Investigation on Microstructure, Hardness, and Corrosion Resistance of Mo–Ni–B Coatings Prepared by Laser Cladding Technique

Xiaojie Ni,Yuantao Zhao,Wenge Li,Xiong Jiao,Shengze Wang

doi:10.3390/coatings9120856

Xiaojie Ni, Yuantao Zhao + Show 3 more

Open Access

https://doi.org/10.3390/coatings9120856

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Journal: Coatings	Publication Date: Dec 13, 2019
Citations: 5	License type: CC BY 4.0

Affiliation: Donghua University, Shanghai Maritime University

Abstract

The hard and corrosion resistant coatings of Mo2NiB2 cermet were prepared by the laser cladding technique. The influences of the Mo:B ratio and the laser scanning speed on the microstructure and property of the Mo2NiB2 cermet coatings were investigated. The results showed that the laser scanning speed of 1.5 mm/s and the Mo:B ratio of 1 were more beneficial to the formation of Mo2NiB2 cermet than 2.0 mm/s and 0.8, 1.2, respectively. The amount of the Mo2NiB2 ceramic phases were decreased from the top layer to the bottom layer of the coating. The changes of microstructure and composition led to the changes of hardness and corrosion resistance of the Mo2NiB2 cermet coatings. The coating prepared at the Mo:B ratio of 1 and the scanning speed of 1.5 mm/s possessed the highest hardness, and the hardness gradually decreased from the top layer to the bottom layer of the coating. The formation of Mo2NiB2 and {FeM} phases led to the enhanced corrosion resistance of the Mo2NiB2 cermet coatings, and the coating prepared at the Mo:B ratio of 0.8 possessed the best corrosion resistance and the minimum corrosion current.

Highlights

The boride-based cermet composites, especially the transition metal borides cermet composites that consisted of the transition metal and transition metal borides like W2 NiB2, WCoB, MoCoB, Mo2 FeB2, Mo2 NiB2, etc., have been extensively investigated in recent years [1]
By comparing the corrosion morphologies of these two kinds of coatings, it was observed that severe corrosion cracks appeared on the surface of the coating prepared at the Mo:B ratio of 1, which indicated that severe corrosion took place and the corrosion resistance of the coating was reduced
The Mo2 NiB2 cermet coatings were successfully synthesized on Q235 steels by laser cladding technique with different Mo:B ratios and laser scanning speeds

Summary

Introduction

The boride-based cermet composites, especially the transition metal borides cermet composites that consisted of the transition metal and transition metal borides like W2 NiB2 , WCoB, MoCoB, Mo2 FeB2 , Mo2 NiB2 , etc., have been extensively investigated in recent years [1]. The high hardness, melting points, and electrical conductivity of the transition metal borides can endow the cermet composites with the desirable properties including the hardness, melting point, wear and corrosion resistance, and optical and thermal performances [2,3,4,5]. These boride cermet composites have already been used in wear and corrosion-resistant fields like bearings for sea water pumps, injection molding machine parts, and offshore engineering parts [6,7]. Takagi et Coatings 2019, 9, 856; doi:10.3390/coatings9120856 www.mdpi.com/journal/coatings

Results

Discussion

Conclusion