Directional Crystallization of 316L Stainless Steel Specimens by Direct Laser Deposition

Abstract

Advantages of direct laser deposition of metal providing the directional crystallization of 316L stainless steel specimens are shown. It is found that direct laser deposition of metal offers exciting possibilities for obtaining monocrystalline structures by directional crystallization of the deposited metal. The metal structure of the obtained specimens is represented by dendritic crystals oriented toward the thermal center. The cross-section view of the structure, formed by the crystal axes of the first order, is of the form of honeycombs. The thickness of the applied layer (200 µm) in the central part of the specimen does not prevent the development of the dendrite structure and it contributes to the formation of the monocrystalline structures (having no pores and cracks). It was stated that the growth orientation of dendritic crystals is driven by the thermal center determined by the position of the laser spot. A technique of manufacturing stainless steel products by direct laser deposition using the developed algorithm which allowed connecting the movement of the robotic center and specimen, laser switching, and feeding of the gas-powder mixture was presented. The possibilities of estimating the inclination angle of dendritic crystals in the metal relative to the symmetry axis of the specimen using a metallographic software package for analysis of digital images of the microstructures, as well as the quality control of the items obtained by the X-ray tomographic quality control, determination of the parameters of the laser spot on the substrate surface using high-speed photography, and estimation of the phase composition of the deposited metal using X-ray diffraction analysis, are shown. In such a case, the roughness of the specimens determined by the size of the powder particles may be removed by mechanical treatment.