Materials Science Forum Vol. 834

Abstract: Selective laser melting is a layer-by-layer technique to form a solid part from powder. The thermal cycle of this process can be as short as one millisecond and less. This is why it is favorable to obtain nanostructured materials with advanced properties. Metal matrix composite WC-Co is studied. Micron-sized Co powder was mixed with WC nanopowder in a planetary ball mill to prepare uniform composite powder. Single remelted beads and monolayers were obtained from the composite powder on the substrates of sintered WC-Co. No cracks and good adhesion to the substrate are observed. The high cooling rate up to 10⁶ K/s explains the fine microstructures. Increasing the scanning velocity is favourable because of refining the microstructure and decreasing the balling-effect. The attained values of surface roughness are as low as 1-2 μm.

Abstract: The influence of the laser-beam radial distribution of the energy flux density is theoretically studied for the Gaussian distribution (mode TEM₀₀), and doughnut distribution of TEM_01* mode for the values of the Peclet number from 0 to 3. The model of linear thermal conduction in the target indicates that profile TEM₀₀ is the best for thermo-activated treatment processes that can be accomplished in a wide temperature range and profile TEM_01* can be advantageous for a narrow range of the permissible processing temperature. If the phase transitions of melting/solidification and evaporation are included into the model, the estimate of the width of the laser-treated band is reduced but the tendencies predicted by the linear model are not changed.

Abstract: The objective of this study is to restore the true temperature in during the process of Selective Laser Melting (SLM) of metal powder (in the present case INOX 316L), that is the actual problem in laser assisted additive technologies. To meet this objective, at the first stage, the temperature was measured on the surface of metal substrate INOX 304L without a powder layer. Based on the results of studies the method of temperature measurementof the molten pool surface on metallic plates and during melting of metal powder layer, that were exposed to laser radiation, using an infrared camera (IR), in the present case FLIR Phoenix RDAS TM, was proposed. To restore the true temperature based on the brightness temperature values measured by IR camera, the results of temperature measurements were compared with the width of the molten track on the surface of the plate in the absence of powder. In case of SLM, the results of IR camera measurements were compared with the width of a welded track (bead). The true temperature profiles and temperature gradients values were determined along the axis of the laser beam for melting of plates without powder. In the case of powder melting, the developed method allows to determine the influence of several key SLM parameters on the molten pool shape.

Abstract: The Ni₃Al intermetallics involve more attention because of inherent material properties especially interesting in high temperature application. In this study the Selective laser melting (SLM) and Direct laser metal deposition (DLMD) are used to manufacture the single-tracks and layers. For the comparison of the methods, the optical microscopy, SEM, XRD and EDX microelement analysis were involved. The materials show no significant differences but each SLM and DLMD have the target application.

Abstract: In this paper the principal feasibility of using cold gas dynamic spraying with laser post treatment technique to create Al-Ni composite coatings is demonstrated. The prepared mixture of two powders was coated on an aluminum substrate and laser annealed. As a result the Al_xN_y intermetallic phases were observed in the coating. Obtained laser-annealed coatings were studied be means of optical and electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry and compared with as-sprayed coatings. Effects of laser processing parameters, such as scanning speed, power and beam shape on microstructural evolution of the composite coatings were discussed and optimal regimes for laser assisted CS were determined.