Multi-layer cylinder of Inconel718 superalloy processed by LBW/SPF technology

Multi-layer cylinder of Inconel718 superalloy can be used in flying vehicle as heat resisting and shielding structure due to its lightweight, high strength and stiffness. As well known, the most preferred method for forming multi-layer structure is SPF/DB technology. But In-conel718 superalloy have not good ability of diffusion bonding. Therefore LBW/SPF technology was adopted to fabricate multi-layer cylinder of Inconel718 superalloy. Superplasticity and microstructure of Inconel718 superalloy was investigated. The results indicates that In-conel718 superalloy with ultra-fine grain has excellent superplasticity. Under 965°C and initial strain rate with 6.1×10^-4s ^-1, the elongation of base material is 368.2% and its strain rate sensitivity m value is 0.39. In addition, effects of superplastic forming process on the microstructure of Inconel718 laser beam welds were studied. Microstructure of Inconel718 laser beam welds is improved obviously. According to the results of LBW and SPF, the experiment of multi-layer cylinder of Inconel718 superalloy was performed. LBW parameters were as follows: welding speed was 180 mm/min, Pulse frequency 32 Hz, peak power per pulse 4500 W and impulse duration 3 ms. The SPF parameters were as follows: Forming temperature T=965°C, forming pressure P=4.2 MPa, and forming time t=130 min.