Refractory high-entropy alloys (HEAs) have attracted significant attention due to their superior mechanical properties at elevated temperature . However, most of them are brittle and suffer from low ductility and toughness at room temperature, and their usage is limitted due to the inadequate fracture-resistance property. Grain boundaries play an important role in the extraordinarily high temperature strength and stability  of bcc HEAs and can also be potential sites for fracture. Here, strongly textured, columnar and nanometer-size grains NbMoTaW HEA thin flims with and without ion beam assisted deposition technique are produced. Mechanical properties, especially fracture toughness are determined by in situ micro-pillar and micro-cantilever tests. Further characterization is conducted by high-resolution SEM images and TEM analysis.
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