Preparation And Properties Of Reactive Thermal Sprayed Ternary Boride Cermet Coatings

In this thesis, ternary boride cermets coatings were prepared by Reactive Flame Sprayed (RFS) on Q235 steel substrate using Mo-FeB-Fe, Mo-FeB-Fe-Al and Mo-FeB-Fe-TiB₂ as reaction system. The sprayed-powders were synthesized by sinter-crushing method at 900℃and polyvinyl butyral (PVB) granulation. Phases, particle size distribution, microstructure, and reaction mechanism of the sprayed-powders were investigated by X-ray diffraction (XRD), laser scattering particle analyzer, scanning electrical microscopy (SEM)/energy dispersive spectrum (EDS) and differential scanning calorimetry (DSC). The bonding strength between the substrate and the ceramic coating, micro-hardness, thermal shock resistance, porosity, corrosion resistance and wear resistance were characterized with the relevant lab testing equipment.The result indicates that the Mo₂FeB₂ cermets coatings were synthesized by sinter-crushing method using Mo powder, Fe-B alloy powder, and Fe powder as raw materials. Fe2B appeared after milling for 15 h in the powder, ternary boride (Mo₂FeB₂) was generated in sinter-crushing powders at 900℃. The coatings are composed of the major phases Mo₂FeB₂ andα-Fe, a little of Fe2O₃,FeO and some pores. There is a transition from high hardness coating to low hardness substrate, the porosity of the coatings is 23%, the thermal-shock times is 38, the corrosion resistance of coatings is 4.89 times, the abrasive wear resistance and adhesive wear resistance are 5.28 times and 5.16 times than those of the substrate, respectively. The comprehensive properties of Mo₂FeB₂ cermets coatings can be improved further after heat-treatment at 1000℃under vacuum for 5 h.The powders for reactive thermal spraying (RTS) were synthesized by sinter-crushing method at 900℃using Mo, Fe-B alloy, Fe and Al powders as raw materials. Mo₂FeB₂ cermet coatings were prepared by RTS on Q235 steel and heat-treatmented at 1000℃under vacuum for 5 h. Ternary boride (Mo₂FeB₂) and inter-metallic compound (Fe3Al) were generated in sinter-crushing powders at 900℃. The coatings are composed of the Mo₂FeB₂, Fe3Al,α-Fe and some metallic oxides and pores. The porosity of coatings is 19%, the thermal-shock times of the coatings without heat-treatment are 43, the abrasive wear resistance and adhesive wear are 3.04 times and 4.24 times, and the corrosion resistance in 5wt. % H₂SO₄ solution is 4.02 times than those of the substrate, respectively. The comprehensive properties of Mo₂FeB₂ cermet coatings can be improved further after vacuum heat-treatment at 1000℃for 5 h.The TiB₂/Mo₂FeB₂ composite ceramic coatings were synthesized using Mo, Fe-B alloy, Fe and TiB₂ powders as raw materials. The coatings are composed of the major phases Mo₂FeB₂, TiB₂ andα-Fe, a little of Fe₂O₃, FeO, and B₂O₃.The thermal-shock times of RTS-sprayed coatings is 50, the coatings prepared by APS have better wear resistance and corrosion resistance than the coatings prepared by RTS at different load, different time and corrosion media.