Abstract
Powder Bed Fusion–Laser Beam (PBF–LB) processing of magnesium (Mg) alloys is gaining increasing attention due to the possibility of producing complex biodegradable implants for improved healing of large bone defects. However, the understanding of the correlation between the PBF–LB process parameters and the microstructure formed in Mg alloys remains limited. Thus, the purpose of this study was to enhance the understanding of the effect of the PBF–LB process parameters on the microstructure of Mg alloys by investigating the applicability of computational thermodynamic modelling and verifying the results experimentally. Thus, PBF–LB process parameters were optimized for a Mg WE43 alloy (Mg-Y3.9wt%-Nd3wt%-Zr0.5wt%) on a commercially available machine. Two sets of process parameters successfully produced sample densities >99.4%. Thermodynamic computations based on the Calphad method were employed to predict the phases present in the processed material. Phases experimentally established for both processing parameters included α-Mg, Y2O3, Mg3Nd, Mg24Y5 and hcp-Zr. Phases α-Mg, Mg24Y5 and hcp-Zr were also predicted by the calculations. In conclusion, the extent of the applicability of thermodynamic modeling was shown, and the understanding of the correlation between the PBF–LB process parameters and the formed microstructure was enhanced, thus increasing the viability of the PBF–LB process for Mg alloys.
Highlights
Magnesium (Mg) alloys are among the lightest structural metals on the market today, demonstrating good specific mechanical properties and excellent biocompatibility [1]
An increase in O content around the surface as well as the bright spots appearing in the map is traces of the oxide polishing suspension (OPS) used for polishing can be seen when comparing the energy dispersive spectroscopy (EDS) maps for O and Si
The calculated property diagrams with the equilibrium phase fractions as a function of temperature are shown in Figure 6a–c for the compositions quoted in Table 3 for the powder and for the material printed with 120 J/mm3, and 60 J/mm3, respectively
Summary
Magnesium (Mg) alloys are among the lightest structural metals on the market today, demonstrating good specific mechanical properties and excellent biocompatibility [1] They are biodegradable and have mechanical properties close to those of bone, making them especially suitable for load-bearing bioresorbable orthopedic implants [2,3,4]. Autografts are the preferable option for treating large bone defects; their limited availability and associated donor site morbidity creates a need for artificial materials as a possible substitution [5,6]. A number of bioresorbable Mg implants based on the WE43 family of alloys has been developed They are limited to smaller devices such as the orthopedic screws based on powder extruded WE43 [21]. Especially Powder Bed Fusion–Laser Beam (PBF–LB) processing, could expand the possible applications of biodegradable Mg alloys to include patientspecific implants for improved healing of large bone defects
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