Abstract
Although Q235 steel materials are widely used in offshore engineering, the service life is severely shortened by its inferior resistance to wear and corrosion in harsh marine working environments. Boride-based cermet composites could be a good surface-protective coating to enhance surface hardness, wear resistance, and corrosion resistance. M3B2 (M: Mo, Ni, Fe, Cr) boride-based cermet coatings composed of hard ceramics of M3B2-type complex borides and an {Fe, Ni} metal matrix was fabricated on Q235 steels with mixed Mo, Cr, B, and Ni60 powders using a laser cladding synthesis technique. The influences of laser cladding parameters on the microstructure, phase composition, microhardness, and corrosion resistance of the coatings were comprehensively investigated. Results showed that the microstructures of the coatings mainly consisted of three layers, which were, from the top to bottom layer, a metal layer with fewer ceramic phases, a ceramic layer with fewer metal phases, and another metal layer with fewer ceramic phases. The ceramic phases were mainly M3B2-type borides, and the metal phases were mainly {Fe, Ni} alloys. The appearance of Fe-enriching metal phases was due to the supply of Fe elements from Q235 substrates. With squash pretreatment and without a remelting aftertreatment, ceramics uniformly dispersed in the cermet coatings, and their sizes decreased. The results of microhardness showed that the microhardness of the coating first increased and then decreased from the top layer to the bottom layer, and maximum microhardness was obtained in the layer of ceramics with less metal phases. An electrochemical corrosion test showed that the cermet coatings (jcorr = 6.35 μA/cm2) could improve the corrosion resistance of Q235 steels (j = 43.76 μA/cm2) by one order of magnitude.
Highlights
Because of its superior properties, such as high strength, plasticity, and weldability, Q235 steel materials are widely used in the fields of offshore engineering and offshore facilities [1]
Boride-based cermet composite coatings consist of a transition metal base matrix with dispersed hard phases, such as TiB2, Mo2 FeB2, and Mo2 NiB2, and they possess high hardness, high melting point, good wear and corrosion resistance, and good optical and thermal properties [3,4,5,6,7,8]
M3 B2 boride complex coatings were developed by laser cladding synthesis
Summary
Because of its superior properties, such as high strength, plasticity, and weldability, Q235 steel materials are widely used in the fields of offshore engineering and offshore facilities [1]. Boride-based cermet composite coatings consist of a transition metal base matrix with dispersed hard phases, such as TiB2 , Mo2 FeB2 , and Mo2 NiB2 , and they possess high hardness, high melting point, good wear and corrosion resistance, and good optical and thermal properties [3,4,5,6,7,8]. These cermet coatings have already been applied to wear- and corrosion-resistant applications such as injection molding machine parts, bearings for sea water pumps, and offshore engineering parts [9]. As emerging and promising materials with superior strength, hardness, and wear and corrosion
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