Direct Alloying of Immiscible Tungsten and Copper Based on Nano Active Structure and Its Thermodynamic Mechanism
W is usually used as plasma-facing components in nuclear fusion reactors because of its high melting point,low sputtering yield,high-temperature strength,and low tritium retention properties.On the other hand,Cu and its alloys show excellent thermal conductivity making them ideal as a heat sink material in reactors.Therefore,W-Cu layered composites have important applications in nuclear fu-sion reactors.Due to the immiscibility between W and Cu,direct alloying between them without using in-terlayer metals is critical for the preparation of such layered composites.In this study,a nanoporous ac-tive structure was used to induce and promote the direct alloying of the W-Cu system.Direct alloying con-sists of three steps.First,a nanoporous active layer is prepared on the surface of a W foil via two-step an-odizing and deoxidized annealing in a hydrogen atmosphere.Second,a Cu coating layer is deposited on the nanoporous W by electroplating.Finally,the obtained W-Cu electrodeposited sample is annealed at temperatures close to the melting point of Cu(i.e.,980℃).The established thermodynamic model for the direct alloying of immiscible metal systems is used for the direct alloying of W and Cu based on a nanopo-rous active structure.There are two problems with this model.First,the surface energy results are arbitrary due to the selection of the number of surface atomic layers.Second,the unit scale in thermodynamic cal-culations.To solve these problems,the calculation methods for surface energy and pressure energy are improved in this work,which makes the thermodynamic calculation for the direct alloying of W-Cu based on a nanoporous active structure feasible.The results show that a nanoporous active structure is formed on the surface of W after nanotreatment.The characterization results of the W/Cu interface show that the diffusion distance between the two metals is about 27 nm and the direct alloying between W and Cu is successful.The average shear strength of the W-Cu layered composites was 101 MPa.This is a 16%increase compared with W-Cu layered composites without a nanoporous structure.The thermody-namic calculation results show that the surface energy of the W-Cu system is greatly improved due to the nanoporous active structure prepared on the W surface.The surface energy can be used as the main thermodynamic driving force for the direct alloying of W-Cu systems.There are different reasons why nanotreatment increases W surface energy.One reason is the increase of crystal planes with high sur-face energy via nanotreatment of the W surface,and another is the shape of the nanoporous structure.
immiscible W-Cu systemnanoporous structuredirect alloyingthermodynamic modelsurface energy
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维普
