EFFECT OF ELECTROLYTE COMPOSITION ON SURFACE PROPERTIES OF - AND -TITANIUM ALLOY AFTER ITS PLASMA ELECTROLYTIC CARBURIZING

DOI: 10.6060/tcct.20165911.5416
Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2016. V. 59. N 11. P. 100-105

This study is devoted to enhance of wear and corrosion resistance of titanium alloy using plasma electrolytic carburizing in different electrolytes. An X-ray diffractometer and an optical microscope were used to characterize the phase composition of the modified layer and its surface morphology. The hardness of the treated and untreated samples was meas-ured using a microhardness tester. The wear of the samples was measured using ball-disk friction under lubricated and dry testing conditions. The effects of electrolyte composition on corrosion resistance of the PEC samples were examined by means of potentiodynamic polar-ization in a solution of sodium sulfate. Anode carburizing of VT6 titanium alloy in electro-lytes containing ammonium chloride, acetone, glycerol, sucrose, and ethylene glycol results in formation of surface layer with TiO2 (rutile) and solid solution of carbon in titanium. The solid solution formation is confirmed by increase in the micro hardness of diffusion layer. Maximal micro hardness of carburized titanium alloy (450 HV) is reached in the glycerol-based electrolyte after treatment at 900 °С during 5 min. Similar value of micro hardness is observed for the carburizing in acetone-based electrolyte, the lower one for electrolyte con-taining sucrose. The minimal micro hardness is obtained using the ethylene glycol-based so-lution. This series of electrolytes are corresponded to their saturation ability. The positive ef-fect of the oxide layer on the corrosion resistance of the material in Ringer's solution is shown. The most decrease in the corrosion current density (2.5 times) and shift of corrosion potential to positive direction from –0.277 V to –0.118 V were established for carburizing in the acetone-based electrolyte owing to protective action of oxide layer. The shift of corrosion potential and reduction of corrosion current density are observed after carburizing in electro-lytes containing glycerol or ethylene glycol in a lesser degree. The use of sucrose-based elec-trolyte leads to increase in the corrosion current density. The results of wear lubricant testing show that wear resistance of titanium samples enhances after carburizing in all electrolytes. The most diminishment of weight loss after testing from 28 mg to 0.3 mg is measured for treatment in electrolyte containing ethylene glycol. Similar value of weight loss is obtained for the carburizing in sucrose-based electrolyte (0.5 mg) and electrolytes containing glycerol (0.9 mg) or acetone (0.7 mg). No correlation between the wear rate and surface micro hardness was found. We can suppose that increase in the wear resistance is associated not only with hardness of diffusive sub-layer but also with good running-in of external layer enriched by ti-tanium oxide.

Key words: alpha- and beta-titanium alloy, plasma electrolytic treatment, micro hardness, wear and corrosion resistance

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2016, Т. 59, № 11, Стр. 100-105

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