Advanced thermal spray technology is widely used in the automotive industry. Transmission and engine parts are coated in large volume using different processes. Some applications have already reached a status of maturity. Other applications are new and represent an important market for the future.Coated transmission parts as synchronizing rings and shift forks are widely coated using wire flame spraying with molybdenum to provide a constant coefficient of friction and prevent scuffing. Piston rings are coated with the plasma spray process in general and also with the HVOF spray process in the case of high performance piston rings for diesel engines. Metal matrix carbides containing coatings are used for the application on piston rings.Since roughly 10 years intensive developments were carried out concerning the coating of the cylinder bore of aluminum cast engine blocks for the automotive industry. [1±6] This paper gives an overview of the materials for engine blocks, the thermal spray processes for cylinder bore coatings and also of the coating materials for the internal plasma spray process.Material for monolithic engine blocks: For more than 100 years cast iron with lamellar graphite is the monolithic solution for engine blocks. This material represents a compromise between tribological properties, low costs production with sand casting technology, good machinability, but limited mechanical properties, especially a relatively low toughness. New developments in foundry technology improving the casting tolerances give renewed interest in this material because it allows some reduction of the weight. Cast iron with vermicular graphite was developed some 20 years ago and is already used in those high loaded diesel engines, when higher mechanical strength and better toughness are required. However the cast iron with vermicular graphite has lower machinability and requires a particular foundry design to ensure the precipitation of the graphite in the required shape. The solidification rate determines graphite precipitation.In the case of monolithic cast aluminum alloy a high silicon content is required to secure the tribological properties. The necessary Si content is in the range of 17 to 20 % weight. Special machining of the liner surface is required to avoid contact between the aluminum matrix and the piston ring material. The size of the primary crystals silicon plays an important role for the tribological properties.Low pressure die casting is required to ensure the integrity of the cast material in this case. The high content silicon has a negative impact on the machinability and the toughness of this hypereutectic AlSi cast alloys.Requirement for improvement and hybrid solutions: To reduce the weight of engine blocks, hypoeutectic aluminum silicon cast alloys were developed and are widely used today. Today more than 60 percent of the engines for passenger cars are produced in cast material from this category.However the hypoeutectic aluminum alloys have poor tribological properties and require liners cast ir...
