Design Of Fe-based Bulk Metallic Glasses With High Cr Content And Study Of Their Wear And Corrosion Properties

Fe-based metallic glasses have been widely concerned because of their high strength,high hardness and excellent corrosion-and wear-resistance,and have shown an attractive application prospect in the field of surface protection coatings.However,in recent years,some studies have shown that the performance of Fe-based metallic glasses and amorphous coatings in the extreme service environment?heavy load,impact or corrosive wear and so on?was still unsatisfactory.Design and performance research of new amorphous alloys with high corrosion-and wear-resistance is one of the most effective ways to solve the above problems.Therefore,through optimizing the composition of the typical Fe-based amorphous alloys by regulating the content of Cr and Mo in this thesis,we establish the relationship between composition and properties,optimize the corrosion and wear properties of amorphous alloys synchronously,then research the mechanism of corrosion and wear deeply.In this paper,a series of Fe_77-x-yCr_xMo_yC₁₅B₆Y₂?x=15-23;y=14-18?amorphous alloys were prepared by using the basic Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Y₂ amorphous alloy system.Using X-ray diffraction?XRD?,differential thermal analysis system?DTA?,scanning electron microscope?SEM?,laser confocal microscope?LSCM?,transmission electron microscope?TEM?,universal mechanical test machine,micro Vickers hardness tester,ultrasonic echo material characterization system,friction and wear tester,electrochemical workstation,X-ray photoelectron spectroscopy?XPS?and so on,we systematically researched the mechanical properties,tribological properties and corrosion properties of Fe-based amorphous alloys.The results showed that the thermal stability and Vickers'hardness of FeCrMoCBY amorphous alloys increased linearly with the increase of Cr and Mo content,but the fracture toughness did not decrease significantly.It was found that the hardness of amorphous alloys was linearly proportional to the elastic modulus,while the fracture toughness decreased slightly with the increase of the ratio of the shear modulus/bulk modulus?G/B?.The test results of friction and wear performance in dry environment showed that the wear resistance changed greatly with the increase of Cr content,while the wear resistance is generally improved with the increase of Mo content.It was found that there were two main frictional mechanisms of Fe-based amorphous alloys,one was the abrasive wear controlled by hardness,the other was the subsurface crack initiation and delamination controlled by the fracture toughness.It was found that the wear resistance of Fe-based amorphous alloys was approximately linear proportional to Kc^3/4Hv^1/2.The optimized composition of Fe-based amorphous alloys was Fe₃₆Cr₂₃Mo₁₈C₁₅B₆Y₂,which had excellent comprehensive properties,including high amorphous formation ability?8 mm?,high thermal stability?T_g=900 K?,high hardness(Hv_300g=1335),and its wear resistance exceeded the most wear-resistant Fe-based metallic glasses.In addition,the corrosion properties of the above optimal amorphous alloys were also systematically studied.The results of immersion test in aqua regia showed that the corrosion rate of the Fe₃₆Cr₂₃Mo₁₈C₁₅B₆Y₂ amorphous alloy was lower than 1.0mm/a,and the electrochemical polarization results showed that the Fe₃₆Cr₂₃Mo₁₈C₁₅B₆Y₂ amorphous alloy had a faster passive film formation rate and a longer pit incubation time than the Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Y₂ amorphous alloy,indicating that the former had a better corrosion resistance.XPS results showed that the composition of passive film of Fe₃₆Cr₂₃Mo₁₈C₁₅B₆Y₂ amorphous alloy was mainly low electrovalence ion of Cr³⁺,Fe²⁺and Mo⁴⁺.In addition,the passive film on the surface of Fe₃₆Cr₂₃Mo₁₈C₁₅B₆Y₂ amorphous alloy was observed directly by FIB/TEM.It was found that the passive film had a double layer structure,the inner layer was Cr-enriched oxide,and the outer layer was Fe-enriched oxide or hydrogen.The double layer structure of passive film and more Cr³⁺and Mo⁴⁺in passive film were the main reasons for the better corrosion resistance of the new amorphous alloy.