Laser drilled microholes in zirconia coated surfaces using two variants to implement the effusion cooling of first stage turbine blades

The deposition process of a thermal barrier coating (TBC) of zirconia was studied in combination with the laser drilling of cooling holes by comparing two variants of deposition. The drilled holes were to implement effusion cooling of first stage turbine blades. The TBC produced by the first variant, where coated substrate was drilled, resulted in an undercut of zirconia columns on the edges of the hole entrances. Depositing the coating after drilling, which was the second variant, was found possible due to a hot argon gas stream that kept the hole open during the deposition. The second variant avoided the undercut of columns, but resulted in a low deposition of zirconia at the surface of the hole entrance.