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The review of corrosion performance of a number of alloy systems documents several metallic glasses with corrosion resistance superior to that of crystalline metals. In other cases, the metallic glasses do not have superior corrosion resistance. The nature of corrosion resistance of the metallic glasses is often directly related to the development of a passive film (protective layer) on the reactive alloy substrate, increased durability of the passive film, or enhanced resistance to localized corrosion where the passive film is broken or damaged. Potential mechanical/environmental degradation processes include stress-corrosion cracking, corrosion fatigue, various forms of hydrogen damage, wear, and abrasion. The availability of bulk metallic glasses in significant three-dimensional sizes will stimulate important work in these areas that will enhance the fundamental understanding of the corrosion behavior and mechanical interactions and develop design guidelines and materials properties database for designers and engineers.

The use of multiple-component systems in orthopedic surgery gives the surgeon increased flexibility in choosing the optimal implant, but introduces the possibility of interfacial corrosion. Such corrosion could limit the longevity of prostheses due either to tissue reactions to corrosion products, or to device failure. The incidence and nature of corrosion of modular total hips was evaluated in a consecutive series of 79 retrieved implants from University Hospitals of Cleveland. Surfaces were examined with stereo- and scanning electron microscopy. Several laboratory studies were undertaken to examine mechanisms that might contribute to the initiation of corrosion. The first set of experiments investigated the effect of head neck extension; the second study looked at the effect of material combinations on fretting corrosion and crevice corrosion. Analysis of retrieved implants demonstrated that fretting corrosion played a major role in the initiation of interface corrosion, and that a correlation existed between corrosion and length of neck extensions. Laboratory studies showed that longer head neck extensions may be more susceptible to fretting corrosion because of an instability at the interface. Short-term mixed-metal corrosion studies demonstrated that the coupling of cobalt and titanium alloys did not render the interface more susceptible to corrosion. It is hypothesized that fretting corrosion contributes to the initiation of modular interface corrosion, and that the problem can be reduced by design changes that increase the stability of the interface.

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The precipitation and growth of AgCl on silver in physiological NaCl solution were investigated. AgCl was found to form at bottom of scratches on the surface which may be the less effective sites for diffusion or the favorable sites for heterogeneous nucleation. Patches of silver chloride expanded laterally on the substrate until a continuous film formed. The ionic transport path through this newly formed continuous film was via spaces between AgCl patches. As the film grew, the spaces between AgCl patches closed and ion transport was primarily via micro-channels running through AgCl patches. The decrease of AgCl layer conductivity during film growth were attributed to the clogging of micro-channels or decrease in charge carrier concentration inside the micro-channels. Under thin AgCl layer, i.e. on the order of a micrometer, the dissolution of silver substrate was under mixed activation-Ohmic control. Under thick AgCl layer, i.e. on the order of tens of micrometers, the dissolution of silver substrate was mediated by the Ohmic resistance of AgCl layer.

An overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was cosponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the U.S. Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition, materials synthesis, thermal stability, corrosion resistance, environmental cracking, mechanical properties, damage tolerance, radiation effects, and important potential applications. Amorphous alloys identified as SAM2X5 (Fe 49.7 Cr 17.7 Mn 1.9 Mo 7.4 W 1.6 B 15.2 C 3.8 Si 2.4 ) and SAM1651 (Fe 48 Mo 14 Cr 15 Y 2 C 15 B 6 ) have been produced as meltspun ribbons (MSRs), dropcast ingots, and thermal-spray coatings. Chromium (Cr), molybdenum (Mo), and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of MSRs and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently, thermal-spray coatings of these amorphous alloys have been made and subjected to long-term saltfog and immersion tests; good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while the open-circuit corrosion potentials (OCPs) were simultaneously monitored; reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal makes this amorphous alloy an effective neutron absorber and suitable for criticality-control applications. In general, the corrosion resistance of such iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional stainless steel and Ni-based materials, and are proving to have excellent wear properties, sufficient to warrant their use in earth excavation, drilling, and tunnel-boring applications. Large areas have been successfully coated with these materials, with thicknesses of approximately 1 cm. The observed corrosion resistance may enable applications of importance in industries such as oil and gas production, refining, nuclear power generation, shipping, etc.

Corrosion has been reported at the modular interfaces of total joint replacement implants, but with conflicting theories as to the cause of such damage. The modular design itself leaves the interface susceptible to galvanic, crevice, or fretting corrosion, or a combination of the three. The purpose of this study was to quantify the effect of material combination on fretting corrosion of orthopedic alloys. Each test specimen consisted of a two-hole plate with spherical countersinks and two cortical bone screws. The plates and screws were made of either Ti6Al4V or wrought cobalt-chromium-molybdenum (CCM), and were tested in all mixed-metal and similar-alloy combinations. Fretting corrosion experiments were conducted for 14 days in 10% calf serum, according to ASTM F897. Corrosion damage was evaluated by weight-loss measurements, atomic absorption spectrophotometry and scanning electron microscopy analyses. The results indicated that Ti6Al4V suffered relatively severe damage when fretted against itself, as a result of adhesive galling. The extent of titanium damage was reduced considerably, however, when Ti6Al4V was fretted against wrought CCM. In contrast, there was essentially no difference in wrought CCM damage when the alloys was fretted against itself compared to fretting against Ti6Al4V. Finally, in similar-alloy combinations, Ti6Al4V suffered more severe damage than wrought CCM.