Study on laser beam welding/superplastic forming technology of multi-sheet cylinder sandwich structure for Inconel718 superalloy with ultra-fine grains

Multi-sheet cylinder sandwich structure of Inconel718 superalloy will be widely used in aerospace as heat resisting and heat shielding structure due to its lightweight, high strength and stiffness. Superplasticity of Inconel718 superalloy was investigated. Under T = 950 °C and initial strain rate with ε˙=1.6×10-4s-1, the elongation of Inconel718 superalloy is 483.6%. The perfect superplastic forming temperature for Inconel718 superalloy is at 950 °C. The laser penetration welding parameters are as follows: power 1200 W, welding speed 1200 mm/min, defocusing amount −1 mm, shield gas flow 0.6 L/min, and the parameters for superplastic forming are as follows: temperature Tf = 950 °C, pressure Pf = 4.2 MPa, time tf = 130 min. The multi-sheet cylinder sandwich structure manufactured by laser beam welding/superplastic forming (LBW/SPF) technology has good shape, uniform wall thickness distribution, high symmetry in internal structure. Laves phase, harmful to the materials, translates to the δ phase which will help improve the performance of the material after SPF process. The hardness of laser welding joints is improved from 331.63 HV to 391.74 HV after the SPF process. The tensile strength of base material of multi-sheet cylinder sandwich structure has been increased about 261 MPa after the SPF process.

► In this study, we design the inner diameter variation of fixture for the structure.
► The welding problem of structure is solved by changing the diameter of the fixture.
► The multi-sheet cylinder sandwich structure is manufactured by LBW/SPF technology.
► Through SPF process, most Laves precipitated phase turns into δ precipitated phase.
► Nb concentration in the dendritics was improved greatly.