Effect of Friction Stir Processing on Hardness and Microstructure in La-Based Bulk Metallic Glass Composites

Abstract

Friction stir processing (FSP) was conducted on a 2.5 mm thick La₆₆Al₁₄Cu₂₀ bulk metallic glass composites (BMGCs) plate. Effects of FSP on the BMGCs have been investigated. Microstructural observations indicated that the crystalline particles were elongated and parallel to the rotating direction of the pin after FSP. Micro-hardness measurement showed that hardness of the stirred zone drops down approximately 50 Hv compared with the as-cast sample. The mechanical properties of the amorphous matrix before and after FSP have been investigated using nanoindentation test. Results shown that creep displacement-time curves of the BMGCs before and after FSP can be accurately fitted by the generalized Kelvin model which was usually used in polymeric materials. The creep compliance and creep retardation spectrum shown that the as-cast specimen is in a more relaxed state.

Fig. 3 SEM micrograph of the La₆₆Al₁₄Cu₂₀ specimen (a) before and (b) after FSP. (c) Same as for micrograph (b) but at lower magnification. (d) Typical SEM micrograph around the indents after indentation measurements for the processed sample and the corresponding high-resolution image (inset).