David C Dunand

Northwestern University | NU · Department of Materials Science and Engineering

Complex shapes are created from Yb14MnSb11, a high‐temperature thermoelectric Zintl phase, via a two‐step process: i) layer‐by‐layer 3D‐extrusion of ink containing partially‐reacted powders which are ball‐milled from a blend of Yb, MnSb, and Sb powders; ii) heat treatment to synthesize the ternary compound Yb14MnSb11 and densify the extruded powder...

Directional freeze‐cast Fe‐W lamellar foams with 10–33 at.% W show distinct microstructural evolutions during steam/hydrogen redox cycling between oxidized and reduced states at 800 ⁰C, depending on W concentration. The Fe‐18 W and Fe‐25 W foams exhibit a sufficient volume fraction of W‐rich phases – λ‐Fe2W to inhibit sintering for α‐Fe in the redu...

This study investigates the substitution of cerium (Ce) with mischmetal (MM) in cast Al-MM alloys, focusing on microstructure, hardness, tensile and compression properties, creep resistance, and coarsening resistance. Al-MM alloys with various MM compositions (Ce, Ce-50La, Ce-33La, and Ce-27La-19Nd, weight percent) exhibit near-eutectic and hyper-e...

To investigate naphthalene as a suspending fluid for freeze-casting applications, sterically stabilized suspensions of copper microparticles suspended in liquid naphthalene are directionally solidified in a Bridgman furnace. Colonies of nearly particle-free naphthalene lamellae, interspersed with particle-enriched interlamellar regions, are predomi...

An oxygen‐resistant refractory high‐entropy alloy is synthesized in microlattice or bulk form by 3D ink‐extrusion printing, interdiffusion, and silicide coating. Additive manufacturing of equiatomic HfNbTaTiZr is implemented by extruding inks containing hydride powders, de‐binding under H2, and sintering under vacuum. The sequential decomposition o...

The study investigates the microstructure and mechanical properties of five cast, coarse-grained intermetallic alloys: binary Al11Ce3 and Al11La3, ternary Al11(Ce0.75La0.25)3 and Al11(Ce0.5La0.5)3, and quaternary Al11(Ce0.54La0.27Nd0.19)3 with mischmetal composition. All compounds exhibit a single phase indicating a solid solution among the rare-ea...

We characterize the microstructure and mechanical properties of cast Al-Ce-Ni-Mn-Sc-Zr alloys designed for structural use above 300 °C. We first report on the effect of Ni on the as-cast phase formation, where all alloys consist of fine Al11Ce3 and Ni-rich eutectic phases, but the identity of the Ni-rich phase varies with Ni content. Furthermore, t...

Hydrogen release/storage materials for iron/air batteries are fabricated as Fe‐16Mo and Fe‐24Ni (at.%) lattices via 3D‐extrusion printing of foamed inks containing oxide microparticles, followed by H2 reduction and sintering. A hierarchical open porosity is designed: (i) channels between walls created during printing, (ii) mesopores within walls, c...

Research on thermoelectric materials – with their vast potential for applications in solid-state cooling or energy-conversion devices – has so far mainly focused on enhancing their conversion efficiency. However, understanding and tailoring the mechanical performance of thermoelectric modules and devices is crucial for their long-term use, as they...

The effects of 1 wt% HfO2 nano-dispersoid addition on the microstructure of a high-γ' Ni-8.5Cr-5.5Al-1Ti (wt%) model superalloy are investigated after manufacturing via laser-based powder-bed fusion (PBF-LB). Despite their very high melting point, HfO2 dispersoids are not fully stable during their short stay in the melt pool. At the nanoscale, the...

We demonstrate that a small addition of a low-melting pointMelting point element such as Sn (0.02 at.%), within the impurity tolerances of commercial aluminum alloys, to an Al-0.5Mn-0.3Si (at.%) model alloy, converts this non-heat-treatable (with negligible precipitation strengtheningPrecipitation strengthening) alloy into a heat-treatable (precipi...

Additive manufacturing of lattices with ∼600 μm diameter struts is achieved via extrusion printing of an ink containing prealloyed powder of the half-Heusler alloy Nb1-xCoSb, followed by debinding and vacuum sintering to a relative density of ∼70-80%. The ink can also be poured and cast into square blocks, which, after debinding and sintering, achi...

Microstructural development during solidification and subsequent aging, and the resulting creep resistance, of laser powder-bed fusion (LPBF) Al-3.6Mn-2.0Fe-1.8Si-0.9Zr (wt%) alloy has been investigated. A bimodal grain structure is observed within the melt pool, with the bottom (MPB) exhibiting ultrafine equiaxed grains (~1 µm in diameter) and the...

This study investigates the microstructure and thermomechanical properties of the intermetallic compound Al11Ce3, which strengthens Al–Ce based eutectic alloys. Arc-melted bulk Al11Ce3, consisting of coarse, elongated grains oriented along the solidifying direction with internal twins, is hard and brittle at ambient temperature, with a microhardnes...

Precipitation-strengthening at ambient and high temperatures is examined in Al-0.5Mn-0.3Si (at.%) alloys with and without 0.02 at.% Sn micro-additions. Isochronal aging experiments reveal that Sn inoculation results in a pronounced age-hardening response: a hardening increment of 125 MPa is achieved at peak-aging (475 °C), which is five times great...

The microstructure and mechanical properties of two die-cast hypoeutectic Al-Ce-based alloys modified with Sc, Zr and Er micro-additions – Al-1.5Ce-0.14Sc-0.03Zr with high Sc content and Al-1.4Ce-0.02Sc-0.06Zr-0.003Er (at%) with low Sc content – are studied, with focus on the two strengthening phases: micron-scale Al11Ce3 platelets formed on solidi...

The effects of the modification of a high‐γ' Ni–8.5Cr–5.5Al–1Ti (wt%) model superalloy with 0.5 wt% Y2O3, manufactured by laser powder bed fusion, on the microstructure and compressive creep resistance, are investigated. Compared with the base alloy, the oxide dispersion‐strengthened (ODS) alloy exhibits 8–10 times slower creep rates at 800 °C, ove...

The effect of Ni and Cr additions on microstructure, lattice misfit, oxidation, and creep properties are investigated for six W- and Mo-free cobalt-based superalloys with compositions Co-xNi-5Al-yCr-3V–2Ti-1.5Nb-1.5Ta-0.08B (at.%), where x = 10, 20, or 30 and y = 4 or 8. In all alloys, the γ + γ′ microstructure is stable for up to 1000 h upon aging...

Cyclical steam oxidation and hydrogen reduction, relevant to iron-air batteries, is performed on freeze-cast Fe-25Ni (at.%) foams consisting of colonies of parallel lamellae separated by channels, both ∼20 µm thick and millimeters in length. This structure is designed to accommodate volumetric changes associated with the cyclical oxidation and redu...

Microlattices with orthogonal 0-90° architecture are 3D-extrusion printed from inks containing a blend of oxide powders (Co3O4, CuO, Fe2O3, and NiO) and metal powder (Cr). Equiatomic CoCrCuFeNi microlattices with ∼170 μm diameter struts are then synthesized by H2-reduction of the oxides followed by sintering and interdiffusion of the resulting meta...

Laser powder bed fusion (LPBF) was used to consolidate powders of a Ni-Cr-Fe-Mo alloy (Hastelloy X) blended with 1 wt% Y2O3 nanometric powders. The nearly-dense, crack-free specimens, with and without oxide dispersion strengthening (ODS), exhibit high-aspect ratio grains, aligned in the build direction and with a strong texture: 〈001〉 is aligned al...

Binary Al-1.7 wt.% Zr (Al-0.5 at.% Zr) alloys, with and without 1 wt.% (0.7 vol.%) Al2O3 nanoparticle additions (80-100 nm), are fabricated by laser powder-bed fusion (L-PBF) from blends of Al, Zr, and Al2O3 powders. Elemental Zr, which is ~80% dissolved in the melt pool, forms primary L12-Al3Zr precipitates upon solidification and is also retained...

The effects of alloying Fe with 25 at% Co or 30 at% Cu are studied in freeze-cast lamellar foams subjected to redox cycling under H2- and H2O-rich atmospheres at 800 ºC, relevant to metal-air batteries. In unalloyed Fe foams, redox cycling causes irreversible Kirkendall porosity growth within lamellae, leading to fracture and buckling in the lamell...

Elemental powder blends are an emerging alternative to prealloyed powders for high-throughput alloy design via additive manufacturing techniques. Elemental Al+Sc(+Zr) powder blends were processed by laser powder bed fusion into Al-Sc and Al-Sc-Zr alloys, with operando X-ray diffraction at the Swiss Light Source extracting the structural and thermal...

The aging behavior and creep resistance of eutectic AlSi10Mg (Al–10Si-0.6Mg, wt.%) manufactured by laser powder bed fusion (L-PBF) are studied at 260 and 300 °C. The Si phase, which forms a fine interconnected network of 100–200 nm filaments in the as-printed alloy, coarsens into blocky, 2–3 μm particles after 1 month exposure at 260 and 300 °C, wi...

The solidification microstructure and the aging- and creep-resistances of a laser powder-bed fused (LPBF) hypoeutectic Al-7.3Ce-7.7Mg (wt. %) alloy were investigated. Optimized process parameters allowed to produce specimens with >99.7% relative density and high hardness (~1650 MPa), without solidification cracking despite a relatively coarse grain...

The microstructural evolutions, upon solidification and subsequent aging, and associated hardening effects for both cast and laser-surface-remelted Al–8Ce-0.2Sc-0.1Zr (wt.%) hypo-eutectic alloy are investigated with focus on precipitation and coarsening behavior of their Al11Ce3 and L12-Al3(Sc,Zr) precipitates. Laser surface remelting, which produc...

Tensile and compressive creep tests were performed at 300 °C on high-temperature Al–Cu–Mn–Zr (ACMZ) alloys with 6 wt% Cu (6Cu) and 9 wt% Cu (9Cu) to evaluate the effect on creep properties of micron-size θ-Al2Cu intergranular precipitates. For compressive creep, the increased volume fraction of θ-precipitates at grain boundaries (from ∼0.7% in 6Cu...

The eutectic Al–6Ni (wt.%) alloy exhibits excellent strength at ambient and elevated temperature, provided by a high volume fraction of Al3Ni microfibers formed during solidification. Here, Al–6Ni is micro-alloyed with Sc and Zr (with 0.1Sc+0.2Zr, 0.2Sc+0.4Zr and 0.3Sc+0.2Zr, wt.%), creating two additional populations of primary and secondary Al3(S...

Tensile and compressive creep properties of a quaternary Al-Cu-Mn-Zr (ACMZ) alloy and its commercial counterpart (Al-Cu-Mn-Zr with Ni, Co and Sb additions, RR350) are investigated at 300°C. At low stresses up to 30 MPa where diffusional creep dominates, creep resistance is the same in tension and compression and RR350 deforms more slowly than ACMZ,...

This study investigates the as-cast and aged microstructures, thermal stability, ambient temperature strengthening, and creep resistance of three ternary Al–Ce–Ni alloys (wt.%): near-eutectic Al–10Ce–5Ni (with both eutectic and hypoeutectic regions), hypoeutectic Al-7.5Ce-3.75Ni (with numerous primary Al dendrites), and hypereutectic Al-12.5Ce-6.25...

Finite element modeling is used to simulate the secondary creep rate of alloys with an inhomogeneous distribution of nano-precipitates, located within colonies of long, parallel dendrites, due to elemental segregation during directional solidification. Three-dimensional, periodic unit cells are created to approximate the aligned dendritic microstru...

Liquid ink-printing followed by sintering is used to fabricate WC-Co microlattices and cutting tools. The microstructure of WC-xCo (x=0.5-20 wt.%) is studied for a range of carbide-to-binder ratio and for various sintering temperatures. For 0.5≤Co≤5 wt.%, struts in microlattices exhibit residual porosity due to incomplete densification, even at the...

Complex-shaped, finely-featured, ultra-high-melting ZrC/W composite structures were produced by coupling, for the first time, three-dimensional (3-D) ink-extrusion printing with shape/size-preserving reactive melt infiltration (the Displacive Compensation of Porosity, DCP, process). Inks containing sub-micron WC powders were printed at ambient temp...

The fabrication of 3D ink-printed and sintered porous Si scaffolds as electrode material for lithium-ion batteries is explored. A hierarchically-porous architecture consisting of channels (~220 μm in diameter) between microporous Si struts is created to accommodate the large volume change from Si (de)lithiation during electrochemical (dis)charging....

The post-processing treatment response of a Y2O3 oxide-dispersion-strengthened (ODS) and γ/γ'-strengthened Ni-8Cr-5.5Al-1Ti (wt.%) model alloy, produced by laser powder bed fusion (L-PBF) is studied. The solutionizing treatment at 1260 °C induces significant recrystallization of the initial elongated grain microstructure, characteristic of L-PBF pr...

The successful synthesis of oxide-dispersion-strengthened (ODS) alloys via laser powder bed fusion (L-PBF) requires a better understanding of the interaction of the oxide dispersoids with the metallic melt pool. Here, a γ/γ’-strengthened Ni-8Cr-5.5Al-1Ti (wt.%) model alloy is studied, as a simplified version of the commercial CM247LC alloy, by melt...

Directional freeze-casting (FC) of powder suspensions followed by freeze-drying and sintering is a versatile and scalable processing route for creating metallic foams with highly elongated pores. Because of the high propensity for oxidation of metal powders, the use of precursor oxide powders is studied here with an additional step of H2-reduction...

We examine the precipitation and creep behavior of Al-0.5Mn-0.02Si (at.%) alloys, with and without the L12-forming elements Zr and Er (0.09 and 0.05 at.%, respectively), utilizing isochronal aging experiments as well as compressive and tensile creep tests performed between 275 and 400 °C. The Al-0.5Mn-0.09Zr-0.05Er-0.05Si alloy exhibits an unusuall...

In-situ and ex-situ X-ray 3D-tomography is used to characterize the microstructure of Ni microwires, with wire diameters spanning 25–100 μm, (i) after vapor-phase deposition of Ti onto their surface and (ii) after subsequent homogenization to achieve the near-equiatomic NiTi composition desired for shape-memory or superelastic behavior. After Ti de...

Cobalt-based superalloy microlattices with γ/γ΄ microstructure are manufactured by combining two additive methods: ink-extrusion 3D-printing and pack-cementation surface alloying. First, a microlattice green structure is 3D-printed at ambient temperature from inks comprised of Co3O4, NiO, and WO3 powders, an elastomeric binder and solvents. Organic...

Commercial aluminum alloys are unusable above ~250 oC (523 K, which is 56% of the absolute melting point of aluminum, Tm = 933 K), due mainly to the rapid coarsening/dissolution of their fine strengthening precipitates. The recently developed L12-strengthened alloys exhibit, however, a significantly better coarsening resistance at high temperatures...

Recently discovered Co-Nb-V- and Co-Ta-V-based superalloys exhibit, with additions of Ni, Cr, Ti and Al, a stable γ+γ’ microstructure leading to excellent creep resistance. Here, to obtain a γ’-volume fraction higher than in the best current alloys, the concentration of all γ’-formers are increased by 25 or 50% (for Al, Ti and V) and by 10% (for Nb...

Additive manufacturing (AM) of non-weldable high-γ’ Ni base superalloys is challenging due to various issues, but notably because of their inherent cracking propensity. Typically, the segregation of melting point-depressant elements to grain boundaries (GB) drastically increases the solidification interval, allowing the high processing-induced stre...

SnO2-Ag composites with designed architectures with sub-millimeter feature sizes can provide enhanced functionality in electrical applications. SnO2-Ag composites consisting of a ceramic SnO2 micro-lattice filled with metallic Ag are created via a hybrid additive manufacturing method. The multistep process includes: (i) 3D extrusion printing of 0/9...

Additive manufacturing of objects with complex geometries from refractory metals remains very challenging. Here, we demonstrate the fabrication of tungsten sheet-gyroids via 3D ink-extrusion of WO3 nano-powder followed by hydrogen reduction and activated sintering with NiO additions, as an alternative route to beam-based additive manufacturing of t...

A micro-addition (0.025 at.%) of slow-diffusing W to an Al-0.26Mn-0.11Mo-0.11Si-0.08Zr-0.02Sc-0.01Er (at.%) alloy accelerates L12-Al3(Zr,Sc) precipitation but retards α-Al(Mn,Mo)Si precipitation. The W micro-addition increases the peak-microhardness of the alloy during isothermal aging but does not improve the coarsening resistance and creep resist...