等离子熔覆TiC/Fe基熔覆层显微组织及碳化物演变机理分析

Analysis of Microstructure and Carbide Evolution Mechanism of TiC/Fe-Based Cladding Coating by Plasma Cladding

目的 为了提高3Cr13马氏体不锈钢的硬度和耐磨性,在其表面制备TiC/Fe基熔覆层,分析熔覆层组织的均匀性及碳化物类型,探究碳化物演变机理和对熔覆层硬度的影响规律。方法 采用等离子同步送粉熔覆,在3Cr13不锈钢基材上熔覆球形TiC/Fe基熔覆层。利用扫描电子显微镜、X射线衍射、能谱仪分析熔覆层微观形貌特征、相组成以及析出相的元素分布规律,利用显微硬度计测量熔覆层的硬度。结果 随着TiC添加量的增加,熔覆层中的Ti和C元素含量也增加,说明有部分TiC熔解。未添加TiC的熔覆层组织主要是Fe-Cr固溶体和(Fe、Cr)_(7)C_(3),TiC/Fe基熔覆层的为Fe-Cr固溶体和TiC、(Fe、Cr)_(3)C_(2)、(Fe、Cr)_(7)C_(3)。两种熔覆层中的析出相主要以(Fe、Cr)_(7)C_(3)为主,但在TiC/Fe基熔覆层中还存在其熔解后重新析出的TiC及过渡相(Fe、Cr)_(3)C_(2)。TiC添加量增加,熔覆层显微硬度也增加。结论 TiC/Fe基熔覆层中的第二相除(Fe、Cr)_(7)C_(3),还有原始TiC、析出的TiC和(Fe、Cr)_(3)C_(2)。在研究范围内,随着TiC添加量增加,熔覆层中熔解的TiC量也增加。析出的TiC.可以作为(Fe_(3)Cr_(4))C_(3)的有效形核质点,促进(Fe_(3)Cr_(4))C_(3)的形成,形成过程是(Fe、Cr)_(3)C_(2)以析出的TiC为形核核心形核长大,随后相变为更加稳定的(Fe、Cr)_(7)C_(3),在快速冷却过程中有未转变完的(Fe、Cr)_(3)C_(2)保留下来。熔覆层中的原始TiC、析出的TiC、生成的(Fe、Cr)_(7)C_(3)和(Fe、Cr)_(3)C_(2)作为硬质相提高了熔覆层的硬度。

In order to improve the hardness and wear resistance of 3Cr13 martensitic stainless steel,TiC/Fe-based cladding coating was fabricated on the 3Cr13 stainless steel substrate.The homogeneity of the microstructure of the cladding coating and the type of carbides were analyzed,and the evolution mechanism of carbides and effect rule on hardness of carbides of the cladding coating were studied.Spherical TiC/Fe-based cladding coating was fabricated on the 3Cr13 martensitic stainless steel substrate by plasma cladding with coaxial powder-feed.The microstructure distribution of the cladding coating and the microscopic morphological characteristics of the precipitated phase were observed by scanning electron microscopy(SEM).The phase composition of the cladding coating was analyzed by X-ray diffraction(XRD),and the chemical composition and the distribution of elements of the precipitation phase in the cladding coating were analyzed by energy dispersive spectroscopy(EDS).With the knowledge of thermodynamics and kinetics of materials,the evolution mechanism of carbides in cladding coating was analyzed,and the hardness of the cladding coating was measured by the microhardness tester.The un-melted TiC particles appeared homogeneous distribution in the cladding coating.With the increase of TiC content,the contents of Ti and C elements increased in the cladding coating.The atomic percentage of C increased from 26.22% to 49.86%;and the atomic percentage of Ti increased from 0 to 9.56%,which indicated that some of TiC was melted.In addition,the scanning results of element distribution showed that there were cracks in the un-melted spherical TiC,which also indicated that a proportion of TiC had melted in the cladding coating.The microstructure without TiC in the cladding coating was mainly formed by Fe-Cr sosoloid and(Fe,Cr)_(7)C_(3),while the phases in the TiC/Fe-based cladding coating were mainly Fe-Cr sosoloid and TiC,(Fe,Cr)3C_(2) and(Fe,Cr)7C_(3).The precipitated phases in the two kinds of cladding coatings were mainly(Fe,Cr)_(7)C_(3),but TiC was re-precipitated after melting in the TiC/Fe-based cladding coating.The misfit between the(111) face of TiC and the(0001) face of(Fe_(3)Cr_(4))C_(3) was δ=10.87%,so precipitated TiC could be used as effective nucleation particles of(Fe_(3)Cr_(4))C_(3) to promote the formation of(Fe_(3)Cr_(4))C_(3).With the increase of TiC content,the hardness of the cladding coating also increased.The average microhardness of Fe-based cladding coating and TiC/Fe-based cladding coatings with 10wt.%TiC,20wt.%TiC and 3 0wt.%TiC were 641.9HV0.1,645.4HV0.1,695.1HV0.1 and 746.3HV0.1 respectively,and the average microhardness was 1.60,1.61,1.74and 1.87 times of the substrate microhardness respectively.The amount of un-melted TiC increased with the increase of the ratios of TiC in the cladding coating.Compared with the cladding coating without TiC,the second phases in the TiC/Fe-based cladding coating included TiC,(Fe,Cr)_(3)C_(2) besides(Fe,Cr)_(7)C_(3).The TiC phases included un-melted original spherical TiC particles and newly precipitated fine TiC.(Fe,Cr)_(3)C_(2) grew with the precipitated TiC as the nucleation core,and then transformed(Fe,Cr)_(3)C_(2) into more stable(Fe,Cr)_(7)C_(3).During the rapid cooling process of the molten pool,some of(Fe,Cr)_(3)C_(2without) transformation were retained.Through summary and analysis of changes in carbides,the evolution process of carbides in the TiC/Fe-based cladding coating can be divided into four stages:the melting of TiC,the re-precipitation of tiny TiC,the formation process of(Fe,Cr)_(3)C_(2) and the phase transition process of(Fe,Cr)_(7)C_(3).The hardness of the cladding coating is improved by the original TiC,the re-precipitated TiC,and the(Fe,Cr)_(7)C_(3) and(Fe,Cr)_(3)C_(2) of generation as hard phases.Carbides play a fine grain strengthening role in the cladding coating and also improve the hardness of the cladding coating.