Formation and biocorrosion behavior of Zr-Al-Co-Nb bulk metallic glasses

Abstract

Ni-and Cu-free Zr-Al-Co-Nb glassy alloys with different Nb and Co contents were synthesized by melt spinning and copper mold casting. The effects of Nb addition to partially replace Co in the Zr 55 Al 20 Co 25 glassy alloy on the glass-forming ability, thermal properties, in-vitro biocorrosion behavior and surface wettability of the metallic glasses were investigated. Although addition of Nb up to 5 at.% slightly decreased the supercooled liquid region and the glass-forming ability (GFA), the alloys could be casted in a bulk glassy rod form with diameters up to 3 mm. The Zr-Al-Co-Nb glassy alloys were spontaneously passivated with low passive current densities in phosphate buffered saline and Hanks' solution. Substitution of "toxic" Co by Nb is effective in improved the corrosion resistance of the Zr-Al-Co glassy alloy. Water contact angle measurements showed that Nb addition increased the hydrophilicity of the glassy alloys, which may enhance cell adhesion of the alloys in biomedical applications. Because of the lack of long-range atomic order, Zr-based bulk metallic glasses (BMGs) exhibit superior strength, high elastic strain limits and fatigue endurance limits, relatively low Young's modulus, and excellent wear and corrosion resistance [1][2][3][4][5], which attracted attention in biomedical applications. However, toxic elements such as nickel and copper are often included in Zr-based metallic glasses to achieve high glass-forming ability (GFA), which are thought to impair cellular metabolism [6]. In recent years, many efforts have been made to remove these elements from Zr-based BMGs to further improve their biocompatibility. (x = 2.5 at.% and 5 at.%) metallic glasses have been developed, and addition of Nb were found to enhance their resistance to pitting corrosion in 3 mass% NaCl solution [20]. From the viewpoint of biomedical engineering, Nb is recognized as a highly biocompatible element. In the quaternary Zr-Al-Co-Nb alloys, Co is more cytotoxic than Al, and excessive amounts of Co or prolonged exposure to Co may result in Co poisoning [21][22][23]. Therefore, rather than substitution of Al with Nb as in the previous study [20], substitution of Co with Nb could further improve the biocompatibility of the alloys. In consideration of potential medical applications, the GFA and in vitro biocorrosion behavior of Zr 55 Al 20 Co 25x Nb x glassy alloys were investigated in the present work. Surface wettability of the

Atomic structure evolution during solidification of liquid niobium fromab initiomolecular dynamics simulations

“…Because of its refractory nature and resistance to corrosion, Nb has found various scientific and industrial applications. For instance, it has been widely used as an additive to improve the glass-forming ability (GFA) of various bulk metallic glasses [21][22][23][24][25][26][27]. In addition, the unique combination of material properties of niobium and niobium alloys is also used in the aerospace industry, where extreme working conditions are demanded [28].…”

Corrosion behavior and in vitro biocompatibility of Zr–Al–Co–Ag bulk metallic glasses: An experimental case study

“…Therefore, in the last decade, great efforts have been devoted to develop Zr-based BMGs with less hazardous elements so as to further improve their biocompatibility. Ni-free glass forming systems such as Zr-Al-Cu [9], Zr-Al-Co-(Cu) [10][11][12][13], Zr-Al-Co-Nb [14,15], Zr-Al-Co-Ag [16], Zr-Al-Cu-Fe [17], Zr-Al-Cu-Ag [18], Zr-Cu-Pd-Al-Nb [19], and Zr-Al-Cu-Fe-(Ti/Nb) [20] have been developed. Among the Ni-free Zr-based BMGs, Zr-Al-Co system BMGs are attractive due to the absence of copper, which is also a toxic element to cellular metabolism and may result in high cytotoxicity if released excessively during corrosion [7].…”

“…Among the Ni-free Zr-based BMGs, Zr-Al-Co system BMGs are attractive due to the absence of copper, which is also a toxic element to cellular metabolism and may result in high cytotoxicity if released excessively during corrosion [7]. In addition, the Zr-Al-Co BMGs are spontaneously passivated with low passive current densities and wide passive potential regions in physiologically relevant environments, indicating their high corrosion resistance [13,15]. Although Co ions are known to be cytotoxic, the total mass of Co ions released by a unit surface area of glassy Zr 56 Al 16 Co 28 alloy (0.3 ng/mm 2 ) is significantly lower than the Co-CrMo alloy (5.8 ng/mm 2 ) [13].…”

“…Although Co ions are known to be cytotoxic, the total mass of Co ions released by a unit surface area of glassy Zr 56 Al 16 Co 28 alloy (0.3 ng/mm 2 ) is significantly lower than the Co-CrMo alloy (5.8 ng/mm 2 ) [13]. Moreover, the corrosion resistance of Zr-Al-Co BMGs can be further improved by the Nb addition due to the formation of highly protective passive film on the alloys' surface [14,15,21]. However, the addition of Nb to the Zr-based BMG shows a detrimental effect on their glass-forming ability, which may hinder their wide application [14,21].…”