## 1 Introduction
The behavior of tungsten and monoblocks has been investigated in many facilities, but fewer have studied the monoblocks that are located on the fusion experimental reactor and have experienced discharge campaigns. In the fusion experimental device, due to the synergistic effect of heat load and plasma irradiation [24], the actual conditions are more complex. The simultaneous exposure to transient heat and stationary plasma loads has been shown to worsen the cracking behavior in tungsten samples [25]. EAST is a fully superconducting tokamak with both single- and double-null divertor configurations possible, which aims to achieve high-power and long-pulse, steady-state plasma operation scenarios relevant to ITER and CFETR [26]. The upper divertor component of EAST was replaced in 2014 [27] by using actively cooled ITER-like tungsten plasma-facing components (PFCs) with W/Cu monoblocks as the target to develop the exhaust ability at a higher power [28]. Additionally, each W/Cu monoblock employed W, oxygen-free high-conductive copper (OFHC-Cu), and copper-chrome-zirconium (CuCrZr) as the plasma-facing material, intermediate layer, and heat sink, respectively. It is the first large-scale application of such actively cooled, ITER-like W/Cu plasma-facing components in a long-pulse tokamak [23]. During the plasma discharge process, the actual steady heat load of EAST is generally lower than 3 MW/m\({}^{2}\)[29], which is far lower than the maximum heat removal capacity of 10 MW/m\({}^{2}\) found in the high heat load experiment [4; 27]. However, in the actual service process, due to the assembly error of adjacent components that form the misalignment, parts of the leading edge will receive an extremely high heat flux, inducing high thermal stress and strain concentrations at the center of the leading edges, at which thermal fatigue cracking or even a melting phenomenon [30] could be initially generated [23]. The macromorphology, temperature distribution, and plasma parameters were also analyzed [22; 23; 30], but a detailed analysis of the evolution of the monoblocks' microstructure has not been carried out. The damage to these monoblocks is due to the loss of coolant. In addition, at the same time, the misalignment between neighboring monoblocks leads to changes in the plasma strike point and an increase in the heat flux, which also causes damage to the monoblock [29]. At the same time, with the further improvements of the discharge power of the experimental fusion reactor, divertor components must withstand even hard load conditions, and therefore, the studies on and the optimization of monoblocks need to be further strengthened. EAST is an experimental device that can provide a certain degree of reference value for ITER-related W plasma-facing component research and a scientific basis for the ITER [31]. In this paper, we characterized the damaged W/Cu monoblock components from the upper divertor and analyzed the damage morphology, the microstructure evolution, and the recrystallization behavior, which are of great significance for the production process, installation requirements, and lifetime prediction of the monoblock components.