Evaluation of the Effect of Surface Preparation on Corrosion Properties of Cerametallic Composites in Titanium Matrix
Abstract
Metal matrix composites reinforced ceramic particles, are widely used in industry, wherever high resistance to abrasive wear, erosion and corrosion is necessary. Cermets, in which titanium carbide (TiC) is used as reinforcing phase, are particularly interesting for improving the strength, stiffness and wear resistance, especially at elevated temperatures. The paper presents the results of corrosion tests of titanium matrix composite reinforced nc-TiC particles, at different stages of surface preparation: grinding, polishing, electropolishing and oxidation in the furnance. Measurements of potentiodynamic polarization curves in 3% NaCl solution were performed. The results have showed the negative impact of the nanocrystalline TiC strengthening phase on corrosion resistance of composites. It was also found that electropolishing treatment is the most preferred way to prepare the surface for titanium as well as TiC reinforced composites.
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Introduction
Titanium (Ti) and its alloys are widely used in aviation, aerospace as well as chemical industries. This is influenced by their excellent properties such as high strength, adequate rigidity and high corrosion resistance [1]. However, titanium has reduced abrasion resistance, which is a significant disadvantage when used in environments where intense abrasion and erosion phenomena occur. One way of overcoming these limitations, which is presented in this work, is the use of hard ceramic materials, being the reinforcing phase in the resulting composites.
In conventional composites in order to improve the anti-abrasive properties ceramic powders of micrometric size, such as WC, TiC, TiN, SiC, TiB2 are used [2,3]. However, the use of large ceramic particles causes that they remain unmelted or only partially melted in the processes of composites manufacturing. Additionally, a low wettability between the ceramic particles and the metal results in formation of a limited number of chemical bonds between the matrix and the reinforcing phase, and this may lead to deterioration in mechanical properties [4]. Therefore, now many research centers use powders of nanometric size as a reinforcing phase in the processes of composites manufacturing [5-7].
Conclusion
The results of testing samples of titanium and TiC/Ti nanocomposites showed that the most favorable properties from the point of view of corrosion resistance after mechanical polishing treatment showed the composite containing 99 vol% Ti + 1 vol% TiC. This sample was characterized by a surface with the fewest defects.
Grinding is the best procedure to prepare the titanium surface compared to the composites, as indicated by the corrosion potentials and currents. In contrast, a passive layer on the surface of the composite containing 1 vol% of nc-TiC particles was characterized by the best stability.
After electropolishing the titanium sample shows the best values of potential and corrosion current. The polarization curves of the samples show large variations. In the anodic section the course of the curve indicates instability of the oxides layer on the surface of titanium. The passive layer on the surface of the composite containing 20 vol% of nc-TiC particles is characterized by the best stability.
After the anodic oxidation the samples of titanium and 1% TiC composite were characterized by comparable corrosion current densities and the lowest passivation current densities A conclusion section must be included and should indicate clearly the advantages, limitations, and possible applications of the paper. Although a conclusion may review the main points of the paper, do not replicate the abstract as the conclusion. A conclusion might elaborate on the importance of the work or suggest applications and extensions.