Superplastic forming by decomposition of (CaCO3 + C) and MgCO3

An innovative method has been developed that replaces argon as the pressure source for superplastic forming. In this new process, several solid materials are placed in a closed system to generate pressure and are capable of forming superplastic alloy plates at specific temperatures. In the present study, the total pressures for the decomposition of (CaCO3 + C) and MgCO3 have been theoretically calculated from thermodynamics. The results show that a pressure range of 40 to 396 psi can be obtained for the (CaCO3 + C) system between 850 and 1000 C, which is suitable for the superplastic forming of Ti-6Al-4V and Superdux 64 (Nippon Yakin Kogy Co., Ltd., San-ei Bridge, Kyobasi 1-5-8, Chyuoku, Tokyo 104, Japan) stainless steel. The pressure for MgCO3 system between 480 and 515 C ranges from 78 to 160 psi, which is suitable for the superplastic forming of 8090 Al-Li and 7475 Al-Zn-Mg alloys. The calculated temperature dependence of pressure is consistent with the experimentally measured results. Furthermore, the forming rates, wall thickness distributions, tensile properties, and microstructures of the four alloys after forming have been shown to be very similar to those of conventional superplastic forming by argon pressurization