Characterization of Powder Metallurgy Processed Pure Magnesium Materials for Biomedical Applications

Abstract

Magnesium with its mechanical properties and nontoxicity is predetermined as a material for biomedical applications; however, its high reactivity is a limiting factor for its usage. Powder metallurgy is one of the promising methods for the enhancement of material mechanical properties and, due to the introduced plastic deformation, can also have a positive influence on corrosion resistance. Pure magnesium samples were prepared via powder metallurgy. Compacting pressures from 100 MPa to 500 MPa were used for samples' preparation at room temperature and elevated temperatures. The microstructure of the obtained compacts was analyzed in terms of microscopy. The three-point bending test and microhardness testing were adopted to define the compacts' mechanical properties, discussing the results with respect to fractographic analysis. Electrochemical corrosion properties analyzed with electrochemical impedance spectroscopy carried out in HBSS (Hank's Balanced Salt Solution) and enriched HBSS were correlated with the metallographic analysis of the corrosion process. Cold compacted materials were very brittle with low strength (up to 50 MPa) and microhardness (up to 50 HV (load: 0.025 kg)) and degraded rapidly in both solutions. Hot pressed materials yielded much higher strength (up to 250 MPa) and microhardness (up to 65 HV (load: 0.025 kg)), and the electrochemical characteristics were significantly better when compared to the cold compacted samples. Temperatures of 300 • C and 400 • C and high compacting pressures from 300 MPa to 500 MPa had a positive influence on material bonding, mechanical and electrochemical properties. A compacting temperature of 500 • C had a detrimental effect on material compaction when using pressure above 200 MPa.

Improvement of AZ91 Alloy Corrosion Properties by Duplex NI-P Coating Deposition

“…Moreover, in the presence of Cl − ions in the solution, this layer is being constantly disrupted. As a result, MgCl 2 soluble in the water solution (corrosive environment) is formed (Equation (4)) [3,21,31]. The formation of MgCl 2 disrupts the compactness of protective Mg(OH) 2 layer.…”

“…This model describes the behavior of uncoated AZ91 alloy exhibited in 0.1 M NaCl solution for 5 min. The model corresponds to the formation of a thin layer of Mg(OH) 2 on the metallic surface of AZ91 alloy [31]. However, formed Mg(OH) 2 layer is not completely uniform due to its porous nature and is also damaged by cracks, and so the metallic surface of AZ91 alloy was in contact with the corrosive environment [3,21].…”

“…In the case of the EC model shown in Figure 7c, R 1 is the resistance of the solution, R 2 is the resistance against the charge transfer between the electrolyte (NaCl solution) and upper high-phosphorus layer of the Ni-P coating, Q 2 is the capacity of double-layer NaCl solution/ Ni-P coating, R 3 is the resistance against the charge transfer between high-phosphorus and low-phosphorus layers of the Ni-P coating, and Q 3 is the corresponding capacity. The resulting polarization resistance value is given by Equation (5) [31].…”

“…The EC model in Figure 7b was used for the analysis of the Nyquist plot for 25 µm thick Ni-P coating on the AZ91 alloy after 168 h in 0.1 M NaCl solution. The resulting polarization resistance value is given by the relation in Equation 6 [31].…”

Biodegradable Metals

“…By contrast, ground samples of AZ61 in HBSS+ solution displayed R p values which are higher than those obtained with polished samples. The effect of processing parameters on mechanical properties and corrosion degradation of pure Mg in terms of powder metallurgy technology was evaluated by Matej Brezina et al [9]. They found that cold-compacted samples were quite brittle, with reduced strength (up to 50 MPa) and accelerated corrosion degradation, as compared to hot-pressed samples that yielded much higher strength (up to 250 MPa) and significantly improved corrosion resistance.…”