Magnesium (Mg)/hydroxyapatite (HA) (10 wt.% and 20 wt.%) composites were prepared by using pure Mg and as synthesized HA powders using the spark plasma sintering (SPS) method. The objective of the present study is to improve the corrosion resistance of spark plasma sintered Mg/HA composites and to ensure that the degradation time of these composites match with that of bone remodeling. Mg and HA powders were ball milled for 2 h and spark plasma sintered at a temperature of 475 °C and pressure of 40 MPa in vacuum. The sintered compacts were further treated by plasma electrolytic oxidation (PEO) in order to improve the corrosion resistance. The structural, microstructural and morphological studies were done using X-ray diffraction, optical microscopy and scanning electron microscopy, respectively. The corrosion resistance of as-sintered and PEO treated Mg/HA composites was studied by potentiodynamic polarization test in a 7.4 pH simulated body fluid (SBF) environment. The corrosion test results of as-sintered composites showed that the corrosion resistance decreases with the increase in percentage of HA in the composite. However, the PEO treated Mg/HA composites have shown delayed onset of degradation. Therefore, it can be hypothesized that the PEO treated Mg/HA composites would serve as bioactive and biodegradable orthopedic implant materials with low corrosion rates.
Thermal
spray coatings (TSCs) are widely utilized for limiting
degradation of structural components. However, the performance of
TSCs is significantly impaired by its inherent non-homogeneous microstructure,
comprising of splat boundaries, porosities, secondary phase-formation,
and elemental segregation. Herein, we report a simplistic approach
for significantly enhancing the corrosion resistance of TSCs. Ni–Cr–5Al
2
O
3
coatings were deposited on stainless steel using
high-velocity oxy-fuel technique. The microstructure of as-sprayed
coating showed significant inhomogeneities in the form of isolated
splats and elemental segregation. The microstructure of developed
coatings was modified using a novel processing technique, known as
stationary friction processing (SFP). The SFP treatment resulted in
complete refinement of coating microstructure with elimination of
splat boundaries and pores along with elemental homogenization. The
corrosion behavior of as-sprayed and SFP treated coating was evaluated
in 3.5% NaCl solution using potentiodynamic polarization and electrochemical
impedance spectroscopy. The SFP treatment reduced the corrosion rate
of as-sprayed coating by an order of magnitude. Long-time immersion
studies showed continuously decreasing impedance of the as-sprayed
coating due to the penetration of the electrolyte along the splat
boundaries. In contrast, impedance for the SFP treated coating increased
with the immersion time due to the removal of all microstructural
defects.
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