One of the main levers to reduce CO2 emissions in cars and trucks is mass and friction reduction, which is often achieved through the use of special coatings. The aim of the present work was to develop metal-ceramic-lubricant composite coatings with the best combination of wear, seizure, fatigue, and thermal resistance. Metal-based coatings incorporating hard particles and solid lubricants were cold sprayed onto steel substrates and the relationship between coating microstructure and tribology was studied. To meet the demanding tribological requirements of heavily loaded engines, the interfaces between the different components were optimized by selecting appropriate feedstock powders and assessing a wide range of process parameters. Alumina-reinforced bronze composite coatings were made from powders with different morphologies. Aggregated ceramic powders were found to be more beneficial in terms of wear than massive powders, and graphite was found to be effective for reducing seizure.

Inconel alloy coatings have been obtained by means of Cold Gas Spray technology with a high efficiency. Alumina has been sprayed simultaneously achieving an homogeneous distribution along the deposit with a good cohesion between particles. Furthermore, the alumina particles were found to improve the spraying feasibility. A proper optimization of the spraying conditions has been carried out in order to obtain the lowest porosity as possible and good embedment of the alumina. Then, the mechanical properties as well as tribological and oxidation behavior have been characterized. Alumina behaves as reinforcement leading to an amelioration of the abrasive and friction performance. Regarding the oxidation and corrosion behavior, the coatings proved to withstand reasonably well up to 800°C and salt fog tests (5% NaCl solution at 35 °C) indicate durability up to 1000 h.

Discontinuously reinforced aluminum (DRA) has many attractive mechanical and physical properties. Discrete hard particles such as B 4 C have been added to aluminum alloys, such as 6061, to add strength and stiffness for an improved performance. Traditionally, these particles are introduced in melt additions and extruded or made into preforms and cast. These ceramic particles are also added in aluminum through a powder metallurgy process resulting in extrusion or forging. Inhomogeneous distribution of these particles in casting results in inferior properties and also it is difficult to produce preforms with high volume fraction materials. While wrought properties can be achieved in the powder metallurgy approach, extrusion directionality of the process introduces anisotropic properties. Though thermal spray has been used to produce DRA coatings, it has been observed that the melting and re-solidification of the aluminum matrix material as well as reaction with potential substrates such as copper is of concern. Since cold spray does not melt the feedstock material, it is ideally suitable for producing DRA coatings. Boron carbide particles and 6061 aluminum alloy were used as reinforcing and matrix material respectively. Experimental studies were carried out to optimize the raw material characteristics, DRA powder preparation technique and spray parameters, and using these optimized parameters, dense and strong coatings and free-forms were produced. Proper selection of the particle size distribution of the matrix and reinforcing materials, wet blending them and subsequent drying yielded the required spray feedstock. Optimization of the spray parameters resulted in strong, dense and well-bonded coatings with acceptable deposition efficiency and deposition rate values. Post spray heat treatments were carried out to retrieve the ductility of the specimens. A series of mechanical property measurements were carried out on the as-sprayed and heat treated specimens. Results of these studies were analyzed to evolve a preliminary model of the DRA structures and establish the feasibility of cold spray production of DRA coatings and free-form structures.