TEM STUDY OF MECHANISM OF STRAIN-AGE HARDENING OF INITIALLY DISORDERED (Co,Fe)_3V ALLOY

TEM study was made to explore the mechanism of the strain-age hardening of initially-dis- ordered (Co_(78)Fe_(22))_3V,which was found to be attributed to the formation of a special disloca- tion-stacking fault configuration in company with disorder-order transformation-disloca- tions extended to stacking faults on{111}planes and got connected with each other through partial dislocation reaction at intersections of{111}planes,leading to dense networks with cells bounded by stacking fault tetrahedrons.The results also indicated that ordered (Co_(78)Fe_(22))_3V has very low stacking fault energy on{111}planes and relative high and isotropie antiphase boundary energy,which implies that it is most likely to be Lomer-Cottrell locks,not Kear-Wilsdof locks,that are responsible for the high strength at high temperatures of this alloy.

Synthesis of super-fine L1_(0)-FePt nanoparticles with high ordering degree by two-step sintering under high magnetic field

Super-fine L1_(0)-Fe Pt nanoparticles(NPs)with high ordering degree were successfully prepared by a modified two-step sintering method,which includes low-temperature pre-sintering,and the high magnetic field(HMF)assisted post-sintering processes.The particle size of the L1_(0)-FePt NPs was obviously refined by lowering the sintering temperature.By applying the HMF during the post-sintering process,the fine size characteristics of L1_(0)-Fe Pt NPs were retained,and the ordering degree was significantly improved.The L1_(0)-Fe Pt NPs with sizes of about 4.5 nm,ordering degree of 0.940,and coercivity of 22.01 k Oe were obtained by this two-step sintering under a magnetic field of 12 T.The mechanism investigation of HMF enhancing the ordering degree indicates that the HMF enhances lattice distortion and magnetization energy(Zeeman energy).The enhanced lattice distortions cause high stress existing in the lattice,which can effectively promote the disordered-order transition.When the magnetic field reaches to 3 T,the Zeeman energy of the NPs is higher than the thermal disturbing energy of the NPs,and the magnetization effect is stronger.Therefore,the HMF(higher than 3 T)can obviously improve the disorder-order transition by lowering the energy barrier and accelerating the orderly diffusions of atoms.The HMF is a promising assistant to synthesize the L1_(0)-phase NPs with both of high ordering degree and super-fine size.

Increasing the Content of β Phase of Poly(9,9-dioctylfluorene) by Synergistically Controlling Solution Aggregation and Extending Film-forming Time

For poly(9,9-dioctylfluorene)(PFO),β phase (coplanar conformation with the intra-chain torsion angle of 165°) has a greater conjugation length and higher degree of order compared to those of α phase, which favors charge carrier transport. However, the highest content of β phase obtained so far is 45%. We propose to increase the content of β phase by promoting the solution aggregation of PFO molecules and extending film-forming time. For this purpose, 1,8-diiodooctane (DIO) is added to PFO o-xylene solution, which enhances the interaction of PFO chains and improves the planarity of PFO backbone, resulting in the formation of ordered aggregation. The aggregates act as nucleation centers to promote the formation of β phase. The content of β phase increases with increasing DIO concentration and reaches a platform of 39% as DIO is more than 4 vol%. Furthermore, the film is kept in a sealed environment with oxylene atmosphere for 3 h, thus the PFO molecules have enough time to diffuse to the crystallization front and achieve disorder-order transition. As a result, the crystallinity of PFO is improved significantly and the content of β phase increases to 52%, reaching the highest value reported so far.