The effects of thin coatings on the mechanical properties and resistance to annealing-induced embrittlement of bulk metallic glass

The effect of thin coating on the strength, plasticity and resistance to annealing-induced embrittlement was investigated for Zr50.7Cu28Ni9Al12.3 bulk metallic glass (BMG). To maintain the BMG structure in the most extent, very thin amorphous CuZr and crystalline W coatings were used. The crystalline coating performed much better in improving BMG plastic deformation than the amorphous one, for its superior retarding effect on shear band (SB) dynamics. Besides the coatings, softer layers near the sputtered surfaces also contributed to the enhanced plasticity of the coated BMG. The presence of these softer layers also led to the slightly lower strength of both amorphous CuZr and crystalline W coated BMGs relative to the uncoated ones. The BMG with crystalline W coating exhibited much better resistance to annealing-induced embrittlement than the amorphous CuZr-coated and uncoated ones, due to its much enhanced decomposition processes upon annealing. These experimental results provide useful guidance on choosing suitable coating materials to elevate BMG plasticity and avoid annealing-induced embrittlement.