Corrosion Resistance of Fe- and Ni- Based Metallic Glasses
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CORROSION RESISTANCE OF Fe- AND Ni- BASED METALLIC GLASSES
B.-O. REINDERS, H. W. BERGMANN Institut f~r Werkstoffkunde und Werkstofftechnik, Technische Universit~t Clausthal, D-3392 Clausthal-Zellerfeld,
FRG
ABSTRACT The corrosion behaviour in liquid electrolytes were investigated for some Fe- and Ni-based metallic glasses varying pH-value, electrolyte temperature and heat treatment. For some (Fe M) B glasses the high temperal00-x x83 17 ture oxidation behaviour was studied.
INTRODUCTION Six years after the discovery that rapidly quenched metallic melts may solidify with a structure similar to glasses F1, the first review of corrosion properties of these materials was published [2 ]. It could be demonstrated that chromium and phosphorous rich iron-based metallic glasses exhibited smaller corrosion rates than 18.8 type stainless steels and hence it was argued that the development of metallic glasses could find application as corrosion resistant materials. These results, obtained on specific alloys, have been unjustifiably extended to metallic glasses in general. It should be pointed out that many conventional corrosion resistant alloys (eg. superferrites) exhibit far better corrosion resistance than 18.8 stainless steel. In a number of recent review articles it is demonstrated that the superior corrosion resistance of metallic glasses compared to their crystalline counterparts is restricted to the chromium rich iron-based metal/ metalloid glasses [3, 4]. Due to their amorphous structure and their reactive components, metallic glasses show a high reactivity, which leads to spontaneous passivation, if suitable alloying elements are present. Another advantage is the absence of grain boundaries, dislocations and macroscopic segregations. This prevents pitting and leads to a uniform attack [ 3].
EXPERIMENTAL Fe-M-B glasses were vacuum spun to ribbons of 2 mm width and % 20 4m thickness, starting from components of 99.99 % purity. The glassy state was investigated using X-ray diffractometer analysis, see Fig. 1. For comparison the commercial metallic glasses Fe Ni4g B (Vitrovac 0040 R ), Ni P and Ni 8Cr4 B (Allied Chemical MBF 68R an ?IF 80 A ) and amorphous fi-P 1 9 coatings (Bayer AG, Leverkusen) were tested. For potentiostatic polarization curve measurements 2 cm strips were point welded onto the electrode. The experiments were carried out using the arrangement shown in Fig. 2. During the tests argon was bubbled through the electrolyte. The ions dissolved in the electrolyte and their valences were determined. The compositions investigated, the electrolytes employed as well as the pretreatment of the tapes are listed in Tables I-III. Annealing treatments to remove internal stresses in the as quenched state or to crystallize the tapes were carried out in a DSC2 calorimeter or by direct current flux. The surfaces produced were investigated using Auger and ESCA in order to determine the compositional changes in the surface. The tendency to pitting and other inhomogeneous corrosion behaviour could be detected by SEM ana
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