Preparation,Mechanical Properties And Electrochemical Corrosion Behavior Of Powder Metallurgy Ti-80 Marine Titanium Alloy

Powder metallurgy can effectively reduce the production cost of titanium alloys,and promote the widespread application of titanium alloys.However,compared with traditional titanium alloys prepared by ingot metallurgy,powder metallurgy titanium alloys still have problems such as higher oxygen content,lower density,and coarser structure,which seriously affect the mechanical properties of powder metallurgy titanium alloys.In this study,TiH2-based powders were used as raw materials,and high-density and fully alloyed powder metallurgy Ti-80 titanium alloys were successfully prepared by rapid induction sintering and hot extrusion under the protection of an argon atmosphere.The structure evolution of powder metallurgy Ti-80 titanium alloys during heat treatment,the mechanical properties and the electrochemical corrosion behavior in simulated seawater of powder metallurgy Ti-80 titanium alloys with different microstructure types were studied.The powder metallurgy Ti-80 titanium alloy extruded rod has a hydrogen content of 0.21 wt.%and an oxygen content of 0.37 wt.%.The density is close to 100%.The microstructure is Widmannstatten microstructure composed of fine ?-platelets and?-transformation structures.After vacuum dehydrogenation and annealing treatment(700?/6h/FC)?the hydrogen content was reduced to 0.006 wt.%,the ?-platelets was broadened and a large number of discontinuous ? phases appeared.The discontinuous? phases is caused by the dehydrogenation phase transition reaction ?(H)??+?+H2(g).After conventional annealing treatment(960?/1h/AC)?high density needle-like ? phases precipitated in the ? phases,forming special ?-transition structures.The yield strength of powder metallurgy Ti-80 titanium alloy with conventional annealing treatment is 1150 MPa,the tensile strength is 1200 MPa,and the elongation to fracture is 10.7%.High density is the prerequisite for powder metallurgy Ti-80 titanium alloys to have higher strength and good plasticity.The higher oxygen content brings about a significant solid solution strengthening effect,and the reduction of the effective slip length of dislocations caused by the special ?-transformation structures,which makes powder metallurgy Ti-80 titanium alloy with conventional annealing treatment have higher strength.A large number of ?/? interfaces are formed by the small ?-platelets,which promotes the formation of geometrically necessary dislocations.The high density geometrically necessary dislocations improve the work hardening rate of the materials,make the materials deformation more uniform,and increase the elongation to fracture.In contrast,there is no special ?-transition structures in the powder metallurgy Ti-80 titanium alloy with vacuum dehydrogenation and annealing,and the higher ? phases content and the widening of the a platelets reduce the ?/? interfaces.The yield strength of powder metallurgy Ti-80 titanium with this structure is reduced to 1040 MPa,the tensile strength is reduced to 1120 MPa,and the elongation to fracture is reduced to 8.1%.The main component of the outermost layer of the powder metallurgy Ti-80 titanium alloy passivation film is the highest valent oxides of each alloy element such as TiO2,Al2O3,Nb2O5,ZrO2,MoO3.As the depth increases,the highest-valent oxide of each element in the passivation film gradually decreases,and the contents of the low-valent oxide and metal state increase.In the micro structure of powder metallurgy Ti-80 titanium alloy with conventional annealing treatment,a small number of ?-platelets and a large number of? phases form a large number of ?/? phase interfaces.On the one hand,these interfaces can promote the formation of passivation films.On the other hand,it can alleviate the uneven distribution of the solute elements between the two phases and suppress the extra galvanic corrosion effect caused by the uneven distribution of the solute elements between the two phases.The corrosion current density in simulated seawater is 36.1 nA/cm2.The corrosion resistance in simulated seawater is better than the powder metallurgy Ti-80 titanium alloy in the other two states,which is equivalent to the corrosion resistance of ingot metallurgy Ti-80 titanium alloy.The powder metallurgy Ti-80 titanium alloy with vacuum dehydrogenation and annealing treatment has the smallest ? phase content and wide ?-platelets.The corrosion current density in simulated seawater is 102.2 nA/cm2,and the corrosion resistance is poor.