The effects of deposited layer thickness on the material and geometrical properties of L-DED processed AISI D2 tool steel

Abstract

ABSTRACT This research focuses on the influences of the deposited layer thickness upon the material characteristics, dimensional accuracy, and also the surface roughness of AISI D2 tool steel processed by laser directed energy deposition (L-DED); while layer thickness was varied, the remaining L-DED system parameters were retained at fixed values. After laser deposition, the D2 specimens were assessed without applying any subsequent machining steps. Sample dimensional accuracy was assessed through both manual measurement and computational methods, with the latter using confocal laser scanning microscopy (CLSM). It was shown that increasing the layer thickness decreases the extent of sample overbuilding. The use of lower layer thicknesses reduced the top surface roughness. However, a monotonic effect was not observed for side surface roughness in relation to the deposited layer thickness. In addition, the microstructures of the L-DED samples were evaluated using a combination of scanning electron microscopy (SEM) with associated energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). It is shown that a dendritic morphology is formed for the L-DED processed samples, with a columnar grain structure. Furthermore, the primary crystalline phase generated with the dendritic structure was found to be austenite. The indentation hardness values for the L-DED fabricated parts were noted to be larger for thinner deposited layer thicknesses.