Complicated hollow turbine blades and surface grain refinement process

The control of grain size in superalloys is critical in the manufacture of gas turbine blades. The aim of the present research is to provide the technology for producing complicated hollow turbine blades with fine surface grains and better comprehensive mechanical properties. By melt superheating treatment and coating the internal surfaces of shell mould using a cobalt aluminate-bearing coating material, the influence of cobalt aluminate as inoculant on the surface grain sizes of turbine blade was studied with addition of cobalt aluminate: 0, 35%, 45% - 65% and 100% respectively. At the same time, the effects of cooling circumstances of the blades on surface grain sizes were also experimented under the same addition of cobalt aluminate. The results showed that the melt superheating treatment plays a significant role in the grain size and carbide morphology; and fine surface grains were obtained when the internal surfaces of shell mould were coated using cobalt aluminate coatings. When the addition of cobalt aluminate in coating is between 45% - 65%, and the melt is poured into preheated shell moulds with fine silica sand as backing sand, the blades satisfied the surface grain size requirement is over 90%. In addition, comparisons of the surface grain size and the mechanical properties were also conducted between home-made and foreign-made blades.