Modification of the structure of the hypereutectic silumin alloy Al-44Si under the action of compression plasma flows

Effects of the high-energy compression plasma flows on the structure, elemental composition, and phase state of Al-44 at.% Si hypereutectic silumin alloy have been investigated. Using scanning electron and optical microscopy it was found decreasing in grain size of both primary silicon particles and Al-Si eutectic parts with increase of absorbed energy density of compression plasma flows. The primary silicon crystals were dispersed down to 300 nm in the result of high cooling rate of the melted layer after its homogenization by means of hydrodynamic mixing. It was found that increase in the absorbed energy density, homogenization of elemental composition in the modifies layer occurs due to increase in lifetime of the melted state and more efficiency mixing process.

Simulating melting of fault gouge at the local scale

<p>Melting of fault gouge during fast co-seismic slip has been widely documented in laboratory studies. Because the real-time observation and local probing of this phenomenon is experimentally out of reach at the present time, the implication of melting on fault weakening are not yet fully understood,. Physics-based numerical modelling of a synthetic sliding interface could thus be a way to bring a better understanding of this physico-mechanical process.</p><p>In this study, we present a numerical work paving the way towards such an understanding. It is implemented in MELODY, a numerical tool combining Discrete Element Method (DEM) and a Multibody Meshfree Approach (i.e. highly deformable DEM). In this model, a small patch of seismic fault filled with granular gouge (composed of perfectly rigid and incrompressible grains with realistic angular shapes) is simulated. By shearing this simulated fault, we produce highly deformable gouge particles within a melted layer.</p><p>Numerical results show that melting processes have strong consequences on the fault rheology, by reducing shear stress and favouring the localization of the deformation on the sliding interface. Results are compared with experimental observations on saw-cut faults deformed in triaxial conditions in the laboratory. Future developments including thermal diffusion within the gouge and in the surrounding medium are described.</p>

The Effects of Laser Remelting on the Microstructure and Performance of Bainitic Steel

The surface of bainitic steel was remelted by fiber laser, and the microstructure and mechanical properties of the melted layer were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), a nanoindentation instrument, and wear equipment. The study of changing the laser scanning speed showed that the depth of the melted layer increases with decreases of the laser scanning speed. The wear-resistance property increased by 55% compared with the matrix and decreased with the reduction of laser scanning speed within a certain range. In the study of changing the laser-scanning space, the thermal effect of laser melting in the back channel on the front channel was further validated. At the same time, it was found that the solidified layer surface of hardness alternating with softness can be obtained by appropriately expanding the scanning space, which is conducive to improving the wear-resistant properties of the steel surface, and properly improving the production efficiency of the laser remelting treatment.

Determination of the fundamental dimension development in building direction for laser-sintered parts

The additive manufacturing process of the laser sintering of polymers (LS) allows the production of complex parts right from CAD data. However, the manufactured parts often show dimensional inaccuracies. In order to fundamentally determine the influencing parameters on the accuracy of LS parts, a hatching specimen, a layer-specimen and defined part geometries are manufactured and subsequently measured. These, combined with a theoretical observation of the layer wise geometry buildup, are used to determine the fundamental portions of the development of dimensions in building direction (z-direction). The results indicated a defined powder adhesion height at the top and the bottom of a melted layer, along with the dependency of melt depth and the hatch number for small structures. Depending on the nominal heights of an LS part, either an oversize or undersize was detected.

Mechanical and Microstructural Evolutions of the Laser Deposited Titanium Layers under Various Shielding Atmospheres

Direct laser melting process is a kind of prototyping process whereby a 3-D part is built layer-wise by melting the metal powder with laser scanning. The properties of laser melted layer are found to be strongly dependent upon the types of shielding gas used. In this study, the effects of shielding gases on the mechanical and microstructural properties of the deposited titanium layers have been investigated. The laser remelting process has also been implemented at various shielding atmospheres to investigate the changes in surface roughness and hardness of deposited layers. The characterization of laser processing parameters, such as laser power, scan rate, gas flow rate, powder layer thickness, beam spot size and hatch distance, is proved to be useful in controlling the mechanical and microstructural properties of the deposited layer.

Simulating of the Flood Runoff in Case of Heavy Rains in the Zone of Many-year Frozen Earths

Special features of the rain floods runoff formation and an approach to their simulating for small catchments of the zone of many-year frozen earths’ spreading are discussed. Information about heavy rains and resulted floods obtained from the observation data from the experimental catchments of the Kolyma and Bomnak runoff stations has been used as initial data. On the basis of the available concepts of the many-year frozen earths’ active layer dynamics and the outcomes of the different years’ experimental investigations, a mathematical model has been proposed. It enables to take into consideration the accumulating role of the soil melted layer and the moss cover. The НЕС-HMS simulating system able to reproduce the flood runoff course with the 1 hour time discontinuity in specific conditions of slope regulation on the basis of the Clark unit hydrograph method was used to take in account special features of the rain runoff formation.

The Effects of Laser Surface Modification on the Microstructure of 1.4550 Stainless Steel

In this study a stainless austenitic steel 1.4550 was laser heat treated with diode laser. The influence a gouache coating on remelted steel substrate was carry out. The cooling system during laser melted was analysis as well. Melted layers were manufactured with different laser beam power between 0.6 kW and 1.4 kW, constant scanning laser beam speed vl = 5.76 m/min and laser beam diameter equal dl = 1.2 mm. The surface was treated at room temperature and under CO2 cooling conditions and the results were compered. With the increase of the laser beam power, the dimensions of the laser tracks increase. The depth of laser tracks varies significantly than their width. The deepest melted layer was observed for a material that wasn’t coated by any of absorbent paste and when there wasn’t cooling system.