基于等离子电解碳氮共渗的水滑石复合渗层制备及耐蚀性能研究

Study on the Preparation and Corrosion Properties of Hydrotalcite Composite Permeation Layer via Plasma Electrolytic Carbonitriding

为了提高钢铁材料在经过等离子电解渗后的耐腐蚀性,以退火后的20钢为试验对象,以等离子电解碳氮共渗过程中形成的微纳孔洞为容器,并负载镁铁水滑石(Mg-Fe-LDHs)作为缓蚀剂,着重探讨了Mg-Fe-LDHs对20钢腐蚀性能的影响。首先,以甲酰胺为碳氮源、KCl为导电盐,与去离子水混合形成电解液;然后在220 V直流脉冲电压下处理9 min获得碳氮共渗层(简称PEC/N试样);随后,将PEC/N试样放入由尿素溶液、MgSO_(4)溶液与Na_(2)CO_(3)溶液构成的Mg-Fe-LDHs前驱体溶液中,在140℃恒温环境下水热晶化10 h获得复合渗层(简称PEC/N-LDHs试样)。随后通过显微硬度计、扫描电镜(SEM)、X射线衍射仪(XRD)、电化学测试分析了复合渗层的不同性能表现。结果表明:复合渗层的显微硬度达到900 HV左右,较基体提高了4.6倍。PEC/N试样渗层约20μm厚,截面光滑、平整,表面崎岖不平、呈多孔蜂窝状;经水热合成LDHs后,表面变得平整,无明显蜂窝状结构,试样表面出现大量片状结晶物。PEC/N试样的XRD谱中出现了Fe_(3)C、Fe_(5)C_(2)、α-Fe、Fe_(3)N物质的吸收峰;在原位负载Mg-Fe-LDHs后,PEC/N-LDHs试样的XRD谱中出现了Mg-Fe-LDHs晶体(003)、(006)与(009)晶面的吸收峰;结合SEM形貌特征可知,Mg-Fe-LDHs被成功负载,呈片状结构。相比20钢,PEC/N试样渗层的腐蚀电位(E_(corr))与腐蚀电流密度(J_(corr))均有所提高,分别达到-0.451 V与75.22μA/cm^(2),但其低频阻抗模值(|Z|_(0.01 Hz))并未显著增大,仅达到998.5Ω·cm^(2);负载Mg-Fe-LDHs后,PEC/N-LDHs试样的E_(corr)、J_(corr)、|Z|_(0.01 Hz)分别达到-0.355 V、39.11μA/cm^(2)、6586.0Ω·cm^(2),较20钢及PEC/N试样均有较大幅度改善。以上结果表明,采用等离子电解浸渗处理20钢,可以获得高硬度的碳氮共渗层;通过水热法负载LDHs后,可进一步提高复合渗层的耐蚀性,且不影响PEC/N渗层的硬度,所获得的PEC/N-LDHs复合渗层同时具有高硬度与较好的耐蚀性。

In order to improve the corrosion resistance of steel materials treated by plasma electrolytic infiltration,annealed 20 steel was used as the experimental substrate.Micro-nanopores formed during the plasma electrolytic carbonitriding process were utilized as containers to load magnesium-iron layered double hydroxides(Mg-Fe-LDHs)as a corrosion inhibitor,and the effects of Mg-Fe-LDHs on the corrosion performance of 20 steel were investigated.First,formamide was used as the carbon and nitrogen source,and KCl was used as the conductive salt.These components were mixed with deionized water to form an electrolyte.Then,the samples were treated at a constant DC pulse voltage of 220 V for 9 min to produce a carbonitrided layer(denoted as PEC/N samples).Subsequently,the PEC/N samples were immersed in a Mg-Fe-LDHs precursor solution containing urea,MgSO_(4)and Na_(2)CO_(3),and hydrothermally crystallized at 140℃for 10 h to obtain a composite infiltration layer(denoted as PEC/N-LDHs samples).The performance of the composite infiltration layers was analyzed using a microhardness tester,scanning electron microscopy(SEM),X-ray diffraction(XRD)and electrochemical testing.Results showed that the microhardness of the composite infiltration layer reached approximately 900 HV,which was 4.6 times higher than that of the substrate.The carbonitrided layer of the PEC/N samples was about 20μm,with a smooth and flat cross-section but a rough,porous and honeycomb-like surface.After hydrothermal synthesis of LDHs,the surface became smooth,lacking a visible honeycomb structure,and a large number of flake-like crystalline deposits appeared on the surface.The XRD spectra of the PEC/N samples showed absorption peaks corresponding to Fe_(3)C,Fe_(5)C_(2),α-Fe and Fe_(3)N phases.After the in-situ loading of Mg-Fe-LDHs,new absorption peaks corresponding to the(003),(006)and(009)crystal planes of Mg-Fe-LDHs appeared in the XRD spectra of the PEC/N-LDHs samples.Combined with SEM morphology analysis,it was confirmed that Mg-Fe-LDHs were successfully loaded,presenting a flake-like structure.Compared with 20 steel,the PEC/N samples exhibited improved corrosion potential(E_(corr))and corrosion current density(J_(corr)),reaching-0.451 V and 75.22μA/cm^(2),respectively,although the low-frequency impedance modulus(|Z|_(0.01 Hz))showed no significant increase,reaching only 998.5Ω·cm^(2).After loading Mg-Fe-LDHs,the PEC/N-LDHs samples demonstrated further improvements,with E_(corr),J_(corr)and|Z|_(0.01 Hz)reaching-0.355 V,39.11μA/cm^(2)and 6586.0Ω·cm^(2),respectively,showing significant enhancement compared to both 20 steel and PEC/N samples.These results indicated that plasma electrolytic carbonitriding treatment of 20 steel could produce a carbonitrided layer with high hardness.Additionally,the hydrothermal loading of LDHs further improved the corrosion resistance of the composite infiltration layer without affecting its hardness.The PEC/N-LDHs composite infiltration layer thus achieved both high hardness and superior corrosion resistance.