Marina A. Volosova

Laser-beam modulation to improve efficiency of selecting laser melting for metal powders

Nowadays additive manufacturing becomes more and more popular. It depends on the results of last achievements in developing of the new constructions for modern machine tools. One of the most developed AM technology is SLM or SLS. About twenty years ago the technology of rapid prototyping started to grow up from building prototypes and developed to real functional item production. Especially this becomes more important in producing medical implants in the full accordance with individual digital 3D-model from metallic powder as Ti6Al4V or CoCr. The additive technology gives the possibility to reduce additional steps in implants production process as work preparation process, forwarding a work piece from one shop to another one, post treatment etc. This approach is very topical to production of tooth, knee and coxal implants. This idea is realized in the commercial SLM machines as EOS M280, SLM Solutions 125HL (Germany), Phenix systems PXS/PXM Dental (France) (fig. 1).

Effect of Wear of Tool Cutting Edge on Detail Surface Layer Deformation and Parameters of Vibro-Acoustic Signals

This paper studies the computing possibilities of estimating the deformation of the surface layer in machining of details with cutting tools of different levels of wear. The calculation results were experimentally compared with the data obtained by the results of a grid distortion analysis in cutting. Results of how deformation intensity evaluation affects the parameters of vibroacoustic signal have also been presented.

Comparative studies of monoclinic and orthorhombic WO3 films used for hydrogen sensor fabrication on SiC crystal

Amorphous WOx films were prepared on the SiC crystal by using two different methods, namely, reactive pulsed laser deposition (RPLD) and reactive deposition by ion sputtering (RDIS). After deposition, the WOx films were annealed in an air. The RISD film possessed a m-WO3 structure and consisted of closely packed microcrystals. Localized swelling of the films and micro-hills growth did not destroy dense crystal packing. RPLD film had layered β-WO3 structure with relatively smooth surface. Smoothness of the films were destroyed by localized swelling and the micro-openings formation was observed. Comparative study of m-WO3/SiC, Pt/m-WO3/SiC, and P-WO3/SiC samples shows that structural characteristics of the WO3 films strongly influence on the voltage/current response as well as on the rate of current growth during H2 detection at elevated temperatures.

New Approach to Study and Research of Causes of Operational Characteristics Disturbance for Ceramic Tool Materials

The system approach to study the causes of operational characteristics disturbance for ceramic tool materials based on complex research and its systematization. In the present study the defects by volume and by surface are researched. The main directions of operational characteristics improvement for tool materials are showed.

Structure, morphology and electrocatalytic properties of WO x thin films prepared by reactive pulsed laser deposition

Nanostructured WO x<3 films were prepared by pulsed laser deposition in air from W target. The pressure of air was varied in a range of 10 – 100 Pa and the temperature of a glassy carbon substrate during the film deposition was 22 or 500°C. For the films deposited at 22°C, thermal post-treatment in air of laboratory humidity at 500°C was applied. The increase of air pressure during PLD at 22°C caused both a decrease in packing density of ball-like amorphous nanoclusters of WO x and decline of their size. Post-treatment in air at 500 °C has initiated crystallization of the nanoclusters but characteristic morphology of the films was preserved in a whole. The PLD of WO x on a heated substrate resulted in the formation of nanoneedles and nanosheets. Fairly good catalytic properties in hydrogen evolution reaction (HER) and in electrolytic Pt deposition were revealed for the WO x films that consisted of loosely packed ball-like nanocrystals possessing a size of ~20 nm. The catalytic activity of the films consisted of nanoneedles and nanosheets was not good enough. Adjustable electrolytic deposition of Pt on the nanostructured WO x support film allowed to prepare effective hybrid HER catalyst containing only ~7 μg/cm2 of Pt.

Activation of electrocatalytic properties of a-C films by doping with MoSe x clusters

Nanocomposite a-C(Mo/MoSe x ) thin films containing amorphous carbon matrix a-C, nano-Mo and MoSe x ≥2 clusters were obtained by pulsed laser co-deposition of carbon and MoSe2. The deposition was carried out at room temperature onto a graphite substrate. Atomic content of the MoSe x≥2 phase did not exceed 25%. The use of a buffer gas at a pressure of 10 Pa allowed to obtain the maximum Se/Mo ratio in the films and to increase the concentration of sp2-hybridized C atoms for high conductivity realization. The formation of MoSe x≥2 cluster inclusions was the essential factor for activation of hydrogen evolution reaction (HER) in 0.5 M H2SO4 aqueous solution. These clusters also promoted cathodic deposition of Pt nanoparticles on the surface of a-C(Mo/MoSe x ) in a H2SO4/KCl solution when a Pt anode was used as a source of Pt. Hybrid Pt/a-C(Mo/MoSe x ) thin-film coatings with a low Pt loading (~6 μg/cm2) exhibit excellent HER property, which noticeably exceeds that of relatively thick Pt coating prepared on a graphite substrate by pulsed laser deposition.

New Method for Synthesis of Hard Coatings Using Pulsed Bombardment with High-Energy Gas Atoms

For deposition of hard coatings is used a source of metal atoms accompanied by high-energy gas atoms. The metal atoms are produced due to sputtering a flat rectangular target in low pressure magnetron discharge. The gas atoms with energy up to 30 keV are produced due to charge exchange collisions of accelerated ions in space charge sheaths near the surfaces of a grid parallel to the target. The ions are extracted from the discharge plasma and accelerated by high-voltage pulses applied to the grid. The metal atoms pass through the grid and deposit on the products. Conjunction of their trajectories with those of gas atoms bombarding the growing coating allows synthesis of the coatings on rotating dielectric products. Mixing by high-energy gas atoms of the coating atoms and atoms of the product material in its surface layer improves the coating adhesion.

New Method for Diamond-Like Carbon Deposition on Ceramic Cutting Tools in Vacuum-Arc Plasma

A study of diamond-like carbon coatings deposition has been carried out. The coatings were deposited on ceramic cutting tools. Vacuum-arc plasma has been used for deposition. Dependencies of the coatings microhardness and density on the tools bias voltage U are presented. The microhardness reaches 50 GPa at U=100 V. With increasing U and temperature it decreases to 15 GPa at U=500 V. Effect of the coatings on oxide ceramics properties was revealed. They were used for lathe turning of hardened steel. The tests proved a high efficiency of the coatings.

Structural and electrochemical properties of W-Se-O layers prepared by pulsed laser pre-deposition and thermal posttreatment

Novel nanostructured thin-film coatings containing WSe2 and WO3 nanosheets were prepared through a simple and highly reproducible method. Pulsed laser pre-deposition of W- Se-O films on a microcrystalline graphite substrate by ablation of WSe2 target in a mixture of Ar and O2 gases was followed by thermal post-treatment. The influence of pre-deposition and post-treatment conditions on the structure, morphology and chemical composition of the W-Se- O films was studied. Thermal annealing at appropriate conditions of pre-deposited amorphous W-Se-O films resulted in the formation of crystalline structure consisted of nanocrystals of WSe2 and WO3 phases. Such structural modification significantly altered the electrochemical properties of the thin-film coatings with consequences, in particular, on their catalytic activity toward hydrogen evolution reaction in an acid solution.

Regulation of nanoparticle impact on the growth of MoSex films during pulsed laser evaporation of MoSe2 target

Irradiation of MoSe2 target with intensive laser pulses caused the formation of micro- and nanoparticles. The particles were observed on the target surface and in MoSex films prepared by deposition of the laser-induced plume. Content of nanoparticles on the film surface was markedly larger than that of microparticles. Transport of the plume in vacuum and in a buffer helium (He) gas was studied. The He pressure was high enough to provide effective atom scattering and plume deceleration. For a medium target-substrate distance, the structure of MoSex film was formed due to intensive deposition of atomic flux scattered in the buffer gas. Impact of nanoparticles on the structure was negligible. For a large distance, deposition of the nanoparticles from the plume was assisted by co-deposition of drifting atomic flux. Such deposition resulted in the formation of relatively smooth film containing nanoparticles transferred with plume, as well as the growth of spherical Se particles on the substrate.