Schlueter, K. (Karsten)
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- Self-passivating tungsten alloys of the system W-Cr-Y for high temperature applications.(Elsevier, 2018-06) Schlueter, K. (Karsten); Neu, R. (Rudolf); Garcia-Rosales, C. (Carmen); Ordas-Mur, N. (Nerea); Iturriza-Zubillaga, I. (Iñigo); Pintsuk, G. (Gerald); Calvo, A. (Aida); Tejado, E. (Elena); Pastor, J.Y. (José Ygnacio)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 thermal 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 ultrafine-grained 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 degrees C is 2-3 times higher than standard Ni-base 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 degrees 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 surface roughening. An additional thermal treatment at 1550 degrees C improves slightly the oxidation resistance and significantly the thermal shock resistance of the alloy.
- Microstructure, oxidation behaviour and thermal shock resistance of selfpassivating W-Cr-Y-Zr alloys(2020) Schlueter, K. (Karsten); Neu, R. (Rudolf); Wirtz, M. (Marius); Garcia-Rosales, C. (Carmen); Hunger, K. (Katja); Pintsuk, G. (Gerald); Andueza, I. (Iñigo); Calvo, A. (Aida); Gago, M. (Mauricio); Sal, E. (Elisa)Self-passivating tungsten based alloys for the first wall armor of future fusion reactors are expected to provide an important safety advantage compare 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 preventing the formation of volatile and radioactive WO3. In this work, Zr is added to self-passivating W-10Cr-0.5Y alloy, manufactured by mechanical alloying and HIP, in view of improving its mechanical strength and thus, its thermal shock resistance. The as-HIPed W-10Cr-0.5Y-0.5Zr exhibits a nanocrystalline microstructure with the presence of an extremely fine nanoparticle dispersion. After heat treatment at 1555 °C for 1.5 h, the grain size growths from less than 100 nm to 620 nm and nanoparticles are present both at the grain boundaries and inside the grains. Oxidation tests at 1000 °C revealed that the alloy with Zr exhibits also a strong oxidation reduction compared to pure W. The long-term oxidation rate is similar to that of the alloy without Zr. Under thermal shock loading simulating 1000 ELM-like pulses at the divertor, the heat treated Zr-containing alloy did not present any damage.