基于纳米活性结构的不互溶W-Cu体系直接合金化及其热力学机制

Direct Alloying of Immiscible Tungsten and Copper Based on Nano Active Structure and Its Thermodynamic Mechanism

利用纳米多孔活性结构诱导和促进W和Cu直接合金化,主要包括3步骤:首先,通过两步阳极氧化和还原退火在W表面制备纳米多孔结构;然后,在纳米多孔W上电沉积Cu层;最后,在近Cu熔点温度(980℃)下退火,得到W/Cu层状复合材料/连接件。W/Cu界面的表征结果表明,2种金属间的扩散距离约为27 nm,W和Cu之间成功实现直接合金化。同时,针对此前建立的不互溶金属直接合金化热力学模型存在的问题,改进了表面能和压力能的计算方法,解决了表面原子层数选用导致表面能结果具有随意性的问题和热力学计算中的单位尺度问题,实现了基于纳米活性结构的不互溶W-Cu直接合金化的热力学计算。热力学计算结果表明,W表面纳米多孔化之后W-Cu体系的表面能大幅提升,可以作为W和Cu直接合金化的热力学驱动力。分析认为,除具有高表面能的晶面增多之外,纳米结构形状也是W表面纳米化后表面能提高的主要原因之一。

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 fusion reactors.Due to the immiscibility between W and Cu,direct alloying between them without using interlayer metals is critical for the preparation of such layered composites.In this study,a nanoporous active structure was used to induce and promote the direct alloying of the W-Cu system.Direct alloying consists of three steps.First,a nanoporous active layer is prepared on the surface of a W foil via two-step anodizing 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.,980oC).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 nanoporous 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 calculations.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 thermodynamic 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 surface energy via nanotreatment of the W surface,and another is the shape of the nanoporous structure.