304钢表面激光熔覆Stellite12钴基涂层组织及腐蚀性能

Microstructure and Corrosion Properties of Laser Cladding Stellite12 Coating on 304 Steel

目的对304不锈钢表面强化处理来提高其耐腐蚀性能。方法使用激光熔覆技术将Stellite12涂层制备在304钢基体上。使用光学显微镜(OM)、扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射(XRD)、三电极电化学工作站对涂层显微组织、元素分布、物相、电化学腐蚀行为进行测试与分析,并对涂层和304不锈钢的耐腐蚀性能进行了对比分析。结果涂层物相主要由面心立方结构α-Co固溶体、CoC_(x)等化合物组成。由于温度梯度和凝固速度的不同,熔覆层截面下、中、上部呈现出了不同的组织形貌特征:依次由平面晶、胞状晶、树枝晶、细小树枝晶组成。涂层枝晶间为Co和碳化物的共晶组织,枝晶内主要为α-Co的初生相。在进行电化学腐蚀后,涂层的自腐蚀电位为-504.5 mV,304钢的自腐蚀电位为-579.7 mV,涂层的腐蚀电位较304钢偏正,比304钢耐腐蚀。涂层表面出现了腐蚀点,腐蚀点位分布均匀、且程度较轻。304钢表面发生了严重的腐蚀,明显可见深度和面积较大的腐蚀孔洞。结论Stellite12合金涂层能够有效地提高304不锈钢表面耐腐蚀性能。

In practical applications,304 stainless steel is prone to pitting and crevice corrosion damage,which will adversely affect the performance of the product.In order to further improve the corrosion resistance and other related properties of 304 stainless steel,surface modification treatment can be carried out on it.At present,the surface modification treatment of laser cladding technology is widely used at home and abroad.The test used a 304 stainless steel plate as the cladding substrate,and the cladding material was Stellite12 alloy powder with an average particle size of 45μm and a spherical powder morphology.After many experimental studies,the processing parameters were set to a laser power of 1400 W,a spot diameter of 3 mm,and a scanning speed of 15 mm/s.Field emission scanning electron microscope SEM(FEI,ZEISS)and OXFORD Ultim Extreme energy spectrometer(EDS)were used to observe the microstructure morphology of the coating,the corrosion morphology of the coating and the substrate,and element analysis.An Empyrean X-ray diffractometer was used to determine the phase structure of the coating.An electrochemical workstation with RST5000 three-electrode system was used to conduct electrochemical experiments on the samples.The overall surface of the stellite12 coating was light green,and the overall perfection of the coating showed no obvious defects.The penetrant inspection of the sample did not find defects such as coating surface cracks,and the coating surface roughness Ra=40.1μm.The upper,middle and lower parts of the coating cross-section showed different microstructure characteristics.The cross-section elements of the coating had abrupt changes in the transition zone,which proved that the coating and the substrate were diluted under strong metallurgical bonding.The dilution rate was calculated to be about 16.9%based on the composition of Fe element in the coating.The coating surface was mainly columnar crystals,small planar crystals,and short dendrites.Compared with the cross-section of the coating,the growth direction of the surface structure of the coating became more disordered.This was because the surface coating had a wide molten pool area and more diversified heat dissipation.The main phase of the coating was α-Co,CoC_(x) and other compounds.The open circuit potential,Tafel polarization curve,Nyquist plot,and Bode plot of the coating and the substrate in the 3.5wt.%sodium chloride test solution.It can be seen from the figure that the open circuit potential measured by the coating and the substrate remains in a stable state,the self-corrosion potential of the coating was-504.5 mV,and the self-corrosion potential of the substrate was-579.7 mV.The corrosion potential of the coating was more positive than that of the substrate,and it was more resistant to corrosion than the substrate.At the same time,the annual corrosion rate of the coating was 0.002 mm/a far less than the substrate rate of 0.05 mm/a.A Stellite12 coating was prepared on a 304 stainless steel substrate,and the structure,phase and electrochemical corrosion performance of the coating and the substrate are studied.The interdendritic was a eutectic structure of Co and carbides,and the primary phase of α-Co was mainly contained in the dendrites.The main components of the coating phase were a-Co,CoC_(x) and other compounds.The self-corrosion potential of the coating was-504.5 mV,and the self-corrosion potential of the substrate was-579.7 mV.The corrosion potential of the coating was more positive than that of the substrate.Stellite12 coating can improve the corrosion resistance of 304 stainless steel.