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Additive manufacturing through selective laser melting and directed energy deposition of 316L stainless steel: effect of process parameters on mechanical properties

Grant number: 19/01829-5
Support type:Scholarships in Brazil - Doctorate
Effective date (Start): May 01, 2019
Effective date (End): March 31, 2022
Field of knowledge:Engineering - Materials and Metallurgical Engineering
Principal Investigator:Piter Gargarella
Grantee:Gustavo Figueira
Home Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
Associated research grant:16/11309-0 - The study, development and application of a hybrid process: Additive Manufacturing (AM) plus High Speed Machining/Grinding (HSM/G), AP.TEM

Abstract

The manufacturing processes where the product is obtained layer by layer are called Additive Manufacturing (AM) processes. Among the AM processes for metallic materials, the Selective Laser Melting (SLM) and Direct Energy Deposition (DED) may be highlighted. In case of SLM, a laser beam melts locally regions of a powder bed previously deposited and in case of DED, the powder is also melted by the laser beam during flight, being deposited right afterwards. There are several parameters to control those processes, such as raw materials' properties, beam power, scanning speed and strategy, hatching and building direction. Any variation of those parameters can induce microstructural changes and modify the product properties, mainly the mechanical properties that are sensibly affected by the way the product is built. For example, some conditions of scanning strategy and building direction can lead to excessive anisotropy, which is deleterious to the mechanical properties. By the other hand, laser power and scanning speed control the cooling rate. The high cooling rate might induce high accumulated residual stresses, which causes an undesirable warping of the product. These examples demonstrate how important it is to understand how the different parameters affect the mechanical properties of the obtained product, considering especially components to critical applications, such as gas turbine blades, molds and dies. Among the most studied and accepted materials for those processes, one can find the 316L stainless steel. This steel generally forms a dendritic-like austenitic microstructure by conventional processes, but it has been observed the formation of a cellular biphasic (austenite and ferrite) microstructure for AM processes. The 316L steel is widely used in furnace components, heat exchangers, jet engines, evaporators and other equipment for chemical, pharmaceutical and naval industries. Although this steel has been used in AM processes, a systematic study about the influence of different parameters on its mechanical properties, mainly fracture toughness, needs to be carried out. Considering this scenario, the aim of the present project is to realize a systematic evaluation of the impact of process parameters on the mechanical and metallurgical properties of 316L stainless steel obtained by SLM and DED, comparing the results for both processes. Samples will be manufactured with different process parameters (beam power, scanning speed and strategy, hatch spacing and building direction) using a commercial powder. The whole analysis will be conducted following a Design of Experiments (DoE) methodology. Samples will have their microstructure characterized through X-Rays Diffraction (XRD), Optical Microscopy (OM), Scanning (SEM) and Transmission (TEM) Electron Microscopy, Electron Backscattered Diffraction (EBSD) and chemical analysis by Energy-Dispersive X-Ray Spectroscopy (EDS) and Chemical Analytic techniques. The mechanical properties which will be evaluate are tensile strength and fracture toughness. The obtained results for SLM and DED samples will be correlated and the influence of different process parameters on the 316L steel mechanical properties will be comprehended. (AU)