Thermal shock properties and microstructure investigation of LVPS and HVOF-CoNiCrAlYSi coatings on the IN738LC superalloy

The thermal shock behavior and microstructural investigation of CoNiCrAlYSi coatings applied by Low Vacuum Plasma Spray (LVPS) and High-Velocity Oxy Fuel (HVOF) techniques on the Ni-base superalloy IN738LC were examined. Thermal shock resistance was investigated by forced water quenching of coated samples from high temperature (1100 °C) to room temperature. Thermal shock life time of coatings were determined by measuring the weight gain of the specimens at regular intervals for a duration of 65 cycles. Characterizations of the coatings and oxide scales were investigated by SEM equipped with EDS and XRD analyses. Oxidation kinetic obtained from weight measurement and morphological observations indicate better thermal shock resistance of LVPS than HVOF coatings. Larger grain size of protective oxides on the HVOF coatings led to more thermal stresses emanated from severe thermal cycling and spallation of the coatings.