Abstract:The influence of intermetallic microstructure on the degradation of Mg-5Nd alloy with different heat treatments was investigated via immersion testing in DMEM + 10 pct FBS under cell culture conditions and subsequent microstructural characterizations. It was found that T4 heat-treated sample had the poorest corrosion resistance due to the lack of finely dispersed precipitates inside grains, continuous lamellar particles along grain boundaries and outer Ca-P layer, and to the formation of a loose corrosion prod… Show more
“…Mg alloys generally have poor corrosion resistance due to the low electrochemical stability of the Mg matrix, the strong cathodic activity of the secondary phases present, refs. [10][11][12], and the limited stability of the MgO surface film in aqueous solutions [13][14][15]. The solid solution of yttrium (Y) decreases the electrochemical activity of the Mg matrix and stabilizes the surface through the formation of Y 2 O 3 [16][17][18].…”
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-Y3.9 wt%-Nd3 wt%-Zr0.5 wt%) 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.
“…Mg alloys generally have poor corrosion resistance due to the low electrochemical stability of the Mg matrix, the strong cathodic activity of the secondary phases present, refs. [10][11][12], and the limited stability of the MgO surface film in aqueous solutions [13][14][15]. The solid solution of yttrium (Y) decreases the electrochemical activity of the Mg matrix and stabilizes the surface through the formation of Y 2 O 3 [16][17][18].…”
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-Y3.9 wt%-Nd3 wt%-Zr0.5 wt%) 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.
“…The β -Mg 12 Nd is a metastable phase, and its amount increases with the Nd levels, based on the statistical results mentioned above. Other reports [ 18 , 44 , 45 ], however, indicated that the β e -Mg 41 Nd 5 phase could also be detected in the as-extruded Mg–Nd alloys and at high temperatures. Actually, the sequence and type of precipitation are affected by the alloy state, solidification condition, heat treatment process, etc.…”
The microstructure and precipitate evolution of as-cast Mg–Nd alloys with different contents of Nd was investigated via experimental and simulation methods. The research showed that the as-cast microstructure of Mg–Nd alloy consisted of α-Mg dendrites and the intermetallic phases. A metastable β phase precipitated, followed by α-Mg dendrites that could be confirmed as Mg12Nd by X-ray diffraction (XRD) analysis. The amount of β-Mg12Nd presented a rising trend with increasing Nd additions. In addition, the tertiary phase was also observed in as-cast Mg–Nd alloy when Nd content was greater than 3 wt.%, which precipitated from the oversaturated α-Mg matrix. The tertiary phase should be β1-Mg3Nd, which is also a metastable phase with a face-centered cubic lattice. However, it is a pity that the tertiary phase was not detected by the XRD technique. Moreover, an effective cellular automaton (CA) model was explored and applied to simulate the time-dependent α-Mg/β1-Mg3Nd eutectic growth. The simulated results of α-Mg/β1-Mg3Nd eutectic growth in Mg-3Nd presented that the growth of α-Mg dendrites was accompanied by the nucleation and growth of β1-Mg3Nd precipitates and eventually formed a eutectic structure. The eutectic morphologies for Mg–Nd system alloys with different Nd contents were also simulated using the proposed model, and the results revealed that α-Mg dendrite was a refinement, and the amount of α-Mg/β1-Mg3Nd eutectic was promoted, with increasing Nd content.
“…Extensive efforts have been devoted to improving the corrosion resistance of Mg through microstructural and surface modifications [42]. The microstructural approach starts with fabricating high purity Mg or alloying it with various elements such as zinc (Zn) [43,44], calcium (Ca) [45], manganese (Mn) [46], lithium [47], or rare-earth elements [48][49][50]. Then the Mg is plastically deformed into desired geometries through extrusion, rolling, forging, or drawing.…”
Porous Magnesium (Mg) is a promising biodegradable scaffold for treating critical-size bone defects, and as an essential element for human metabolism, Mg has shown sufficient biocompatibility. Its elastic moduli and yield strengths are closer to those of cortical bone than common, inert metallic implants, effectively reducing stress concentrations around host tissue as well as stress shielding. More importantly, Mg can degrade and be absorbed in the human body in a safe and controlled manner, thereby reducing the need for second surgeries to remove implants. The development of porous Mg scaffolds via conventional selective laser melting (SLM) techniques has been limited due to Mg’s low boiling point, high vapor pressures, high reactivity, and non-ideal microstructures in additively manufactured parts. Here we present an exciting alternative to conventional additive techniques: 3D weaving with Mg wires that have controlled chemistries and microstructures. The weaving process offers high throughput manufacturing as well as porous architectures that can be optimized for stiffness and porosity with topology optimization. Once woven, we dip-coat the weaves with polylactic acid (PLA) to enhance their strength and corrosion resistance. Following fabrication, we characterize their mechanical properties, corrosion behavior, and cell compatibility in vitro, and we use an intramuscular implantation model to evaluate their in vivo corrosion behavior and tissue response.
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