Thermomechanical analysis for the theoretical optimization of W/Cu monoblocks with functionally graded interlayer

Abstract

In fusion devices, plasma-facing components (PFCs) play a critical role in withstanding severe thermal conditions resulting from cyclic high heat flux (HHF) loads. The International Thermonuclear Experimental Reactor (ITER) and next-generation fusion devices are expected to employ actively cooled tungsten/copper (W/Cu) monoblocks as divertor targets due to their excellent heat removal capabilities. Although ITER-like monoblocks utilize a soft Cu interlayer to alleviate stress, interface fatigue cracking still occurs under cyclic HHF loads. The issue of interface bonding between the W armor and heat sink has been a limiting factor for the long-term stable operation and structural integrity of these monoblocks. Functionally graded materials (FGMs) are regarded as an effective approach to address severe local stress concentration at the bonding interface. The number of layers, composition distribution, and thickness of the FGM layers are analyzed by evaluating the stress and strain after the loading and cooling phases in finite element simulations. The simulation results indicate that the graded interlayer can significantly reduce stress concentration at the interface, and a two-layer FGM (25 vol% and 66.7 vol% W) with each layer 0.6 mm thick can greatly mitigate both stress and strain. Such results provide important guidance for the development of graded W/Cu monoblocks for fusion applications.