Effect Of Surface Boronizing On Mechanical Property And Corrosion Resistance Of New ?-titanium Alloy

Due to the low density of titanium and titanium alloy,it has the advantages of high specific strength and stiffness.Compared with common metals,titanium has excellent biocompatibility and strong corrosion resistance.?-type titanium alloy is a new type of titanium alloy,which has low elastic modulus,high strength and good processing performance.It has promising applications in biomedical,aerospace,transportation machinery and other industrial fields.However,its properties are unstable,low surface hardness and poor wear resistance,which further lead to fatigue cracks,these problems severely limit its application range and service life.In practical industrial production,a convenient and economic method to improve the mechanical properties of titanium alloy is needed,so in this paper,boriding can form the hard boride layers on Ti-33Nb-4Sn(334 titanium),which is a new type of?-type titanium alloy,by this way,the surface hardness,wear resistance and corrosion resistance of 334 titanium can be improved.Firstly,it is important to choose the suitable sample preparation device,pack cementation boriding method was used to make the boride surface of 334 titanium alloy,the boride coatings were prepared in air atmosphere and N₂ atmosphere respectively,and different reaction temperatures(900?,950?,1000?)were selected.The substrate and boronizing coatings were characterized by means of X-ray diffraction(XRD)and scanning electron microscopy(SEM),and the results showed that dense and continuous boronizing coatings could be formed on the surface of 334 titanium alloy under different preparation conditions.The boronizing coating is a two-layer structure composed of a dense sedimentary layer and a needle-like diffusion layer.As the boronizing temperature rised,the thickness of the sedimentary layers increased.The thickness of the sedimentary layers prepared in N₂ atmosphere is larger than that prepared in air atmosphere at the same temperature.The mechanical properties of the modified coatings prepared under different conditions were tested by nano-indentation experiments.The experimental results showed that the surface hardness,elastic modulus and elastic resilience of 334titanium were improved by boronizing modification.Wear resistance of 334titanium and boronizing coatings were analyzed by friction coefficient,wear surfaces and wear debris.The results indicated that the boriding coatings could improve the wear resistance of the substance.The wear mechanism of substance was the serious abrasive wear.The wear mechanism of modified boronizing coatings were mild abrasive wear and adhesive wear.The open circuit curves,polarization curves and impedance curves of substance and boronizing coatings were obtained by electrochemical test.The results showed that the modified boronizing layer could improve the corrosion resistance of 334 titanium,and the corrosion resistance of the coatings prepared in N₂ atmosphere were better than in air atmosphere.