Tribological properties and milling performance of HSS-Co-E tools with fluorinated surfactants-based coatings against Ti-6Al-4V

This research focuses on performances of fluorinated surfactants-based coatings, which deposited on HSS-Co-E by sol-gel dip coating treatment. Fluorinated surfactants used in coating treatment consist of perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl phosphonic acids (PFPAs). Compositions of coatings were identified by Fourier Transform Infrared spectroscopy (FTIR), and surface morphologies were investigated by atomic force microscopy (AFM). Pin-on-disc frictional tests were carried out at room temperature and 300 °C, using uncoated and coated HSS-Co-E as pins and Ti-6Al-4 V as discs. Finish milling tests were carried to evaluate the performance of uncoated and coated tools by measuring cutting force, cutting temperature. Tool wear mechanisms were analyzed using scanning electron microscopy (SEM). Results showed that (1) Coated pins showed a much lower coefficient of friction (COF), and contact surfaces of coated pins were smoother with less titanium adhesive on it after tests. (2) Abrasive wear, adhesive wear and micro chipping were the main wear mechanisms of these two kinds of tools. Fluorinated surfactants acted as solid lubricants and protected the substrate, which obviously decreased adhesion and oxidation. The tool life of coated tool extended 50% compared with the uncoated one. (3) Surface integrity was analyzed by surface roughness and morphology. Surface roughness of plain surface machined by coated tools was much smaller than uncoated ones. In all, fluorinated surfactants-based coatings have the ability of reducing friction, anti-wear and smoothing surfaces due to their high chemical stability, high thermal stability and directional absorption on the substrate.