Fracture toughness testing of Bulk Metallic Glass - a discussion on sample size effects and new insights on Stress Corrosion Cracking of Zr52.5Cu17.9Ni14.6Al10Ti5Wednesday (26.09.2018) 11:30 - 11:45 S1/01 - A1 Part of:
Macroscopically brittle behaviour vs. intrinsic plasticity, failure mechanisms and fracture as well as fracture toughness determination of Bulk Metallic Glasses (BMG) are still a controversial issue and subject of intense research. In fact, a huge spread of fracture toughness values for individual BMG alloys and in some cases very high fracture toughness values for this material class with respect to polycrystalline metals and alloys are reported. Yet, BMG specimen dimensions for fracture toughness testing are mostly smaller than usual and do not always follow the rules of classical test standards. In this context it is discussed whether geometrical/mechanical constraints of small scale sample testing have an important impact on the fracture toughness results under typical test conditions for BMG samples. These theoretical considerations are also motivated by experimental investigations on in-situ fracture and stress corrosion cracking (SCC) of Zr52.5Cu17.9Ni14.6Al10Ti5 BMG. Current results on the in-situ and post-mortem microscopic observation of crack propagation are presented for in-situ 3-point bending of notched specimens. SCC experiments on notched 3-point bending beams suggest that, apart from the well documented pitting susceptibility and the anodic pitting corrosion of Zr-based BMG alloys in halide containing aqueous solutions, hydrogen embrittlement is acting as a co-process after the initiation of pitting corrosion. From fracture surface analysis and the in-situ monitored corrosion characteristics, it is concluded that hydrogen embrittlement is the major failure cause for fracture under the harsh SCC test conditions applied upon Zr52.5Cu17.9Ni14.6Al10Ti5 BMG.