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Title: Selective laser melting of SAM 1651, an iron-based bulk metallic glass
Author: Manai, Navid
ISNI:       0000 0004 7228 3601
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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Fe-based bulk metallic glasses, have been shown to demonstrate exceptional strength, hardness, soft magnetic properties, high electrical resistivity, high corrosion resistance and large glass forming ability. They also have low production costs, since the main constituent element is Iron which in comparison to other bulk glass forming alloys are much cheaper to manufacture. Hence, various magnetic and structural applications have been suggested for parts made out of these alloys. Selective laser melting process as an additive manufacturing route was utilised to circumvent the issue of size and shape limitation in fabrication of parts out of bulk metallic glasses. Specimens of the SAM1651 Fe-based BMG alloy were fabricated to investigate the effects of different SLM processing parameters on the microstructure of these parts. They were examined through optical microscopy and X-ray diffraction and the influence of point distance, hatch spacing, layer thickness, laser power, exposure time and substrate temperature was individually investigated to demonstrate how they result in different amounts of porosity, lack of fusion defects, cracking and crystallization in the fabricated samples. Through utilising the results of a finite element analysis, it was shown that a combination of the occurring thermal gradient and cooling rate in individual melt pools produced as a result of using different laser power and exposure time values can determine and predict the existence and relative amount of crystallization in these specimens. It was also demonstrated that through increasing the temperature of the substrate, the amount of cracking occurring in the microstructure of the specimens can be reduced, which is due to decreasing the influence of the thermal gradient mechanism through decreasing the amount of thermal gradient present in the heat affected zone of individual melt pools. Furthermore, normalized energy density input was shown to be an appropriate indicator to predict the level of defect formation and crystallization relatively and therefore a processing map was constructed which consequently presented a processing window for fabrication of specimens by selective laser melting out of SAM1651 BMG alloy. Using the processing parameters in this processing window, samples with complex shapes were manufactured to demonstrate the feasibility of their fabrication with amorphous microstructure and minimal defect formation. Since the making of specimens out of SAM1651 alloy, with no cracking and porosity, was unsuccessful, future approaches were suggested in order to manufacture fully amorphous dense parts with no cracking using the SLM process and glass forming alloys. Also, further modelling was proposed to investigate the effect of hatch spacing, layer thickness and point distance values on the residual thermal stresses occurring in the selective laser melting process.
Supervisor: Todd, Iain ; Mark, Rainforth Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available