Freeze-casting produces materials with complex, three-dimensional pore structures which may be tuned during the solidification process. The range of potential applications of freeze-cast materials is ...vast, and includes: structural materials, biomaterials, filtration membranes, pharmaceuticals, and foodstuffs. Fabrication of materials with application-specific microstructures is possible via freeze casting, however, the templating process is highly complex and the underlying principles are only partially understood. Here, we report the creation of a freeze-casting experimental data repository, which contains data extracted from ∼800 different freeze-casting papers (as of August 2017). These data pertain to variables that link processing conditions to microstructural characteristics, and finally, mechanical properties. The aim of this work is to facilitate broad dissemination of relevant data to freeze-casting researchers, promote better informed experimental design, and encourage modeling efforts that relate processing conditions to microstructure formation and material properties. An initial, systematic analysis of these data is provided and key processing-structure-property relationships posited in the freeze-casting literature are discussed and tested against the database. Tools for data visualization and exploration available through the web interface are also provided.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Porous metals and metallic foams are presently the focus of very active research and development activities. There are currently around 150 institutions working on metallic foams worldwide, most of ...them focussing on their manufacture and characterisation. Various companies are developing and producing these materials which are now being used in numerous industrial applications such as lightweight structures, biomedical implants, filters, electrodes, catalysts, and heat exchangers. This review summarizes recent developments on these materials, with particular emphasis on research presented at the latest International Conference on Porous Metals and Metallic Foams (MetFoam 2007).
Porous metals and metallic foams are presently the focus of very active research and development activities. There are currently around 150 institutions working on metallic foams worldwide, most of them focussing on their manufacture and characterisation. Various companies are developing and producing these materials which are now being used in numerous industrial applications such as lightweight structures, biomedical implants, filters, electrodes, catalysts, and heat exchangers. This review summarizes recent developments on these materials, with particular emphasis on research presented at the latest International Conference on Porous Metals and Metallic Foams (MetFoam 2007).
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The off‐stoichiometric Ni2MnGa Heusler alloy is a magnetic shape‐memory alloy capable of reversible magnetic‐field‐induced strains (MFIS). These are generated by twin boundaries moving under the ...influence of an internal stress produced by a magnetic field through the magnetocrystalline anisotropy. While MFIS are very large (up to 10%) for monocrystalline Ni‐Mn‐Ga, they are near zero (<0.01%) in fine‐grained polycrystals due to incompatibilities during twinning of neighboring grains and the resulting internal geometrical constraints. By growing the grains and/or shrinking the sample, the grain size becomes comparable to one or more characteristic sample sizes (film thickness, wire or strut diameter, ribbon width, particle diameter, etc), and the grains become surrounded by free space. This reduces the incompatibilities between neighboring grains and can favor twinning and thus increase the MFIS. This approach was validated recently with very large MFIS (0.2‐8%) measured in Ni‐Mn‐Ga fibers and foams with bamboo grains with dimensions similar to the fiber or strut diameters and in thin plates where grain diameters are comparable to plate thickness. Here, we review processing, micro‐ and macrostructure, and magneto‐mechanical properties of (i) Ni‐Mn‐Ga powders, fibers, ribbons and films with one or more small dimension, which are amenable to the growth of bamboo grains leading to large MFIS, and (ii) “constructs” from these structural elements (e.g., mats, laminates, textiles, foams and composites). Various strategies are proposed to accentuate this geometric effect which enables large MFIS in polycrystalline Ni‐Mn‐Ga by matching grain and sample sizes.
In Ni‐Mn‐Ga alloys the large twinning magnetic‐field‐induced strains (MFIS) present in monocrystals become negligible in polycrystals due to grain‐boundaries constraints. When grain and sample sizes become comparable, constraints are relaxed and high MFIS become again possible. We review Ni‐Mn‐Ga powders, fibers, ribbons, and films where bamboo grains produce large MFIS, and “constructs” from these elements (mats, laminates, textiles, foams and composites).
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The effect of substituting 0.01 or 0.02
at.% Er for Sc in an Al–0.06 Zr–0.06 Sc
at.% alloy was studied to develop cost-effective high-temperature aluminum alloys for aerospace and automotive ...applications. Spheroidal, coherent, L1
2-ordered Al
3(Sc, Zr, Er) precipitates with a structure consisting of an Er-enriched core surrounded by a Sc-enriched inner shell and a Zr-enriched outer shell (core/double-shell structure) were formed after aging at 400
°C. This core/double-shell structure strengthens the alloy, and renders it coarsening resistant for at least 64
days at 400
°C. This structure is formed due to sequential precipitation of solute elements according to their diffusivities,
D, where
D
Er
>
D
Sc
>
D
Zr at 400
°C. Zr and Er are effective replacements for Sc, accounting for 33
±
1% of the total precipitate solute content in an Al–0.06 Zr–0.04 Sc–0.02 Er
at.% alloy aged at 400
°C for 64
days. Er accelerates precipitation kinetics at 400
°C, resulting in: (i) strengthening due to the elimination of lobed-cuboidal precipitates in favor of spheroidal precipitates; and (ii) a decrease in the incubation time for nucleation because
D
Er
>
D
Sc. Finally, a two-stage aging treatment (24
h at 300
°C
+
8
h at 400
°C) provides peak microhardness due to optimization of the nanostructure.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A ternary Al-6.9Ce-9.3Mg (wt.%) hypoeutectic alloy, consisting of equal amounts of α-Al(Mg) solid-solution regions and Al(Mg)-Al11Ce3 eutectic colonies, is investigated in terms of its aging and ...creep resistance. The eutectic regions exhibit a microhardness of 1230 MPa, which is thrice the value of Al-Al11Ce3 eutectic regions in a binary Al-12.5Ce (wt.%) near-eutectic alloy, demonstrating that Mg in solid-solution enhances the strengthening provided by the micron-scale highly-branched Al11Ce3 phase. X-ray diffraction measurements during ambient-temperature tensile testing reveal that load is being transferred from the Al(Mg) matrix to the Al11Ce3 phase, confirming that the fine eutectic microstructure displays composite strengthening in addition to the expected precipitation- and solid-solution strengthening. The hardness remains effectively unchanged after aging at 450 °C for up to 8 weeks, indicating excellent coarsening resistance of the Al11Ce3 phase. The ternary alloy exhibits creep resistance at 300 °C slightly inferior to the near-fully eutectic binary Al-12.5Ce (wt.%) alloy, consistent with the presence of large regions of fast-creeping primary Al(Mg) solid-solution matrix between the strong Al(Mg)-Al11Ce3 eutectic colonies in the hypoeutectic ternary alloy.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Additive manufacturing of high-entropy alloys combines the mechanical properties of this novel family of alloys with the geometrical freedom and complexity required by modern designs. Here, a ...non-beam approach to additive manufacturing of high-entropy alloys is developed based on 3D extrusion of inks containing a blend of oxide nanopowders (Co
O
+ Cr
O
+ Fe
O
+ NiO), followed by co-reduction to metals, inter-diffusion and sintering to near-full density CoCrFeNi in H
. A complex phase evolution path is observed by in-situ X-ray diffraction in extruded filaments when the oxide phases undergo reduction and the resulting metals inter-diffuse, ultimately forming face-centered-cubic equiatomic CoCrFeNi alloy. Linked to the phase evolution is a complex structural evolution, from loosely packed oxide particles in the green body to fully-annealed, metallic CoCrFeNi with 99.6 ± 0.1% relative density. CoCrFeNi micro-lattices are created with strut diameters as low as 100 μm and excellent mechanical properties at ambient and cryogenic temperatures.
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, consistent with RR350 alloy's larger linear fraction of intergranular precipitates (Al7Cu2(NiFe) and Al9FeNi for RR350 vs. θ-Al2Cu for ACMZ) and a reduced fraction of precipitate-free zones near grain boundaries. At stresses between 30 and 80 MPa, dislocation creep with a stress exponent n ∼ 3 becomes rate-limiting in compression, which is expected to be controlled by θ′ precipitates within the grain bulk. By contrast, in tension, enhanced creep rate and higher apparent stress exponents are measured, consistent with cavitation at intergranular precipitates becoming increasingly dominant as the stress increases. In the dislocation creep regime, RR350 alloy is again more creep resistant than ACMZ alloy, which is related to three mechanisms (i) a reduced fraction of softer precipitate-free zones, (ii) more effective load transfer to intergranular precipitates, and (iii) reduced cavitation. A model for cavitation is applied to calculate tensile creep rates from compressive creep rates and the model successfully predicts the improved tensile creep resistance of the RR350 alloy. The present investigation underscores the importance of intergranular grain boundary precipitates, in addition to strengthening θ′ precipitates, in enhancing the creep resistance of Al-Cu alloys.
Display omitted
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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 produces solidification conditions typical of additive manufacturing (AM) processes, suppresses formation of undesirable primary Al11Ce3 and Al3(Sc,Zr) precipitates on solidification. It also greatly refines the interlamellar spacing of the eutectic Al11Ce3 phase, thus enhancing the Orowan strengthening effect as compared to the cast alloy, beyond the load-transfer effect from the Al11Ce3 phase. Subsequent aging at 325 °C leads to further hardening of both alloys due to secondary Al3(Sc,Zr) nanoprecipitation, with much more pronounced hardness increases in the laser-remelted alloy, owing to a higher number density of finer Al3(Sc,Zr) nanoprecipitates, as compared to the cast alloy. This improvement is rationalized by an enhancement of Al3(Sc,Zr) nucleation rate upon aging of laser-remelted alloy, as compared to the cast alloy, considering differences in elemental supersaturation within the α-Al regions of these alloys. Prolonged aging, up to 1000 h, at 325 °C causes the hardness of both alloys to decline relatively slowly, implying that this alloy is suitable for AM processes and subsequent applications where high strength and good heat resistance are needed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study investigates the creep behavior of a cast, coarse-grained Al-12.5 wt.% Ce (Al-2.7 at.% Ce) alloy, consisting of an eutectic microstructure (α-Al with ~11 vol.% submicron Al11Ce3 “Chinese ...script” platelets) with ~3 vol.% primary, micron-scale Al11Ce3 plates. Upon aging at 322 °C for 8 weeks or at 400 °C for 12 weeks, the microhardness of the alloy remains unchanged, demonstrating excellent coarsening resistance of the strengthening Al11Ce3 phase. In addition, no coarsening of Al11Ce3 is observed metallographically after 3 weeks under compressive loads of 13–70 MPa at 260–350 °C. When tested to failure under a constant tensile stress of 23 MPa at 300 °C, the alloy shows primary, secondary and tertiary creep regimes, and fails after 19 days at 17% tensile strain, demonstrating both high creep ductility and high creep resistance. Under compressive and tensile creep conditions, the alloy exhibits high apparent stress exponents (n = 9–11), which translate into threshold stresses for dislocation creep of 34, 22, and 14 MPa at 260, 300 and 350 °C, respectively. The creep resistance of Al-12.5 wt.% Ce is higher than that of Al-Sc-Zr-based alloys (with ~0.3 vol.% of coherent nanoprecipitates) and similar to cast, eutectic Al-6 wt.% Ni (with ~11 vol.% of incoherent Al3Ni micro-fibers). For as-cast grain sizes of 2–3 mm, Al-12.5 wt.% Ce exhibits a transition from dislocation creep to diffusional creep at strain rates of ~10−7 s−1, with a threshold stress of 19 MPa in compression at 260 °C and 5 MPa in tension at 300 °C.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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 at 850 °C. As Ni increases from 10 to 30 at.%, the γ′ area fraction increases from 32 to 49% in the three low-Cr alloys, while remaining constant (45%) for the high-Cr alloys. All alloys show positive γ/γ′ lattice misfits of 0.8 ± 0.2%, consistent with γ’ rafting observed after creep. Both Cr and Ni additions increase oxidation resistance, more so for 8% Cr than for 30% Ni, as expected from the high stability of chromium oxide. Increasing Cr from 4 to 8 at.% slightly increases creep resistance at 850 °C and increasing Ni from 10 to 30% has a similar effect.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
