PAN基碳纤维原丝结晶态结构的研究

利用XRD的赤道扫描和子午扫描对PAN原丝进行研究,证实了PAN原丝是二维有序的准晶结构,并计算了纤维结晶度的和其晶粒尺寸的大小。同时,研究了PAN原丝晶区择优取向的方向,计算分析出各碳纤维原丝的结晶态结构参数。

二甲基亚砜对间位芳纶结构调控与染色性能的影响研究

为了克服间位芳纶染色难以拓展其在服用防护领域的应用,探究不同晶态结构间位芳纶的染色性能差异机理并改善其染色性能具有重要意义。本文选用二甲基亚砜(DMSO)作为PMIA大分子结构调控剂,研究其对PMIA晶态结构和染色性能的影响。采用分子动力学模拟,分别构建了PMIA和DMSO/PMIA不同晶态下的分子模型,并计算DMSO调控前后PMIA的氢键变化、链运动的均方位移及PMIA和染料分子的界面结合能。进一步对PMIA纤维进行扫描电子显微镜(SEM)、傅里叶红外光谱仪(FTIR)、X射线衍射(XRD)表征和表观得色量(K/S值)、上染率的测试,并与分子动力学模拟相互验证,从分子尺度解析了DMSO对PMIA结构调控机制和染色性能的影响。结构模型的计算结果表明:DMSO可以有效地破坏PMIA氢键网络,使得其非结晶区与结晶区氢键数量分别减少了56.5%和25.7%,并显著增加PMIA非结晶区的链运动性能。此外,经调控后的PMIA不同晶态与染料的界面结合能大于调控前,非结晶区与染料的结合能提升程度大于结晶区。实验结果表明:DMSO可有效提高PMIA纤维的表面粗糙度,同时对PMIA的化学结构和结晶度均无明显影响;PMIA的染色性能显著提高,K/S值与上染率分别提升了72.34%和65.6%,耐湿摩擦色牢度提升半级,耐日晒色牢度提升一级。实验结果与分子动力学模拟结论相一致,为提高PMIA的染色性能提供了新途径。

Effect of hot deformation conditions on grain structure and properties of 7085 aluminum alloy

The influences of deformation conditions on grain structure and properties of 7085 aluminum alloy were investigated by optical microscopy and transmission electron microscopy in combination with tensile and fracture toughness tests. The results show that the volume fraction of dynamic recrystallization increased with the decrease of Zener-Hollomon （Z） parameter, and the volume fraction of static recrystallization increased with the increasing of Z parameter. The strength and fracture toughness of the alloy after solution and aging treatment first increased and then decreased with the increase of Z parameter. The microstructure map was established on the basis of microstructure evolution during deformation and solution heat treatment. The optimization deformation conditions were acquired under Z parameters of 1.2×10^10-9.1×10^12.

Studies on the Crystallization Properties and Morphology Structure of the Cationic Dyeable Polypropylene Fibers

The crystallization properties and morphology structure of the cationic dyeable polypropylene fibers which were produced by the blending spinning method were studied by making use of X-ray and scanning electron microscopy (SEM). It comes to the conclusions that the larger the crystallite size in the fibers is , the better the dyeable properties of the fibers are and there is a little compatibility between the dyeable agent and polypropylene resin. And the dye-uptake of the fibers may be up to 90% because the dyeable agent can uniformly be scattered in polypropylene.

Preparation and thixoforging of semisolid billet of AZ80 magnesium alloy

Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed.The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation.Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA.Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape.The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.

Microstructure evolution of 7050 aluminum alloy during hot deformation

Hot compression of 7050 aluminum alloy was performed on Gleeble 1500D thermo-mechanical simulator at 350 ℃ and 450 ℃ with a constant strain rate of 0.1 s-1 to different nominal strains of 0.1, 0.3 and 0.7. Microstructures of 7050 alloy under various compression conditions were observed by TEM to investigate the microstructure evolution process of the alloy deformed at various temperatures. The microstructure evolves from dislocation tangles to cell structure and subgrain structure when being deformed at 350 ℃, of which dynamic recovery is the softening mechanism. However, continuous dynamic recrystallization (DRX) occurs during hot deformation at 450 ℃, in which the main nucleation mechanisms of DRX are subgrain growth and subgrain coalescence rather than particle-simulated nucleation (PSN).

Effect of initial microstructure on superplastic deformation of AZ70 magnesium alloy

The mechanical properties and deformation mechanism of semi-continuously casting and as-extruded AZ70 magnesium alloys in a wide range of grain sizes(from 14 to 103μm)were investigated at 653 K and 1×10-3s -1.It is discovered that with reducing grain size,flow stress is weakened and plasticity is improved and even superplasticity exhibits.SEM and OM were used to clarify the deformation mechanism.It is suggested that dynamic recrystallization(DRX)is the coordination deformation mechanism of grain boundary sliding(GBS)for coarse grain,and cavity and intracrystalline slip are the coordination deformation mechanisms of GBS for fine grain.

Corner forming of AZ61A magnesium alloy tube within warm hydroforming

The comers with small radii on cross sections are crucial for forming hydroformed components with polygonal sections. In this paper, warm hydroforming experiments of AZ61A magnesium alloy tubes were cartied out to study the forming regularity of round comers by using a demonstration part with square sections. Effects of temperature on radius forming, thinning ratio distribution and microstructure were revealed and a component with relative outer corner radius of 3.0 was obtained by warm hydroforming at 240℃. The minimum thickness of the formed square section was located in the transition position between the corner and the straight wall. The thinning ratio of the round corner increased with the increase of forming temperature. Fotmability of the magnesium tube was improved by raising temperature under the effect of dynamic recrystallization at 240℃.

Forming electron traps deactivates self-assembled crystalline organic nanosheets toward photocatalytic overall water splitting

Most biological photoredox reactions occur in sophisticated molecular assemblies consisting of highly organized light-harvesting moieties and catalytic centers.Mimicking these prototypes by creating supramolecular assemblies could be a potentially viable approach toward artificial photosynthesis.Although self-assembled organic materials are known to carry out water splitting reactions,developing self-assembled organic materials for photocatalytic overall water splitting still remains a critical challenge.Herein,we first demonstrate that crystalline organic nanosheets assembled from linear oligo(phenylene butadiynylene)(OPB)are able to catalyze overall water splitting under visible light irradiation.Further investigations reveal that the photocatalytic activity of self-assembled organic structures is closely related to the crystalline structure along with the corresponding electronic structure.Structural disorders in OPB nanosheets and extrinsic factors such as adsorbed water molecules will induce the formation of electron traps which can make the OPB nanosheets thermodynamically unfavorable for photocatalytic overall water splitting.The deactivation mechanism unveiled in this study provides crucial insights into the assembling of artificial organic materials for future solar-to-chemical energy conversion.

Spherical periodicity as structural homology of crystalline and amorphous states

It has been widely accepted that spherical per- iodicity generally dominates liquid and amorphous structure formation, where atoms tend to gather near spherically peri- odic shells according to Friedel oscillation. Here it is revealed that the same order is just hidden in the atomic global packing modes of the crystalline phases relevant to bulk metallic glasses. Among the multiple nearest-neighbor dusters devel- oped from all the non-equivalent atomic sites in a given phase, there always exists a principal duster, centered by which the spherical periodicity, both topologically and chemically, is the most distinct. Then the principal dusters plus specific glue atoms just constitute the cluster-plus-glue-atom structural units shared by both metallic glasses and the corresponding crystalline phases. It is further pointed out that the spherical periodicity order represents the common structural homology of crystalline and amorphous states in the medium-range through scrutinizing all binary bulk-glass-relevant phases in Cu-（Zr, Hf）, Ni-（Nb, Ta）, Al-Ca, and Pd-Si systems.

Preparation of sound ribbons with submicrometer-grained microstructure on a Mg–Zn alloy

In this paper, a viable way to fabricate Mg alloy sound ribbons with ultra-fine-grained microstructure was presented. The hot-rolled and annealed Mg-0.4Zn （at%） alloy exhibited excellent rollability to form sound ribbons with submicrometer grains when subjected to one-pass cold rolling process. The more balanced multi-mode dislocation slips originated from the significant decrease of critical resolved shear stress for non-basal slip with the addition of solute Zn and the favorable crystallographic orientation were suggested to be responsible for the excellent cold rollability. The formation of ultra-fine-grained microstructure was attributed to low-temperature dynamic recrystallization occurring during the cold rolling process with large strain.

Chip formation dependence of machining velocities in nano-scale by molecular dynamics simulations

In this study, molecular dynamics simulations were carried out to study the effect of machining velocities on the mechanism of chip formation in nano-metric copper. A wide range of cutting velocities was performed from 10 to 2000 m/s, and the microstructure's evolution from a crystalline state to an amorphous state was studied. At the low machining velocity, dislocations were generated from the surface in front of the tool, and the immobile dislocation deduced by the cross slip of dislocation was observed. At the high machining velocity, no crystal dislocation nucleated, but instead disorder atoms were found near the tool. Temperature near the tool region increased with the increasing machining velocities, and the temperature had an important effect on the phase transition of the crystal structure.