Bulk metallic glasses (BMG) have recently garnered interest due to superior properties such as higher strength, toughness and hardness, arising out of the amorphous struc- ture of these metallic alloys, as compared to their crystalline counterparts. However, BMGs are brittle and fail catastrophically following their elastic limit, which severely restricts their use in structural applications. To offset their brittleness, studies of various combinations of hard nano/micro particles, in situ precipitated crystalline phases and fibers embedded within the BMG, exist in the literature. These resulting materials are known as metallic glass matrix composites. In this work, we study the high strain-rate response of two novel Fe-based metallic glass matrix composites, both of the same composition Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4, containing varying amounts of in situ crystalline phases, when subjected to shock compression. Shock response is determined by making velocity measurements using interferometry techniques such as the Velocity Interferometer System for Any Reflector (VISAR) and Photonic Doppler Velocimetry (PDV) at the rear free surface of BMG samples, which have been subjected to impact from a high-velocity projectile launched from a powder gun. Plate impact experiments have yielded repeatable results indicating a Hugoniot Elastic Limit (HEL) to be 12.5 GPa and 8 GPa respectively for the two composites. The former HEL result is higher than elastic limits for any BMG reported in the literature thus far. The effect of partial crystallization in the amorphous matrix of BMG on the observed shock response is fur- ther explored through a comparison of the results from both composites. It was found that the presence of products of devitrification, although small in volume fraction, plays a significant role in strengthening the material (as evidenced by its larger HEL) as well as lending it more ductility (from retaining shear strength beyond the HEL). This is likely a result of the high hardness and strength of devitrification products such as Fe23B6 as well as the arrest of shear bands by clusters of nanocrystallites. Therefore, it has been demonstrated that the extent of devitrification is an important adjustable parameter to tune the mechanical response of the material as desired.;In addition, the sensitivity of the fracture morphology of a Zr-based BMG Vitreloy 106 to strain rate is examined through a series of low-velocity impact experiments using a single-stage gas gun. Post-mortem microscopic examination of the fracture surfaces of the retrieved failed specimens was conducted. The dynamic fracture morphology for the Zr-BMG showed a clear strain-rate dependence in the form of various unique features at the micro-scale resulting from the occurrence of different fracture mechanisms at varying levels of loading rate.
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