Abstract
Owing to the unique properties, such as excellent mechanical performance, and nano-scale surface roughness, metallic glass can be applied in various novel fields. Meanwhile, the improvement of thermal stability and hardness is the common target in these applications. Minor alloying is an effective method to enhance the thermal and mechanical properties of metallic glasses. Different from elements used to be doped into metallic glass, the role nitrogen atoms play in metallic glass is quite distinct and critically important, owing to its strong electronegativity and small atomic radius. In this work, an alternative class of metallic glass is developed. By adding nitrogen into Zr-Cu-Al-Ag TFMG, the configuration energy of short range structure is greatly modified. From the viewpoint of thermal behavior, the evolution of Tg and elastic modulus with nitrogen could be well correlated, implying significant effect of nitrogen atoms on the potential energy landscape (PEL) of the TFMGs. Besides, more amounts of nitrogen addition lead to the increase of short range order structure in the amorphous matrix. That is, most metallic atoms are strongly attracted by nitrogen, forming the nitrogen-centered cluster, in which more energy is required to cause plastic deformation. On the other hand, a meta-stable state with lower energy is attained as indicated by the much higher Tx than normal Zr-based metallic glasses. However, the amorphicity region of nitrogen in Zr-Cu-Al-Ag metallic glass is not wide enough, restricting the enhancement amount of thermal and mechanical performances. By incorporating Ta firstly, the competing ZrN crystalline phase is destabilized, leading to the wider amorphicity region of nitrogen in Ta-Zr-Cu-Al-Ag TFMG. As a result, hardness over 10 GPa, Tg near 800 K, and supercool liquid region as wide as 112K is achieved in the nitrogen-doped Ta-Zr-Cu-Al-Ag TFMG.