钨极氩弧熔覆原位自生铁基复合涂层组织与性能

Microstructure and Properties of In-situ Synthesized Fe-Based Composite Coating by Tungsten Inert Gas Cladding

目的以钨极氩弧作为热源,在Q235钢表面原位自生铁基复合涂层。方法以铁粉、铁基合金粉(G302)、B4C粉末作为预置合金粉,设置两种粉末质量比Fe:B4C=15:1(记为S1)、G302:B4C=8:1(记为S2),在Q235钢表面原位合成铁基复合涂层。对涂层进行一系列组织性能表征,利用扫描电镜(SEM)分析涂层的显微组织,采用X射线衍射仪(XRD)分析涂层的物相组成,利用MHV-2000型数字式显微硬度计测量熔覆试样显微硬度的变化。结果在试样S1和S2中,涂层与基体呈现良好的冶金结合,在结合界面处没有气孔、裂纹等缺陷。通过XRD分析可知,预置合金粉末发生了化学反应且反应比较充分,没有B4C剩余。试样S1中的增强相主要由Fe_2B、Fe_7C3、Fe_3C组成,试样S2中的增强相主要由Cr-Fe、(Cr,Fe)7C3、(Fe,Cr)2B组成。试样S1中的硼化物及碳化物呈不连续网状分布;试样S2中的网状结构减弱,出现了块状和短棒状结构。试样S1和S2基体至涂层的显微硬度呈梯度变化,且涂层的显微硬度明显比基体高,S2中涂层的显微硬度达到1200HV0.1,约是基体硬度的6倍。结论利用上述预制合金粉可以原位合成铁基复合涂层。随着硼元素含量的提高以及Cr元素的加入,有助于改善硼化物形态,使其由网状结构向块状转变。原位生成复合陶瓷增强相均匀分布在铁基体上,涂层硬度显著提高。

The work aims to prepare Fe-based composite coating in situ on Q235 steel with argon arc as a heat source. With iron powder, Fe-based alloy powder （G302） and B4C powder as preset alloy powders, Fe-based composite coating was synthe-sized in situ on Q235 steel by tungsten inert gas cladding at two powder ratios of Fe：B4C=15：1 （mass ratio） （denoted as S1） and G302：B4C=8：1 （mass ratio） （denoted as S2） . Structure property was characterized in a series of methods. Microstructure of coatings was analyzed with scanning electron microscope, phase composition of coatings with X-ray diffractometer and micro-hardness variation with MHV-2000 digital microhardness tester.Interfaces between the coatings and substrates in sample S1 and sample S2 exhibited good metallurgical bonding property, and free from pores, cracks and other defects. XRD analysis showed that preset alloy powders reacted adequately and no residual B4C was left in coatings. Reinforced phase in sample S1 was main-ly composed of Fe2B, Fe7C3 and Fe3C while main phases in sample S2 were composed of Cr-Fe, （Cr,Fe）7C3 and （Fe,Cr）2B. Bo-rides and carbides in sample S1 were in noncontinuous network-like distribution, network-like structure in sample S2 weakened, and block or short rod-like structure appeared. Microhardness of substrate to coating in sample S1 and sample S2 was subject to gradient change, microhardness of coating was obviously higher than that of the substrate. Microhardness of the coating in sam-ple S2 was up to 1200HV0.1, about 6 times as high as that of substrate. Fe-based composite coatings can be synthesized in situ using the above prefabricated alloy powders. The increase of boron and Cr element content can improve boride morphology to transform boride from network-like structure to block structure. Reinforced phase of in-situ synthesized composite ceramic is distributed uniformly in the iron substrate, hence hardness of the prepared coatings increases significantly.