Studies on Stress Corrosion Cracking of Vit 105 Bulk Metallic Glass

Gebert A, Geissler D, Pilz S, Uhlemann M, A. Davani F, Hilke S, Rösner H, Wilde G

Research article (journal)

Abstract

The project “Stress Corrosion Cracking of Zr-based Bulk Metallic Glasses” (SCC of Zr-BMGs) within PP1594 mainly dealt with mechanical–corrosive interactions and failure ofthis class of metastable materials. It focused on one of the most application-relevantzirconium (Zr)-BMG, Vit(reloy) 105, with composition Zr52.5Cu17.9Ni14.6Al10Ti5 (at.%).Even though this BMG is known as an extraordinary glass former, the metallurgicalprocessing is still a critical issue. In contrast to conventional processing, i.e., arc meltingof master alloy ingots from single constituents, a different route using binary pre-alloysfor the master alloys production was applied and led to superior mechanical propertiesupon mechanical testing under tensile and three-point-bending (3PB) conditions in air.As a reference and for a detailed understanding of failure, fracture, and cracking ofZr-based BMG in air, notched specimen 3PB experiments with in situ microscopicobservation were done and the still controversial interpretation of the mechanicalbehavior of BMG in the framework of fracture mechanics was addressed. Thespecimen from the in situ 3PB tests served for transmission electron microscopy (TEM)investigations on the structural nature of shear bands in BMG on the atomistic scale.Altogether, complete crack paths could be observed and analyzed, and based on this,details of the shear band-driven crack growth are described. While in first SCC studiesusing a newly developed setup full cross section (3PB) bars were investigated, in recentin situ experiments, notched specimens were tested in 0.01 M NaCl, yielding strongevidence for a catastrophic failure due to hydrogen embrittlement (HE). The knownsusceptibility to pitting corrosion in halide-containing environments is only the initialstage for failure under SCC conditions. Once pitting is initiated, the local electrodepotential is severely reduced. Further, the hydrolysis reaction of oxidized Zr4C tozirconyl ions ZrO2C during local BMG dissolution produces HC and, thus, a localacidic environment that enables proton reduction and hydrogen absorption in thestressed BMG region. The peculiar failure and fracture surface characteristics as wellas the proven local reduction of the pH value in the vicinity of the notch during in situexperiments clearly account for the proposed HE-SCC failure mechanism.

Details zur Publikation

Release year: 2020
Language in which the publication is written: English