Influence of B, Al and Nb addition on the glass forming ability and stability of mechanically alloyed Zr-Ni amorphous alloys

Abstract

We investigated the influence of minor additions of B, Al and Nb that have representative atomic sizes on the glass forming ability (GFA) and stability of Zr-Ni amorphous alloys during mechanical alloying. The results show that the minor addition of B, Al or Nb does not shorten the initial time of the full amorphization reaction or improve the glass forming ability of the Zr-Ni alloys at a low rotation speed. However, B addition can effectively improve the mechanical stability of the amorphous phase against mechanically induced crystallization. Furthermore, the amorphous phase gradually transforms into a metastable fcc-phase with increasing milling time. The addition of Al and Nb that have similar atomic sizes has a similar effect on the GFA and the mechanical stability of the Zr-Ni amorphous phase. Moreover, Al and Nb addition can alter the crystallization behavior and improve the thermal stability of the Zr-Ni amorphous phase. Many researchers are interested in the origin of the glass forming ability (GFA) of amorphous alloys. Minor alloy additions or microalloying technologies have been important metallurgical practices and dominant concepts for the development of new metallic crystalline materials in the late half of the 20th century. It has recently been reported that appropriate minor additions are very effective in increasing GFAs and enhancing the thermal stability and mechanical properties of some metallic glasses [1-10]. Moreover, the minor addition approach also represents a feasible way to develop and design novel amorphous alloys. Our previous findings have shown that minor additions of single metalloid elements, metal elements or outphase amorphous alloys can effectively improve GFAs or enhance the mechanical stability of Zr-based alloys using mechanical alloying (MA) at given milling revolutions [11][12][13][14][15]. However, the mechanism of the minor addition has not been explained by fundamental theory in terms of glass formation and properties tailoring. It has been suggested that the additional atomic number, size mismatch or chemical affinity with constitutional elements may affect metallic glass formation and properties. According to their atomic radii, elements that have been used for minor addition can be categorized into three groups [16]: large atoms (Zr, 0.16025 nm [17]), intermediate atoms (Al, 0.14317 nm, Nb, 0.14290 nm, and Ni, 0.12459 nm [17]) and small atoms (B, 0.082 nm [17]). In this paper, we aim to systematically investigate the effect of the small atom B, and the intermediate atoms Al and Nb with similar atomic sizes on the microstructural evolution of a mechanically alloyed Zr 66.7 Ni 33.3 amorphous alloy under the same milling conditions. It should be noted that we selected a lower milling speed (150 r min 1 ) compared to our previously reported experimental conditions (200 or 300 r min 1 ). Therefore, the influence of minor additions and milling speed on the solidstate amorphization and phase evolution of Zr-Ni alloys is