| The in-situ Ti-based bulk metallic glass matrix composites?BMGMCs?((Ti0.45Zr0.31Be0.17Cu0.07)100-xNbx?x=4,6,8,10,and 12?)with high strength and good ductility are prepared by combining with arc melting and water-cooled copper mold suction casting method.The potentiodynamic polarization curves and electrochemical impedance spectroscopy?EIS?of Ti-based bulk metallic glasses?BMGs?and BMGMCs are tested in different corrosion solutions.The weight loss and corrosion rate are also measured by chemical immersion test.The phase composition,microstructure,surface morphologies before and after corroded,surface roughness and element distribution of the Ti-based BMGs and BMGMCs are analyzed and characterized by X-ray diffraction?XRD?,transmission electron microscopy?TEM?,scanning electron microscopy?SEM?,energy-dispersive spectroscopy?EDS?,X-ray photoelectron spectroscopy?XPS?and atomic force microscopy?AFM?.The corrosion behavior of Ti-baded BMGMCs in different solutions is studied,as well as the effect of Nb on the formation of dendrites and corrosion behavior in BMGMCs is also discussed.By studing the corrosion behavior of Ti-based BMGMCs in different solutions of HCl,NaCl,NaOH,and H2SO4,it is found that the characteristics of corrosion solutions and the constituent elements of the materials play an important role in corrosion behavior of Ti-based BMGMCs.The results indicate that the corrosion resistance of Ti-based BMGMCs decreased as the acid concentrations increased;and in the chloride-containging solutions,due to the local adsorption of chloride ions,obvious pits appear on the surface after electrochemical corroded.In the NaOH solution,because the high reactivity activity of Be in an alkaline environment,it combined with OH-,and then produces a soluble product,which results in a large amount of corrosion dents appeared on the surface after corroded.However,the corrosion black spots can be observed on the corroded surface for the samples after polarization in H2SO4 solution,which was caused by the different content of Nb in the Ti-based BMGMCs,resulting in the oxide content in the passive film,therefore,the protective property of the passivation film is differenc.The distribution and content of surface elements for the corrosion samples were tested by XPS.It was found that there was oxygen element on the surface of corroded samples,indicating that the oxides formed on the surface which was an important factor to affect the corrosion properties of Ti-based BMGMCs.Nb is an important element to promote and stabilize the formation of the second dendrites phase in the Ti-based BMGMCs and to control the size and morphology of the dendrites.It has a great influence on the corrosion performance of the Ti-based BMGMCs.In the chloride-containing solution,the addition of Nb can effectively improve the pitting-corrosion resistance,and the critical pitting potential,Epit,shifted from about 59mV to 1211 mV with the increase in Nb content from 4 to 12 at.%in the BMGMCs system.The alloy with 8 at.%Nb exhibits the best corrosion resistance in three different corrosive solutions of NaCl,NaOH,and H2SO4,and the corrosion current density is 2.7?±0.06?×10-8,2.4?±0.30?×10-8 and 1.3?±0.17?×10-8 A/cm2.The results show that the Ti-based BMGMCs have the best corrosion resistance in H2SO4 solution.The size,morphology and content of the second dendrites phase of Ti-based BMGMCs have an important influence on the corrosion resistance of the amorphous composites.The content of dendrites in the Ti-based amorphous composites(Ti43.2Zr29.8Cu6.7Nb4Be16.3)with the diameters of 3 mm,5 mm,8 mm,and 10 mm are measured.The results show that with increasing in the diameter of the amorphous composites,the size of dendrite increased rom 3.21?m to 32.28?m and the content is 5057 vol%.At the same time,the corrosion resistance decreased as dendrite size and content increased,which means that the dendrite size and content play an important role in corrosion characteristics.Ultimately,it is caused by the element state in the surface film after electrochemical corrosion.At the end of this paper,a comparision of corrosion behavior between Ti-based BMGs and BMGMCs,316 stainless steel,titanium alloy and zirconium alloy is carried out in different corrosion solutions.The weight loss and corrosion rate for the above alloy materials are also measured in HCl solution.The results show that the corrosion behavior of Ti-based BMGs is better than the Ti-based BMGMCs,and the corrosion resistance of Ti-based BMGMCs is significantly better than that of the 316 stainless steel,but it is inferior to zirconium alloys and titanium alloys.The research in this paper provides valuable process parameters and theoretical support for the application of Ti-based BMGs and BMGMCs in the field of corrosion resistance engineering. |
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