In a process for the manufacture of a hollow turbomachine blade in which die-forged and machined sheets are assembled and diffusion welded face to face after applying an antidiffusion coating to areas of the sheets where the assembly is to be expanded in forming the hollow blade, the welded assembly is subjected to a step of unsticking the coated areas of the sheets which are pressed together during the diffusion welding step, the unsticking step including subjecting the assembly to localized heating in a region where the intermediate sheet is provided with intercavity communication holes, and injecting pressurized gas into the welded assembly in a controlled manner to hot form a gas distribution duct in the locally heated region of the assembly to facilitate unsticking of the remainder of the coated areas. Apparatus for use in carrying out the unsticking step is also described.