Thermal stability of a highly-deformed warm-rolled tungsten plate in the temperature range 1100–1250 °C

Abstract

Pure tungsten is considered as armor material for the most critical parts of fusion reactors (i.e. the divertor and the first wall), among other reasons due to its high melting point (3422 °C) and recrystallization temperature. The thermal stability of a pure tungsten plate warm-rolled to a high plastic strain by 90% thickness reduction was investigated by isothermal annealing for up to 190 h in the temperature range between 1100 °C and 1250 °C. Vickers hardness testing allowed tracking the changes in mechanical properties caused by recovery and recrystallization. The hardness evolution could be rationalized in terms of a logarithmic recovery kinetics and a Johnson-Mehl-Avrami-Kolmogorov recrystallization kinetics accounting for an incubation time of recrystallization. The observed time spans for recrystallization and the corresponding recrystallization activation energy for this highly deformed plate suggest that large plastic deformations (e.g. applied during shaping) are only suitable to produce tungsten components to be used at relatively low temperatures (up to 900 °C for a 2 years lifespan). Higher operation temperatures will lead to fast degradation of the microstructure during operation.

Mechanical properties and thermal stability of rolled W-0.5wt% TiC alloys

“…From the Arrhenius plot shown in Fig. 6, the E ΔHV/2 can be estimated by linear fitting as 612 (1 74%) kJ/mol, which is higher than that value of 579 kJ/mol obtained in a previous study on deformed pure tungsten plates [30]. Such a higher activation energy for recrystallization implies that fine dispersed TiC particles can drag grain boundaries and inhibit grain growth to raise the thermal activation energy for recrystallization.…”

“…The microhardness of the as-rolled samples is 513 HV in normal direction (ND), 80 HV higher than that of moderate ( $ 67%) rolled pure tungsten plate [30]. The hardness of samples annealed at 1500°C decreases slightly from 513 HV to 498 HV as recovery of the internal stress and dislocations.…”

Microstructure, mechanical behaviour and fracture of pure tungsten wire after different heat treatments

“…This reduces the recrystallization temperature because of a higher driving force from possible energy release as well as a higher nucleation rate due to the abundance of defects [36]. Therefore, the drawn wire undergoes recrystallization during 3 hours at 1273 K which is a much lower temperature than the normally reported recrystallization temperature of tungsten (1523 K-1773 K) [37][38][39].…”

Hardness loss and microstructure evolution of 90% hot-rolled pure tungsten at 1200–1350 °C

“…The experimentally determined hardness values are averages over recrystallized and non-recrystallized regions according to the rule of mixtures [15]: HV = HV rex + (1 − )HV rec (1) with the hardness of the recrystallized regions HV rex and the hardness of the recovered matrix HV rec weighted by their respective volume fractions X and (1 − ), respectively. For the hardness of the recovered matrix, the hardness values measured at the onset of recrystallization (i.e.…”

“…Even though many studies have been performed on pure tungsten, e.g., material design, mechanical behavior, high heat flux properties [12] and irradiation behavior [13,14], there are only limited data available for recrystallization kinetics of rolled pure tungsten, e.g. [2,15]. The present work investigates the recrystallization behavior of pure tungsten hot-rolled to 90% thickness reduction for four different annealing temperatures.…”