Ceramic coatings on diesel engine components. Period covered: January 1979-August 1979

Diesel engines with imporved thermal efficiency and fuel economy or flexibility will be required to meet automotive energy conservation goals. These goals can be met by minimizing engine heat loss to the coolant, i.e., by the use of a thermal insulating barrier on the interior surfaces of the combustion space. The development and testing of ceramic coatings for diesel engine components are discussed. These coatings include oxides of Al, Cr, Zr, Mg, Si, Ti, and Ca, and Mo and Ch carbides. Data on their application and thermodynamic and wear characteristics are presented. It was concluded that, although the spraying processes used have not been optimized, plasma-spray technology has made it possible to coat diesel engine parts with ceramic materials. Preliminary results show that, relative to valves and piston crowns: stabilized ZrO/sub 2/ coating under certain conditions increases the working life of various components; higher combustion temperature may improve the thermal efficiency by increased turbocharger air delivery; reduction in the component temperatures decreases the thermal stresses; the ZrO/sub 2/.MgO shows improved corrosion resistance in combustion gases compared to ZrO/sub 2/.Y/sub 2/O/sub 3/ and ZrO/sub 2/.CaO; the limitations of the coatings have to be defined in more detail; and the adherence of thicker coatings has to be improved. Optimization of the spraying process with respect to particle fusion is necessary. Also, Mo and Ch carbide coatings were found to increase the service life of piston rings. (LCL

Development and engine testing of coatings on diesel engine components, January 1978--December 1978

A series of coating has been tested in a laboratory combustion test rig in order to select coating for further testing on valves and pistons onboard ships. These coatings bonded well to the base material, but had different corrosion resistance. A nickel--chromium--aluminum--yttrium alloy proved to be the best alloy coatings as far as corrosion resistance is concerned. High proportion of oxide in a metal coating did increase the corrosion rate. Coatings of nickel--chromium--aluminum--yttrium alloy with an intermediate layer of chromium and a top coat of yttria stabilized zirconia show no sign of corrosion of cracks even after 120 hours testing in the combustion rig or after 6000 hours on a valve plate in a large bore diesel engine in service. A detailed microstructure analysis of the SI-thermalbarrier coating system used in full scale onboard a ship has to be postponed due to delay in getting the valves returned to Norway