Study On Microstructure And Properties Of Ti-4Si;-xZr-yY₂O₃/5TiO₂ Composites Prepared By High-energy Milling And Cold Pressed Sintering

Titanium composite has many advantages,such as corrosion resistance,high temperature resistance and good plasticity.It has broad application prospects in the fields of national defense,high tech,information security,civil technology and so on.Therefore,the development of titanium matrix composites with excellent properties is of great significance.This paper selects the technology of high energy ball milling and cold pressing sintering to prepare four kinds of composites:Ti-4Si/5TiO₂,Ti-4Si-1.3Zr/5TiO₂,Ti-4Si-0.3Y₂O₃/5TiO₂,Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂.The phase composition,microstructure and apparent porosity of the composites were analyzed and the hardness,modulus of elasticity and fracture toughness of the materials were analyzed.The properties of high temperature oxidation,thermal corrosion and wear resistance of the series composite materials are compared.It provides a reference for the research and application of high performance titanium matrix composites.The main research work and achievements are as follows:The microstructure and phase composition of the composites were analyzed,and the alloying effect of Zr and Y₂O₃ was confirmed,and the microscopic strengthening mechanism of titanium matrix composites was revealed.The particle size of mixed powder is smaller,uniform after high energy ball milling.After repeated cold welding process,effect of alloying is obvious.After adding Zr and Y₂O₃ oxides to the Ti-4Si/5TiO₂ basic formula,Ti₂Zr and Zr₃Si₂ phases appeared.The Ti₅Si₃ content in the mixed powder increased,effect of alloying increased,and the local agglomeration occurred.After vacuum pressureless sintering,part of titanium silicon phase is transformed into Ti₅Si₃ compound,and the XRD diffraction peak intensity of Ti₅Si₃ phase in Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂ composite is the strongest,indicating that Zr element and Y₂O₃ oxide can promote the reaction between Ti and Si elements,and improve the alloying effect of elements.The microstructure of the composite is uniform and the compactness is improved.The apparent porosity of Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂ composite is the lowest,only 2.9%.It shows that Zr and Y₂O₃ oxide can increase the density of the composite,and the density of the composite is small.The Zr has a solid solution strengthening effect,and the Y₂O₃ has the effect of dispersion strengthening and fine grain strengthening.By comparing the microhardness and fracture toughness of the composites,it is found that Zr and Y₂O₃ can improve the microhardness of the composites and improve the fracture toughness of the composites.Zr and Y₂O₃ can increase the content of Ti₅Si₃ compounds,and the content of Ti-Si solid solution is increased,dispersion strengthening and solid solution strengthening can be produced,thus improving the hardness of the composite.The microhardness（1478 HV）of Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂ composite is 2.2 times higher than that of Ti-4Si/5TiO₂ composite（672 HV）,which is about 41%higher than that of Ti-4Si-1.3Zr/5TiO₂ composite.The modulus of elasticity of Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂composite is the highest,reaching 120.68 GPa.Zr and Y₂O₃ can improve the fracture toughness of composite.Among them,the K_ICC value of Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂ composite is the highest,reaching 8.68 MPa.m^1/2,and the fracture toughness is the best.Based on the oxidation kinetics curve,the high-temperature oxidation resistance of the composites was studied,and the oxidation mechanism of the composites under the action of Zr and Y₂O₃ was determined.The oxidation products of the composites were mainly composed of anatase and rutile TiO₂ and SiO₂ for 100 h at 900℃,1000℃,1100℃.The oxide layer is mainly composed of the TiO₂ layer and the composite oxide layer composed of TiO₂ and SiO₂,and the thickness of the oxide film increases with the increase of temperature.After adding Zr and Y₂O₃,part of anatase TiO₂ was transformed into rutile TiO₂.The high temperature oxidation products of the composites grow outward in a prism,and the oxide size increases with the increase of temperature.The kinetics curve of the composite oxidation is in accordance with the parabolic law.Zr and Y₂O₃ can refine the oxidation products of composite materials,increase the densification of oxide film,block the outward diffusion of Ti and Si elements,inhibit the infiltration of O elements,reduce the oxidation rate of composites,and improve the high-temperature oxidation resistance of composites.The four kinds of composites all reach the antioxidant grade at 900℃.The average oxidation speed of Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂composite was smallest,only 0.206 g.m^-2.h^-1,which was reduced by 33.76%compared with that of Ti-4Si/5TiO₂ composite.The oxidation speed of the four composites are all less than 1g.m^-2.h^-1,and the oxidation rate of Ti-4Si-0.3Y₂O₃/5TiO₂ composite is the lowest,only 0.359g.m^-2.h^-1,and the oxidation rate of Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂ composite is 0.383 g.m^-2.h^-1.Except for Ti-4Si-5TiO₂ composite,all other composites reach the antioxidant grade at 1100℃.The average oxidation speed of Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂ composite is lowest,only 0.711g.m^-2.h^-1.After adding the Zr,the selective oxidation of the Ti can be promoted.The oxidation mechanism of the composite in three high temperature environments is mainly from the inside to the outside.After adding Y₂O₃ to make up for defects such as voids,the adhesion between the composite oxide and the substrate is enhanced,the adhesion performance is improved,the thickness of the oxide film is reduced.The oxidation mechanism is mainly the diffusion of Ti,Si and O elements,and SiO₂ affects the oxidation speed of the composite.The thermal corrosion properties of the composite were studied and analyzed.After corrosion of the composites at 750℃sodium chloride and sodium sulfate mixed molten salt for30 h,the corrosion resistance of Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂ composite is the best,and the corrosion weight per unit area（0.6856 mg/cm²）compared with Ti-4Si-5TiO₂ composite（0.9846 mg/cm²）decreased 30.4%,and showed good corrosion resistance.The corrosion products of the surface of the composite are mainly composed of rutile TiO₂ and SiO₂ oxide,with a small amount of NaTiO₂,Na₂Si₂O₅,Ti（SO₄）₂,TiS₂ and other compounds.The thickness of the corrosion layer of the composite is uniform,and the adhesive is good with the matrix.The hot corrosion process has no serious defects,such as the cracking and falling off of the corrosion layer,and shows good thermal corrosion resistance.The friction and wear properties of the composite were studied and analyzed.The friction coefficientofTi-4Si/5TiO₂,Ti-4Si-1.3Zr/5TiO₂,Ti-4Si-0.3Y₂O₃/5TiO₂and Ti-4Si-1.3Zr-0.3Y₂O₃/5TiO₂ composite is 0.34,0.52,0.48 and 0.39 respectively,and the width of wear scar is 500μm、388μm、416μm、222μm,respectively.With the addition of Zr element in Ti-4Si-5TiO₂ composite,the friction factor increases,but the width of the grinding mark decreases,and the friction and wear properties of the composite are greatly improved.The wear scar width of Ti-4Si-1.3Zr-0.3Y₂O₃-5TiO₂ composite is the smallest and the friction and wear properties are the best.Compared with Ti-4Si-5TiO₂ composite,the wear scar width of Ti-4Si-1.3Zr-0.3Y₂O₃-5TiO₂ composite is reduced by about 31%,indicating that Y₂O₃ oxide can significantly improve the friction and wear properties of the composite.The wear mechanism of composite is mainly fatigue wear,supplemented by oxidation wear,adhesive wear and abrasive wear.To sum up,this paper creatively prepared light and high temperature resistant Ti-4Si-xZr-yY₂O₃/5TiO₂ composites,in which Zr and Y₂O₃ can significantly improve the hardness,elastic modulus,fracture toughness,high temperature oxidation resistance,thermal corrosion and friction and wear properties of Ti-Si alloy matrix composites.It provides scientific basis and technical foundation for the design and development of Ti-Si alloy matrix composites.