The surface of the metallic glass Zr 59 Ti 3 Cu 20 Al 10 Ni 8 has been modified by hydrofluoric a... more The surface of the metallic glass Zr 59 Ti 3 Cu 20 Al 10 Ni 8 has been modified by hydrofluoric acid (HF) etching treatment. The devitrification and crystallisation process has been mainly studied by isothermal differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The nucleation-growth process is the mechanism of crystallisation; nevertheless the JMA-model is not applicable in every situation. Alternative methods are used to interpret the data. Results show the devitrification process is strongly affected by surface nucleation, which depends on the surface topology. Zr 3 Al 2 is the first phase formed on the concave areas whereas the quasicrystalline and Zr 2 Ni-based phases appears in the flatter ones. Nevertheless, the presence of an oxide surface layer acts upon the surface nucleation and dwarfs the consequences of such topological differences. Moreover, the quasicrystalline formation appears also to be in competition with the parallel formation of ZrO 2 due to thermal re-oxidation during the DSC experiments.
Ultrafine structured Ti70.5Fe29.5 and Ti67.79Fe28.36Sn3.85 eutectic rods comprising of β-Ti and T... more Ultrafine structured Ti70.5Fe29.5 and Ti67.79Fe28.36Sn3.85 eutectic rods comprising of β-Ti and TiFe phases were prepared by copper mould casting. The corrosion and passivation behaviour were investigated in halide free aqueous media (pH 1–13) by means of potentiodynamic polarisation and potentiostatic current transient measurements. Both eutectic alloys exhibit excellent corrosion resistance due to spontaneous passivation. The passive film compositions grown several
Production of bulk amorphous Zr-based alloys with a significant supercooled liquid region was car... more Production of bulk amorphous Zr-based alloys with a significant supercooled liquid region was carried out by die casting into a copper mold. Fully amorphous and partially crystalline samples were prepared. The microstructure was analyzed by X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), and chemical analysis with special emphasis on the size and composition of the crystallites. The
Amorphous alloys are good candidates for application as soft magnetic materials because of the la... more Amorphous alloys are good candidates for application as soft magnetic materials because of the lack of crystal anisotropy. Amorphous materials with enhanced glass formability give an opportunity to improve the value in use of amorphous materials further. Conventional soft magnetic alloys often have very high mechanical strength and high resistance against corrosion which may be important for application as magnetic
A novel phase-separated Ni-based amorphous alloy is prepared in a glass forming system by rapid q... more A novel phase-separated Ni-based amorphous alloy is prepared in a glass forming system by rapid quenching of a Ni 58.5 Nb 20.25 Y 21.25 melt. The microstructure consists of two amorphous Nb-enriched and Y-enriched regions with a size distribution from micrometer dimensions down to several nanometers. Decomposition takes place in the melt prior to solidification. The miscibility gap in the solid and liquid state of the binary Nb-Y system extends into the ternary Ni-Nb-Y alloy as a consequence of the positive mixing enthalpy between Nb and Y. The two-phase amorphous Ni 58.5 Nb 20.25 Y 21.25 alloy crystallizes in a first step by the primary precipitation of the cubic Ni 2 Y phase from the Y-rich amorphous phase. At much higher temperatures the remaining Nb-rich amorphous phase crystallizes into Ni 7 Nb 6 .
The absorption of hydrogen by means of gas–solid reaction and its consequence on the structure ha... more The absorption of hydrogen by means of gas–solid reaction and its consequence on the structure have been studied for fully amorphous alloys as well as quasicrystals/glassy composite alloys based on the composition Zr59Ti3Cu20Al10Ni8. The process of hydrogen absorption has been performed and monitored under 20bar of H2 using high pressure-differential scanning calorimetry (HP-DSC). The structure evolution of the samples has
Cobalt (Co) layers with a thickness of up to 50 nm have been electrodeposited under the influence... more Cobalt (Co) layers with a thickness of up to 50 nm have been electrodeposited under the influence of magnetic fields up to 10 T aligned perpendicular or parallel to the electrode surface. The crystallographic orientation and the phase composition of these layers have been investigated by X-ray diffraction and transmission electron microscopy. The layers consist mainly of the face centered cubic phase with a 〈111〉 orientation perpendicular to the electrode surface which results from the low surface free energy of these planes. An influence of magnetic fields on the crystallographic orientation has not been observed. It was found that magnetic fields affect the phase composition which results predominantly from the influence of the magnetic fields on the electrochemistry. The nucleation has been studied by in-situ scanning tunneling microscopy.
Bulk samples with 3mm diameter of the Zr66Nb13Cu8Ni6.8Al6.2 and Ti66Nb13Cu8Ni6.8Al6.2 alloys with... more Bulk samples with 3mm diameter of the Zr66Nb13Cu8Ni6.8Al6.2 and Ti66Nb13Cu8Ni6.8Al6.2 alloys with in situ formed nanostructured matrix and dendritic bcc phase were prepared by copper mould casting and characterized regarding their microstructure. The passivation ability and the localized corrosion susceptibility were determined from electrochemical dynamic and static polarization tests. Both alloys show excellent passivity in acidic as well as in
Materials and Corrosion-werkstoffe Und Korrosion, 2004
A bulk amorphous Fe 65.5 Cr 4 Mo 4 Ga 4 P 12 C 5 B 5.5 alloy was investigated for its electrochem... more A bulk amorphous Fe 65.5 Cr 4 Mo 4 Ga 4 P 12 C 5 B 5.5 alloy was investigated for its electrochemical behaviour in different electrolytes. The investigations showed substantial differences in response between the rapidly quenched and cast samples of the same composition. Annealing of the cast samples improved their corrosion resistance, which was possibly due to structural relaxation processes. The alloy was found to have very good resistance to neutral and slightly acidic chloride solutions in the rapidly quenched form.
Journal of the Mechanical Behavior of Biomedical Materials, 2014
Recent developments showed that E-type Ti-Nb alloys are good candidates for hard tissue replaceme... more Recent developments showed that E-type Ti-Nb alloys are good candidates for hard tissue replacement and repair. However, their elastic moduli are still to be further reduced to match the Young's modulus values of human bone, in order to avoid stress shielding. In the present study, the effect of indium (In) additions on the structural characteristics and elastic modulus of Ti-40Nb was investigated by experimental and theoretical (ab initio) methods. Several
Corrosion phenomena are investigated for a Zr59Ti3Cu20Al10Ni8 metallic glass immersed in hydroflu... more Corrosion phenomena are investigated for a Zr59Ti3Cu20Al10Ni8 metallic glass immersed in hydrofluoric acid (HF) in open-circuit conditions and by means of electron microscopies (SEM and TEM). Several morphologies develop on the corroded surface and especially large and deep pits. TEM study demonstrates that Cu-rich nanocrystals of 5–10nm are formed inside the corrosion pits (on their walls) during the corrosion process.
Ti-based metallic glasses show high potential for implant applications; they overcome in several ... more Ti-based metallic glasses show high potential for implant applications; they overcome in several crucial respects their well-established biocompatible crystalline counterparts, e.g. improved corrosion properties, higher fracture strength and wear resistance, increased elastic strain range and lower Young's modulus. However, some of the elements required for glass formation (e.g. Cu, Ni) are harmful for the human body. We critically reviewed the biological safety and glass forming tendency in Ti of 27 elements. This can be used as a basis for the future designing of novel amorphous Ti-based implant alloys entirely free of harmful additions. In this paper, two first alloys were developed: Ti(75)Zr(10)Si(15) and Ti(60)Nb(15)Zr(10)Si(15). The overheating temperature of the melt before casting can be used as the controlling parameter to produce fully amorphous materials or bcc-Ti-phase reinforced metallic glass nano-composites. The beneficial effect of Nb addition on the glass-formation and amorphous phase stability was assessed by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. Crystallization and mechanical behavior of ribbons are influenced by the amount and distribution of the nano-scaled bcc phase existing in the as-cast state. Their electrochemical stability in Ringer's solution at 310 K was found to be significantly better than that of commercial Ti-based biomaterials; no indication for pitting corrosion was recorded.
The corrosion behaviour of two bulk glass-matrix composite alloys formed by copper mould casting ... more The corrosion behaviour of two bulk glass-matrix composite alloys formed by copper mould casting was analysed: (i) Zr 66.4 Nb 6.4 Cu 10.5 Ni 8.7 Al 8.0 with precipitated bcc dendrite phase and (ii) Zr 57 Ti 8 Nb 2.5 Cu 13.9 Ni 11.1 Al 7.5 with quasicrystalline phase, respectively. The electrochemical behaviour was tested on the cross-sectional areas of the composite rod samples in 0.5 M sulphuric acid solution with up to 0.5 M sodium chloride addition by potentiodynamic polarization measurements. The composition of anodically formed passive films was studied by means of Auger electron spectroscopy (AES). The morphology of local damages generated by a chloride-induced pitting process was examined with scanning electron microscopy. In result of those studies, a pitting mechanism is described. For both composites in chloride media, a pronounced selective dissolution of the glassy matrix phase occurs, whereas the crystalline phases are not attacked. Niobium and titanium components are beneficial in inhibiting the pitting initiation due to their participation in the passive film formation. The dissolution of the glassy matrix phase is explained by the principal higher chloride reactivity of metastable phases compared to that of stable crystalline phases and by the detected enrichment of copper in these phase regions. The chloride attack progressing along the matrix phase causes the formation of deep channels in the bulk composite material leading to an excavation and, finally, detachment of the bcc dendrites or quasicrystals, respectively. The re-passivation ability is very poor.
Bulk amorphous Zr Al Cu Ni alloy samples can be prepared by slow cooling from the melt due to the... more Bulk amorphous Zr Al Cu Ni alloy samples can be prepared by slow cooling from the melt due to their low critical cooling rate for amorphization. The passivation behaviour of the amorphous Zr 55 Al 10 Cu 30 Ni 5 alloy in a 0.1 M Na 2 SO 4 (pH=8) electrolyte is characterized in comparison to its crystalline alloy counterpart and to zirconium. Potentiodynamic and potentiostatic polarization measurements reveal that the alloys form strong protective surface layers by anodization, which is, in general, quite similar to the behaviour of zirconium. The barrier effect of surface layers grown on the alloys is slightly lower than that of films on zirconium. From AES investigations, it is obvious that all alloying elements participate in the formation of anodic films, which also show a gradient of composition along the growth direction. In 0.001 -0.1 M NaCl electrolytes, pitting occurs on bulk amorphous Zr Al Cu Ni samples due to the existence of micrometer-sized crystalline inclusions. The oxygen-induced formation of such crystalline phases during slow cooling is studied in detail by characterizing samples of different oxygen content with X-ray diffraction, optical and scanning electron microscopy and differential scanning calorimetry.
Cylindrical Zr 55 Cu 30 Al 10 Ni 5 (numbers indicate at.%) alloy specimens with 3 mm diameter wer... more Cylindrical Zr 55 Cu 30 Al 10 Ni 5 (numbers indicate at.%) alloy specimens with 3 mm diameter were prepared by copper mould casting and characterised concerning their microstructure and thermal stability by X-ray diffraction, optical and scanning electron microscopy and by ...
Amorphous and multiphase crystalline Mg 65 Y 10 Cu 15 Ag 10 samples were subjected to potentiodyn... more Amorphous and multiphase crystalline Mg 65 Y 10 Cu 15 Ag 10 samples were subjected to potentiodynamic polarisation in electrolytes with pH = 5-8.4 and 13. Potentiostatic current transients were recorded for studying anodic passive layers growth mechanisms. Surface states were characterised by Auger electron spectroscopy (AES) depth profiling and atomic force microscopy (AFM). The corrosion behaviour of the quaternary alloy samples containing silver is markedly different compared to that of the earlier studied Mg 65 Y 10 Cu 25 alloy. The free corrosion potential is more noble and corrosion current densities are lower. Stable anodic passivation was observed in electrolytes with pH ≥ 6, whereas in acidic media dissolution sets in. In neutral to weakly alkaline electrolytes, a mainly high field driven layer growth occurs which was similarly observed for the ternary alloy. In strongly alkaline electrolyte, the growth mechanism tended to shift from diffusion control (ternary alloy) to a more high field driven growth pattern due to the presence of silver in the alloy. Passive layers formed in weakly alkaline electrolyte under participation of all alloying elements, especially copper, are thick and porous. Magnesium and yttrium oxide/hydroxides are the main constituents of the thinner passive layer formed in the highly alkaline electrolyte, but also traces of silver oxides were detected. Also, for this quaternary alloy composition, the multiphase crystalline material exhibits a poorer stability and passivation ability than the single amorphous phase.
The corrosion behaviour of the amorphous Mg65Y10Cu25 alloy was studied in aqueous alkaline electr... more The corrosion behaviour of the amorphous Mg65Y10Cu25 alloy was studied in aqueous alkaline electrolytes and compared with that of the corresponding multiphase crystalline alloy and of magnesium. Alloy samples were prepared by melt-spinning and die-casting and characterised concerning their microstructure and thermal stability by X-ray diffraction, optical and scanning electron microscopy and differential scanning calorimetry. In 0.3 m H3BO3/Na2B4O7 buffer
The surface of the metallic glass Zr 59 Ti 3 Cu 20 Al 10 Ni 8 has been modified by hydrofluoric a... more The surface of the metallic glass Zr 59 Ti 3 Cu 20 Al 10 Ni 8 has been modified by hydrofluoric acid (HF) etching treatment. The devitrification and crystallisation process has been mainly studied by isothermal differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The nucleation-growth process is the mechanism of crystallisation; nevertheless the JMA-model is not applicable in every situation. Alternative methods are used to interpret the data. Results show the devitrification process is strongly affected by surface nucleation, which depends on the surface topology. Zr 3 Al 2 is the first phase formed on the concave areas whereas the quasicrystalline and Zr 2 Ni-based phases appears in the flatter ones. Nevertheless, the presence of an oxide surface layer acts upon the surface nucleation and dwarfs the consequences of such topological differences. Moreover, the quasicrystalline formation appears also to be in competition with the parallel formation of ZrO 2 due to thermal re-oxidation during the DSC experiments.
Ultrafine structured Ti70.5Fe29.5 and Ti67.79Fe28.36Sn3.85 eutectic rods comprising of β-Ti and T... more Ultrafine structured Ti70.5Fe29.5 and Ti67.79Fe28.36Sn3.85 eutectic rods comprising of β-Ti and TiFe phases were prepared by copper mould casting. The corrosion and passivation behaviour were investigated in halide free aqueous media (pH 1–13) by means of potentiodynamic polarisation and potentiostatic current transient measurements. Both eutectic alloys exhibit excellent corrosion resistance due to spontaneous passivation. The passive film compositions grown several
Production of bulk amorphous Zr-based alloys with a significant supercooled liquid region was car... more Production of bulk amorphous Zr-based alloys with a significant supercooled liquid region was carried out by die casting into a copper mold. Fully amorphous and partially crystalline samples were prepared. The microstructure was analyzed by X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), and chemical analysis with special emphasis on the size and composition of the crystallites. The
Amorphous alloys are good candidates for application as soft magnetic materials because of the la... more Amorphous alloys are good candidates for application as soft magnetic materials because of the lack of crystal anisotropy. Amorphous materials with enhanced glass formability give an opportunity to improve the value in use of amorphous materials further. Conventional soft magnetic alloys often have very high mechanical strength and high resistance against corrosion which may be important for application as magnetic
A novel phase-separated Ni-based amorphous alloy is prepared in a glass forming system by rapid q... more A novel phase-separated Ni-based amorphous alloy is prepared in a glass forming system by rapid quenching of a Ni 58.5 Nb 20.25 Y 21.25 melt. The microstructure consists of two amorphous Nb-enriched and Y-enriched regions with a size distribution from micrometer dimensions down to several nanometers. Decomposition takes place in the melt prior to solidification. The miscibility gap in the solid and liquid state of the binary Nb-Y system extends into the ternary Ni-Nb-Y alloy as a consequence of the positive mixing enthalpy between Nb and Y. The two-phase amorphous Ni 58.5 Nb 20.25 Y 21.25 alloy crystallizes in a first step by the primary precipitation of the cubic Ni 2 Y phase from the Y-rich amorphous phase. At much higher temperatures the remaining Nb-rich amorphous phase crystallizes into Ni 7 Nb 6 .
The absorption of hydrogen by means of gas–solid reaction and its consequence on the structure ha... more The absorption of hydrogen by means of gas–solid reaction and its consequence on the structure have been studied for fully amorphous alloys as well as quasicrystals/glassy composite alloys based on the composition Zr59Ti3Cu20Al10Ni8. The process of hydrogen absorption has been performed and monitored under 20bar of H2 using high pressure-differential scanning calorimetry (HP-DSC). The structure evolution of the samples has
Cobalt (Co) layers with a thickness of up to 50 nm have been electrodeposited under the influence... more Cobalt (Co) layers with a thickness of up to 50 nm have been electrodeposited under the influence of magnetic fields up to 10 T aligned perpendicular or parallel to the electrode surface. The crystallographic orientation and the phase composition of these layers have been investigated by X-ray diffraction and transmission electron microscopy. The layers consist mainly of the face centered cubic phase with a 〈111〉 orientation perpendicular to the electrode surface which results from the low surface free energy of these planes. An influence of magnetic fields on the crystallographic orientation has not been observed. It was found that magnetic fields affect the phase composition which results predominantly from the influence of the magnetic fields on the electrochemistry. The nucleation has been studied by in-situ scanning tunneling microscopy.
Bulk samples with 3mm diameter of the Zr66Nb13Cu8Ni6.8Al6.2 and Ti66Nb13Cu8Ni6.8Al6.2 alloys with... more Bulk samples with 3mm diameter of the Zr66Nb13Cu8Ni6.8Al6.2 and Ti66Nb13Cu8Ni6.8Al6.2 alloys with in situ formed nanostructured matrix and dendritic bcc phase were prepared by copper mould casting and characterized regarding their microstructure. The passivation ability and the localized corrosion susceptibility were determined from electrochemical dynamic and static polarization tests. Both alloys show excellent passivity in acidic as well as in
Materials and Corrosion-werkstoffe Und Korrosion, 2004
A bulk amorphous Fe 65.5 Cr 4 Mo 4 Ga 4 P 12 C 5 B 5.5 alloy was investigated for its electrochem... more A bulk amorphous Fe 65.5 Cr 4 Mo 4 Ga 4 P 12 C 5 B 5.5 alloy was investigated for its electrochemical behaviour in different electrolytes. The investigations showed substantial differences in response between the rapidly quenched and cast samples of the same composition. Annealing of the cast samples improved their corrosion resistance, which was possibly due to structural relaxation processes. The alloy was found to have very good resistance to neutral and slightly acidic chloride solutions in the rapidly quenched form.
Journal of the Mechanical Behavior of Biomedical Materials, 2014
Recent developments showed that E-type Ti-Nb alloys are good candidates for hard tissue replaceme... more Recent developments showed that E-type Ti-Nb alloys are good candidates for hard tissue replacement and repair. However, their elastic moduli are still to be further reduced to match the Young's modulus values of human bone, in order to avoid stress shielding. In the present study, the effect of indium (In) additions on the structural characteristics and elastic modulus of Ti-40Nb was investigated by experimental and theoretical (ab initio) methods. Several
Corrosion phenomena are investigated for a Zr59Ti3Cu20Al10Ni8 metallic glass immersed in hydroflu... more Corrosion phenomena are investigated for a Zr59Ti3Cu20Al10Ni8 metallic glass immersed in hydrofluoric acid (HF) in open-circuit conditions and by means of electron microscopies (SEM and TEM). Several morphologies develop on the corroded surface and especially large and deep pits. TEM study demonstrates that Cu-rich nanocrystals of 5–10nm are formed inside the corrosion pits (on their walls) during the corrosion process.
Ti-based metallic glasses show high potential for implant applications; they overcome in several ... more Ti-based metallic glasses show high potential for implant applications; they overcome in several crucial respects their well-established biocompatible crystalline counterparts, e.g. improved corrosion properties, higher fracture strength and wear resistance, increased elastic strain range and lower Young's modulus. However, some of the elements required for glass formation (e.g. Cu, Ni) are harmful for the human body. We critically reviewed the biological safety and glass forming tendency in Ti of 27 elements. This can be used as a basis for the future designing of novel amorphous Ti-based implant alloys entirely free of harmful additions. In this paper, two first alloys were developed: Ti(75)Zr(10)Si(15) and Ti(60)Nb(15)Zr(10)Si(15). The overheating temperature of the melt before casting can be used as the controlling parameter to produce fully amorphous materials or bcc-Ti-phase reinforced metallic glass nano-composites. The beneficial effect of Nb addition on the glass-formation and amorphous phase stability was assessed by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. Crystallization and mechanical behavior of ribbons are influenced by the amount and distribution of the nano-scaled bcc phase existing in the as-cast state. Their electrochemical stability in Ringer's solution at 310 K was found to be significantly better than that of commercial Ti-based biomaterials; no indication for pitting corrosion was recorded.
The corrosion behaviour of two bulk glass-matrix composite alloys formed by copper mould casting ... more The corrosion behaviour of two bulk glass-matrix composite alloys formed by copper mould casting was analysed: (i) Zr 66.4 Nb 6.4 Cu 10.5 Ni 8.7 Al 8.0 with precipitated bcc dendrite phase and (ii) Zr 57 Ti 8 Nb 2.5 Cu 13.9 Ni 11.1 Al 7.5 with quasicrystalline phase, respectively. The electrochemical behaviour was tested on the cross-sectional areas of the composite rod samples in 0.5 M sulphuric acid solution with up to 0.5 M sodium chloride addition by potentiodynamic polarization measurements. The composition of anodically formed passive films was studied by means of Auger electron spectroscopy (AES). The morphology of local damages generated by a chloride-induced pitting process was examined with scanning electron microscopy. In result of those studies, a pitting mechanism is described. For both composites in chloride media, a pronounced selective dissolution of the glassy matrix phase occurs, whereas the crystalline phases are not attacked. Niobium and titanium components are beneficial in inhibiting the pitting initiation due to their participation in the passive film formation. The dissolution of the glassy matrix phase is explained by the principal higher chloride reactivity of metastable phases compared to that of stable crystalline phases and by the detected enrichment of copper in these phase regions. The chloride attack progressing along the matrix phase causes the formation of deep channels in the bulk composite material leading to an excavation and, finally, detachment of the bcc dendrites or quasicrystals, respectively. The re-passivation ability is very poor.
Bulk amorphous Zr Al Cu Ni alloy samples can be prepared by slow cooling from the melt due to the... more Bulk amorphous Zr Al Cu Ni alloy samples can be prepared by slow cooling from the melt due to their low critical cooling rate for amorphization. The passivation behaviour of the amorphous Zr 55 Al 10 Cu 30 Ni 5 alloy in a 0.1 M Na 2 SO 4 (pH=8) electrolyte is characterized in comparison to its crystalline alloy counterpart and to zirconium. Potentiodynamic and potentiostatic polarization measurements reveal that the alloys form strong protective surface layers by anodization, which is, in general, quite similar to the behaviour of zirconium. The barrier effect of surface layers grown on the alloys is slightly lower than that of films on zirconium. From AES investigations, it is obvious that all alloying elements participate in the formation of anodic films, which also show a gradient of composition along the growth direction. In 0.001 -0.1 M NaCl electrolytes, pitting occurs on bulk amorphous Zr Al Cu Ni samples due to the existence of micrometer-sized crystalline inclusions. The oxygen-induced formation of such crystalline phases during slow cooling is studied in detail by characterizing samples of different oxygen content with X-ray diffraction, optical and scanning electron microscopy and differential scanning calorimetry.
Cylindrical Zr 55 Cu 30 Al 10 Ni 5 (numbers indicate at.%) alloy specimens with 3 mm diameter wer... more Cylindrical Zr 55 Cu 30 Al 10 Ni 5 (numbers indicate at.%) alloy specimens with 3 mm diameter were prepared by copper mould casting and characterised concerning their microstructure and thermal stability by X-ray diffraction, optical and scanning electron microscopy and by ...
Amorphous and multiphase crystalline Mg 65 Y 10 Cu 15 Ag 10 samples were subjected to potentiodyn... more Amorphous and multiphase crystalline Mg 65 Y 10 Cu 15 Ag 10 samples were subjected to potentiodynamic polarisation in electrolytes with pH = 5-8.4 and 13. Potentiostatic current transients were recorded for studying anodic passive layers growth mechanisms. Surface states were characterised by Auger electron spectroscopy (AES) depth profiling and atomic force microscopy (AFM). The corrosion behaviour of the quaternary alloy samples containing silver is markedly different compared to that of the earlier studied Mg 65 Y 10 Cu 25 alloy. The free corrosion potential is more noble and corrosion current densities are lower. Stable anodic passivation was observed in electrolytes with pH ≥ 6, whereas in acidic media dissolution sets in. In neutral to weakly alkaline electrolytes, a mainly high field driven layer growth occurs which was similarly observed for the ternary alloy. In strongly alkaline electrolyte, the growth mechanism tended to shift from diffusion control (ternary alloy) to a more high field driven growth pattern due to the presence of silver in the alloy. Passive layers formed in weakly alkaline electrolyte under participation of all alloying elements, especially copper, are thick and porous. Magnesium and yttrium oxide/hydroxides are the main constituents of the thinner passive layer formed in the highly alkaline electrolyte, but also traces of silver oxides were detected. Also, for this quaternary alloy composition, the multiphase crystalline material exhibits a poorer stability and passivation ability than the single amorphous phase.
The corrosion behaviour of the amorphous Mg65Y10Cu25 alloy was studied in aqueous alkaline electr... more The corrosion behaviour of the amorphous Mg65Y10Cu25 alloy was studied in aqueous alkaline electrolytes and compared with that of the corresponding multiphase crystalline alloy and of magnesium. Alloy samples were prepared by melt-spinning and die-casting and characterised concerning their microstructure and thermal stability by X-ray diffraction, optical and scanning electron microscopy and differential scanning calorimetry. In 0.3 m H3BO3/Na2B4O7 buffer
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