Effect of Ti content on microstructures and mechanical properties of cast Al-2Li-2Cu-0.5Mg alloy

Ti is regarded as one of the promising grain refiners in cast Al-Li-Cu alloys,but few research works have been done on its independent role.In this study,the effect of Ti on the microstructure evolution and mechanical properties of cast Al-2Li-2Cu-0.5Mg base alloy was investigated.The results revealed that the grains can be prominently refined with the increase of Ti addition.After adding Ti,high density TiB_(2)-Al_(3)Ti composite particles with a low lattice misfit form as heterogeneous nucleation sites for the α-Al matrix.δ’(Al3Li) and T_(1)(Al_(2)CuLi) precipitates that provide enhanced strength are dominated in the alloys after T6 aging treatment.The average size of both δ’ and half-width of δ’-precipitation free zone(PFZ) decreases gradually with the increase of Ti content.This is because the higher binding energy between Ti atoms and vacancies limits the diffusion efficiency of Li atoms,and thus results in a higher ductility.Additionally,no nano-sized Al_(3)Ti or core-shell structure of Al_(3)(Li,Ti) particles are found.The tensile property test results indicate that the Al-2Li-2Cu-0.5Mg alloy achieves optimal properties after aging at 175 °C for 32 h when 0.15wt.% Ti is added.It exhibits a yield strength of 352±5 MPa,an ultimate tensile strength of 423±6 MPa,and an elongation of(3±0.4)%.These findings are expected to offer a reliable theoretical guidance for the industrial composition design of the Al-Li-Cu series cast alloys.

Magnetoresistance effect in vertical NiFe/graphene/NiFe junctions

For convenient and efficient verification of the magnetoresistance effect in graphene spintronic devices, vertical magnetic junctions with monolayer graphene sandwiched between two Ni Fe electrodes are fabricated by a relatively simple way of transferring CVD graphene onto the bottom ferromagnetic stripes. The anisotropic magnetoresistance contribution is excluded by the experimental result of magnetoresistance(MR) ratio dependence on the magnetic field direction. The spin-dependent transport measurement reveals two distinct resistance states switching under an in-plane sweeping magnetic field. A magnetoresistance ratio of about 0.17 % is obtained at room temperature and it shows a typical monotonic downward trend with the bias current increasing. This bias dependence of MR further verifies that the spin transport signal in our device is not from the anisotropic magnetoresistance. Meanwhile, the I–V curve is found to manifest a linear behavior, which demonstrates the Ohmic contacts at the interface and the metallic transport characteristic of vertical graphene junction.

Nonlinear Branching Processes with Immigration

The nonlinear branching process with immigration is constructed as the pathwise unique solution of a stochastic integral equation driven by Poisson random measures. Some criteria for the regularity, recurrence, ergodicity and strong ergodicity of the process are then established.

一类连续状态非线性分枝过程的离散逼近

本文考虑一类连续状态非线性分枝过程.直观上,这是一类带竞争且分枝速率与状态相依的连续状态分枝过程.我们可以用由Brown运动和Poisson随机测度驱动的随机微分方程的解来构造该类过程.本文的主要结果是构造一列离散状态Markov链,并在较弱的条件下,通过胎紧性结论以及构造无穷维乘积空间上的收敛序列的方法证明其在轨道空间上弱收敛于上述连续状态的非线性分枝过程.