Impact of heat treatment on tensile properties of 97W[sbnd]2Ni[sbnd]1Fe heavy alloy

Abstract

To avoid failures caused by the inherent brittleness of pure tungsten below its ductile to brittle transition temperature, tungsten heavy alloy was proposed as an alternative solution of the plasma facing material. Plasma facing components manufactured of tungsten heavy alloy have been installed partly in the tokamak ASDEX Upgrade instead of pure tungsten targets. Opposite to the pure tungsten targets, no deep cracks have been identified in these targets after one experimental campaign. In order to understand and improve the material behavior of tungsten heavy alloy as plasmam facing material in ASDEX Upgrade, the impact of heat treatment on tensile properties of 97W2Ni1Fe heavy alloy has been studied in this work. The heat treatments have been conducted in the vacuum for the tensile specimen cut from an ASDEX Upgrade target at different temperatures (600 °C, 1100 °C and 1350 °C) with various durations (15 min, 60 min and 120 min). After the heat treatment, the tensile properties were remarkably improved. The increase of the interfacial strength between tungsten grains and matrix phase as well as growth of grains are considered as the main reasons for the increase of elongation after heat treatment. The experimental results reveal that electrical discharge machining reduces the total elongation of the specimens. Furthermore, no big impact on the tensile properties is found after low energy deuterium plasma implantation.