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Corrosion behavior of amorphous and crystalline Cu50Ti50 and Cu50Zr50 alloys
Journal of Non-Crystalline Solids 30 (1978) 29-36 © North-Holland Publishing Company
CORROSION BEHAVIOR OF AMORPHOUS AND CRYSTALLINE CusoTiso AND Cus oZr5o ALLOYS M. NAKA, K. HASHIMOTO and T. MASUMOTO The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendal, Japan
Received 26 April 1978
Corrosion rates and anodic polarization curves of amorphous and crystalline Cu50Tis 0 and Cus 0Zr5o alloys have been examined in various acidic, neutral and alkaline solutions. The amorphous alloys are very stable in acidic and alkaline solutions, but unstable in agressire chloride solutions. The corrosion resistance of these amorphous alloys is higher than that of the crystallized alloys. The high corrosion resistance of amorphous alloys is attributable to the high chemical homogeneity of amorphous alloys without localized crystalline defects such as precipitates, segregates, grain boundaries, etc. Metalloid elements play an important role in the corrosion behavior of amorphous alloys; the addition of phosphorus to amorphous Cu-Ti alloy greatly increases the corrosion resistance, even in 1N HCI.
1. Introduction Corrosion behavior of amorphous alloys produced by rapid quenching from the liquid state has recently attracted considerable attention. The present authors [1,2], in reporting the first observation of corrosion behavior of amorphous alloys, have stated that amorphous FeCrPlaC7 and FeCrNiP13C7 alloys containing 8 at.% or more chromium show an extremely high corrosion resistance in various environments, especially to pitting in acidic and neutral solutions containing chloride ions. Such a high corrosion resistance has been attributed to the high protective quality of the surface film [ 3 - 5 ] provided by the chemically homogenous single-phase nature of amorphous alloys [ 5 - 9 ] and the beneficial effect of metalloid additives in large amounts [4-6,9,10]. The studies of corrosion behaviors of amorphous alloys have so far been focused on the metal-metalloid systems. On the other hand, amorphous metal-metal systems such as Cu-Zr, Cu-Ti and Ni-Nb with high strength and thermal stability [11-13] can also be prepared by rapid quenching of alloy liquids. These systems are desirable for the study of the effect of non-crystallinity of alloys on the corrosion behavior, without the influence of metalloid additives. For this reason, amorphous CusoTiso and CusoZrso alloys were used in the present work. 29
30
M. Naka et al. / Corrosion behavior o f Cu5oTi50, Cu5oZr50 alloys
2. Experimental Alloy ingots were prepared by arc-melting commercial Cu (99.99%), Ti (99.9%), Zr (99.9%) and Cu3P under argon atmosphere. The rotating cylinder method was applied to the preparation of amorphous alloy ribbons of about 2 mm in width and 30/am in thickness. This technique consists of impinging a jet of molten alloy ont to the outer surface of a rotating cylinder. The formation of the amorphous structure of the alloys was confirmed by X-ray diffraction. Arc-melted ingots were used as crystalline specimens for comparison. In the crystalline state, the Cus oTiso alloy consists of two intermetallic bc tetragonal compounds, and the CusoZr5o alloy a single intermetallic compound [14]. The number annexed to the respective elements denotes the nominal content in atomic percent. Corrosion tests and electrochemical measurements were carried out in 1N H2 SO4, 1N HC1, 1N HNOa, 1N NaOH and 3% NaCI, which were prepared by using reagent-grade chemicals and deionized water and were open to the air. The average corrosion rate was estimated from the weight loss during immersion in the solutions at 303 -+ 1 K. Polarization curves were measured by a potentiodynamic method with a potential sweep rate of 2.37 X 10 -a V • s-1, starting from the corrosion potential at room temperature.
3. Results The corrosion rates of pure metals of Cu, Ti and Zr in 1N n2so4, 1N HNO3, 1N NaOH, 1N HC1 and 3% NaC1 are shown in fig. 1. Copper is not completely stable in all solutions, particularly in oxidizing acid such as HNO3. The corrosion rate in 1N HC1 is higher than that in 1N H2SO4, because of the formation of a CuCI~ complex anion. On the other hand, titanium and zirconium are extremely stable in various solutions owing to their high capability to form a passive film. Both metals exhibit no weight losses, even after immersion for 350 h in the solutions, except for titanium in IN H2SO4. Figure 2 shows the comparison of corrosion rates of amorphous and crystalline Cus0Tis0 alloys in various solutions. The corrosion rate of the amorphous alloy is significantly lower than that of pure copper, particularly in 1N HNOa. The high corrosion resistance is caused by the presence of titanium in the alloy. On the other hand, the corrosion rate of the crystalline Cus0Tis0 alloy is higher than that of the amorphous alloy in all solutions except for 1N H2SO4. A difference in the corrosion rates of amorphous and crystalline alloys is especially distinct in chloride solutions. For example, the corrosion rate of the crystalline alloy in 1N HC1 is of the order of 1.2 mm/year, while that of the amorphous alloy is only 0.15 mm/year. Figure 3 shows the comparison of corrosion rates of amorphous and crystalline CusoZrs0 alloys in various solutions. Both alloys show undetectable weight losses after immersion for 350 h in 1N H2SO4, 1N HNO3 and 1N NaOH, but are relatively
M. Naka et al. / Corrosion behavior of Cu s oTis o, Cu s oZr s o alloys
6
- -
31
005
oQJ I Ti
0 c~lJne ~ous
CusoT% CusoTi~
2 --
E 0.04 0,4 rr
# 0~
i
o3
"~ 002 U
1 --
-
t~o
0.1 0
m
. . . . . .
INH~
i
0.01 1 _
1NHbK)3
INNa0H 3%NaCI INHCI
1NH-zSO . 1NHNO31NNaOH
3*/.NaCI 1NHCI
Fig. 1. Average corrosion rate estimated from the weight loss of pure Cu, Ti and Zr in 1N H2SO4, 1N HNO3, 1N NaOH, 3% NaC1 and 1N HCI at 303 K. Fig. 2. Average corrosion rate estimated from the weight loss of amorphous and crystalline Cus 0Ti5o alloys in 1N H2SO4, 1N NaOH, 3% NaCI and 1N HCI at 303 K.
005, 0 C.rys~t~ Cu~Zrso
[] ~ o m h ~ CusoZrso
E E01N Q;
~a0c c
n
jj Jl
;,op
.Q
I
!
!
L
0o2 !
001
1NH2Sq, 1NPIqO3 INNaOH
3 NaCI 1NHCI
-05
0
05
!
1.0 t5 2.0 2_5 Potential V(SCE)
Fig. 3. Average corrosion rate estimated from the weight loss of amorphous and crystalline CusoZrso alloys in IN H2SO4, IN HNO3, IN NaOH, 3% NaCI and IN HC1 at 303 K. Fig. 4. Potentiodynamic polarization curves of pttre Cu in 1N H2SO4, 1N HNOa, 3% NaC1 and 1N HC1.
M. Naka et al. / Corrosion behavior of CusoTiso, CusoZrso alloys
32
~o
i~ l o~
id #. ~oo E
H u.5
I 0
05
• 1.0 1.5 F'olential
2-0 25 V(SCE)
IC)05 " •
0
0.5
1.0
Potential
1.5
2D 25 V(SCE)
Fig. 5. Potentiodynamic polarization curves of pure Ti in 1N H2SO4, 1N HNO 3, 3% NaC1 and 1N HC1.
Fig. 6. Potentiodynamic polarization curves of pure Zr in 1N H2SO4, 1N HNOa, 3% NaC1and 1N HC1.
unstable in chloride solutions such as 1N HC1 and 3% NaCI. The corrosion rate of the amorphous alloy in chloride solutions is less than one-half that of the crystalline alloy. Further examination has been made by potentiodynamic polarization measurements. Figs. 4 - 6 show anodic polarization curves of pure metals in various solutions. Copper tends to be passivated in 1N HC1 and 3% NaC1, but the current density in the passive region is fairly high. On the contrary, in 1N HNOa and 1N H2SO4, anodic passivation does not take place, although the corrosion potentials in these solutions are higher than those in the solutions containing chloride ions (fig. 4). Titanium is spontaneously passivated in all solutions employed and shows a wide passive region (fig. 5), while zirconium is passivated in the solutions without chloride ions (fig. 6). Anodic polarization curves of amorphous and crystalline Cus0Tis0 alloys are given in figs. 7 and 8, and those of CusoZrso alloys in figs. 9 and 10, respectively. All four alloys are spontaneously passivated in 1N HNOa and 1N H2SO4, in spite of the fact that copper cannot be passivated in these solutions. The spontaneous passivation of the alloys is caused by alloying with titanium or zirconium which have a high susceptibility to passivation. The current densities of both amorphous alloys in 1N HNO3 and 1N H~SO4 are lower than those of both crystalline alloys. Similarly, the current density of the amorphous CusoZrso alloy in 1N HC1 and 3% NaC1 is lower than that of the crystalline alloy. On the contrary, the current density of amorphous CusoTiso alloy in the active region in 1N HC1 and 3% NaC1 is more than one order of magnitude higher than that of the crystalline alloy, despite the fact
M. Na ka et aL
/ Corrosion behavior of
Cu s o Ti s o, Cu s oZrs o alloys
I¢
33
10
+~I~0_I~~ 1~ ~ I(~
lo'
10'
d-0.5
0
0.5
1.0 1.5 Potential
0
2.0 25 V(SCE)
05
1.0 1.5 Z0 Z5 Potential V(SCE)
Fig. 7. Potentiodynamic polarization curves of amorphous CusoTis o alloy in 1N H2SO 4, 1N HNO3, 3% NaC1 and 1N HC1. Fig. 8. Potentiodynamic polarization curves of crystalline CusoTiso in 1N H2SO4, 1N HNO3, 3% NaC1 and 1N HC1.
that the corrosion rates of the former are distinctly lower than those of the latter in these solutions. The addition of phosphorus to the metal-metal systems is significantly effective
Id
1¢
>,
.
-05
.
0
.
0.5
.
1.0 1.5 2.0 25 Potential V (SCE)
>~
10;
'
I
0
05
I
-O5
1.0 1.5 2.0 Z5 Potential V (SCE)
Fig. 9. PotentJodynamic polarization curves of amorphous CusoZrs o alloy in 1N H2SO4, 1N HNO3, 3% NaC1 and 1N HC1. Fig. 10. Potentiodynamic polarization curves of crystalline CusoZrso alloy in 1N H2SO4, 1N HNO3, 3% NaCI and 1N HCI.
34
M. Naka et al. / Corrosion behavior of Cu5oTiso, CusoZrso alloys
ld
0
(15
tO 15 Potential
ZO 2.5 V(SCE)
Fig. 11. Comparison of potentiodynamic polarization curves of amorphous Cus0Ti5o and Cu45TisoPs alloys in IN HC1.
in increasing the corrosion resistance. As an example, fig. 11 gives the anodic polarization curve of an amorphous CuasTisoPs alloy in 1N HC1. Included in the figure for comparison is the polarization curve of an amorphous Cus0Tis0 alloy in 1N HCI. The spontaneous passivation takes place on the amorphous Cu4sTisoPs alloy, even in 1N HC1, and the current density in the passive region is nearly two orders of magnitude lower than that of the amorphous CusoTiso alloy.
4. Discussion
The high corrosion resistance of amorphous alloys has been interpreted by the chemically homogeneous single-phase nature of amorphous alloys without crystalline defects such as precipitates, segregates, grain boundaries and dislocations where it is difficult to form a stable passive film. The high homogeneity of alloys provides the formation of a uniform, highly protective passive fdm [5-9]. This interpretation is applicable to the high corrosion resistance of amorphous CusoTiso and Cus oZr5o alloys in comparison with crystalline alloys having the same compositions. On the other hand, the corrosion behavior of alloys used is, in general, determined by the high corrosion resistance of titanium and zirconium which are easily passivated in various environments. For this reason, there are no environmer~ts in which the amorphous alloys exhibit a higher corrosion resistance than pure titanium or zirconium except 1N H2SO4. [In 1N H2SO4, both amorphous and crystalline CusoTiso alloys are more corrosion-resistant than titanium, because the addition of copper to titanium facilitates spontaneous passivation due mainly to the
M. Naka et al. / Corrosion behavior of Cu5oTiso, Cu5oZrsoalloys
35
acceleration of cathodic reaction (figs. 1,2, 4, 5 and 7).] The addition of phosphorus to amorphous metal-metal systems is especially effective in increasing the corrosion resistance. As the present authors and their coworkers [4,6,9,10] have reported, the metalloids change the composition and formation rate of protective passive f'dm on amorphous F e - C r alloys. Among various metalloid elements, phosphorus remarkably accelerates an enrichment of chromium in the passive film and consequently greatly enhances the corrosion resistance by the synergistic effect with the high homogeneity of amorphous alloys. The present result (fig. 11) suggests that phosphorus facilitates spontaneous passivation due to the rapid enrichment of titanium in the alloy-solution interface and enhances the corrosion resistance, as is found for amorphous F e - C r - P alloys. Consequently, the transformation of the crystalline phase to the amorphous substantiaUy increases the corrosion resistance by an increase in the chemical homogeneity of the alloys, which results in the formation of to a uniform passive film without weak points susceptible to corrosion. On the other hand, the addition of phosphorus to alloys greatly enhances the corrosion resistance when the alloys are in the amorphous phase, i.e. the chemically homogeneous phase.
5. Conclusions From immersion tests and electrochemical measurements of amorphous CusoTiso and CusoZrso alloys, the following conclusions can be drawn. The amorphous CusoTis0 and CusoZrso alloys are stable in 1N H2SO4, 1N HNOs and 1N NaOH, but not in aggressive chloride solutions such as 1N HC1 and 3% NaC1. The corrosion resistance of amorphous alloys is higher than that of crystalline alloys with the same compositions. The improvement of corrosion resistance arises from the increase in the chemical homogeneity of alloys due to glass-formation. The addition of phosphorus to amorphous metal-metal systems greatly increases the corrosion resistance; the amorphous Cu4sTisoPs alloy is spontaneously passivated in various solutions and shows a wide passive region, even in IN HC1.
References [1] [2] [3] [4] [5] [6] [7] [8]
M. Naka, K. Hashimoto and T. Masumoto, J. Japan Inst. Metals 38 (1974) 835. M. Naka, K. Hashimoto and T. Masumoto, Corrosion 32 (1976) 146. K. Asami, K. Hashimoto, T. Masumoto and S. Shimodaira, Corros. Sci. 16 (1976) 909. K. Hashimoto, M. Naka, K. Asami and T. Masumoto, Corros. Eng. (Boshoku Gijitsu) 27 (1978) 279. K. Hashimoto, M. Naka, K. Asami and T. Masumoto, Corros. Sci., 18 (1978) in press. K. Hashimoto, K. Osada, T. Masumoto and S. Shimodaira, Corros. Sd. 16 (1976) 71. R.B. Diegle and J.E. Starer, Corrosion 32 (1976) 155. T.M. Devine, J. Electrochem. Soc. 124 (1976) 38.
36
M. Naka et al. / Corrosion behavior of Cus oTis & Cu s oZrs o alloys
[9] K. Hashimoto, M. Naka, J. Noguchi, K. Asami and T. Masumoto, Passivity of Metals, Proc 4th Int. Symp. of Passivity (1977), in press. [10] M. Naka, K. Hashimoto and T. Masumoto, J. Non-Crystalline Solids 28 (1978) 403. [11] R. Ray, B.C. Giessen and N.J. Grant, Scripta Met. 2 (1968) 357. [12] S. Tomizawa and T. Masumoto, Sci. Rep. Res. Inst. Tohoku Univ. A-26 (1977) 263. [13] L.E. Tanner and R. Ray, Scripta Met. 11 (1977) 783. [14] M. Hansen, Constitution of Binary Alloys (McGraw-Hill, New York, 1966).
CORROSION BEHAVIOR OF AMORPHOUS AND CRYSTALLINE CusoTiso AND Cus oZr5o ALLOYS M. NAKA, K. HASHIMOTO and T. MASUMOTO The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendal, Japan
Received 26 April 1978
Corrosion rates and anodic polarization curves of amorphous and crystalline Cu50Tis 0 and Cus 0Zr5o alloys have been examined in various acidic, neutral and alkaline solutions. The amorphous alloys are very stable in acidic and alkaline solutions, but unstable in agressire chloride solutions. The corrosion resistance of these amorphous alloys is higher than that of the crystallized alloys. The high corrosion resistance of amorphous alloys is attributable to the high chemical homogeneity of amorphous alloys without localized crystalline defects such as precipitates, segregates, grain boundaries, etc. Metalloid elements play an important role in the corrosion behavior of amorphous alloys; the addition of phosphorus to amorphous Cu-Ti alloy greatly increases the corrosion resistance, even in 1N HCI.
1. Introduction Corrosion behavior of amorphous alloys produced by rapid quenching from the liquid state has recently attracted considerable attention. The present authors [1,2], in reporting the first observation of corrosion behavior of amorphous alloys, have stated that amorphous FeCrPlaC7 and FeCrNiP13C7 alloys containing 8 at.% or more chromium show an extremely high corrosion resistance in various environments, especially to pitting in acidic and neutral solutions containing chloride ions. Such a high corrosion resistance has been attributed to the high protective quality of the surface film [ 3 - 5 ] provided by the chemically homogenous single-phase nature of amorphous alloys [ 5 - 9 ] and the beneficial effect of metalloid additives in large amounts [4-6,9,10]. The studies of corrosion behaviors of amorphous alloys have so far been focused on the metal-metalloid systems. On the other hand, amorphous metal-metal systems such as Cu-Zr, Cu-Ti and Ni-Nb with high strength and thermal stability [11-13] can also be prepared by rapid quenching of alloy liquids. These systems are desirable for the study of the effect of non-crystallinity of alloys on the corrosion behavior, without the influence of metalloid additives. For this reason, amorphous CusoTiso and CusoZrso alloys were used in the present work. 29
30
M. Naka et al. / Corrosion behavior o f Cu5oTi50, Cu5oZr50 alloys
2. Experimental Alloy ingots were prepared by arc-melting commercial Cu (99.99%), Ti (99.9%), Zr (99.9%) and Cu3P under argon atmosphere. The rotating cylinder method was applied to the preparation of amorphous alloy ribbons of about 2 mm in width and 30/am in thickness. This technique consists of impinging a jet of molten alloy ont to the outer surface of a rotating cylinder. The formation of the amorphous structure of the alloys was confirmed by X-ray diffraction. Arc-melted ingots were used as crystalline specimens for comparison. In the crystalline state, the Cus oTiso alloy consists of two intermetallic bc tetragonal compounds, and the CusoZr5o alloy a single intermetallic compound [14]. The number annexed to the respective elements denotes the nominal content in atomic percent. Corrosion tests and electrochemical measurements were carried out in 1N H2 SO4, 1N HC1, 1N HNOa, 1N NaOH and 3% NaCI, which were prepared by using reagent-grade chemicals and deionized water and were open to the air. The average corrosion rate was estimated from the weight loss during immersion in the solutions at 303 -+ 1 K. Polarization curves were measured by a potentiodynamic method with a potential sweep rate of 2.37 X 10 -a V • s-1, starting from the corrosion potential at room temperature.
3. Results The corrosion rates of pure metals of Cu, Ti and Zr in 1N n2so4, 1N HNO3, 1N NaOH, 1N HC1 and 3% NaC1 are shown in fig. 1. Copper is not completely stable in all solutions, particularly in oxidizing acid such as HNO3. The corrosion rate in 1N HC1 is higher than that in 1N H2SO4, because of the formation of a CuCI~ complex anion. On the other hand, titanium and zirconium are extremely stable in various solutions owing to their high capability to form a passive film. Both metals exhibit no weight losses, even after immersion for 350 h in the solutions, except for titanium in IN H2SO4. Figure 2 shows the comparison of corrosion rates of amorphous and crystalline Cus0Tis0 alloys in various solutions. The corrosion rate of the amorphous alloy is significantly lower than that of pure copper, particularly in 1N HNOa. The high corrosion resistance is caused by the presence of titanium in the alloy. On the other hand, the corrosion rate of the crystalline Cus0Tis0 alloy is higher than that of the amorphous alloy in all solutions except for 1N H2SO4. A difference in the corrosion rates of amorphous and crystalline alloys is especially distinct in chloride solutions. For example, the corrosion rate of the crystalline alloy in 1N HC1 is of the order of 1.2 mm/year, while that of the amorphous alloy is only 0.15 mm/year. Figure 3 shows the comparison of corrosion rates of amorphous and crystalline CusoZrs0 alloys in various solutions. Both alloys show undetectable weight losses after immersion for 350 h in 1N H2SO4, 1N HNO3 and 1N NaOH, but are relatively
M. Naka et al. / Corrosion behavior of Cu s oTis o, Cu s oZr s o alloys
6
- -
31
005
oQJ I Ti
0 c~lJne ~ous
CusoT% CusoTi~
2 --
E 0.04 0,4 rr
# 0~
i
o3
"~ 002 U
1 --
-
t~o
0.1 0
m
. . . . . .
INH~
i
0.01 1 _
1NHbK)3
INNa0H 3%NaCI INHCI
1NH-zSO . 1NHNO31NNaOH
3*/.NaCI 1NHCI
Fig. 1. Average corrosion rate estimated from the weight loss of pure Cu, Ti and Zr in 1N H2SO4, 1N HNO3, 1N NaOH, 3% NaC1 and 1N HCI at 303 K. Fig. 2. Average corrosion rate estimated from the weight loss of amorphous and crystalline Cus 0Ti5o alloys in 1N H2SO4, 1N NaOH, 3% NaCI and 1N HCI at 303 K.
005, 0 C.rys~t~ Cu~Zrso
[] ~ o m h ~ CusoZrso
E E01N Q;
~a0c c
n
jj Jl
;,op
.Q
I
!
!
L
0o2 !
001
1NH2Sq, 1NPIqO3 INNaOH
3 NaCI 1NHCI
-05
0
05
!
1.0 t5 2.0 2_5 Potential V(SCE)
Fig. 3. Average corrosion rate estimated from the weight loss of amorphous and crystalline CusoZrso alloys in IN H2SO4, IN HNO3, IN NaOH, 3% NaCI and IN HC1 at 303 K. Fig. 4. Potentiodynamic polarization curves of pttre Cu in 1N H2SO4, 1N HNOa, 3% NaC1 and 1N HC1.
M. Naka et al. / Corrosion behavior of CusoTiso, CusoZrso alloys
32
~o
i~ l o~
id #. ~oo E
H u.5
I 0
05
• 1.0 1.5 F'olential
2-0 25 V(SCE)
IC)05 " •
0
0.5
1.0
Potential
1.5
2D 25 V(SCE)
Fig. 5. Potentiodynamic polarization curves of pure Ti in 1N H2SO4, 1N HNO 3, 3% NaC1 and 1N HC1.
Fig. 6. Potentiodynamic polarization curves of pure Zr in 1N H2SO4, 1N HNOa, 3% NaC1and 1N HC1.
unstable in chloride solutions such as 1N HC1 and 3% NaCI. The corrosion rate of the amorphous alloy in chloride solutions is less than one-half that of the crystalline alloy. Further examination has been made by potentiodynamic polarization measurements. Figs. 4 - 6 show anodic polarization curves of pure metals in various solutions. Copper tends to be passivated in 1N HC1 and 3% NaC1, but the current density in the passive region is fairly high. On the contrary, in 1N HNOa and 1N H2SO4, anodic passivation does not take place, although the corrosion potentials in these solutions are higher than those in the solutions containing chloride ions (fig. 4). Titanium is spontaneously passivated in all solutions employed and shows a wide passive region (fig. 5), while zirconium is passivated in the solutions without chloride ions (fig. 6). Anodic polarization curves of amorphous and crystalline Cus0Tis0 alloys are given in figs. 7 and 8, and those of CusoZrso alloys in figs. 9 and 10, respectively. All four alloys are spontaneously passivated in 1N HNOa and 1N H2SO4, in spite of the fact that copper cannot be passivated in these solutions. The spontaneous passivation of the alloys is caused by alloying with titanium or zirconium which have a high susceptibility to passivation. The current densities of both amorphous alloys in 1N HNO3 and 1N H~SO4 are lower than those of both crystalline alloys. Similarly, the current density of the amorphous CusoZrso alloy in 1N HC1 and 3% NaC1 is lower than that of the crystalline alloy. On the contrary, the current density of amorphous CusoTiso alloy in the active region in 1N HC1 and 3% NaC1 is more than one order of magnitude higher than that of the crystalline alloy, despite the fact
M. Na ka et aL
/ Corrosion behavior of
Cu s o Ti s o, Cu s oZrs o alloys
I¢
33
10
+~I~0_I~~ 1~ ~ I(~
lo'
10'
d-0.5
0
0.5
1.0 1.5 Potential
0
2.0 25 V(SCE)
05
1.0 1.5 Z0 Z5 Potential V(SCE)
Fig. 7. Potentiodynamic polarization curves of amorphous CusoTis o alloy in 1N H2SO 4, 1N HNO3, 3% NaC1 and 1N HC1. Fig. 8. Potentiodynamic polarization curves of crystalline CusoTiso in 1N H2SO4, 1N HNO3, 3% NaC1 and 1N HC1.
that the corrosion rates of the former are distinctly lower than those of the latter in these solutions. The addition of phosphorus to the metal-metal systems is significantly effective
Id
1¢
>,
.
-05
.
0
.
0.5
.
1.0 1.5 2.0 25 Potential V (SCE)
>~
10;
'
I
0
05
I
-O5
1.0 1.5 2.0 Z5 Potential V (SCE)
Fig. 9. PotentJodynamic polarization curves of amorphous CusoZrs o alloy in 1N H2SO4, 1N HNO3, 3% NaC1 and 1N HC1. Fig. 10. Potentiodynamic polarization curves of crystalline CusoZrso alloy in 1N H2SO4, 1N HNO3, 3% NaCI and 1N HCI.
34
M. Naka et al. / Corrosion behavior of Cu5oTiso, CusoZrso alloys
ld
0
(15
tO 15 Potential
ZO 2.5 V(SCE)
Fig. 11. Comparison of potentiodynamic polarization curves of amorphous Cus0Ti5o and Cu45TisoPs alloys in IN HC1.
in increasing the corrosion resistance. As an example, fig. 11 gives the anodic polarization curve of an amorphous CuasTisoPs alloy in 1N HC1. Included in the figure for comparison is the polarization curve of an amorphous Cus0Tis0 alloy in 1N HCI. The spontaneous passivation takes place on the amorphous Cu4sTisoPs alloy, even in 1N HC1, and the current density in the passive region is nearly two orders of magnitude lower than that of the amorphous CusoTiso alloy.
4. Discussion
The high corrosion resistance of amorphous alloys has been interpreted by the chemically homogeneous single-phase nature of amorphous alloys without crystalline defects such as precipitates, segregates, grain boundaries and dislocations where it is difficult to form a stable passive film. The high homogeneity of alloys provides the formation of a uniform, highly protective passive fdm [5-9]. This interpretation is applicable to the high corrosion resistance of amorphous CusoTiso and Cus oZr5o alloys in comparison with crystalline alloys having the same compositions. On the other hand, the corrosion behavior of alloys used is, in general, determined by the high corrosion resistance of titanium and zirconium which are easily passivated in various environments. For this reason, there are no environmer~ts in which the amorphous alloys exhibit a higher corrosion resistance than pure titanium or zirconium except 1N H2SO4. [In 1N H2SO4, both amorphous and crystalline CusoTiso alloys are more corrosion-resistant than titanium, because the addition of copper to titanium facilitates spontaneous passivation due mainly to the
M. Naka et al. / Corrosion behavior of Cu5oTiso, Cu5oZrsoalloys
35
acceleration of cathodic reaction (figs. 1,2, 4, 5 and 7).] The addition of phosphorus to amorphous metal-metal systems is especially effective in increasing the corrosion resistance. As the present authors and their coworkers [4,6,9,10] have reported, the metalloids change the composition and formation rate of protective passive f'dm on amorphous F e - C r alloys. Among various metalloid elements, phosphorus remarkably accelerates an enrichment of chromium in the passive film and consequently greatly enhances the corrosion resistance by the synergistic effect with the high homogeneity of amorphous alloys. The present result (fig. 11) suggests that phosphorus facilitates spontaneous passivation due to the rapid enrichment of titanium in the alloy-solution interface and enhances the corrosion resistance, as is found for amorphous F e - C r - P alloys. Consequently, the transformation of the crystalline phase to the amorphous substantiaUy increases the corrosion resistance by an increase in the chemical homogeneity of the alloys, which results in the formation of to a uniform passive film without weak points susceptible to corrosion. On the other hand, the addition of phosphorus to alloys greatly enhances the corrosion resistance when the alloys are in the amorphous phase, i.e. the chemically homogeneous phase.
5. Conclusions From immersion tests and electrochemical measurements of amorphous CusoTiso and CusoZrso alloys, the following conclusions can be drawn. The amorphous CusoTis0 and CusoZrso alloys are stable in 1N H2SO4, 1N HNOs and 1N NaOH, but not in aggressive chloride solutions such as 1N HC1 and 3% NaC1. The corrosion resistance of amorphous alloys is higher than that of crystalline alloys with the same compositions. The improvement of corrosion resistance arises from the increase in the chemical homogeneity of alloys due to glass-formation. The addition of phosphorus to amorphous metal-metal systems greatly increases the corrosion resistance; the amorphous Cu4sTisoPs alloy is spontaneously passivated in various solutions and shows a wide passive region, even in IN HC1.
References [1] [2] [3] [4] [5] [6] [7] [8]
M. Naka, K. Hashimoto and T. Masumoto, J. Japan Inst. Metals 38 (1974) 835. M. Naka, K. Hashimoto and T. Masumoto, Corrosion 32 (1976) 146. K. Asami, K. Hashimoto, T. Masumoto and S. Shimodaira, Corros. Sci. 16 (1976) 909. K. Hashimoto, M. Naka, K. Asami and T. Masumoto, Corros. Eng. (Boshoku Gijitsu) 27 (1978) 279. K. Hashimoto, M. Naka, K. Asami and T. Masumoto, Corros. Sci., 18 (1978) in press. K. Hashimoto, K. Osada, T. Masumoto and S. Shimodaira, Corros. Sd. 16 (1976) 71. R.B. Diegle and J.E. Starer, Corrosion 32 (1976) 155. T.M. Devine, J. Electrochem. Soc. 124 (1976) 38.
36
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[9] K. Hashimoto, M. Naka, J. Noguchi, K. Asami and T. Masumoto, Passivity of Metals, Proc 4th Int. Symp. of Passivity (1977), in press. [10] M. Naka, K. Hashimoto and T. Masumoto, J. Non-Crystalline Solids 28 (1978) 403. [11] R. Ray, B.C. Giessen and N.J. Grant, Scripta Met. 2 (1968) 357. [12] S. Tomizawa and T. Masumoto, Sci. Rep. Res. Inst. Tohoku Univ. A-26 (1977) 263. [13] L.E. Tanner and R. Ray, Scripta Met. 11 (1977) 783. [14] M. Hansen, Constitution of Binary Alloys (McGraw-Hill, New York, 1966).