Development and characterization of mullite lanthanum oxide thermal barrier coatings on a356 aluminium piston crown for ic engine application

Abstract

The energy produced due to the combustion process in any Internal Combustion (IC) engine is used for cooling, to do useful work and remaining is lost through exhaust. It has been estimated that only 1/3 of the total energy is converted into useful work. The efficiency of an IC engine can be improved by reducing the heat loss and converting the available energy into useful work (Evans 1987). The Internal Combustion (IC) Engine components usually made of Aluminium are exposed to temperatures in the range above 600°C. Hence there is a demand for structural rigidity and good tribological properties at those elevated temperatures (Ramaswamy, et al. 2000, Zhu and Miller 1999, Winkler and Parker 1992, Beardsley 1997). Thermal Barrier Coating (TBC) of the ceramic material on aluminium is one such coating method developed to protect the base material and improve tribological properties like thermal, wear and corrosion resistance. Thermal barrier coatings application in pistons using mullite (3Al2O3.2SiO2) as a material is more common in the automobile industry (Merlo 2003). The ceramic coating is used for thermal insulation and reduces the engine temperature thereby causing the reduction in intake air temperature (Churchill, et al. 1988). Though ceramic coatings on pistons are possible in different advanced methods, plasma spraying of ceramic coatings is the most reliable and economical (Merlo 2003, Allan Levy and Stuart Macadam 1987, Pierz 1993). In this research work, two different composites - MZ (Mullite ZrO2) and ML (Mullite La2O3) at 10 to 30% weight ratio as top coat and NiCr as bond coat (Kvernes and Fartum 1978, Chakraborty 2008 and Piotr Bialuckiet and Stefan Kozerski 2006) are plasma-sprayed on AISI 1045 steel, Aluminium A356 billets and piston crowns. The ML and MZ coated samples were studied for its microstructure, mechanical properties (liketensile, coating thickness, hardness and adhesion) and tribological properties (like thermal and corrosion resistance). The results were compared with traditional Zircon