Analysis of hardness and microstructural changes in Tungsten mono-blocks exposed to high heat flux at 10 MW/m2

•Investigation of the material properties in the near surface region of tungsten mono-blocks through the microstructure and hardness profiling before and after high heat flux test.•The correlation between the decrease of hardness and the grain growth near surface was identified through the depth profiling.•The degraded depth of tungsten armor was affected by the bonding quality of mockups and subsequent occurrence during the cyclic high heat flux loading experiment.•Depth of tungsten armor degradation even in the heat flux condition chosen in this study (10 MW/m2) is influenced by the power handling capability of PFC. In this study, we investigated the material properties of tungsten mono-blocks undergone high heat flux test. The ITER-like tungsten mono-block specimens were fabricated by two kinds of joining methods. The tungsten-Cu interlayer joint was made by gas pressure casting and Cu interlayer-CuCrZr cooling tube were joined by hot radial pressing (HRP) or brazing method. To evaluate the integrity of the fabricated mono-blocks, high heat flux tests were done on the small mockups under cyclic heat load of 10 MW/m2 up to 5,000 cycles. We measured the microstructure, hardness, and surface state of the tungsten armors before and after the heat flux exposure experiment. The Vickers hardness profile measured from the surface down to the Cu interlayer showed a noticeable reduction around 200 μm ~ 500 μm depth after high heat flux test compared to that before the test depending on the bonding quality of mockup specimens. At depth beyond 800 μm, the Vickers hardness did not show any notable difference before and after the high heat flux test, which indicates the material property of tungsten is not so much affected in this region at the above heat flux condition. The microstructure and grain size distribution was measured and analyzed by SEM and EBSD. The correlation between the microstructure and hardness profile, and the impacts of the mockup performance under HHF test to the integrity of tungsten armors are analyzed.