In the perpendicular magnetic tunnel junctions, we have observed antiferromagnetic interlayer coupling when the spacer thickness is larger than 12 Å, and a transition to ferromagnetic coupling for lower MgO thickness. The dependence of the interlayer coupling strength on the MgO spacer thickness is well fitted by the theory of free-electron model, providing an unambiguous experimental proof for interlayer exchange coupling theory. The thermal behavior of interlayer coupling shows a translation from antiferromagnetic to ferromagnetic coupling at 145 K. It can be mainly ascribed to the temperature-dependent enhancement of the magnetization of the ferromagnetic layers.
The hot deformation behavior of a new Al–Mn–Sc alloy was investigated by hot compression conducted at temperatures from 330 to 490 °C and strain rates from 0.01 to 10 s−1. The hot deformation behavior and microstructure of the alloy were significantly affected by the deformation temperatures and strain rates. The peak flow stress decreased with increasing deformation temperatures and decreasing strain rates. According to the hot deformation behavior, the constitutive equation was established to describe the steady flow stress, and a hot processing map at 0.4 strain was obtained based on the dynamic material model and the Prasad instability standard, which can be used to evaluate the hot workability of the alloy. The developed hot processing diagram showed that the instability was more likely to occur in the higher Zener–Hollomon parameter region, and the optimal processing range was determined as 420–475 °C and 0.01–0.022 s−1, in which a stable flow and a higher power dissipation were achieved.
During the separation between satellite and launch vehicles, large steel springs are often used as compression separation spring sets in a catapult separation system. Replacing the steel springs with titanium alloy springs could reduce weight by about 50%. Although titanium alloy springs have been widely used in the aerospace field due to their excellent performance, there are few reports on the design of high-precision titanium alloy springs. The current spring design standards mainly focus on steel springs with helix angles between 5° and 9°, which are not applicable to titanium springs. Moreover, the change in spring rate with ambient temperature should also be considered. In this paper, β-C titanium alloy was used to design and prepare large compression separation springs, replacing steel springs in the catapult separation system. The design of titanium alloy springs took into account the big helix angle. The relationship between helix angle and the number of active coils was calculated. The parameters of titanium alloy springs were determined by the shear stress of the spring at working length. The effects of aging temperature and aging duration on the mechanical properties and modulus of β-C alloy were studied. By adjusting the aging process, the β-C alloy spring rate was controlled to meet the design requirements. The effect of ambient temperature on the mechanical properties and modulus of β-C titanium alloy were also investigated. It was found that as the ambient temperature increased, the rate of the β-C alloy spring gradually decreased.