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Synergism of Reciprocating Sliding Wear and Electrochemistry (Tribocorrosion) of NiTiNOL60 Alloy in Corrosive Media

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Thesis (Chapters 4 & 5 embargoed until 5th September 2026)(18.69 MB)

Date

2025

Authors

Supervisor

Ramezani, Maziar
Nand, Ashveen

Item type

Thesis

Degree name

Doctor of Philosophy

Journal Title

Journal ISSN

Volume Title

Publisher

Auckland University of Technology

Abstract

A fundamental quest of modern tribo-electrochemistry is to unravel the prevailing failure mechanisms on the surface interactions of materials and tools when operated in tribological and corrosive environments. This follows their global economic impacts and the associated costs of remediating the corrosion-tribological-related failures in load-bearing applications, primarily where NiTiNOL60 alloy is widely utilised. Thereby making it imperative to investigate the tribocorrosion behaviour of this alloy. Although previous studies have explored the performance of this alloy in corrosive environments, particularly in artificial seawater, limited information exists regarding the tribocorrosion behaviour in a broader range of hydrogen (H+) and hydroxyl (OH–) ion groups. Hence, this study discusses the sliding wear, electrochemical activities and the synergistic tribo-corrosion interactions of NiTiNOL60 alloy in various corrosive media (H2SO4, NaOH, and saline solution) prepared in accordance with the standards for analytical grades. In this work, the investigation of NiTiNOL60 alloy under various electrochemical and sliding wear test conditions employed experimental procedures compliant with the ASTM standards. The setup configuration involves coupling a linear reciprocating tribometer to a 3-electrode cell potentiostat. This allowed the sliding of Al2O3 against the flat surface of the specimens in dry and wet conditions. The simultaneous reciprocating sliding and the potentiodynamic polarisation measurements were initiated after the system stabilised in an open circuit potential (OCP). The material preparations and characterisations confirmed the compositions of the Ni-rich alloy featuring a dense network of B2-NiTi + Ni4Ti3 cubic and rhombohedral crystal matrix structures. Our findings revealed that the recorded surface and microstructural deformations emanated from the combined effects of electrochemical reactions and sliding wear. While the reciprocating sliding promoted delamination, abrasion, and adhesion, the electrochemical activities accelerated oxidational and corrosive wear mechanisms in both cathodic and anodic regimes. This validated the significant role of pH in the tribocorosion process, where the depassivation rate depends on factors like contact pressure, sliding velocity, and passive film properties. These factors triggered plastic deformations along the wear tracks, particularly in the severe and mild wear regimes. This resulted in material losses, and the maximum wear volume recorded in the saline environment was accelerated by mechanical wear, corrosion, and third-body abrasion. Due to shear forces, grain deformations and elongation were predominant in the alkaline environment. Delamination and micro-cracks were prominent under higher applied loads due to surface tensile stress and contact pressure, which initiated and propagated cracks perpendicular to the sliding direction. This research has demonstrated that, as opposed to an independent electrochemical test, direct measurement utilising electrochemical impedance spectroscopy can yield a substantially better estimate of the ohmic resistance in a tribocorrosion system. The measurements with the linear reciprocating sliding wear indicated that surface damages recorded on the sample in load-bearing actions were promoted by the tribocorrosion synergy. The findings and deductions provide insight into wear mechanisms and localised corrosion and highlight the influence of pH on corrosive wear and crack propagation. These have practical implications for optimising the performance and durability of NiTiNOL60 alloy in the investigated corrosive environments, offering valuable insights for load-bearing engineering applications.

Description

Keywords

NiTiNOL60 alloy; Al2O3 ball; Electrolytes; Tribocorrosion; Sliding wear; Electrochemical potential; Oxidation; Thermal effect; Wear mechanisms.

Source

DOI

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Permanent link

http://hdl.handle.net/10292/18811

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Doctoral Theses