Abstract:The isothermal compression experiment of as-rolled Ti-55 alloy was carried out on a Gleeble-3800 thermal simulation test machine at the deformation temperature range of 700-1050 • C and strain rate range of 0.001-1 s −1 . The hot deformation behavior and the microstructure evolution were analyzed during thermal compression. The results show that the apparent activation energy Q in α + β dual-phase region and β single-phase region were calculated to be 453.00 KJ/mol and 279.88 KJ/mol, respectively. The deformation softening mechanism was mainly controlled by dynamic recrystallization of α phase and dynamic recovery of β phase. Discontinuous yielding behavior mainly occurred in β phase region, which weakened gradually with the increase of deformation temperature (>990 • C) and strain rate (0.01-1 s −1 ) in β phase region. The processing map derived from Murty's criterion was more accurate in predicting the hot workability than that derived from Prasad's criterion. The optimized hot working window was 850-975 • C/0.001-1 s −1 , in which sufficient dynamic recrystallization occurred and α + β-transus microstructure was obtained. When deformed at higher temperature (≥1000 • C), coarsened lath-shape β-transus microstructure was formed, while deformed at lower temperature (≤825 • C) and higher strain rate (≥0.1 s −1 ), the dynamic recrystallization was not sufficient, thus flow instability appeared because of shear cracking.
In this study, benefiting from the sensitive molecular conformation transversion in azobenzene, a new strategy for fabricating alginate gels with the abilities of splicing and photo-responsive mechanical adjustment is reported. Firstly, a 4,4’-azobis(benzoylhydrazide) (Azo-hydrazide) linker was used to crosslink alginate physically via the electrostatic interaction between hydrazide groups and carboxyl groups. It was then shaped and transferred in situ to a chemically crosslinked gel via 450 nm light irradiation. Under the irradiation, the molecular conformation change of azobenzene in the linker was able to form covalent bonds at the crosslinking points of the gels. Furthermore, the reversible conformation transformation of azobenzene was able to induce the increase and decrease of the storage modulus under irradiation with 365 nm light and 450 nm light, respectively, while also providing gel-like mechanical properties, depending upon the irradiation time and given wavelength. Meanwhile, the results also indicated that active groups could contribute to the splicing ability of the gel and construct a hollow cavity structure. It is believed that this work could provide a versatile strategy for preparing photo-responsive gels with reversibly tunable mechanical properties.
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