Influence Of Lanthanum Oxide On Properties Of Solid Boronized Layer Of TB2 Alloy

Titanium alloys have attracted wide attention due to their excellent comprehensive properties.However,the hardness of titanium alloy is low and the wear resistance is poor,which will lead to the surface wear of workpiece due to sliding or rotating contact,even fatigue crack,and further development will make the parts invalid or scrapped.Therefore,it is necessary to modify the surface of titanium alloy.Solid boriding is the most widely used surface modification technology because of its advantages such as simple process equipment,convenient operation,and easy adjustment of boriding agent formula and easy cleaning of workpieces after boriding.In this paper,TB2 titanium alloy was borided by solid boriding method.An orthogonal experiment with four factors and three levels was designed to analyze the influence of the type and content of rare earth oxide,boriding temperature and time on boriding layer morphology,boriding layer thickness,surface hardness and friction coefficient,and to determine the best process parameters of solid powder+rare earth oxide boriding.The results of orthogonal experiment show that the type of rare earth has the least influence on boriding layer thickness,surface hardness and friction coefficient;while the boriding temperature and time have the most influence.The best boriding parameters of solid powder and rare earth oxide are La₂O₃,4%,1373K and 20 h.The results of surface and cross-sectioned morphology analysis show that the surface smoothness of boridzed layer can be improved by adding La₂O₃.The XRD and XPS results of borided layer surface show that La₂O₃ does not react with Ti and B,but only promotes the borided layer growth.The TEM results indicate that the enrichment of trace elements occurs in some areas of the grain boundary of TiB and Ti,and the relationship between TiB and Ti is as follows:(001)TiB//(100)Ti and[0-10]TiB//[0-10]Ti.The surface hardness and wear resistance of TB2 titanium alloy can be greatly improved by La-B infiltration.The dense and hard boronized layer can slow down the wear of the material surface,reduce the adhesive wear,improve the wear resistance of the material and increase the service time.After La-B infiltration,the sample is more corrosion-resistant than TB2 titanium alloy,and the appearance of boronizing layer makes the material tend to uniform corrosion in the corrosion process,local corrosion and pitting corrosion are reduced,so that TB2 titanium alloy can serve under more severe workpiece conditions and extend its working life.Two diffusion models,d²=Dt and d=kt^0.5,were used to simulate the growth kinetics of the boronized layer of TB2 titanium alloy.The results show that the diffusion model d²=Dt has high accuracy in predicting the thickness of borided layer.The natural logarithm of diffusion coefficient of B in TiB₂ layer and TiB whisker and the slope of fitting line of reciprocal of boriding temperature are analyzed by Arrhenius equation.The diffusion activation energies of B in TiB₂ layer and TiB whisker are 229.815 kJ/mol and 342.559 kJ/mol respectively.