Microstructure And Wear Resistance Of In Situ Synthesized ZrB₂-ZrC/Fe Composite Coating Produced By Plasma Cladding

Diborides and carbides of zirconium (ZrB2 and ZrC) have many excellent properties such as high melting point, low density, high hardness, good thermal shock resistance and high thermal conductivity, due to these advantages ZrB2, ZrC reinforced metal-based composite coating have a wide range of applications in cutting tools, refractories, wear parts and aerospace and other fields.After years of research, Plasma cladding technology, with its excellent surface strengthening effect,simple and flexible operation process and low cost of processing advantages, has gradually matured,using plasma cladding technology to produce ceramic-reinforced composite coatings on the surface of steel can greatly improve the wear resistance of steel, prolong the service life of materials, save material and production costs.Under the support of the National 863 Project(Preparation and characterization of wear resistant composite coatings by plasma spray deposition, 2015AA034404), In this study, A kind of Fe-based ceramic coatings with ZrB2 and ZrC as multi scale strengthening phases on the surface of Q235 steel were fabricated by plasma cladding using Fe, Zr, B4C and SiC powder mixture as precursor. The phase composition, microstructure, microhardness and the wear resistance comparative test of ZrB2-ZrC/Fe coating and Q235 steel were investigated. The effects of different Zr + B4C addition, different cladding current and SiC addition on the morphology, quantity, size and distribution of the enhanced phase were studied, The microstructure evolution, the formation of the phase and the wear mechanism were discussed, which provides the basis for the application of plasma cladding technology. The main research results are as follows:(1)By changing the Zr+B4C addition amount, the plasma cladding current and the addition amount of SiC in the raw powder,Using plasma cladding technology,The ZrB2 and ZrC composites coating were successfully prepared on the surface of Q235 steel matrix with the Fe, Zr and B4C powder as raw materials, The plasma clad ZrB2-ZrC/Fe composite coating have no cracks, pores,inclusions and other defects, ZrB2-ZrC/Fe composite coating is closely and metallurgically bonded to the Q235 steel substrate.(2)When the amount of Zr+B4C added in the raw powder were changed,ZrB2-ZrC/Fe coatings are composed of ZrB2, ZrC, a-Fe, Fe3C and Fe2B phases. ZrB2 phase presents acicular, clubbed and petal forms. ZrC phase are irregular polygon shape. With the increasing of Zr+B4C raw powder,the contents of ZrB2 and ZrC are increasing, the size of ZrB2 and ZrC become large. Compared with Q235 steel substrate, the wear resistance of the coating have improved significantly, up to 5.45 times than that of the substrate. The main wear mechanism of ZrB2-ZrC/Fe composite coating are abrasive wear, the main fracture mode of the composite coating are transgranular fracture.(3)When the cladding current were changed,the main phase of the coating is ZrB2, ?-Fe,ZrC,and the rest contains a certain amout of Fe2B,Fe3C,when the cladding current is 110A and 120A,there is a small amount of ZrO2, and the content of ZrO2 increases with the increase of cladding current. ZrB2 phase presents acicular, clubbed and petal forms. ZrC phase are irregular polygon shape, with the increase of the cladding current, the size of the ZrB2 and ZrC reinforced phases increases gradually, and the moldability of the coating becomes poor. The microhardness of ZrB2-ZrC/Fe coating is obviously improved compared with that of Q235 steel, and the microhardness of coating decreases with the increase of cladding current. The wear resistance of ZrB2-ZrC/Fe coating is 3?5 times of the wear resistance of Q235 steel matrix,with the increase of cladding current, the wear resistance of ZrB2-ZrC/Fe coating is gradually deteriorated. The abrasion of the ZrB2-ZrC / Fe coating is gradually changed from abrasive wear to abrasive wear and abrasion wear.(4) When the addition amount of SiC in the raw powder were changed, the main phase of the coating is ZrB2, a-Fe and ZrC,and the rest contains a certain amout of ZrO2, Fe2B,Fe3C,Fe3Si and trace amount of SiO2. ZrB2 phase presents acicular,clubbed and petal forms. ZrC phase are irregular polygon shape, ZrO2 showed a white agglomeration, with the increase of SiC addition in the raw powder, the forming properties of ZrB2-ZrC/Fe coating gradually deteriorated, and the defects such as pores and cracks increased gradually, and the content of white agglomerated ZrO2 gradually increased. With the increase of SiC addition in the raw powder, the microhardness of ZrB2-ZrC/Fe coating decreases and the wear resistance gradually deteriorates.