Electrochemical Evaluation of a Discontinuously Reinforced TiC/Ni-20Cr Composite
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.68
Electrochemical Evaluation of a Discontinuously Reinforced TiC/Ni-20Cr Composite Rocio J. Gonzalez-Esquivel1, Carlos A. Leon-Patiño1*, Ricardo Galvan-Martinez2, Ena A. Aguilar-Reyes1 1 Instituto de Investigación en Metalurgia y Materiales, Universidad Michoacana de San Nicolás de Hidalgo, Av. Francisco J. Mujica S/N Ciudad Universitaria, Morelia 58030, Mich., México. *[email protected]
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ABSTRACT
The work focuses on the analysis of electrochemical corrosion in synthetic salt medium of the TiC/Ni-20Cr composite through the polarization curve technique at four exposure times (0, 6, 12 and 24 h). The composite was prepared by liquid infiltration of the liquid alloy into a porous body of TiC. It was found a continuous and homogeneous distribution of the reinforcing material in the interconnected matrix, having a residual porosity of 6.49 vol.%. According to the electrochemical results, in both samples the highest corrosion rate (CR) was obtained at 12 h exposure due to the rupture of the film of the corrosion products, allowing the interaction of chloride ions with the metal surface. The CR of the composite was slightly higher than that of the alloy at all exposure times, so that the presence of the reinforcing particles and the residual porosity reduce the corrosion resistance of the matrix in the composite. The mechanism of corrosion observed in the alloy and the composite was by pitting, however, the composite also presents crevice corrosion by a differential aeration cell mechanism formed between the metal matrix and the ceramic reinforcement, affected by the residual porosity as confirmed by electron microscopy examination.
INTRODUCTION Metal matrix composite materials (MMC) are susceptible to corrosion, but the proper design and combination of reinforcement and matrix materials can mitigate damage. Nickel-based superalloys emerge as the materials of choice for high temperature
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applications that require resistance to creep, fatigue and environmental degradation [1]. TiC ceramic as reinforcement offers excellent thermal stability, high elastic modulus, hardness, high thermal conductivity and low density. Recent studies show that, incorporated into nickel alloys, TiC makes possible composites of good electrical conductivity, good mechanical properties and oxidation resistance [2-5]. Among the methods of manufacturing MMCs, pressureless infiltration represents a simple and lowcost route that allows the incorporation of medium to high volume of reinforcing phase [6]. Under conditions of good wettability at the right temperature and atmosphere, the liquid metal penetrates and is transported inside a porous ceramic preform by simple capillary action. Once solidified, a metal matrix composite is obtained [7]. Nickel
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