Applications of superplastic forming and diffusion bonding to hollow engine blades

The practical application of technology based on superplastic forming combined with diffusion bonding (SPF/DB) to advanced aircraft engine blade manufacturing is investigated in this paper. Four-sheet hollow engine blades, a Ti–6Al–4V sandwich structure, have been fabricated through the SPF/DB process after determining the design dimensions and deformation procedures. Some novel designs and special auxiliary techniques have been developed to facilitate the superplastic SPF/DB process. The finished blades can meet the property and profile demands, particularly in the boundary region (the leading and the trailing). The effects of the microstructure on the SPF/DB process were discussed. Slight grain growth was observed after the thermal exposure. Tensile tests show a strength reduction of 30% from the as-received sheets to the formed sheets. The microstructures at the interfaces indicate that a bonding ratio of 100% can be reached in most bonding areas. Low bonding ratios in some regions such as cell corners and triple angles were unavoidable. The bonds present in the blade structures can be divided into four types, based on their formation quality characteristics. The distribution in thickness and bonding ratio within a formed cell were investigated, revealing two deformation localization zones and a poor-bonding area. Further processing of the formed structures involves electric spark machining and surface polishing.