Date of Graduation

5-2021

Document Type

Thesis

Degree Name

Bachelor of Science in Mechanical Engineering

Degree Level

Undergraduate

Department

Mechanical Engineering

Advisor/Mentor

Zou, Min

Committee Member

Wejinya, Uchechukwu C.

Abstract

Diamond-like carbon (DLC) coatings have a wide array of desirable characteristics such as low friction, high hardness, and scratch resistance. Due to high residual stress and thermal mismatch, DLC films experience adhesion difficulties when bonded with metallic substrates, leading to cracking and delamination. In this study, the properties of a new coating with a polydopamine underlayer and silica nanoparticles bonded to a stainless-steel substrate (PDA+SiO2/DLC) were studied alongside three other samples, one with a polydopamine underlayer (PDA/DLC), one with a trimethylsilane (TMS) underlayer (TMS/DLC), and one with no underlayer (DLC only). Nanoscratch tests were performed with a 1 μm spheroconical tip at constant normal loads ranging from 500 μN up to 3000 μN and at linearly increasing normal loads of 0-3000 μN. The normal displacement and coefficient of friction was measured during the scratches. A scanning electron microscope (SEM) was used to image the permanent deformation after the scratches. The PDA+SiO2/DLC was found to have a great scratch resistance at high contact pressures and had no crack propagation unlike the other tested samples. The average area of the permanent deformation resulting from the scratches was 2 to 3 times smaller than that of the TMS/DLC and DLC only at higher loads. The addition of the silica nanoparticles to a PDA underlayer was shown to increase resistance to crack propagation and delamination of the film.

Keywords

diamond-like carbon; adhesion; nanoscratch

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