Search

Abstract Copper matrix composite materials with diamond particles are considered to be among the leading candidates as the heat sink materials for future electronic devices. However, today, these materials are mostly produced by high temperature-high pressure (HTHP) processes, which can be very costly. In order to explore an economically more viable approach of producing copper-diamond composite materials, we used electrodeposition to synthesize such materials and measured their thermal conductivities. The maximum thermal conductivity observed was 454 W/mK at 68.2 vol % diamond. In an attempt to improve the thermal conductivity further, titanium carbide (TiC) coatings were implemented on the diamond particles. The TiC coated diamond particles embedded in the electrodeposited copper matrix improved the thermal conductivity to 557 W/mK at 34.7 vol % , which is ∼ 40 % higher than 400 W/mK for pure copper. This value is comparable to currently available commercial HTHP heat sink materials. These results show that there is a potential of using electrodeposition an alternative synthesis method for producing copper-diamond composite materials for thermal managements. However, the formation of the microstructure at different electrodeposition current densities suggests that a careful process optimization is required to obtain a void-free Cu matrix between the embedded diamond particles. Highlights • Copper-diamond composite materials were produced using electrodeposition. • Thermal conductivity of copper was increased from 400 W/mK to 557 W/mK at 34.7 vol.% diamond. • Effects of diamond intermetallic coatings on the electrodeposition process are discussed. [ABSTRACT FROM AUTHOR]

High-entropy alloy (HEA) design is an emerging methodology that stabilizes nanocrystalline materials, which themselves are highly sought after due to their high strength and hardness resulting from grain boundary hardening. In the past decade, studies have examined the synthesis and performance of such materials made primarily from vapour- and solid-state processing methods, which offer little flexibility in scalability. By contrast, electrodeposition is a relatively low-cost, highly scalable fabrication route for nanocrystalline materials that can be applied to almost any substrate shape or material, which also has industrial-scale infrastructure already in place. Here, we report the first comprehensive study on the synthesis and characterization of electrodeposited HEAs made from aqueous electrolytes, building on the groundwork of past work on electrodeposited medium-entropy alloys. High-quality alloys of NiFeCo-W, NiFeCo-Mo, and NiFeCo-MoW were deposited onto Cu substrates at thicknesses in the range 31–44 µm. W-containing alloys took on banded structures with underlaying growth-oriented features that are postulated to be nanoglass domains. NiFeCo-Mo exhibited the highest hardness-to-density ratio among these alloys, owing to its laminated nanocrystalline-amorphous structure. We also revealed an inverse Hall-Petch relationship in NiFeCo-W, as well as a linear dependence of hardness on Ni content in the alloys. Our study continues to build a framework for electrodeposition of HEAs, paving the way for developing new high-strength, thermally stable, and scalable nanostructured materials. [Display omitted] • First comprehensive investigation of the use of electrodeposition to fabricate nanostructured HEAs. • Alloys containing W exhibit what is postulated to be nanoglass character, with boundaries elongated in the growth direction. • Post-process annealing can be used to drive nanocrystal formation in amorphous precursor alloys. • Inverse Hall-Petch hardening exists in NiFeCo-W alloys at grain sizes below 10 nm. [ABSTRACT FROM AUTHOR]

Copper coatings on steel, manufactured by a novel combination of two different manufacturing technologies, electrodeposition and cold spraying, are employed as a corrosion barrier in the current design of used fuel containers (UFCs) for the long-term storage of Canada's used nuclear fuel. This study examines such copper coatings on a prototype container section, with a particular focus on the interface region where copper materials fabricated by the two processes converge. Distinct microstructures for the electrodeposited and cold sprayed copper layers were observed. An unexpected recrystallized layer on top of electrodeposited copper was identified for the first time. Local annealing at 350 °C and 600 °C for one hour resulted in more homogeneous microstructures and Vickers hardness profiles among the copper layers, which is favorable for this application by reducing processing related heterogeneity in the interface region. More homogenized structures with high fractions of special grain boundaries in this region are expected to provide enhanced mechanical and corrosion properties. • Microstructural analysis was performed on Cu coatings for used fuel containers. • A recrystallized layer between electrodeposited and cold sprayed Cu was identified. • Annealing reduces microstructural and mechanical heterogeneity. • Nanotwinned electrodeposited Cu experiences texture evolution during annealing. [ABSTRACT FROM AUTHOR]

Copper coatings produced by additive manufacturing techniques often present complex microstructural heterogeneity. Reducing microstructural heterogeneity is critical for promoting uniform mechanical and corrosion behavior. The current study examines copper coatings at the closure weld zone of a prototype steel container designed to store used nuclear fuel. In this region, the copper coating is produced by two additive manufacturing processes: electrodeposition and cold spray. Microscopy analysis revealed a highly non-uniform microstructure in the as-processed state. After heat treatment at 350 °C for 1 h under inert conditions, this heterogeneity was significantly reduced resulting in favourable microstructural characteristics for the current application. Unlabelled Image • Corrosion barrier Cu coating for used nuclear fuel containers was analyzed. • Cu coating is made by electrodeposition and cold-spray at the closure weld zone. • Significant microstructural heterogeneity was observed in the as-deposited coating. • After an annealing treatment, the heterogeneity was greatly reduced. • The annealed microstructure is more favourable for the current application. [ABSTRACT FROM AUTHOR]

In the design of used nuclear fuel containers for deep geological repositories, copper is considered to be a suitable and long-lived barrier for corrosion resistance. The microstructures of state-of-the-art copper materials used in this application produced through extrusion, a grain boundary engineered electrodeposition technique and cold spraying were studied via electron backscattered diffraction. Desirable microstructural characteristics for localized corrosion resistance of pure copper were compiled from the literature considering grain size, grain boundary character distribution, and crystallographic texture. The subject copper materials were found to have favourable microstructures for localized corrosion resistance, in particular, a high fraction of special grain boundaries, especially Σ3 twins, rendering them suitable for the given application. • Cu coating materials for used nuclear fuel containers were characterized with EBSD. • Both electrodeposited and cold-sprayed Cu contain many special grain boundaries. • The microstructural features are favourable for localized corrosion resistance. [ABSTRACT FROM AUTHOR]