Correlation of radius of cathode spot of vacuum arc of metals on the size of generated droplets

The simple relation to estimate the cathode spot radius of a vacuum arc of pure metals is obtained. On its basis, is established between the cathode spot radius and the size of droplets generated by the cathode spot a correlation. This enables to find ways to reduce droplets in the plasma flow, which forms coatings by the vacuum electric arc method. The paper presents the results of experimental study of the droplet sizes depending on the vacuum arc current iд. The size and amount of the droplets on an area of 1 mm2 of the coating surface are determined using the ImageSP program. As the initial data, the microstructures of the coatings are used with an increase of: ç100, ç200, ç500, ç1000, ç1500. The droplets have been generated by a cathode spot of a vacuum arc for the alloy of the composition, at.%: 68Al–8Cr–4Nb–20Si. It is established that the number of droplets with a diameter of < 2 μm is generated most of all, and the number of droplets with a diameter > 10 μm is generated least of all. The number of generated droplets with a diameter from 2 to 10 μm slightly depends on the arc current iд. It is noted that the diameter of the alloy droplet is smaller than the diameter of the droplets generated by the cathode spot on its components due to the fact that the radius of the cathode spot on the alloy is smaller than the radius of the cathode spot on its pure components.

Verification of Possibility of Molten Steels Decopperization with ZnAl2O4

In the previous research works, ZnAl2O4 material was considered as one of the solutions for the decopperization process of molten steels; up to 33% of decopperization efficiency was reported by utilising the ZnAl2O4 filter. In order to verify the decopperization possibility of ZnAl2O4 materials, iron-based alloys with various copper and carbon contents were interacted with ZnAl2O4 substrates in a heating microscope under an argon gas atmosphere at 1600 °C. Fe-Cu alloys were found to react with the ZnAl2O4 substrate during the interaction process, and a reaction layer with a complex composition around the alloy droplet was formed; however, Cu was not detected in the reaction layer. Cu was later found diffused inside of the ZnAl2O4 substrates. Furthermore, the Cu-Zn compounds were detected when the copper content in Fe-Cu alloys was 10 wt% Cu. After interaction experiments, copper was decreased in all cases. Thereby, the copper evaporation and infiltration into the ZnAl2O4 substrate were considered as the reasons for copper loss. Moreover, oxygen dissolved in melt was found to have a great effect on the copper evaporation process.

Numerical Study on Successive Liquid Metal Alloy Droplet Depositions

Successive liquid metal alloy droplet impingements find extensive applications in additive manufacturing technologies and a detailed knowledge about the flow behavior, phase transformation and free surface deformation is required to have a complete understanding and optimization of the process parameters. Experimental research in this field is limited due to extremely small length and time scales involved. Numerical simulation of such process involves challenges like tracking deforming interfaces, modelling the successive droplets, surface tension, flow field and solidification. A non-isothermal enthalpy-based porosity model is used to numerically study the phase change characteristics of successive liquid metal droplet depositing onto a substrate. The flow governing equations are solved using the finite volume scheme. The Coupled Level Set Volume of Fluid (CLSVOF) method is used to track the free surface and the surface tension is modelled using the Continuum Surface Force (CSF) method. The splat morphology, phase change characteristics and effects of various impact conditions on successive columnar droplet depositions are examined.

Temperature-Dependent Morphology Evolution of Boron Nitride and Boron Carbonitride Nanostructures

Boron nitride (BN) and boron carbonitride (BCN) nanostructures with versatile morphology were synthesized at different temperatures. The morphologies such as smooth microspheres, nanoflake-decorated microspheres, solid nanowires, hollow nanotubes (bamboo-like nanotubes, quasi-cylindrical nanotubes, and cylindrical nanotubes), and nanosheet-assembled microwires have been observed. Systematic investigation showed that the reaction temperature was responsible for the versatile morphologies through influencing the guiding effect of catalyst alloy droplet and the diffusion rates of growth species. The diffusion rate differences between surface diffusion (along the surface of the droplet) and bulk diffusion (through the bulk of the droplet) at different reaction temperatures were suggested to affect the final structure of the BN and BCN nanostructures.