and good elongation at fracture. Exceptional fatigue strength was observed during cyclic tests in HCF and LCF conditions. The novel materials outpass duplex-steels and Super Duplex steels in this respect. The Charpy V-notched specimens show toughness values just above the requirements. The wear and corrosion resistance are competitive with super-duplex steels, however potentiodynamic tests in 3.5 wt.% NaCl solution reveal an earlier onset of pitting in anodic polarization.

The project was successfully completed with TRL4 and opens up clear exploitation options. As proof of a successful realization of TRL4, demonstrator components were manufactured both additively (several impeller designs) and by casting (a large pump housing).

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Dong, Y., Gao, X., Lu, Y., Wang, T., and Li, T. (2016). A multi-component AlCrFe2Ni2 alloy with excellent mechanical properties. Mater. Lett. 169, 62–64. https://doi:10.1016/j.matlet.2016.01.096.

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Warstwy półprzewodnikowe o kontrolowanej mikrostrukturze nanoszone metodą impulsowego rozpylania magnetronowego (OPUS NCN 2017-2022)

(Semiconducting layers with controlled microstructure deposited by pulse magnetron sputtering)

​Project results

Technology of thin layer deposition by magnetron sputtering from single target was developed for a number of semiconducting compounds encompassing silicides, selenides or tellurides starting from undoped materials with further specific modifications, e.g., Ag or Cu. Focus was placed on the development of polycrystalline layers by optimizing deposition conditions or further heat treatment steps. The research was directed in particular at process development including powder production, consolidation/densification of powders to produce targets and deposit layers with well-defined compositions and microstructures and assess their functional properties, here including thermoelectric and/or optical properties.

The starting point at the beginning of the project was selection of semiconducting materials with confirmed or anticipated very good functional properties, based on binary or ternary systems: Mg-Si, Sn-Se, Cu-Se, Bi-Te, Ge-Sb-Te. Further improvements were expected upon switching to a thin film geometry suitable for microelectronic and photonic systems.

The research effort was focused on the synthesis of powders, densification of powders, production of targets for magnetron sputtering, and process development to arrive at desired results, with each step demanding specific adjustments related to particular systems.

As a highlight of research results, we can indicate development of a totally original innovative power supply mode for a uniform and effective sputtering processes securing extended lifetimes of targets with low thermal conductivities. The microstructure and composition of layers were characterized by SEM/EDS/XRD, thermoelectric properties including electrical conductivity, thermopower, thermal conductivity, Hall coefficient, concentration and mobility of carriers, were all measured on a single sample by means of LINSEIS Thin Film Analyzer and optical properties were determined from absorption and transmission spectra.

The investigated thin layers were compact, uniform and well-adhering to the substrate. Particularly good thermoelectric properties were achieved for undoped Ge2Sb2Te5 and very good optical properties for undoped SnSe. Further improvements are possible by optimizing  process parameters and/or doping.

Theoretically predicted spectacular increase in thermoelectric performance related to phonon scattering in a thin-layer geometry were not  confirmed experimentally.

The project successfully achieved most of the objectives which opens up clear exploitation options.