Friction coefficient and adhesion of the PLD formed Ti-B/Ti-Si-C coatings to steel substrates

Abstract

Ceramic, bilayer Ti-B/Ti-Si-C coatings produced by pulsed laser ablation of TiB2 and Ti[x]Si[y]C target (containing 92% of Ti[3]SiC[2] weight) on a substrate of AISI 316L (X2CrNiMo17-12-2 / 1.4404). The process for the preparation of coatings was carried out in vacuum (10[-2] Pa) using a beam of Nd: YAG laser having a wavelength λ = 266 nm. The morphology of coated samples surface was examined using scanning electron microscopy methods accompanied by the analysis of chemical composition by EDS. Chemical bonds were studied by Raman microspectroscopy in a low and high resolution modes. Ti-B/Ti-Si-C coatings deposited on steel substrates were continuous, thin and flat. Droplets of different diameter size were present on the top. EDS analysis showed the presence of Ti, Si and oxygen in the coatings. Raman spectra indicated complex nature of chemical bonds. The peaks at positions characteristic of TiSi, TiSi[2], Ti[5]Si[3], Ti[3]SiC[2], TiB[2] and TiO[2] were present. The friction coefficient determined for coated steel substrates in a scratch-test with diamond pin as counterpart did not exceed the value of 0.23, which was almost ¼ the value of the coefficient of friction for the diamonduncoated steel. Adhesion of coatings obtained by pulsed laser deposition method was not satisfying. Coatings were easily delaminated from steel substrates. Hard and brittle particles and droplets present in the scratch track significantly contributed to the increased wear rate of the tested coating-substrate system.