Study On Nitriding Strengthening Of Titanium Alloy With Hollow Cathode Plasma Source And Its Wear Corrosion Behavior

With high specific strength,toughness,corrosion resistance,high temperature resistance and good biocompatibility,titanium and titanium alloys are the basic materials for aerospace manufacturing,biomedical implants,marine engineering equipment and automotive products.In order to meet the use scenario of titanium alloy,titanium alloy workpieces will develop in the direction of large,integral,miniaturized and complex,so 3D printed titanium alloy applied in medical and health care,aerospace,marine engineering and other industries is getting more and more attention.However,their poor tribological properties often limit titanium and titanium alloys.In order to improve the defects of titanium and titanium alloys,several surface strengthening techniques have been attempted to improve the overall performance of titanium alloys.Nitriding is a chemical heat treatment process in which nitrogen atoms are infiltrated into the surface of a workpiece under certain temperature conditions in a nitriding medium containing nitrogen elements.The hollow cathode ion source is a plasma-based cathode gas discharge ion source.In this paper,surface modification of cast TC4 and EBMTC4 samples was performed using the hollow cathode plasma source nitriding（HCPSN）technique.The relationship between the microstructure of the modified layer and corrosion-tribology resistance is discussed using analytical characterization such as XRD,XPS,TEM,HRTEM,nano-hardness,UMT-5 friction wear test,three-dimensional white light morphological interference,electrochemical workstation,etc.The friction behavior of TC4 titanium alloy after nitriding at different temperatures is studied to investigate the friction mechanism,and the corrosion-tribology performance of EBMTC4 after nitriding to investigate the wear mechanism.The results show that:（1）the surface of the sample after nitriding consists of a mixture of Ti N,Ti₂N andα-Ti（N）phases.The compound layer from the sample surface to the core matrix consists of nanocrystalline Ti N surface top layer,crystal Ti N secondary surface layer,Ti₂N interlayer and interstitial solid solutionα-Ti（N）bottom layer.（2）The surface hardness of the nitrided samples increased by 2-5 times,the surface roughness increased,and the effective layer thickness reached 50-110μm.（3）Compared with the untreated TC4 alloy,the Ti N-based nitriding layer showed an obvious passivation zone,a significantly lower corrosion rate,and a significantly higher pitting resistance.The corrosion resistance of the nitride layer with Ti₂N phase on the surface is relatively deteriorated.the passivation film on the surface of the Ti N nitride layer has higher triboresistance and lower impedance capacitance,which can effectively hinder the penetration and migration of reactive ions,thus resulting in a significant improvement in corrosion resistance.（4）The average friction coefficient of TC4 titanium alloy substrate is 0.41,and it can be assumed that the wear mechanism of TC4 substrate is plastic deformation and severe adhesive wear.After nitriding,the sample has higher resistance to plastic deformation and improved tribological properties,and the wear mechanism is slight adhesive wear and abrasive wear,and the friction coefficient and ink mark depth are reduced.（5）The open-circuit potential of the nitrided EBM samples is more stable,and the corrosion current density of the EBM530 samples is reduced by a factor of 10 compared to that of the EBMTC4 substrate.（6）The wear mechanism of the EBMTC4 substrate during corrosion friction is corrosion wear and adhesive wear with slight abrasive wear,while the EBM510 sample has the best friction and wear reduction performance with slight abrasive wear and corrosion wear.The corrosion and wear resistance of the nitrided EBM samples increased significantly.