Study On Friction And Wear Properties Of Borocarburized Layer Of TC4 Titanium Alloy

TC4 titanium alloy is a kind ofα+βtitanium alloy,which is widely used in aviation,aerospace,chemical engineering and ships.However,its low hardness and wear resistance limit its further use.In many surface treatment technologies,solid boronizing method can greatly improve the hardness and wear resistance of TC4 and its operation is widely used.But the single solid boronized layer has many defects such as low toughness and big brittleness.In this paper we adopt the borocarburizing to enhance the surface hardness and wear resistance of TC4 titanium alloy and to improve the permeability of brittle ductile layer.We ues B₄C and anhydrous borax as for boron carbon agent,rare earth lanthanum oxide as catalyst,SiC and graphite as filler,at 950°C insulation 10 h,to get the borocarburized layer.SEM,EDS and XRD were used to analyze the morphology,composition and phase composition of the infiltration layer,and the roughness,hardness and wettability of the permeability were detected,and the experiments of scratches and indentation were carried out.In the end,the friction and wear properties of the infiltration layer under different loads and different friction pairs were studied.The results showed that:（1）after the borocarburizing,the surface of TC4 titanium alloy was obtained by TiB2 and TiB double phase structure,the total thickness of the infiltration layer was about17μm,the outer layer was TiB₂,and the thickness was about 5μm,and the hardness was about3001HV.The subsurface is TiB phase whisker structure with a thickness of about 12μm and hardness of about 1800HV.At the junction of I TiB layer and the TC4,there are diffused TiC phases,because of the C in the osmotic agent is less effective in forming the effective TiC layer.The overall hardness gradient of the infiltration layer is steep,the impression of indentation is complete and the brittleness is 3.（2）In order to get the effective TiC transition layer and reduce the brittleness of the layer the carburized layer is pretreated by the solid carburizing.After pretreatment,the surface of TC4 forms a TiC layer of about 11μm,and the outer layer is rugged and has the sediment layer of rich C atoms.（3）after the borocarburizing,TC4 titanium alloy surface was obtained with TiB₂,TiB and TiC three-phase structure,and the thickness was about 34μm.The outermost layer is mainly TiB₂,whose thickness is about 15μm,and the hardness is about 2656HV.The subsurface is mainly TiB,whose thickness is about 6μm,and the hardness is about 1500HV.The innermost layer is mainly TiC,and the layer increases before pretreatment,and the thickness is about 13μm,and the hardness is about 910HV.The performance of the layer is good,the surface roughness Ra of about 0.316μm,water contact Angle of about 60.88°.The hardness gradient is slow,the indentation is good and the brittleness is1.（4）the ball-disk wear experiment shows that the borocarburizing layer can effectively improve the friction and wear resistance of TC4 titanium alloy under different loading and friction conditions.The more large of the loading and the hardness of the friction,the more better of the friction wear resistance of the layer.Compared with the matrix,the friction coefficient and wear area of the permeability layer decreased significantly,and the abrasion resistance of the abrasive particles increased greatly.（5）The pretreatment can improve the rate of diffusion of B atoms,and restrain the growth of the TiB phase.The formation of TiC transition layer can effectively improve the permeability of brittle ductile and improve the friction and wear resistance...