Microstructural, tribological and corrosion aspects of thermally sprayed Ti–Cr–Si coatings

Abstract

This paper is a first report of thermally sprayed Ti 60Cr 32Si 8 (at.%) alloy coating. It has been reported previously that such an alloy assumes quasicrystallinity in the presence of oxygen, when made to undergo rapid quenching. In these cases, either TiO or SiO 2 is used as an ingredient in the alloy so that it can act as a source of oxygen. This paper describes an attempt to produce a quasicrystal by thermally spraying the alloy in air, i.e., in the presence of oxygen, either by flame or atmospheric plasma spraying. The spray parameters for both the processes have been varied in the experiment in a wide range. A vacuum plasma sprayed coating served as the reference. This investigation includes a detailed study of the microstructure and phases by optical microscopy, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), microhardness and porosity. An estimate of the composition of the coating has been done using Glow Discharge Optical Emission Spectroscopy (GDOES).The parametric variations have been correlated with the coating microstructure. The tribological properties of these coatings were studied using a ball on disc reciprocating tribometer. The corrosion properties of one representative coating have been studied using potentio-dynamic method and the corrosion response has been correlated with the microstructure. It has been found in the study that there is a likelihood of obtaining quasicrystal by atmospheric plasma spraying of this alloy under favorable parametric conditions. Some of the coatings produced in this study have very good wear resistance. The corrosion property of the coating under study has been dominated by microcracks. During corrosion testing the corroding media has been found to percolate through these cracks and attack the substrate.