Tailoring structure and morphology during additive manufacturing of metallic components

Sammanfattning: The work described in this thesis explores the use of laser process parameters to functionalize the material properties by the control of microstructure and optimization of morphology in components by selective laser melting. The microstructure in amorphous and crystalline metallic alloy systems is influenced by changing the laser power density and scanning strategies respectively. A combination of X-ray/neutron diffraction and optical/electron microscopy is used to evaluate the microstructure and phase formation in SLM components. The influence of the microstructure on the mechanical properties of as-printed samples was investigated using hardness and uniaxial tensile testing methods. To begin with, the process parameters for selective laser melting of a Zr-based bulk metallic glass Zr59.3Cu28.8Al10.4Nb1.5 (trade name AMLOY-ZR01) are developed to obtain high density and crack-free bulk components. The influence of oxygen on the thermal stability and crystallization pathway in AMLOY-ZR01 was found to be significant in determining the formation of metastable crystalline phases within the amorphous matrix. It was also shown that the mechanical properties in AMLOY-ZR01 can be influenced by changing the amount of crystalline phases formed within the amorphous matrix.  This was achieved by changing the laser power density during the SLM process. The alloy composition was also investigated for its biocompatibility, and the cell-material interactions under in-vitro test conditions showed no cytotoxic effect. These findings demonstrate that AMLOY-ZR01 is a promising candidate for orthopedic bio-implant applications. The latter half of this work demonstrates the influence of microstructure and crystallographic texture on the mechanical properties of 316L SS. This was achieved by changing the "laser scanning methodology" during the SLM process and a correlation between the applied scanning methodology and structure-property relation was identified.  A single crystalline-like texture can be obtained using a bi-directional scanning methodology, whereas a fiber texture is achieved when rotating the laser scan vectors by 67° to melt consecutive powder bed layers. The mechanical properties of 316L SS are influenced by the type of laser scan used to fabricate the components, as it dictates the final grain orientation within the SLM samples. It is also shown that the scanning patterns can be altered during the SLM process to create position-specific crystallographic grain orientation within the component. This opens up the possibility to fabricate functionally graded components which contain a spatial variation in composition and/or microstructure for the specific purpose of controlling material properties. Finally, the functionalization of material properties through design of components by additive manufacturing was demonstrated by fabricating waveguides with the specific geometries.