Preparation And Properties Of B-Al Composite Infiltration Layer On TA2 Pure Titanium Surface

Titanium and titanium alloys are widely used in aerospace,medicine,sports and other fieldsdue to their low density,high specific strength,excellent corrosion resistance,and good biocompatibility.However,their low hardness,poor wear resistance,and poor high temperature oxidation resistance limit the further promotion and application of titanium and titanium alloys.Surface modification technology is one of the important means to improve the surface properties of titanium and titanium alloys.Among them,the solid powder infiltration method is widely used due to its convenient operation and simple process.In this paper,the surface modifications of TA2 commerce pure titanium are performed usingsingle boriding,single aluminizing and boron-aluminum duplex infiltration.The effects of surface treatment process on the structure and performance of the infiltrated layer are studied,and the surface treatment process to improve of TA2 pure titanium and titanium alloys is explored.The single boriding temperatures are 950,1000,1050℃,and the boroiding time is 4h.The single aluminizing temperature range is 850～1100℃ with the temperature interval of 50℃,and the aluminizing time is 4h.The boron-aluminum duplex infiltration process is performed boriding at 1050℃ for 4 hours,and then aluminizing at 950,1000,and 1050℃ for 4 hours.Using XRD,SEM,EPMA,the microstructure morphology and growth of the infiltration layer are investigated.Morever,the best process of boron-aluminum duplex infiltration treatment parameters are determined by the comparison of microstructure and performance using single boriding,single aluminizing and boron-aluminum duplex infiltration.The results show that the boriding layer of single boriding is composed of a dense and flat TiB₂outer layer and an inner TiB whisker layer.The thickness of the boriding layer increases with the increase of temperature,the best boronizing temperature is 1050℃.The single aluminizing layer consists of Al₃Ti,and the thickness increases first and then decreases as the temperature rises in a parabolic form,the best aluminizing temperature is 1000℃.The structure of the boron-aluminum composite layer in sequence from the surface to the matrix is the TiB₂ outermost layer,TiB whisker+Al₃Ti aluminized secondary outer layer,the transition zone and the matrix,the best temperature condition for composite infiltration is 1050℃boronizing first and then aluminizing at 1050℃..Corrosion resistance,hardness and friction and wear tests were carried out on the substrate,single boronizing,single aluminizing and boron-aluminum composite infiltrating samples.The corrosion test results show that the single boronizing sample has the best corrosion resistance,the corrosion resistance of composite penetration is slightly better than that of the matrix,and the single aluminizing has worse corrosion resistance than the TA2 matrix.The post-boronizing layer is composed of a harder TiB₂ layer and TiB whiskers,and the hardness is greatly improved compared to the matrix;the hardness of the single aluminized sample is close to that of the matrix;the hardness of the boron-aluminum composite layer is higher than that of the matrix About 3.01 times.Although the hardness of the composite layer is lower than that of the single boron layer,it has a gentle hardness gradient and lower brittleness,so the comprehensive mechanical properties are excellent.The friction and wear type of the TA2 surface is mainly adhesive wear with poor wear resistance.After single boriding,the wear resistance of the TA2 surface is significantly improved.The surface of the single aluminizing sample is uneven and the roughness is large,which intensifies that the adhesive wear increases and the wear resistance reduces.The wear type of the surface of the boron-aluminum duples infiltration sample is mainly abrasive wear,and the wear resistance improves.As the temperature increases,the coefficient of friction and wear of the sample surface increase,and the wear resistance at high temperatures will decrease.The high temperature oxidation resistancesof TA2 matrix and the samples after single boronizing,single aluminizing and boron-aluminum duplex infiltration are tested at 600℃,700℃ and 800℃,and then the antioxidant properties are analyzed combined with morphology,phase and oxidation weight gain curve.The results show that,as the temperature increases,the thickness of the outermost oxide layer of the TA2 matrix sample increases significantly,and the oxidation resistance is the worst.The oxidation resistance of the single boriding sample is slightly better than that of the matrix,but it cannot protect the matrix under high temperature conditions,and the oxidation resistance is also poor.After oxidized at three different high temperatures,the aluminized layer is still composed of Al₃Ti,and the morphology has no obvious change,which belongs to the oxidation resistance level.The structure of the boron-aluminum duplex infiltration sample after high temperature oxidation,from the surface to the matrix,is composed of Al₂O₃ layer,boronized layer,TiB whisker+Al₃Ti aluminized layer,transition zone and matrix.It belongs to the oxidation resistance level at the experimental temperature.The oxidation resistance is slightly lower than that of the aluminized sample,but it is better than the matrix and has good oxidation resistance.