Duplex stainless steels have a large number of industrial applications and may replace high cost materials, especially in chloride-containing environments like seawater in off-shore platforms due to their high mechanical properties and good corrosion resistance. The influence of the ferrite content on the performance of duplex stainless steels in these corrosive environments is not well known. For the present paper, new superduplex stainless steels with ferrite between 30 and 60% were developed and their microstructure and corrosion resistance were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests in NaCl 3.5% (wt %) at 26°C and 78°C. The results obtained at 26°C showed that the pitting potential (E pitt ) is little affected by the ferrite content, but for the materials with higher ferrite it was possible to observe an increase in the repassivation potential with a decrease in the corrosion potential and passive currents due to the presence of more resistive passive films. Tests performed at 78°C indicated a high decrease in the E pitt for all the samples, independently of the ferrite percentage, although maintaining superiority in higher ferrite content. Alloys with a 55% ferrite phase content, i.e. less dependent of Ni element, present a superior performance of corrosion resistance.
Background
Implants or implantable devices should integrate into the host tissue faster
than fibrous capsule formation, in which the design of the interface is one
of the biggest challenges. Generally, bioactive materials are not viable for
load-bearing applications, so inert biomaterials are proposed. However, the
surface must be modified through techniques such as coating with bioactive
materials, roughness and sized pores. The aim of this research was to
validate an approach for the evaluation of the tissue growth on implants of
porous alumina coated with bioactive materials.
Methods
Porous alumina implants were coated with 45S5 Bioglass® (BG) and
hydroxyapatite (HA) and implanted in rat tibiae for a period of 28 days. Ex
vivo resections were performed to analyze osseointegration, along with
histological analysis, Scanning Electron Microscopy with Energy Dispersive
X-Ray spectroscopy (SEM-EDX) line scanning, radiography and biomechanical
testing.
Results
Given that the process of implant integration needs with the bone tissue to
be accelerated, it was then seen that BG acted to start the rapid
integration, and HA acted to sustaining the process.
Conclusions
Inert materials coated with bioglass and HA present a potential for
application as bone substitutes, preferably with pores of diameters between
100 μm and 400 μm and, restrict for smaller than 100 μm, because it prevents
pores without organized tissue formation or vacant. Designed as functional
gradient material, stand out for applications in bone tissue under load,
where, being the porous surface responsible for the osseointegration and the
inner material to bear and to transmit the loads.
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