Laser surface sealing and strengthening of zirconia coatings

Abstract Plasma-sprayed zirconia coatings are of general interest as thermal barriers in diesel and gas turbine engines. However, their residual porosity and poor mechanical properties require surface sealing and strengthening. Moreover, dense zirconia is not impervious to oxygen at high temperatures (ionic conductivity). Surface densification was achieved by melting a thin layer, using a continuous wave CO 2 laser. The cracks induced by shrinkage and differential stresses were controlled by spraying alumina powder in the laser beam during surface melting. The formation of alumina-zirconia composites, or possibly eutectics, generates improved chemical resistance and mechanical properties. Both laser-sealed and as-sprayed coatings were tested for bond strength, wear, corrosion and thermal cycling up to 900 °C. The bond strength and thermal barrier efficiency of as-sprayed coatings were retained after laser treatment, whilst wear, corrosion and thermal shock resistances were clearly improved. Future works include thermal cycling up to 1200 °C and erosion tests. The main objective is to lower the operating and maintenance costs of gas turbine engines for electric power generation.