High-pressure torsion of metastable austenitic stainless steel at moderate temperatures

We subjected samples of a 304 metastable austenitic stainless steel to high-pressure torsion (HPT) in the temperature range of 303–573 K, (i.e. at different austenite stabilities), to examine their microstructures and mechanical properties. HPT processing at room temperature led to the formation of a lamellar microstructure with austenitic and martensitic phases, of which sizes were characterised by prior austenite grains, whereas HPT processing at moderate temperatures produced nanostructured austenite grains through mechanical twinning. The nanostructured 304 steel with an average grain size of ~70 nm exhibited a fine balance between tensile strength (~1.7 GPa) and reduction of area (~55%).     

On anomalous channelling effects in ion-implanted silicon

Abstract

In this work results of a Monte Carlo simulation of the ion penetration in a crystalline silicon target are reported. It is shown that, contrary to the common expectation, channelling is sustained by a non-vanishing divergency of the ion beam for a nominally random orientation of the target.     

A thermodynamic model for nanocrystallization in bulk metallic glasses

The structural complexity of glass-forming alloys, which generally contain more than three components, can lead by partial crystallization during annealing to a dispersion of nanocrystals in an amorphous matrix, giving the material a very high mechanical strength. In the present study, the evolution of the driving force for crystallization is expressed as a function of the composition and the chemical potentials of the components. Application to Zr₆₀Al₁₀Cu₃₀ and Zr₆₀Al₁₀Cu₂₀Pd₁₀ bulk metallic glasses shows that the first crystallization step leads to a metastable equilibrium between nanocrystals of an intermetallic and a percolating amorphous phase. The effects of the number of components and of chemical bonding on the fraction crystallized is analysed and discussed.     

Partitioning and segregation of trace element Sn in a low-alloy steel

The partitioning of the trace element Sn into Cu-rich precipitates in a low-alloy pressure-vessel steel has been characterized using the three-dimensional atom probe (3DAP) technique. This investigation has revealed for the first time that the trace element Sn, present at only 0.007?at.% in the steel, partitions strongly to both small spherical precipitates (<4?nm in diameter) and to large non-spherical precipitates (largest dimension 10–50?nm) during thermal ageing. Sn was also seen to segregate strongly to the precipitate/matrix interface of a large Cu precipitate and particularly in the region where a dislocation appears to intersect the precipitate. The strong attraction of large solute atoms to special sites probably drives the interfacial segregation of Sn. This is consistent with the observation of stronger segregation of Sn to the interface of large precipitates than to the coherent interface of smaller precipitates.     

Diffusion kinetics for divacancies in the bcc lattice

In this letter we employ high-precision Monte Carlo simulations to investigate tracer diffusion kinetics for diffusion via divacancies in the bcc lattice. We utilize the mechanisms originally identified by Mehrer in which the divacancy can move by nearest-neighbour jumps with stable first-nearest-neighbour, second-nearest-neighbour and fourth-nearest-neighbour configurations of the divacancy. The tracer correlation factor and the 'impurity-form' correlation factor were found to be some 4-6% lower than those found by the matrix method. The tracer diffusion data and isotope effect for sodium were revisited in terms of monovacancy and divacancy contributions. The main change is a revision upwards from 0.55 to 0.61 of the j K kinetic factor for divacancies.     

Mechanically driven alloying forces in the fabrication of a Cr–Zr nanocomposite

A highly supersaturated nanocrystalline Cr–25?wt% Zr alloy has been prepared by mechanical alloying of elemental crystalline powders. High-purity powders of Cr and Zr were milled for up to 20?h. The development of the microstructure was investigated by X-ray diffraction (XRD) and scanning electron microscopy. XRD patterns confirmed complete alloying of the Zr and Cr. The contribution of grain boundaries, the chemical potential of a solute atom induced by dislocations, and the elastic strain energy arising from the different sizes of Cr and Zr atoms have been calculated. The alloy formation is discussed with respect to the thermodynamic conditions of the material. The role of internal strains and stored enthalpies by dislocations on solute atoms is the major mechanical driving force for alloying and this is critically assessed in this article.     

High-efficiency single-layer organic light-emitting diode based on green fluorescent protein

We have fabricated a molecular organic light-emitting device comprising indium–tin oxide/a molecular organic layer/aluminum in which the organic layer is a green fluorescent protein. The device exhibits peak external quantum and power efficiencies of 8?±?0.2% and 13?±?0.7?lm?W?^??1 at a current of J?=?1.5?A?m^?2, respectively. In addition, the turn-on voltage is 2.5?V for 1?cd?m^?2 and the maximum luminance achieved is 1275?cd?m^?2. This good performance can be explained by the presence of singlet-excited states, leading to a high internal efficiency.     

Scaling properties of three-dimensional random fibre networks

Random fibre networks have unique mechanical properties and appear as the primary building blocks of many biological and structural materials. Although fibre networks are usually three-dimensional in nature, prior studies have mainly used simplistic two-dimensional models to characterize their properties. The present study creates a 3D strain-based nonaffinity measure and investigates the mechanical behaviour and scaling properties of 3D fibre networks. This measure is used to fully examine the influence of primarily characteristic length scales, i.e. mean segment length and bending length, on nonaffine mechanical behaviour of 3D filamentous networks. It is observed that all nonaffinity measure components exhibit a power-law variation with the probing length scale. Furthermore, it is found that while the degree of nonaffinity in both 2D and 3D systems decreases with increasing the probing length scale, the two power-law scaling regimes previously reported for 2D networks do not appear in 3D.     

利用组织工程治疗骨缺损中的几点问题

骨缺损是临床上的常见病,也是骨科治疗的难题之一。近年来,骨组织工程发展迅速,利用骨组织工程治疗骨缺损成为研究的热点。组织工程应用的主要问题在于种子细胞的培养和细胞种植基质材料的优化。在此领域的发展过程中,渗透着丰富的哲学思想,理解和把握这些哲学思想对完善利用骨组织工程治疗骨缺损的工作将大有益处。     

提取抑制:来自听觉定向遗忘的证据

两个实验采用语音材料考察了词表表达方式下听觉通道的定向遗忘效应以及相应的机制。实验一中,采用2（组别）&#215;2（词表）混合实验设计获得了听觉通道的定向遗忘效应,但是较为模糊,部分数据显示可能是额外的被试个体差异导致的;实验二中,采用2（性别）&#215;2（词表）&#215;2（条件）&#215;2（科系）混合实验设计,严格控制了被试个体差异等因素,获得了较清晰的定向遗忘效应,且支持提取抑制理论。