SLM additive manufacturing of Alloy 718: effect of process parameters on microstructure and properties
Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
Selective laser melting (SLM) is one type of the Additive Manufacturing (AM) processes as a novel technique to fabricate 3D components in a layer-upon-layer style with less need to post-processing. In the SLM process, samples can be designed by computer-aided design (CAD) software, and produced in any shape. Compared to other AM processes, SLM method presents several advantages, one of which is manufacturing of complex-shape samples with very high accuracy. In SLM process, the microstructure characteristics and mechanical properties can be controlled by changing process parameters. Therefore, SLM process can be used to manufacture many industrial components, e.g. combustion chambers, medical components, and nuclear reactors.
In the present survey, SLM process with different process parameters is used to create 25 cubic samples from Alloy 718 with 10×10×10 mm3 dimension. The as-fabricated samples are cut into two subsets in order to study the influence of two main process parameters including point distance and laser exposure time on the microstructure and properties. The samples are hot mounted to examine the normal reference planes (parallel to build direction). Microstructural characterization has been carried out using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Energy Dispersive spectroscopy (EDS) and X-ray Diffraction (XRD). Microstructure in the as-fabricated section of sam-ples illustrated highly dendritic growth parallel to build direction in the normal reference planes. The microstructures present some changes within the build direction; the top layers show coarser columnar dendrites compare to the bottom layers with slimmer columnar dendrites owing to a higher cooling rate. SEM/EDS analysis show the presence of some fine phases e.g., Laves and metallic carbides in the γ-matrix and verify the segregation of Nb element in all 25 test samples due to high cooling rate. The porosity content of samples is measured using two methods of image analysis and point counting. The effect of laser energy input, which comprises the effect of laser exposure time and point distance is investigated on the total porosity (round and irregular pores). It is observed that the round porosity content is lower than irregular porosity and the minimum amount of total porosity is around 0.07 vol. % gained at laser energy input of about 265 J/mm3. Mechanical properties is represented by measuring the Micro-Vickers hardness (HV). The microhardness of as-fabricated samples shows a dependency on the laser energy input on the normal reference plane in all the samples. The average microhardness in the as-fabricated samples varies from 291 to 339 HV0.5.
Place, publisher, year, edition, pages
2016. , 46 p.
selective laser melting, Alloy 718, microstructure, porosity, mechanical properties
IdentifiersURN: urn:nbn:se:hv:diva-9806Local ID: EXP800OAI: oai:DiVA.org:hv-9806DiVA: diva2:955575
Subject / course