Abstract
In this paper, hot gas pressure forming (HGPF) of Ti-55 high temperature titanium alloy was studied. The hot deformation behavior was studied by uniaxial tensile tests at temperatures ranging from 750 to 900 °C with strain rates ranging from 0.001 to 0.05 s−1, and the microstructure evolution during tensile tests was characterized by electron backscatter diffraction. Finite element (FE) simulation of HGPF was carried out to study the effect of axial feeding on thickness distribution. Forming tests were performed to validate this process for Ti-55 alloy. Results show that when the temperature was higher than 750 °C, the elongation was large enough for HGPF of Ti-55 alloy. Dynamic recrystallization (DRX) occurred during the tensile deformation, which could refine the microstructure. The thickness uniformity of the formed part could be improved by increasing feeding length. The maximum thinning ratio decreased from 27.7% to 11.5% with the feeding length increasing from 0 to 20 mm. A qualified Ti-55 alloy component was successfully formed at 850 °C, the microstructure was slightly refined after forming, and the average post-form yield strength and peak strength were increased by 8.7% and 6.9%, respectively. Pre-heat treatment at 950 °C before HGPF could obtain Ti-55 alloy tubular component with bimodal microstructure and further improve the post-form strength.
Highlights
Complex thin-walled components made of titanium alloys are always very popular in the aviation and aerospace industries due to their excellent comprehensive mechanical properties and the pronounced effect in reducing weight [1,2]
The deformed grains were full of low angel grain boundaries (LAGBs) inside, which was inherited from the previous rolling deformation
The maximum thinning occurred at the corner area of the right or left side, and it decreased from 27.7% to 11.3% with the feeding length increasing from 0 to 25 mm
Summary
Complex thin-walled components made of titanium alloys are always very popular in the aviation and aerospace industries due to their excellent comprehensive mechanical properties and the pronounced effect in reducing weight [1,2]. Complex thin-walled titanium alloys components were traditionally formed by superplastic forming [9]. Both the high forming temperature and long forming time increased the cost greatly and impaired the post-form properties [10], which limited its wide application. The recrystallization of Ti-55 alloy during the hot compression process was simulated by cellular automaton in [17]; it was found that temperature and strain rate affect recrystallization a lot and most of the recrystallized grains nucleate at the deformed grain boundaries. Most of the researches about Ti-55 alloy focused on the relation between the microstructure and properties, hot pressing, and superplastic forming. A Ti-55 alloy tubular component with a large diameter variance was successfully formed by HGPF, and pre-heat treatment was employed to tailor the post-form microstructure and properties
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