Nomsombuluko Masia

By Duduzile Nkomo and Nomsombuluko Masia

Corrosion resistance is an important requirement in the study of biomedical implants. Implant surface can be modified to provide good adherence and/or optimum biocompatibility with the human body at the bone-implant interface. Titanium alloys are typically used because of their excellent corrosion resistance and biocompatibility. However, to improve these properties, the alloy surface is roughened using alumina (Al2O3). More details on the corrosion resistance of these alloys can be obtained by using electrochemical impedance spectroscopy (EIS) method. EIS is the most suitable method for monitoring corrosion rate values due to its reproducibility, it is non-destructive and has reliable determination of small corrosion rates, much lower than those measured by other techniques. It can also study high-impedance systems, such as coatings and linings, high-purity water, and organic coating/metal systems or corrosion in a low-conductive solution. This method has been used to evaluate electrochemical properties of modified surfaces. This chapter will explore the effectiveness of EIS in studying the corrosion behaviour of machined and surface-modified Pure Ti grade 4 for dental implant applications. The basic EIS concepts are discussed and their derivation thereof to provide information about the corrosion resistance of biomedical implants is explored.

Part of the book: Corrosion

By Duduzile Nkomo and Nomsombuluko Masia

Austenitic stainless steels require approximately 8% Ni to maintain austenitic microstructure at room temperature for alloys such as 304 stainless steel (304SS). Ni contributes approximately 60% of the total material cost and its price fluctuates, making the cost of austenitic stainless steel unpredictable. The use of low-nickel austenitic stainless steels as a substitute has been considered in order to remedy costs associated with Ni price fluctuations. Alloying elements such as Mn and N have been considered, however they have been found to reduce corrosion resistance. A new alloy namely Hercules™ has been developed with reduced Ni content (1.8–2% Ni). This chapter presents a comparative study of the corrosion behavior of Hercules™ and 304SS in different solutions. The alloys were evaluated using cyclic polarisation technique and immersion tests. The results demonstrated that the corrosion resistance of Hercules™ is comparable to that of 304SS. This presents the alloys as potential industrial substitutes of each other.

Part of the book: Stainless Steels