Effects of helium implantation on tensile properties and microstructure of amorphous nickel phosphorous metallic glasses

Abstract

Nuclear reactions generate insol. helium, which forms nano-sized bubbles that can lead to swelling and embrittlement of irradiated materials. Innovative structural materials must be created and utilized to enable new-generation nuclear reactors to withstand harsh thermomech. environments and to suppress helium-induced embrittlement. One family of candidate structural materials is metallic glasses, which offer high elastic limit and strength, corrosion resistance, and potential for improved ductility upon irradn. A significant detriment in their use for structural applications is catastrophic failure under tensile loadsWe use templated electron-beam lithog. and electro-deposition to fabricate 100 nm-diam. amorphous Ni-P metallic glass cylindrical nano-tensile specimens. Earlier studies in our group demonstrated the emergence of brittle-to-ductile transition in nano-sized metallic glasses upon tension, with useful ductility in excess of 20% in some cases. In this work we explore the effects of Helium implantation into already-ductile nano-sized metallic glasses. Helium was implanted uniformly into each sample at a concn. of 3 at% at 25°C and at 280°C to result in the bubble sizes between 2-3nm and ∼10nm. In-situ uniaxial tension expts. revealed that He-ion implantation increased available plastic strain in the nano-metallic glass tensile specimens by a factor of 2 and maintained the high strength of ∼2.1 GPa. We discuss these promising results in the framework of microstructural and defect response to ion irradn. in metallic glasses.