Efficient production of a high-performance dispersion strengthened, multi-principal element alloy

Abstract

Additive manufacturing currently facilitates new avenues for materials discovery that have not been fully explored. In this study we reveal how additive manufacturing can be leveraged to produce dispersion strengthened (DS), multi-principal element alloys (MPEA) without the use of traditional mechanical alloying or chemical reactions. This new processing technique employed resonant acoustic mixing to coat an equiatomic NiCoCr powder with nano-scale yttrium oxides. Then, through laser powder bed fusion (L-PBF), the coated powder was successfully consolidated into 99.9% dense parts. Microstructural analysis confirmed the successful incorporation and dispersion of nano-scale oxides throughout the build volume. Furthermore, high temperature mechanical testing of the DS alloys showed significant improvements in strength and ductility over the baseline NiCoCr. As a result, this recently discovered processing route opens a new alloy design and production path that is synergistic between additive manufacturing and dispersion strengthening, possibly enabling a new generation of high-performance alloys. Additive manufacturing (AM) techniques have broadened many aspects of component design, enabled part count reduction, and decreased commissioning time for prospective NASA hardware and industrial applications 1. Currently, the bulk of metallic AM research has been conducted on traditional alloys 2-4. Yet, AM facilitates new avenues for materials discovery that have not been fully explored 5,6. For laser powder bed fusion (L-PBF), the finely focused, laser melting of powder is analogous to welding and is thus problematic for alloys that are difficult to weld. Unfortunately, many of the alloys used for ultra-high temperature applications (>1000 °C) fall within this criterion. Therefore, there currently exists a need for high temperature alloys that can be produced through L-PBF or similar AM processes. One alloy system that has shown promise is the multi-principal element alloy (MPEA) class. The discovery and growth of this interesting new class of alloys, coined "High Entropy alloys", has coincided with the development of AM. High entropy alloy development has led to the identification of a wide range of MPEAs, such as the ternary alloy NiCoCr, which has demonstrated impressive mechanical properties over a wide range of temperatures and stresses 7,8. Recent studies have also presented favorable results from producing the NiCoCr alloy using AM 9. The success of fabricating the "Cantor alloy" (NiCoCrMnFe) and its derivatives through AM may result from the small gap between their solidus and liquidus temperatures 10 , thereby, reducing the risk of heat affected zone (HAZ) cracking and lowering residual stresses 11. Unfortunately, the phase simplicity that enhances the manufacturability of alloys such as NiCoCr will also limit their high temperature mechanical properties. An additional strengthening mechanism must be introduced, such as dispersion strengthening (DS). Dispersion strengthening, primarily through the use of oxides,...

Coated Metal Powders for Laser Powder Bed Fusion (L-PBF) Processing: A Review

“…Other solution-based methods for coating powders are reported in literature [21,56,[134][135][136]. Ma et al [136] adopted an electro-codeposition process where mechanical mixing and sonication were used to distribute Al 2 O 3 nanoparticles and maintain dispersion.…”

“…This coating process did not particularly affect the size, flowability, and morphology of the powders. Smith et al [56] used acoustic mixing to coat NiCoCr powders with Y 2 O 3 nanoparticles. The acoustic mixing uses a wave that attained a resonance among the container, the powders, and the vibrating spring system [137], providing homogenization of the powder in one hour.…”

“…L-PBF printed parts can be post-treated with hot isostatic pressing (HIP) technique [54,55]. HIP removes residual stresses, promotes grain growth and recrystallization [56], improves mechanical properties, particularly creep and fatigue resistance [57,58]. In addition, HIP can reduce porosity generated during the previous process, as demonstrated with steels [59], Ti [60], and also Al [61] ingots obtained from casting.…”

Challenges in Qualifying Additive Manufacturing for Turbine Components: A Review

“…However, this recipe did not work out well for difficult to weld Ni-based, such as IN738, IN713, MM247, etc. alloys [110].…”

Nanoparticle Tracing during Laser Powder Bed Fusion of Oxide Dispersion Strengthened Steels

“…While widely employed, the control of the final nanoparticle size and degree of dispersion by this methodology is limited, and the steel microparticles size and shape can also be affected [19]. To address this drawback, alternative supporting procedures have been proposed [20] such as resonant acoustic mixing [21], solid-liquid reaction [22], or colloidal dielectrophoretic deposition [23,24]. Once the nanoparticle-additivated powder is obtained, the processing technique employed to generate the ODS steel samples and the experimental parameters selected determine the evolution of the nanoparticles, their final size, and dispersion in the ODS steel [12,25].…”