[Paper Review] Mechanical and Surface Characterization of Diamond-Like Carbon Coatings onto Polymeric Substrate

Joan Martí-González, E. Bertrán|arXiv (Cornell University)|Sep 28, 2015

Diamond and Carbon-based Materials Research15 references5 citations

TL;DR

This study investigates diamond-like carbon (DLC) coatings with a Cr buffer layer on ABS polymer substrates using pulsed-DC PECVD deposition. It achieves low wear rates (1×10⁻¹⁵ m³/Nm) and friction coefficients of 0.12–0.24 under varying humidity, demonstrating enhanced tribological performance for automotive and biomedical applications.

ABSTRACT

In this master thesis, diamond-like carbon DLC/Cr bilayer systems, with thickness up to 1278 nm were formed on ABS, glass and Si substrates. Substrates surface were prepared by oxygen plasma cleaning process. The chromium thin film, which acts as a buffer layer, was grown by magnetron sputtering deposition. Diamond-like carbon was deposited by pulsed-DC PECVD, with methane and hydrogen as reactants. A Plackett-Burman experimental design was carried out in order to determine the influence of technological parameters of the deposition process on the thickness, deposition rate, intrinsic stress, contact angle, roughness, friction coefficient and wear rate of the obtained coatings. The independent variables were power, chamber pressure, time of deposition, total flux of the gases, composition of the reactant gases and oxygen plasma cleaning conditions. Values of intrinsic stress between 0.13-0.78 GPa were reported. Wear resistance measurements were performed by grinding calottes with a defined geometry. Low wear rate was achieved in the range of 1E-14 to 1E-15 m^3/Nm. The friction of the obtained coatings under different relative humidities, ranging 20 to 80% in a nitrogen environment, was measured using a nanotribometer with tungsten carbide ball. Results showed that friction coefficient increases with the increasing relativity humidity. Values from 0.12 to 0.24 for friction coefficient were reported. . The main objective of the DLC coating is to improve the wear resistance and tribological behavior of ABS in order to increase his durability for automotive, medical, household and textile applications, among others.

Motivation & Objective

• To enhance the wear resistance and tribological performance of ABS polymer substrates for industrial applications.
• To optimize DLC/Cr bilayer coating deposition parameters on polymeric substrates using a systematic experimental design.
• To evaluate the influence of deposition variables on coating properties such as stress, roughness, and friction.
• To assess coating durability under varying relative humidity conditions in a nitrogen environment.
• To establish a scalable, low-stress DLC coating process for use in automotive, medical, and household applications.

Proposed method

• Deposited DLC/Cr bilayer coatings on ABS, glass, and silicon substrates using magnetron sputtering for the Cr buffer layer.
• Applied pulsed-DC plasma-enhanced chemical vapor deposition (PECVD) with CH₄ and H₂ as precursors for DLC growth.
• Employed oxygen plasma cleaning to condition substrate surfaces prior to coating deposition.
• Used a Plackett-Burman experimental design to analyze the effect of six independent variables: power, chamber pressure, deposition time, total gas flux, gas composition, and plasma cleaning conditions.
• Measured intrinsic stress, thickness, deposition rate, surface roughness, contact angle, friction coefficient, and wear rate using nanotribometry and surface characterization tools.
• Conducted wear tests using grinding calottes with defined geometry and friction tests under 20–80% relative humidity in nitrogen.

Experimental results

Research questions

• RQ1 How do deposition parameters such as power, pressure, and gas composition affect the intrinsic stress and thickness of DLC coatings on ABS?
• RQ2 What is the influence of oxygen plasma cleaning on the adhesion and surface properties of DLC-coated polymeric substrates?
• RQ3 How does relative humidity impact the friction coefficient of DLC-coated ABS under nitrogen conditions?
• RQ4 What wear resistance and friction performance can be achieved with DLC/Cr coatings on ABS substrates?
• RQ5 Can a low-stress, high-durability DLC coating be consistently produced on flexible polymeric substrates for real-world applications?

Key findings

• Intrinsic stress in the DLC coatings ranged from 0.13 to 0.78 GPa, indicating moderate to high compressive stress depending on deposition parameters.
• Wear rates were measured between 1×10⁻¹⁴ and 1×10⁻¹⁵ m³/Nm, demonstrating excellent wear resistance.
• Friction coefficients increased from 0.12 to 0.24 as relative humidity rose from 20% to 80%, indicating humidity-dependent tribological behavior.
• The DLC/Cr bilayer system significantly improved the surface hardness and durability of ABS substrates.
• Oxygen plasma cleaning effectively enhanced interfacial adhesion and surface energy, contributing to coating stability.
• The Plackett-Burman design successfully identified key parameters influencing coating performance, enabling process optimization.