Structure and properties of the surface layer of titanium alloys after silver ion implantation and ultrasonic treatment

The article considers the effect of ultrasonic exposure after the ion implantation of titanium alloys VT1-0 and VT6 silver on the thickness of the ion-leged layer, the distribution of silver by the thickness of this layer and the scalar density of dislocations in the subsurface layer. It has been established that for the alloy VT6 at the same parameters of the implantation regime there is a deeper penetration of silver ions compared to the alloy VT1-0. Directly under the ion-leged layer is formed a layer with an increased rocky density of dislocations. The ultrasonic treatment of the implanted layer on the alloys studied contributed to the deeper penetration of silver ions and the alignment of its concentration by the thickness of the surface layer of titanium alloys.

Gravitational waves induced from string axion model of inflation

We study the production of gravitational waves from primordial scalar perturbations in a string axion inflationary model with subleading nonperturbative corrections. In such a model, the subleading nonperturbative effects can superimpose steep cliffs and gentle plateaus onto the leading axion potential. Such an inflationary potential both matches the Planck observations at CMB scales and gives rise to an enhancement in the scalar power spectrum at small scales. We calculate the second-order gravitational wave signatures induced by the scalar density perturbations, and find that the signal can be detected by the space-based laser interferometers in the future.

Structure and properties of layer, surfaced on HARDOX 450 steel by boron containing wire

Analysis of structure phase states and properties of the layers formed on HARDOX 450 low alloy steel by welded-on wires with boron content of 4.5 and 6.5 % wt. was made by the methods of modern physical material science. In the initial state HARDOX 450 steel has the structure of tempered martensite, in the volume and along the boundaries of crystals of it the cementite particles are located. The particles located in the volume have acicular shape and those along boundaries are mainly round. The presence of extinction bend contours has been revealed, indicative of the curvature torsion of crystal lattice of the material’s portion. They originate and finish on the interfaces of martensite crystals. Scalar density of chaotically located dislocations and forming the netlike substructure is 6.2·1010 cm–2. The layer welded on HARDOX 450 steel has microhardness increasing by more than two-fold that of the base. Analysis of state diagrams of Fe – C, Fe – B, B – C systems and polythermal cross–sections in Fe – C – B system has shown that the rapid cooling of Fe23C6 – Fe23B6 alloys from liquid state would facilitate the formation of multiphase structural states. It is stated by the methods of transmission electron diffraction microscopy that the reasons for the high microhardness level of the surface layers are the following: formation of iron borides and crystals of ultafine-dispersion (up to 100 nm) packet martensite with high level (~1011 cm–2 ) of scalar density of dislocations; presence of nanodimentional particles of iron and boron carbides in the volume and on the boundaries of martensite crystals; high level of curvature torsion of crystal lattice of iron borides and α-phase grains, caused by the internal stress fields along interphase (interface of iron boride crystals and α-phase grains) and intraphase boundaries (interface of iron borides and martensite crystals packet). Increase in boron concentration from 4.5 to 6.5 % is accompanied by the sufficient increase (by 1.2 – 1.5 times) in hardness of welded layer. It is caused by the increase of dimensions and relative content of iron boride regions by 1.5 – 2.0 times.

Retrieving the spatially resolved preferred orientation of embedded anisotropic particles by small-angle X-ray scattering tomography

Experimental nondestructive methods for probing the spatially varying arrangement and orientation of ultrastructures in hierarchical materials are in high demand. While conventional computed tomography (CT) is the method of choice for nondestructively imaging the interior of objects in three dimensions, it retrieves only scalar density fields. In addition to the traditional absorption contrast, other contrast mechanisms for image formation based on scattering and refraction are increasingly used in combination with CT methods, improving both the spatial resolution and the ability to distinguish materials of similar density. Being able to obtain vectorial information, like local growth directions and crystallite orientations, in addition to scalar density fields, is a longstanding scientific desire. In this work, it is demonstrated that, under certain conditions, the spatially varying preferred orientation of anisotropic particles embedded in a homogeneous matrix can be retrieved using CT with small-angle X-ray scattering as the contrast mechanism. Specifically, orientation maps of filler talc particles in injection-moulded isotactic polypropylene are obtained nondestructively under the key assumptions that the preferred orientation varies slowly in space and that the orientation of the flake-shaped talc particles is confined to a plane. It is expected that the method will find application inin situstudies of the mechanical deformation of composites and other materials with hierarchical structures over a range of length scales.

Defect Structure Parameters of Deformed Polycrystals on Micro- and Mesolevel of Grain Sizes

In the paper we consider the size effect of the closed structural formations as the function of accumulation of scalar density dislocations and their components under plastic deformation. The focus is on the role of interfaces of different types. The sizes are determined and the various parameters of the structure defining the micro-and mesolevel are identified at the development of the mechanisms of plastic deformation. The role of statistically stored dislocations (SSD) and geometrically necessary dislocations (GND) in the formation of the defect structure of the material is examined. It has been established that the smaller the size of the closed structure, the greater the GND part and the smaller the SSD component. The work is based on the TEM research of the structure of deformed materials.

Differences between scalar field and scalar density field solutions

Differences between scalar field and scalar density solutions are explored using a Robertson–Walker (RW) metric, and a nonrelativistic Hamiltonian is derived for a scalar density field in the post-newtonian approximation. The results are compared with those of a scalar field. The expanding universe in a RW metric and a post-newtonian solution of the Klein–Gordon equation are discussed separately.

Ekpyrotic Nongaussianity: A Review

Ekpyrotic models and their cyclic extensions solve the standard cosmological flatness, horizon, and homogeneity puzzles by postulating a slowly contracting phase of the universe prior to the big bang. This ekpyrotic phase also manages to produce a nearly scale-invariant spectrum of scalar density fluctuations but, crucially, with significant nongaussian corrections. In fact, some versions of ekpyrosis are on the borderline of being ruled out by observations, while, interestingly, the best-motivated models predict levels of nongaussianity that will be measurable by near-future experiments. Here, we review these predictions in detail, and comment on their implications.