Examination of the friction and wear properties of brake discs used in heavy commercial vehi̇cles

The friction and wear properties of brake discs used in heavy commercial vehicles are fundamental to ensuring the safety and reliability of the transportation sector. Heavy commercial vehicles, especially those that must carry significant loads over long distances under harsh conditions, demand advanced braking systems that can withstand high torques, extreme temperatures and long operating cycles on the vehicle. In addition to safety concerns, awareness of the environmental impact of brake systems, especially dust from disc wear, is increasing. Brake dust, consisting of fine particulate matter released during braking, contributes to air pollution and poses a risk to both human health and the environment. Therefore, reducing brake disc wear not only increases the performance and life of brake systems, but also reduces their environmental impact. This study investigates the potential of using Laser Metal Deposition (LMD) technology to coat brake discs with a Nickel-Ti₂AlC (Titanium Aluminum Carbide) composite to improve friction and wear properties. LMD is a modern additive manufacturing technique that uses a high-energy laser to melt and deposit metal powders onto a surface. The process provides improved wear resistance and other desired tribological properties by creating strong metallurgical bonding between the coating material and the substrate. Specifically, this study focuses on the application of different Ti₂AlC MAX phase compositions with pure Nickel to evaluate their effects on the tribological performance of brake discs. Brake discs are critical components in vehicle safety systems and convert the kinetic energy of moving vehicles into heat through friction. This process requires materials with high wear resistance, good thermal conductivity and the ability to maintain constant friction coefficients under various conditions. Conventional brake discs, usually made of cast iron, provide adequate performance, but improvements can be achieved by using advanced coating materials. Cast iron, which is widely used due to its excellent thermal properties, suffers from certain limitations such as relatively low wear resistance and tendency to corrosion under harsh conditions. Therefore, this research aims to develop a more durable brake disc by applying a Nickel-Ti₂AlC LMD coating. The basic methodology of the study includes several stages, starting with the preparation of brake disc samples. The base material used for brake discs is cast iron, which was chosen because it is widely used in the automotive industry. LMD is used to coat the surface of these discs with various compositions of Ti₂AlC MAX phase combined with pure Nickel. The compositions tested include pure Nickel, Ni + 5% Ti₂AlC, Ni + 10% Ti₂AlC, Ni + 15% Ti₂AlC and Ni + 30% Ti₂AlC. The Ti₂AlC MAX phase was chosen because it provides a unique combination of metallic and ceramic properties, self-lubricating behavior, high thermal stability and improved wear resistance.The LMD process involves directing a high-power laser onto the surface of cast iron brake discs and simultaneously feeding Nickel-Ti₂AlC composite powders into the laser beam. This creates a metallurgical bond between the disc substrate and the coating, creating a hardened surface layer. Laser coating process parameters such as laser power, scanning speed and powder feed rate are carefully selected to ensure uniform coating thickness and optimum bond strength. After the brake discs are coated, various tests are performed to evaluate their microstructural and tribological properties. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) are used to analyze the microstructure of the coated brake discs, focusing on the distribution of Ti₂AlC particles within the Nickel matrix and the integrity of the bond between the coating and the substrate. X-ray Diffraction (XRD) is used to identify the phases present in the coatings and to verify the formation of hard phases that increase the wear resistance of the discs. Another aspect of the coating that is also examined is the tribological testing of the coated brake discs. Wear tests are performed using a tribometer under varying loads (1N, 3N and 5N) to simulate real-world braking conditions. These tests measure the friction coefficients and wear rates of brake discs while operating under different pressures and temperatures. In addition, a 3D profilometer is used to examine wear marks on brake disc surfaces, providing a detailed analysis of wear mechanisms. The results of the tribological tests reveal that Nickel-Ti₂AlC coatings significantly improve the wear resistance and friction stability of brake discs compared to uncoated cast iron discs. While uncoated cast iron discs exhibit high friction and wear issues, Nickel-Ti₂AlC coatings effectively mitigate these problems, making the discs more durable and reliable in terms of performance. These coatings, applied using the laser cladding method, offer a distinct advantage, especially under the high temperatures and pressures encountered in heavy commercial vehicles. Among the different compositions tested, the Ni + 30% Ti₂AlC coating demonstrated the most balanced performance, exhibiting a stable friction coefficient under various loads and temperatures while showing minimal wear. Notably, the fact that the friction coefficient remains largely unchanged as the loads increase, along with the low wear rates, proves the superior performance of this coating. This finding suggests that the Ni + 30% Ti₂AlC coating holds great potential, especially for brake systems operating under prolonged and high-stress conditions. Microstructural analyses show that Ti₂AlC particles are evenly distributed throughout the Nickel matrix, and this homogeneous distribution significantly contributes to the high hardness and wear resistance of the coating. This uniform distribution within the coating material is one of the key factors that enhances its durability. Additionally, this even distribution helps prevent the formation of microscopic cracks on the coating surface, allowing it to remain intact for a longer time. Ti₂AlC's self-lubricating properties also help maintain a low friction coefficient, improving the overall efficiency of the brake discs. This resistance to overheating and deformation further enhances the performance of the brake discs. The strong metallurgical bond between the coating and the cast iron substrate ensures that the coatings remain intact under stress conditions. This metallurgical bond, formed during the laser cladding process, provides seamless integration between the coating and the substrate, preventing the coating from separating. This strong bond offers a significant advantage, particularly in brake systems operating under high pressure and temperature. The fact that the coatings do not peel off or crack under extremeconditions increases the overall reliability of the braking system and reduces maintenance requirements. One of the key findings of the study is the clear correlation between the Ti₂AlC content in the coatings and their wear resistance. Tests clearly show that as the Ti₂AlC content increases, the hardness and wear resistance of the coatings improve. Particularly, the combination of metallic and ceramic properties of Ti₂AlC imparts high hardness to the coatings, resulting in better wear resistance. Since harder materials are more resistant to wear, the lifespan of the coatings is extended, allowing the brake discs used in commercial vehicles to perform reliably over longer periods. In this regard, the Ni + 30% Ti₂AlC coating provides the highest hardness and the best wear resistance. The findings also show a notable decrease in the friction coefficient as the Ti₂AlC content increases, further highlighting the critical role of Ti₂AlC in optimizing the friction performance of the coatings. While the highest hardness and wear resistance values were achieved with the Ni + 30% Ti₂AlC coating, the findings suggest that careful adjustment of the composition ratios is necessary to optimize the overall tribological performance of the coatings. This emphasizes the importance of optimizing the coating composition to achieve the best balance between hardness, wear resistance, and friction stability. In conclusion, this study has shown that Ti₂AlC additive-enriched Nickel coatings applied using laser cladding method provide significant improvements in friction and wear performance of brake discs used in heavy commercial vehicles. It has been shown that incorporation of Ti₂AlC in varying percentages significantly increases wear resistance and decreases friction coefficient compared to pure Nickel coatings, making these improved coatings highly suitable for demanding applications such as commercial vehicle brake systems. As confirmed by SEM analyses, homogeneous distribution of Ti₂AlC particles within the Nickel matrix plays a critical role in increasing the surface hardness, which directly contributes to improved durability and wear resistance of the coatings. Furthermore, microhardness tests revealed that the mechanical properties of the coatings significantly increase with increasing Ti₂AlC content, with the highest microhardness values being observed in coatings containing 30% Ti₂AlC. Tribological tests further confirmed the superior performance of Ti₂AlC reinforcedcoatings with minimal surface deformation under stress and improved wear resistance. In addition, surface topography analysis showed smoother and more uniform surfaces on Ti₂AlC coatings, which helped reduce surface roughness and extend the life of coated brake discs. These results suggest that Ti₂AlC reinforced Nickel coatings offer a promising approach to developing safer, more durable, and more efficient brake systems for heavy-duty vehicles, potentially leading to improved safety, reduced maintenance costs, and overall improved performance under real-world operating conditions. Future research could investigate the use of other MAX phase materials in combination with Nickel or other metal matrices to further enhance the performance of brake disc coatings. In addition, further improvement of LMD process parameters could lead to improved coating quality and performance. Overall, this work contributes to the ongoing development of safer, more efficient braking systems for heavy commercial vehicles and aligns with the industry's goals of improving vehicle safety, reducing wear-related maintenance, and promoting sustainability in transportation.