Thesis Defence: Tribological evaluation of plasma-based coatings on aluminum engine cylinder bore

Siddharth Banerjee, supervised by Dr. Dimitry Sediako, will defend their dissertation titled “Tribological evaluation of plasma-based coatings on aluminum engine cylinder bore” in partial fulfillment of the requirements for the degree of Master of Applied Science in Mechanical Engineering.

An abstract for Siddharth Banerjee thesis is included below.

Defences are open to all members of the campus community as well as the general public. Registration is not required for in person defences.

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ABSTRACT

International Environment Agency report on global fuel economy initiatives estimates that fuel-efficient vehicles have the potential to reduce net emissions by 1 Gt-CO2 equivalent per year, which is 3 % of the total global annual GHG emissions. The environmental impetus for fuel-efficient vehicles motivates the automotive industry to pursue innovations that necessitate higher engine operating pressures, reducing engine durability. Over time, aluminum alloys became the preferred material for engine manufacturers due to its lightweight properties and higher thermal conductivity. To overcome the poor tribological characteristic of aluminum, a heavy cast iron liner is press fit or cast-in as the cylinder bore. As emission norms get stringent, auto industry focuses on further weight reduction and durable cylinder liner alternatives.

An alternative strategy involves a quasi-monolithic framework, that combines the advantages of a monolithic Al-Si engine block with a coating that enhances the tribological properties of the cylinder bore. Thermal spray coatings are finding more and more applications in high-production volume engines. One such industry-accepted coating is the Plasma Transfer Wire Arc (PTWA) coating. Recently, Electrolytic Jet Plasma Oxidation (EJPO) coating has emerged as an environmentally safe option that offers bi-directional coating growth, leading to more robust bonding with the substrate.

This study aims to analyze the tribological characteristics of engine cylinder bore coatings and piston rings on a custom-designed linear reciprocating tribometer. The coatings deposited on the cylinder bores with the Plasma Transfer Wire Arc (PTWA) and Electrolytic Jet Plasma Oxidation (EJPO) processes, were investigated in the boundary lubrication regime. Chrome-coated cast iron piston rings were tested against the samples cut from an as-cast engine block. Scanning electron microscopy and profilometry were used to compare the evolution of wear, skewness, kurtosis, porosity, and the prevalent wear mechanisms. The study also presents the verification and repeatability analysis of the custom-built tribometer for advanced wear testing applications. The results showed that the EJPO coating provides a better run-in and steady-state wear resistance than its PTWA counterpart. The tribological evaluation of actual engine cylinder bore specimen in practical loading conditions constitute a link between simplified component testing and expensive full-scale bench tests.