Through an integrated process involving thermal/mechanical analysis, coating property characterization, plasma spray process control, and rig testing under simulated engine thermal conditions, plasma sprayed zirconia coatings have been defined which offer a high degree of thermal insulation.
Analytical and rig tests results showed that a multi-layer coating, combined with control of residual stress during fabrication, offered the greatest potential for meeting the thermal insulation goals while providing the required durability in piston crown and cylinder head applications. Coating thicknesses ranging from 1.5 to 2.5 mm (0.06 to 0.10 inch) were evaluated and tested in the laboratory.
Single cylinder engine tests of the multi-layer thermal barrier coatings have demonstrated that coatings up to 2.54 mm (0.10 in.) thick on pistons can operate at 1.03 MPa (150 psi) brake mean effective pressures (BMEP). Thermal barrier coatings on ductile iron and fiber reinforced aluminum pistons have been tested at these conditions for greater than 50 hours without any evidence of coating deterioration.