Tungsten–vanadium–yttria alloys for fusion power reactors (II): Mechanical characterization

Abstract This is the second part of a study in which the aim is to evaluate the influence of adding 2 or 4 wt.% vanadium (V) and 0.5 wt.% yttria (Y2O3) to pure tungsten (W) and the effects on the mechanical properties at high temperature. In the first part, the microstructure at room temperature was analysed. These W-based alloys were processed by powder metallurgy and consolidated by hot isostatic pressing. Smooth and single edge laser-notched beam specimens were tested to determine the flexural strength, yield strength and fracture toughness. Three-point bending tests were performed in both oxidising and vacuum atmospheres at temperatures ranging from 77 K, via immersion in liquid nitrogen, to 1473 K. The hardness and elastic modulus were measured via Vickers microindentation and impulse excitation technique, respectively. The results were compared with nanoindentation tests to determine the possible size effect on both parameters. The fracture surfaces of the tested alloys at different temperatures were analysed with a field emission scanning electron microscope, which was useful for establishing the link between the macroscopic behaviour and the micromechanisms of failure. The results show improvement of the mechanical properties in the entire temperature range from the addition of V and Y2O3 to W. The formation of a W-V solid solution benefits the conglomeration of the material and drastically reduces porosity, whereas Y2O3 helps to stabilise high-temperature degradation. The combination of both alloying elements creates a synergistic effect that triples the microhardness and flexural strength values in comparison with pure W produced by the same powder metallurgy route.