Microstructure, microhardness and corrosion resistance of laser cladding Al2O3@Ni composite coating on 304 stainless steel

Abstract

The microstructure, microhardness and corrosion resistance of laser cladding Al 2 O 3 @Ni composite coating were investigated. The Al 2 O 3 @Ni core-shell metalceramic powders synthesized via electroless plating method were used as laser cladding materials. According to the results of scanning electron microscopy and energy dispersive spectrometer, the microstructure of the Al 2 O 3 @Ni composite coating gradually transitioned from columnar crystal to cellular crystal and equiaxed crystal along the bottom to the surface. Furthermore, the Ni particles and Al 2 O 3 particles separated when laser heating, then formed Ni metallurgical bonding layer and Al 2 O 3 ceramic layer, respectively. The microhardness of Al 2 O 3 @Ni composite coating was up to 917.0 HV, which was about 5.7 times that of 304 stainless steel. In addition, immersion and electrochemical tests revealed that Al 2 O 3 @Ni composite coating exhibited excellent corrosion resistance compared with 304 stainless steel. The corrosion current density of the Al 2 O 3 @Ni composite coating (36.493 lA cm -2 ) was about 67.0% lower than that of 304 stainless steel (110.592 lA cm -2 ). Meanwhile, the corrosion mechanism of Al 2 O 3 @Ni composite coating was revealed. Dense Al 2 O 3 @Ni composite coating can inhibit the penetration of Cland H ? , making the corrosion reaction difficult to occur. Instruction 304 stainless steel is extensively used in chemical plants, food processing and mechanical engineering due to a combination of excellent corrosion resistance, good processing performance and low cost [1, 2]. In most corrosive conditions, 304 stainless steel proves excellent corrosion resistance, because passive film forms on the surface, which can provide important protective properties [3]. However, many

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