Laser Cladding of Thermal Barrier Coatings

The feasibility of laser cladding zirconia and alumina thermal barrier coatings on Udimet 700 alloy and AISI 4140 steel substrates was investigated; the objective was to extend the high temperature performance of thermal barrier coatings. Two continuous wave CO₂ gas lasers with power levels of 1.2 and 5 kW were employed for cladding. Laser power, powder flowrate, scanning spot size, and travel speed were the major parameters varied during cladding. Zirconia claddings obtained were thin (5–15 μm), dense, hard (800–1700 HV0.2), and crack free, possessing unusually fine microstructures, glassy surfaces, excellent adhesion, and good surface integrity. It was possible to produce thicker claddings, but these tended to crack, delaminate, and chip off from the substrate. The power density was the key process variable that determined the transition from a thicker, cracked coating to a thin, crack free one. The results indicate that a promising approach to generating thicker flawless claddings would be one based upon an improved understanding of the role of power density on the mechanism of melt pool formation. Data are presented on the effects of various laser parameters and coating powder variables on clad thickness and quality.