Plasma electrolytic modification of commercial titanium
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BELKIN, V., KUSMANOV, S., DYAKOV, I., BELKIN, Pavel. Plasma electrolytic modification of commercial titanium. In: Materials Science and Condensed Matter Physics, Ed. 7, 16-19 septembrie 2014, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2014, Editia 7, p. 299.
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Materials Science and Condensed Matter Physics
Editia 7, 2014
Conferința "Materials Science and Condensed Matter Physics"
7, Chișinău, Moldova, 16-19 septembrie 2014

Plasma electrolytic modification of commercial titanium


Pag. 299-299

Belkin V., Kusmanov S., Dyakov I., Belkin Pavel
 
Kostroma State University
 
Disponibil în IBN: 19 martie 2019


Rezumat

This report is devoted to feature of plasma electrolytic treatment (PET) of commercial titanium including the study of current-voltage and temperature-voltage characteristics of the processing, the analysis of the phase composition and structure of the surface layer, as well as its corrosion behavior.  Cylindrical samples (diameter 20 mm and height 10 mm) were subjected to PET. The electrolyte was an aqueous solution of ammonium chloride (5–15 wt. %) with addition of ammonia (5 wt. %) or glycerol (10 wt. %). It was found that the maximum temperature of PET is reached at the lower voltage in contradistinction to the steels treatment because of increase of the system conductivity.  Anode PET leads to always the formation of a surface oxide layer contained micropores to 100 nm. The phase composition of the layer corresponds of rutile TiO2 with the use of solution ammonium chloride or TiO in the case of addition of ammonia to the initial electrolyte. In this case, nitrogen diffusion through the oxide layer is observed. It is leads to formation of the solid solution with microhardening up to 2.2 GPa (initial microhardness is 1.4 GPa). It can be assumed that the penetrability of the oxide layer is insufficient for the formation of the nitride zone.  Diffusion layer thickness has maximum after nitriding at 850°C during 5 minutes and increases parabolically with treatment time that points out to the constant nitrogen concentration on the sample surface.  Titanium dissolution is found to prevail over oxidation at 210 V and ammonium chloride content of 10 wt. %, that is, mass loss of the sample takes place. Mass gain is observed when voltage is increased to 260 V or ammonium chloride concentration rises to 15 wt. % that indicates to dominance of oxidation over dissolution. Observed regularity is associated with oxidation intensification when sample temperature is increased. Nonlinear dependence of the mass loss on the time is also found that may be evidence about exfoliation of the oxide layer part during treatment.  Positive influence the oxide layer on the electrochemical behavior of commercial titanium after PET treatment in the glycerol electrolyte is shown. Dependence of the corrosion current density on the oxide layer thickness is established. This dependence is determined by the temperature, treatment time and cooling conditions of the workpiece. Processing temperature increase from 800 to 900oC with following quenching and corresponded the rise of the oxide layer thickness decrease significantly the corrosion current density. Under this condition the oxidation dominates over the anode dissolution therefore the corrosion resistance decrease may be associated with degradation of the oxide layer, porosity increase, cracks formation, etc.