Variability in the yield strength of a metallic glass at micron and submicron length scales

Abstract

This work presents an in-depth investigation of the dispersion in the compressive yield strength of a Zr-based bulk metallic glass as the specimen dimensions decrease from the micron to the submicron length scale. While the investigated alloy belongs to one of the so-called “ductile” glass families, the degree of variation in strength exhibited in the submicron size range approaches that of conventional brittle ceramics. Using a three-parameter Weibull analysis, however, we find that the engineering reliability of the glass is independent of specimen size. The glass exhibits a size-independent failure-free stress of 1825MPa, below which yielding is not expected. The three-parameter Weibull modulus is also size independent. The dispersion in yield strengths above the failure-free stress is due to the change in the sampling volume for specimens 1μm in diameter or larger, while interactions between defects and the surface actually limit the breadth of the strength distribution observed in specimens 200–330nm in diameter relative to what may be expected for that volume. Using an instability criterion for a penny-shaped crack under shear with interfacial friction, a relationship between yield strength and the corresponding defect size is established, and the defect concentration is estimated.