THERMAL ANALYSIS AND CHARACTERIZATION OF FGM COATING USING HVOF FOR CYLINDER LINER OF I.C. ENGINE

Abstract

This research focuses into the development and evaluation of Functionally Graded Material (FGM) coatings applied to cast steel cylinder liners of internal combustion engines using the High-Velocity Oxygen Fuel (HVOF) technique. The focus is on understanding the performance of coatings prepared using three powder compositions: WC-10wt%Co-4wt%Cr (C1), WC-12wt%Co (C2), and Ni-25wt%Cr (C3). These materials were selected Because of their special qualities, like resistance to wear, thermal stability, and ability to bond effectively under high-temperature spraying conditions. Microstructural analysis using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) revealed significant differences in the porosity of the powders. C3, composed of 75%Ni and 25%Cr, exhibited the highest porosity among the powders. This is attributed to its particle morphology and the lower density of nickel-based powders, which inherently reduces packing efficiency during deposition. Conversely, C2, consisting of 88%WC and 12%Co, showed the lowest porosity due to its higher tungsten carbide content and spherical morphology, which enhances packing density and cohesion. The intermediate porosity of C1 (86%WC-10%Co-4%Cr) results from its balanced composition, with chromium acting as a grain growth inhibitor while maintaining reasonable density and bonding capabilities. The coatings, deposited in five layers using different combinations of these powders, were designated as Specimens 1, 2, and 3. Mechanical characteristics including durability and hardness were assessed using Vickers hardness tests and Linear tribometry. Specimen 1, comprising a combination of C1 and C2, showed the highest wear resistance and hardness. The inclusion of WC-12Co (C2) enhanced hardness due to its high tungsten carbide content, which contributes to superior resistance to abrasive wear and load-carrying capacity. ix Additionally, the presence of WC-10Co-4Cr (C1) in the coating provided a balance between hardness, with chromium improving adhesion and wear resistance by limiting grain growth. In contrast, Specimens 2 and 3, containing combinations of C2 with C3 and C1 with C3, exhibited high wear and low hardness. The higher porosity of powder C3 reduced the overall cohesion and strength of these coatings, highlighting the critical effects of powder composition on the mechanical behaviour of FGM coatings. Corrosion resistance was evaluated using immersion tests in 50% H₂SO₄. Specimen 1 again outperformed the others, with a minimal corrosion weight loss of 0.47%, compared to 1.37% for Specimen 2 and 1.87% for Specimen 3. This superior performance is attributed to the dense microstructure and uniform composition of Specimen 1, which effectively limited the penetration of the corrosive medium. The study also emphasized the critical role of optimizing HVOF process parameters. Parameters such as oxygen flow (867 m/min), kerosene flow (24 liters/hour), stand-off distance (340 millimetre), and feed rate (86 grams/minute) was found to significantly influence the quality of the coatings. A higher oxygen flow ensures complete combustion of the fuel, producing a stable and high-temperature flame that enhances the bonding of the particles. Similarly, an optimal stand-off distance ensures the particles reach the substrate at the right temperature and velocity, avoiding defects such as un-melted particles or excessive thermal stresses. The thermal performance of the developed coatings was investigated through numerical analysis using Ansys Fluent software. The analysis of Specimen 2 demonstrated a negligibly small temperature difference along the thickness of coating. This result highlights the ability of the coatings to maintain high thermal conductivity due to presence of highly conductive powders like nickel-chromium (NiCr) alloys and tungsten carbide (WC). This property is x essential for engine applications, as cylinder liners must dissipate heat efficiently to prevent overheating while maintaining structural integrity. The findings demonstrate the efficacy of FGM coatings in improving the performance of cast steel cylinder liners. Specimen 1 (Combination of Powder 1 and 2), with its superior corrosion resistance, wear resistance, and hardness, emerged as the best-performing coating. The study underscores the importance of material selection, microstructural control, and process optimization in achieving high-performance coatings. By taking care of these issues, engine parts longevity, effectiveness, and dependability can be greatly increased, opening the door for developments in the automobile and other high-performance sectors.