Improved strength and heat transfer of W/Cu joints via surface nano-activation of W

Abstract

Joining of tungsten (W) and copper (Cu) is of significance in fusion reactors. In this research, a novel method for enhancing direct alloying of W/Cu using nanoporous structures, but without using interlayer metals, is presented. The method mainly includes three steps: firstly, a pure-metal nanoporous layer was prepared on the surface of the W foil via anodizing and deoxidized annealing in H2 atmosphere; secondly, a layer of copper was electrodeposited on the nanoporous W and then annealed at the temperature close to TmCu (980°C); finally, the W/electroplated Cu layer/Cu joints were obtained by diffusion bonding in H2 atmosphere. The Owen-Wendt method was used to measure the surface energy of W. The test results showed that surface nano-activation of W can significantly promote the direct alloying and improve the tensile strength of W/Cu joints. The high-resolution transmission electron microscopy observation results showed that the diffusion distance between W and Cu reaches 32 nm (vs. 22 nm in our previous work). The maximum average tensile strength for W/Cu joints with nano-activation reached approximately 128 MPa, which is approximately 110% higher than that of W/Cu joints without nano-activation. Surface nano-activation can also enhance the thermal diffusivity of W/Cu joints at high temperatures. This nano-activation can promote direct alloying between W and Cu because it enables an increase in the amount of W crystal surfaces with high surface energy.