Applications of superplastic forming and diffusion bonding to hollow engine blades

The practical application of technology based on superplastic forming combi ned with diffusion bonding (SPF/DB) to advanced aircraft engine blade manuf acturing is investigated in this paper. Four-sheet hollow engine blades, a Ti-6Al-4V sandwich structure, have been fabricated through the SPF/DB proce ss after determining the design dimensions and deformation procedures. Some novel designs and special auxiliary techniques have been developed to faci litate the superplastic SPF/DB process. The finished blades can meet the pr operty and profile demands, particularly in the boundary region (the leadin g and the trailing). The effects of the microstructure on the SPF/DB proces s were discussed. Slight grain growth was observed after the thermal exposu re. Tensile tests show a strength reduction of 30% from the as-received she ets to the formed sheets. The microstructures at the interfaces indicate th at a bending ratio of 100% can be reached in most bonding areas. Low bondin g ratios in some regions such as cell corners and triple angles were unavoi dable. The bonds present in the blade structures can be divided into four t ypes, based on their formation quality characteristics. The distribution in thickness and bonding ratio within a formed cell were investigated, reveal ing two deformation localization zones and a poor-bonding area. Further pro cessing of the formed structures involves electric spark machining and surf ace polishing. (C) 2000 Published by Elsevier Science S.A. All rights reser ved.