Femtosecond laser fabricated micro/nano interface structures toward enhanced bonding strength and heat transfer capability of W/Cu joining

W/Cu joining is key for the fabrication of plasma facing components for fusion reactors, which however is very challenging due to the immiscible nature of Cu-W binary system and the mismatch of thermal expansion coefficient between W and Cu. In this research, we proposed a method for comprehensive enhancement of the bonding strength and heat transfer capability of W/Cu joining based on femtosecond (fs) laser fabricated micro/nano interface structures. Four kinds of surface structures, namely pristine structure, nano ripples, micro-cubes array and micro-pits array were designed and fabricated on W by fs laser ablation, which were then introduced into W/Cu interfaces by hot pressing joining at 1000 degrees C, 80 MPa. The micro/nano interface structures lead to significant enhancement of W/Cu bonding strength, which reaches 101.58 MPa for W/Cu direct joining and 120.43 MPa for W/Cu joining with Cu interlayer, increased by about 150% and 190% compared with W/Cu joining with a flat interface. The thermal diffusivity and thermal stress resistance of W/Cu joining are also improved. The strengthening mechanism is recognized to be the combined effects of micro/nano interface structures related interdiffusion between W and Cu and increased resistance against W/Cu interfacial debonding. Our research provides a method for enhanced joining between W and Cu, as well as a vast range of dissimilar materials. (C) 2016 Elsevier Ltd. All rights reserved.