The surface orientation of crystals has an influence on various material properties, like the oxidation. A method was developed to correlate the oxidation rate for individual single crystal grains with their surface orientation. The surface orientation of many grains of polycrystalline, recrystallized tungsten samples was determined using electron backscatter diffraction. Subsequently, the samples were oxidized in a thermobalance, measuring the time dependent weight increase. The grain dependent oxidation rates were determined by measuring the thickness of the oxide layer for many individual grains with confocal laser scanning microscopy and scanning electron microscopy on focus ion beam prepared cross-sections. In the temperature range of 720 K to 870 K, tungsten grains with {100} surface orientation have the highest oxidation rate, which is two times higher than the lowest oxidation rate. The lowest oxidation rate belongs to the {111} surfaces orientation, while the {110} surfaces orientation has an intermediated rate. The derived oxidation rates are consistent with gravimetric measurements. They follow an Arrhenius behavior with an activation energy of 190 kJ/mol.
Self-passivating tungsten based alloys for the first wall armor of future fusion reactors are expected to provide a major safety advantage compared to pure tungsten in case of a loss-of-coolant accident with simultaneous air ingress, due to the formation of a stable protective scale at high temperatures in presence of oxygen which prevents the formation of volatile and radioactive WO3. This work analyses the oxidation and thermo-shock resistance of W-Cr-Y alloys obtained by mechanical alloying followed by HIPing. Alloys with different Cr and Y contents are produced in fully dense form with nanocrystalline or ultrafinegrained microstructure and a dispersion of Y-rich oxide nanoparticles located mainly at the grain boundaries. Isothermal oxidation experiments confirm an excellent oxidation resistance due to the formation of protective oxide scales at the very surface. These layers mainly consist of Cr2O3 and mixed Y-W and Cr-W oxides. The superior oxidation resistance of these alloys is confirmed by tests simulating accident-like conditions. The thermal conductivity of these alloys at 600-1000°C is 2-3 times higher than standard Nibase superalloys like Inconel-718. The material also exhibits outstanding thermal-shock resistance: 1000 pulses of 0.19 GW/m 2 power density and 1 ms duration at 400°C base temperature resulted in no damage, while an increased power density of 0.38 GW/m 2 resulted in the formation of a crack-network and slight
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