Study On Microstructure And Properties Of Low-cost Titanium Fabricated Of TiH2 Powder

Titanium and titanium alloys are widely used in various industries,such as aerospace,medical equipment,shipbuilding and automobile manufacturing fields,for their high specific strength,low density,extremely high corrosion resistance and high temperature resistance.However,high cost of raw materials and complicated production process of titanium alloys limit its application.Therefore,in this paper TiH2 powder was used as the raw material to prepare TC4 alloy and Ti,combined with powder metallurgy technology and extrusion technology.The microstructure and mechanical properties of extruded TC4 alloy and Ti bar were studied.The heat treatment process parameters were further improved to optimize the microstructure and mechanical property of TC4 alloy and Ti.In addition,the defects in the microstructure of extruded TC4 alloy and Ti by hot press sintering were eliminated,through the heat treatment process.According to the experiment,the mechanical properties of extruded TC4 alloy by vacuum sintering were excellent.Its tensile strength of 1231 MPa,yield strength of 1084 MPa,and elongation of 9.6%.The hydrogen content of the extruded rod by vacuum sintering was 0.015%(wt%).The microstructure in the shear band of the extruded bar at the bottom consisted of ? lamella grains and fine equiaxed grains with an average grain size of about 3.1 ?m.Dynamic recrystallization is the main softening mechanism.The extruded Ti bar was obtained by the same process and no pore defects were observed.The microstructure at the top of the bar consisted of a full lamellae with the ?lamellae width of about 13?m,at bottom of the bar is composed of equiaxed grains with a size of about 4.3?m,because sufficient deformation given rise to dynamic recrystallization.The tensile strength of about 786 MPa.Compared with the TC4 alloy prepared by other powder metallurgy processes,the extruded TC4 alloy bar by vacuum sintering in this paper has excellent mechanical properties,and simple process and low production cost.The hydrogen content of extruded TC4 alloy and pure Ti by hot pressing was extremely high,resulting in that the release of hydrogen produced a large number of pores and the composition segregation defects.during the extrusion process.At the same time,the pores in the billet becomed the channel for oxygen to enter the inside of the bar during the extrusion process,causing serious oxygen absorption inside the bar.On the other hand,the ultrafine ?lamellar grains with a width of about 1 ?m were formed.The main reason is that the hydrogen-rich ? phase in the material reached the eutectoid point during the extrusion process,and an eutectoid reaction occurred to precipitate TiH phase and ultrafine grain ?-Ti.The lattice structure of TiH is a face-centered cubic structure and it seriously affects the microstructure and mechanical properties extruded bar.After heat treatment at 1200? for 1h,the segregation and pore defects were elminated in the extruded TC4 alloy and Ti bar by hot pressing,forming a full lamellar microstructure,and the distribute of microstructure was homogeneous.The tensile strength and elongation have been greatly improved,because under high temperature,the alloying elements of TC4 diffused uniformly to eliminate segregation,and the rate of hydrogen removal was fast to reduce the hydrogen content in the material.The solution aging treatment significantly improved the tensile strength of the extruded TC4 alloy bar by vacuum-sintered.The tensile strength reaches1287 MPa under the solution temperature of 990? and the aging temperature of490?.The microstructure consisted of needle-shaped martensite.The formed band structure by the fine ? lamellae alternated with the formed band structure by the coarse lamellae.The reason for the formation of the microstructure is that the large amount of energy accumulated in the extrusion streamline,it is easier to precipitate ? lamellae and grew rapidly during heat treatment.As the aging temperature increasing 530?,the band structure transformed into a block structure with the coarse grains and the mechnical properties gradually decreased.