Electrically assisted superplastic forming/diffusion bonding of the Ti2AlNb alloy sheet

Electrically assisted superplastic forming and diffusion bonding (EASPF/DB) is based on the electrically assisted technique in which the electric current is directly and simply introduced into metallic sheets during hot processing. Through the rapidly increasing heat by the Joule effect after several minutes, the advantages of the EASPF/DB process are further strengthened, and the limitations of commercial exploitation (e.g., long processing period) are partly overcome. In this study, an experimental setup of EASPF/DB was assembled for the experimental validation of this concept. The Ti2AlNb alloy sheet, which is regarded as a superior substitute for the nickel-based alloy, was diffusion-bonded and formed, and a double-layer structure was fabricated by means of the EASPF/DB process. The temperature distribution measured by an infrared imaging camera was apparently influenced by detour effects of the electric current. To examine the forming and bonding effects, the height and thickness were measured in different positions. The microstructures of the bonding interface were observed, and no microcavity and crack were found, which indicated the feasibility of the variant of the SPF/DB process. Meanwhile, the large-size grains of B2 phase compose the microstructure of forming zone with some fine needle-like precipitates. Finally, the hardness test showed higher values of Vickers hardness than that of the as-received sheet and the compression test showed three stages of the double-layer structure during continuous loading. The important values and significance for use of this variant are presented by markedly reducing the heating and cooling time and the targeted heating manner for metallic sheets.