*2.1.1.3. Effect of other elements content (Ti, Zr, V, Nb, W, Mn, Co, Cu, Ru, Rh, Pd, Pt)*

The effect of other alloying elements to Fe-based glass alloy on its corrosion resistance has been addressed in one study [18]. Hence, titanium, zirconium, vanadium, niobium, chromium, molybdenum, tungsten, manganese, cobalt, nickel, copper, ruthenium, rhodium, palladium, and platinum were all added to the Fe-X-P13C7 glassy alloy [18]. All elements, except manganese, decreased the corrosion rate of the iron glassy alloy in H<sup>2</sup> SO4 , HCl, HNO<sup>3</sup> , and

Metallic glassy Ni-P has been recently investigated, which appeared to resist to chlorideinduced corrosion [23]. In fact, its *E*-log (*i*) potentiodynamic behavior was basically identical whether in a chlorinated or chlorine-free environment. A form of chemical passivity has been proposed to explain its corrosion behavior. Passivation in the Ni-P system was mainly due to the formation of an ionic barrier layer rather than a classical passive oxide film. This barrier layer consists of hypophosphite ion adsorbed on the nickel phosphorous surface, with

water to the surface and thus prevents the hydration of nickel, which is the first step in the

More recently, there have been growing efforts to decrease the additions of P due to its effective action on the loss of ductility of the Fe amorphous alloy [24]. Overall, the strategic approach that is found to be most effective in increasing the corrosion resistance depends on

There has been a consensus that additions of suitable metals to amorphous Ni-based alloys tend to increase their corrosion resistance. The electrochemical behavior of Ni-based amorphous alloys containing Ti, Ta, Zr, Nb, Cr, and/or P has been of a great concern for a number of investigators [20, 25–27]. One of the most significant studies was led by Shimamura et al. [20] who investigated the effect of P and other valve metals (e.g., Ta) on the corrosion proper-

without any of Cr6+ ions content or in a boiling 6 M HCl electrolytes. Ta additions have been proven to be the most efficient in lowering the corrosion rates of Ni-based MG alloy. The addition of critical amounts of Ta resulted in undetectable corrosion rates (<10−3 mm year−1).

rate of Ni60Ti40 was estimated to be close to 1 mm year−1. After adding of 30 at.% Ta, however, the Ni60Ti10Ta30 MG alloy exhibited an immune response to corrosion for the same period of exposure, i.e., 168 h. Immunity was attributed to the formation of a kind of a protective layer. Although, the authors Shimamura et al. [20] claimed that amorphous Ni-Ta alloys required more than 35 at.% Ta in a boiling 6 M HCl solution to form a tantalum oxyhydroxide

Alternatively, the addition of a small amount of P to Ni-Ta glassy alloys has been proven to be effective in significantly reducing their corrosion rates. The corrosion rate of Ni70Ta30 in a

tested under similar conditions [20]. The authors believed that the addition of P promoted the

sary for the passive film formation [20]. However, when experiments were performed in solutions with a high oxidizing power, the authors found that the addition of P to Ni-Ta alloys was not necessary to promote the growth of the passive film. Interestingly, many research works have suggested that a Ta-enriched passive film would probably be one of the reasons for the high corrosion resistance of Ni-based amorphous alloys in aggressive solutions [20, 21].

Moreover, it has been proven that the addition of approximately of 7 at.% Cr was sufficient to

prevent pitting corrosion of Ni-Cr-P-B alloy systems immersed in 10% FeCl<sup>3</sup>

(OH) passive film by accelerating selective dissolution of elements unneces-

whether the solution is strongly oxidizing or not (e.g., 9 M HNO<sup>3</sup>

ties of Ni-based amorphous ribbons immersed either in boiling 9 M HNO<sup>3</sup>

For example, after being immersed in a boiling 9 N HNO<sup>3</sup>

[OH]) shielding passive film.

boiling 6 M HCl solution was more than 104

*2.1.2.1. Effect of elements content (Ti, Zr, Ta, Nb, Cr, P)*

O bonded outer layer. This barrier reaction layer inhibits the ion transport of

A Tribo-Electrochemical Investigation of Degradation Processes in Metallic Glasses

http://dx.doi.org/10.5772/intechopen.79387

117

).

solutions with and

solution for 168 h, the corrosion

.H<sup>2</sup>

O at 30°C [27].

times greater than that of Ni68Ta30P2 alloy when

hydrogen/H<sup>2</sup>

(TaO<sup>2</sup>

growth of TaO<sup>2</sup>

nickel dissolution process.

**Figure 2.** Potentiodynamic polarization curves of the cast glassy Fe-based BMGs (rods with a diameter of 1.2 mm) in 1 and 6 M HCl open to air at 298 K. Reproduced from [13, 29] with permission from Elsevier Science.

NaCl solutions. Although the base alloy, Fe-P13C7, did not passivate; additions of any of the foregoing elements at levels from 0.5 up to 40 at.% enabled passivation to occur during anodic polarization in 0.1 N H<sup>2</sup> SO4 . Chromium was the most efficient, still, molybdenum, and titanium were very beneficial. No pitting was observed in 3% NaCl for passivated alloys. The alloys that did not passivate, such as Fe-Co-P13C7, did not pit, but rather they dissolved uniformly.

Fe-W resisted to pitting corrosion up to 2.5 V/SCE in both acidic and neutral chloride solutions (pH 1 and 7, respectively) [19]. Addition of tungsten to Fe-WxP13C7 has the effect of increasing the critical pitting potential, *E*crit, to a level above 2 V/SCE for x = 6 at.%, but when x = 10 at.% of W was added it caused transpassive dissolution at 1 V/SCE of the MG alloy [19].

#### *2.1.2. Ni-based BMG materials*

Generally, Ni-based metallic glass systems exhibit a good resistance to uniform and localized corrosion. A number of investigations on the electrochemical characteristics of Ni-based amorphous alloys have been performed on ribbons [20–22] due to the struggle in producing amorphous bulk samples (i.e., having thickness > 1.5 mm). The elemental constituents that have typically been used to ensure a good corrosion resistance were either additions of metalloids such as P [20, 22] or additions of metals such as Ta [20, 21] and Nb [20].

Metallic glassy Ni-P has been recently investigated, which appeared to resist to chlorideinduced corrosion [23]. In fact, its *E*-log (*i*) potentiodynamic behavior was basically identical whether in a chlorinated or chlorine-free environment. A form of chemical passivity has been proposed to explain its corrosion behavior. Passivation in the Ni-P system was mainly due to the formation of an ionic barrier layer rather than a classical passive oxide film. This barrier layer consists of hypophosphite ion adsorbed on the nickel phosphorous surface, with hydrogen/H<sup>2</sup> O bonded outer layer. This barrier reaction layer inhibits the ion transport of water to the surface and thus prevents the hydration of nickel, which is the first step in the nickel dissolution process.

More recently, there have been growing efforts to decrease the additions of P due to its effective action on the loss of ductility of the Fe amorphous alloy [24]. Overall, the strategic approach that is found to be most effective in increasing the corrosion resistance depends on whether the solution is strongly oxidizing or not (e.g., 9 M HNO<sup>3</sup> ).
