Sintering of powders is a common means of producing bulk materials when melt casting is impossible or does not achieve a desired microstructure, and has long been pursued for nanocrystalline materials in particular. Acceleration of sintering is desirable to lower processing temperatures and times, and thus to limit undesirable microstructure evolution. Here we show that markedly enhanced sintering is possible in some nanocrystalline alloys. In a nanostructured W–Cr alloy, sintering sets on at a very low temperature that is commensurate with phase separation to form a Cr-rich phase with a nanoscale arrangement that supports rapid diffusional transport. The method permits bulk full density specimens with nanoscale grains, produced during a sintering cycle involving no applied stress. We further show that such accelerated sintering can be evoked by design in other nanocrystalline alloys, opening the door to a variety of nanostructured bulk materials processed in arbitrary shapes from powder inputs.

Grain boundary (GB) segregation can markedly improve the stability of nanostructured alloys, where the fraction of GB sites is inherently large. Here, we explore the concept of entropically supported GB segregation in alloys with a tendency to phase-separate and its role in stabilizing nanostructures therein. These duplex nanocrystalline alloys are notably different, both in a structural and thermodynamic sense, from the previously studied "classical" nanocrystalline alloys, which are solid solutions with GB segregation of solute. Experiments are conducted on the W-Cr system, in which nanoduplex structures are expected. Upon heating ball-milled W-15 at.% Cr up to 950°C, a nanoscale Cr-rich phase was found along the GBs. These precipitates mostly dissolved into the W-rich grains leaving behind Cr-enriched GBs upon further heating to 1400°C. The presence of Cr-rich nanoprecipitates and GB segregation of Cr is in line with prediction from our Monte Carlo simulation when GB states are incorporated into the alloy thermodynamics.

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The development and application of all-solid-state batteries with a fast lithium-ionic conductor are hampered by structural instability and rigid stoichiometry restrictions. Here, we present a family of lithium thiophosphate prototypes with a novel principle, controlling sulfur deficiencies with the addition of nickel sulfide-based additives, for fast lithium-ion conduction and distinct electrochemical stability under the extended material constituent. Well-controlled sulfur deficiency of the Li 3 PS 4 framework accompanied by nickel sulfide additive offers the notable increase of lithium-ion conductivity (2 × 10 −3 S cm −1 at 25 °C) and high electrochemical stability (up to 10 V vs Li/Li + ) in a wide composition range. We further confirm the potential application of our fast composite lithium-ion conductor as an electrolyte for the all-solid-state battery with 117 mAh g −1 capacity delivery and stable cycle life.

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