Microstructure and polarisation behaviour of TiN–TiB₂ matrix coating prepared by reactive plasma spraying

Authors: Ma, J.¹; Mao, Z. P.²; Sun, B. D.²; Wang, J.²

Source: Materials Science and Technology, Volume 26, Number 5, May 2010 , pp. 615-620(6)

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Abstract:

Two TiN–TiB₂ matrix coatings were prepared by reactive plasma spraying with two spraying powders (Ti+B₄C+Cr, Ti+B₄C). Their microstructure, phases, microhardness and polarisation behaviours in 3·5 wt-% NaCl solution have been investigated by SEM, XRD, hardness tester and electrochemical analyser. The thermodynamics analysis for reactive plasma spraying was discussed and the effect of addition of Cr on adiabatic temperature of TiB₂ forming reaction was also analysed. The thermodynamics analysis shows that the reaction temperature during reactive spraying process is >2030 K. To satisfy the criterion of self-propagating high temperature TiB₂ forming reaction, the addition of Cr should be >192·6 wt-% of the total weight of Ti and B₄C. The experimental results show that the addition of Cr decreases the stress in the coating so as to the cracks of coating at the expense of microhardness, yet the microhardness of both two coatings is a high value. The corrosion resistance of TiN–TiB₂ matrix coating was greatly improved. The anodic polarisation curve of TiN–TiB₂ coating includes a narrow activation zone and a broad passivation zone, which indicates the stability of coating is very excellent. The addition of Cr increases the corrosion potential of coating, yet an overpassivation zone appears, which is due to the breakage of passivation film.

Keywords: ADIABATIC TEMPERATURE; REACTIVE PLASMA SPRAYING; TIN-TIB2 MATRIX COATING; POLARISATION BEHAVIOUR; MICROHARDNESS

Document Type: Research Article

DOI: http://dx.doi.org/10.1179/174328409X443272

Affiliations: 1: School of Material, Hebei University of Science and Technology, Shijiazhuang 050018, China; State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China 2: State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China

Publication date: 2010-05-01

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