Nickel based alloys have been developed as a material offering superior general and localized corrosion resistance compared to the more traditionally used in chemical and oil plant in the most aggressive environment such as hydrochloric acid and ferric chloride. Hence the addition of Cr and Mo to Ni creates alloys with exceptional corrosion resistance in a diverse range of environments. This study examines the roles of Cr and Mo in the corrosion behavior of Ni alloys. The performance of three nickel-base alloys IN600, IN601 and C22 was examined in increasing saline solution severity of sodium chloride, concentrated hydrochloric acid and ferric chloride solution at pH = 0.0. The passive corrosion and breakdown behavior of these alloys suggests that Cr is the primary element influencing general corrosion resistance, while the repassivation potential is strongly dependent on the Mo content. This indicates that Cr plays a strong role in maintaining the passivity of the alloy, while Mo acts to stabilize the passive film after a localized breakdown event. Corrosion fatigue test results indicate that fatigue life of IN600, IN601 and C22 specimens tested in 3.5 % sodium chloride solution are essentially the same as for specimens tested in air. Test results also showed that for IN600, IN601 and C22 alloys, the number of cycles to failure was highest in air and sodium chloride solution, followed by specimens fatigued in hydrochloric acid, and was least in specimens fatigued in ferric chloride solution. No evidence of surface pitting was found on C22 specimens in all three solutions whereas IN600 and IN601 were both pitted. However, pits were generally larger in IN600 likely due to lower Cr content than in IN601.

Nickel based alloys have been developed as a material offering superior general and localized corrosion resistance compared to the more traditionally used in chemical and oil plant in the most aggressive environment such as hydrochloric acid and ferric chloride. Hence the addition of Cr and Mo to Ni creates alloys with exceptional corrosion resistance in a diverse range of environments. This study examines the roles of Cr and Mo in the corrosion behavior of Ni alloys. The performance of three nickel-base alloys IN600, IN601 and C22 was examined in increasing saline solution severity of sodium chloride, concentrated hydrochloric acid and ferric chloride solution at pH = 0.0. The passive corrosion and breakdown behavior of these alloys suggests that Cr is the primary element influencing general corrosion resistance, while the repassivation potential is strongly dependent on the Mo content. This indicates that Cr plays a strong role in maintaining the passivity of the alloy, while Mo acts to stabilize the passive film after a localized breakdown event. Corrosion fatigue test results indicate that fatigue life of IN600, IN601 and C22 specimens tested in 3.5 % sodium chloride solution are essentially the same as for specimens tested in air. Test results also showed that for IN600, IN601 and C22 alloys, the number of cycles to failure was highest in air and sodium chloride solution, followed by specimens fatigued in hydrochloric acid, and was least in specimens fatigued in ferric chloride solution. No evidence of surface pitting was found on C22 specimens in all three solutions whereas IN600 and IN601 were both pitted. However, pits were generally larger in IN600 likely due to lower Cr content than in IN601.

Heritage iron objects are ubiquitous in the archaeological assemblage, frequently covered in thick, chloride-containing corrosion layers. Accurate monitoring of their corrosion rates is crucial for continued preventative conservation. Measurement of storage environment corrosivity is commonplace for a variety of metals, but use un-corroded metal as a proxy. Corrosion rates measured will be different with respect to chloride infused and corroded artefacts and data recovered difficult to reconcile with actual artefact degradation. Electrical resistance corrosion monitors have been applied to create proxy corrosion rates for various metals in industry, academia and heritage contexts. Pre-corrosion of such has previously been shown to be effective in providing altered corrosion rates in atmospheric environments. This research sets out to develop and refine the manufacture of such probes, to create sensors which will corrode similarly to chloride infested heritage iron and can be used in heritage environments to inform conservation strategy. Photochemical milling was used to create ERCM. Salt loading on the surface was achieved through a piezoelectric inkjet printer, shown to be adept at printing a variety of salt concentrations (down to 4μg/cm) and patterns, with consistency, regularity and reliability. The results of the methodology show the potential of the technique for future salt loading and corrosion testing applications. Corrosion products were grown on the treated ERCM by controlled atmospheric corrosion, shown to create a constant corrosion layer, no significant localised corrosion and good reproducibility. The products formed were shown to be compositionally similar to those found on archaeological iron. The sensors have been tested in both stable and dynamic relative humidity environments, within a test chamber and in ersatz heritage type, desiccated boxes. The corrosion rates and reactions were compared to those of heritage iron. Pre-corroded ERCM are shown to give similar corrosion rates to heritage iron; though direct calibration was not possible, further research is likely to remedy this. The final outcomes of the project are discussed with respect to the closeness of fit between proxy and archaeological iron corrosion rate data, benefits and shortcomings of the system and how the corrosion data affects current conservation understanding. It is concluded that the technique can detect corrosion rates down to storage relative humidity levels, provides more accurate representation of corrosion rate for chloride infested iron objects than bare metal ERCM, can be calibrated to suite specific objects and could represent excellent cost-effectiveness for environmental monitoring in heritage institutions.