Liam Ward

The effects of metal ion post-implantation on the near surface properties of TiN deposited by CVD

In contrast to the effect of non-metal ion implantation where changes in properties are related to the chemical and tribological character of the implanted zone, metal ion implantation hardens the substrate and enhances wear resistance to depths well beyond that zone. In the present work the surface properties of TiN deposited by chemical vapor deposition (CVD) and subjected to a metal ion implantation post-treatment: surface topography, frictional properties and residual stress are studied. It is found that the residual stress becomes increasingly compressive with increasing ion energy, with a slight concomitant fall in the coefficient of friction; neither the surface roughness nor the surface topography is affected. The data support the model, presented earlier, which proposes that defects, including dislocations, are generated in the surface by the implantation process and lead to the development of a work-hardened zone below the surface that enhances wear resistance.

Corrosion behavior of Zr modified CrN coatings using metal vapor vacuum arc ion implantation

In recent years, attention has focused on the use of alternative metal nitride coatings as replacements for TiN for not only improved wear resistance and surface hardness but also for increased corrosion resistance in selected environments. While these coatings display excellent wear resistance and surface hardness, like many nitride coatings, their corrosion behavior is determined to a large extent by the presence of defects such as pinholes within the coating. Improved corrosion resistance is expected through minimizing the porosity/number of pinholes within the coating, through postdeposition surface modification. The aim of this study was to modify the surface of CrN coatings using metal vapor vacuum arc ion implantation. CrN coatings were deposited on AISI 316 stainless steel and AISI 1020 mild steel substrates using physical vapor deposition technology, followed by implantation of Zr ions into the coating at doses varying from 6×1016to2×1017ions∕cm2. The corrosion behavior was assessed in saline env...

Effect of Pseudomonas fluorescens on Buried Steel Pipeline Corrosion

Buried steel infrastructure can be a source of iron ions for bacterial species, leading to microbiologically influenced corrosion (MIC). Localized corrosion of pipelines due to MIC is one of the key failure mechanisms of buried steel pipelines. In order to better understand the mechanisms of localized corrosion in soil, semisolid agar has been developed as an analogue for soil. Here, Pseudomonas fluorescens has been introduced to the system to understand how bacteria interact with steel. Through electrochemical testing including open circuit potentials, potentiodynamic scans, anodic potential holds, and electrochemical impedance spectroscopy it has been shown that P. fluorescens increases the rate of corrosion. Time for oxide and biofilms to develop was shown to not impact on the rate of corrosion but did alter the consistency of biofilm present and the viability of P. fluorescens following electrochemical testing. The proposed mechanism for increased corrosion rates of carbon steel involves the interactions of pyoverdine with the steel, preventing the formation of a cohesive passive layer, after initial cell attachment, followed by the formation of a metal concentration gradient on the steel surface.