RESUMO
FeCoCrNi and FeCoNiCrMo0.2 high-entropy alloy powders were prepared by gas atomization. Two kinds of coatings were prepared on the surface of 304 stainless steel by laser cladding technology. The effect of Mo element on the microstructure of laser cladding FeCoCrNi coating and its corrosion behavior in 3.5 wt.% NaCl solution was investigated. Both FeCoCrNi and FeCoCrNiMo0.2 powders exhibit a single-phase FCC structure. Due to the remelting and multiple heat treatments during the preparation of the laser cladding coating, a small amount of σ and µ phases appeared in the FeCoCrNiMo0.2 coating. The microstructures of the two coatings from the bonding area to the top layer are planar, columnar and equiaxed grains, respectively. The addition of the Mo element causes the dendrite size in the middle region of the FeCoCrNiMo0.2 coating increases significantly and exhibits obvious orientation characteristics. FeCoCrNiMo0.2 coating has high corrosion potential (-0.01 VSHE) and low current density (0.94 × 10-7 A/cm2) in 3.5 wt.% NaCl solution, showing excellent corrosion resistance. The passivation film formed on corroded the FeCoCrNiMo0.2 coating contains high content of oxides of Cr and Mo. The addition of the Mo element enhances the compactness and pitting resistance of the passivation film.
RESUMO
The oxidation of the metal powder during the thermal spraying process usually leads to significant deterioration of the microstructure and performance of the coating. In order to isolate the metal powder from oxygen during the spraying process, the CoNiCrAlY-Al2O3 core-shell structured powder with Al2O3 as the shell was designed in this study. The influence of the core-shell structured powder on the microstructure and corrosion resistance of the HVOF coating has been studied in detail. The results show that the temperature field of the molten CoNiCrAlY powder during the spraying process is significantly changed by the Al2O3 shell. The poor deformability of the CoNiCrAlY-Al2O3 droplets leads to an increase in the porosity and unmelted particles of the coating. In addition, the significant difference is that the coating also maintains a high content of ß-NiAl phase. The lower oxide content in the CoNiCrAlY-Al2O3 coating indicates that the core-shell structured powder significantly inhibits the oxidation of the CoNiCrAlY core powder during the spraying process. The CoNiCrAlY-Al2O3 coating exhibits high corrosion potential, passive film resistance, charge transfer resistance, and low corrosion current density in 3.5 wt.% NaCl solution, indicating that the coating has excellent corrosion resistance.
RESUMO
OBJECTIVE: To investigate the detailed biomechanics of TiNi shape-memory sawtooth-arm embracing plate (TiNi SMA) by comparing with limited-contact dynamic compression plate (LC-DCP) and static interlocking intramedullary nail (SIiN), so as to provide theoretical evidence for clinical application. METHODS: Eight paired cadaveric femurs immersed in formaldehyde were harvested from eight specimens of adults. After making X-ray films and modeling midpiece transverse fracture, one side randomly was fixed by TiNi SMA (group A) and SIiN (group C) orderly, the other side was fixed by LC-DCP (group B). The axial compression, three-point bending (pressed from plate side and opposite side both of group A and group B, from inside of group C), and torsion were tested, and the stress shielding rate was compared. RESULTS: At every classified axial compression load, the strains of group A were greater than those of group B and group C (P < 0.05), the displacements of group A were greater than those of group B and group C (P < 0.05) except 100 N. At every classified three-point bending moment, the displacement of group A were greater than those of group B and group C pressed both from two sides, but there was no difference when pressing from two sides under the same load of group A (P > 0.05). At every torsion moment, the torsion angels of group A were greater than those of group B (P < 0.05), but equal to those of group C (P > 0.05). At 600 N of axial compression load, the stress shielding rates of groups A, B, C were 48.30% +/- 22.99%, 89.21% +/- 8.97%, 95.00% +/- 3.15%, respectively, group A was significantly less than group B and group C (P < 0.01). CONCLUSION: The anti-bending ability of TiNi SMA is weaker than LC-DCP and SIiN; the anti-torsion ability of TiNi SMA is weaker than SIiN, but TiNi SMA is a center-type internal fixation, the superior stress shielding rate and micromovement promote the stress stimulation of fracture, which makes it an ideal internal fixation device.
