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Abstract
This paper describes ways of improving the tribological properties of the Ti-6Al-4V titanium alloy at room and elevated temperatures by electrophoretic deposition of Al2O3/PEEK708 composite coatings and post-heat treatment. The microstructure of the coating components and the coatings was examined by scanning and transmission electron microscopy as well as x-ray diffractometry. The influence of cooling rate after heating of the coated alloy on the PEEK structure and coating surface topography was investigated. It was found that slow cooling with a furnace produced a semi-crystalline structure, whereas fast cooling in water generated an amorphous polymer structure. The semi-crystalline coatings exhibited a more developed surface topography than the amorphous ones. The coatings with a semi-crystalline structure revealed higher scratch resistance than the amorphous ones. The corrosion resistance of the uncoated and coated specimens was examined using electrochemical techniques in a 3.5 wt.% NaCl aqueous solution. Both coatings increased the corrosion resistance of the alloy. The friction and wear properties of the coated specimens against an alumina ball in dry sliding contact at room temperature and elevated temperatures of 150 and 260 °C at ball-on-disk were examined. Both amorphous and semi-crystalline coatings increased the wear resistance and decreased the friction coefficient of the titanium alloy at room temperature. In addition, the semi-crystalline coating was also very effective in improving the titanium alloy’s tribological properties at elevated temperatures. The obtained results clearly show that the composite alumina/PEEK coatings are promising for tribological applications in mechanical engineering.
Highlights
Polyetheretherketone (PEEK) is an organic, polyaromatic linear thermoplastic polymer, excellent for applications where thermal, chemical and combustion properties are critical to performance (Ref 1)
Analysis of the selected area electron diffraction (SAED) and XRD patterns taken from the Al2O3 particles revealed the presence of a-Al2O3 phase (SAED and grazing incidence x-ray diffractometry (GIXRD) patterns in Fig. 1(a) and in 2, respectively), while transmission electron microscopy (TEM)-EDS microanalysis confirmed the presence of Al and O only
The highest wear was found for the semi-crystalline Al2O3/ PEEK708 coating after the test at 260 °C, and its specific wear rate Wv = 33 9 10À6 mm3/Nm was seven times greater than Wv = 4.49 9 10À6 mm3/Nm for the semi-crystalline PEEK708 coating after friction in the same conditions (Ref 19)
Summary
Polyetheretherketone (PEEK) is an organic, polyaromatic linear thermoplastic polymer, excellent for applications where thermal, chemical and combustion properties are critical to performance (Ref 1). In recent years, it has been widely used in a variety of structural and insulation applications in different environments, including moisture, due to its high chemical. Several coating techniques have been developed to deposit PEEK-based composite coatings on metallic substrates, e.g., electrostatic powder spray (Ref 8), printing method (Ref 9-11) and electrophoretic deposition (EPD) (Ref [12-15]). EPD is of growing importance in the development of composite coatings, due to the high flexibility of co-deposition of organic polymers and inorganic ceramic particles on metallic substrates (Ref [17, 18])
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