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Edited by
HLOCH, S., et al. 25
Republic 26th November 2010,
Manufacturing of Lightweight Components with Superplastic Forming Technology Ho-Sung Lee* Future Launch Vehicle Technology Department, Korea Aerospace Research Institute E-mail:
[email protected], Tel.: +82428602512, Fax.: +82428602214
Jong-Hoon Yoon Structure & Materials Department, Korea Aerospace Research Institute E-mail:
[email protected], Tel.: +82428602049, Fax.: +82428602214
Joon-Tae Yoo Structure & Materials Department, Korea Aerospace Research Institute E-mail:
[email protected], Tel.: +82428602928, Fax.: +82428602214
Young-Moo Yi KSLV Technology Division Korea Aerospace Research Institute E-mail:
[email protected], Tel.: +82428602414, Fax.: +82428602233 Abstract: By using superplastic forming technology, it is possible to form a complex shape in one piece with saving materials. In this paper, a brief review of superplastic materials and application is described. The present study constructs an analysis model to predict forming behavior of duplex steel and titanium alloy. The experimental results show a complex shape was successfully formed from bonded sheets by superplastic forming. The results demonstrate that the developed technology to process design of high temperature superplastic forming by the finite element method can be applied for near net shape forming of a combustion chamber skin and a cylindrical hollow tank of ramjet engine. Keywords: superplastic forming, duplex steel, titanium, bonding
INTRODUCTION Superplasticity is used to describe the ability of materials, usually metal alloys, to exhibit large elongations, typically 200 to 1000% under exceptionally low stress which is strongly dependent on strain rate. Currently grain boundary sliding is known to be responsible for the main mechanism of superplastic behavior. In the presence of a suitable microstructure and temperature, superplasticity has been exhibited only over a narrow range of strain rates, typically about 10-2 to 10-5 per sec. In general, since the strain rate is inversely related to grain size, the strain rate can increase with decreasing grain size or increasing temperature. At a certain temperature, there is a maximum strain rate where superplasticity by grain boundary sliding becomes no longer the dominant process, and dislocation slip is important. Even though the high elongation and low flow stress are the two most practical manifestations of micrograin superplasticity, the best measure of the degree of superplasticity exhibited by a metal is its strain rate
sensitivity. When most metal is deformed by tension force, typical failure is due to the localized deformation and necking. However, during superplastic deformation, the metal will not neck because any local reduction in section leads to an increase in strain rate which in turn increases the flow stress. Therefore, the strain rate sensitivity controls the degree of neck-free elongation. The empirical and experimental parameters for materials when deformed at elevated temperature have been represented in a form of a following equation(MukherjeeBird-Dorn equation): kT GbD
n A
G
b d
p
(2)
where is the flow stress, G the shear modulus, b the Burgers vector, d the grain size, n the stress exponent, p the strain rate dependence on grain size, k the Boltzman 100
