Study On Microstructure And Friction And Wear Properties Of The Cold Deformation TC4 Alloy By Plasma Nitriding Treatment And Aging

Titanium alloy TC4?Ti–6A1-4V?as the important engineering alloy material with low density,high specific strength,good corrosion resistance and biocompatibility etc,are widely used in aerospace,automotive,chemical and biological medicine industry.But its poor tribological performance limits its application in the field of engine valve,turbocharger,etc.In this paper,plasma nitriding technology was used on distortional TC4.By means of metallographic microscope,scanning electron microscope,X-ray diffractometer,vickers microhardness tester and friction and wear testing machine the microstructures and properties of TC4 were analyzed.The experimental results show that after plasma nitriding process,many white particles are irregularly distributed on the surface of nitriding layer,energy spectrum analysis testify that the white particles are ceramic particles TiN and Ti₂N.Observation on the section of samples through scanning electron microscope found that there are second phase precipitating dispersedly on the sample matrix,the edge of sample is clear and white nitriding layer and spectral results show that the nitrogen content in gradient distribution with the decrease from surface to the core.After 540?nitriding,the sample hardness is significantly increased,about 300HV higher than that of original TC4 material,about 140HV higher than that of TC4 with equal time aging treatment.With the increase of nitriding temperature,nitriding time,and the deformation of TC4 alloy,ceramic particles on the nitriding surface grew up and coarsened,the hardness value present a tendency of increasing.Under 540?,the layer thickness of samples nitriding for 8h is 3.52?m,for 22h is 1.7?m.For the samples nitriding in 540?for 8h,nitriding layer thickness of 10%deformation is about 3.52?m,that of 30%deformation is 3.55?m and that of 50%deformation is3.6?m.Compared to original TC4 samples,the samples after 540?nitriding have lower friction coefficient and wear rate.The results show that,compared with the samples in nitriding temperature of400?,nitriding layer thickness of samples in 540?increased about 2.5 times.Hard phase nitrides TiN,Ti₂N,Ti₄N_3-X,Ti₃N_2-X and sosoloid TiN_0.3 TiN_0.26 are produced on the surface of 540?samples which results in hardness increase.In 540?,as the extension of nitriding time,surface structure roughened,surface hardness increased;As the extension of nitriding time,permeability layer become thicken and then thin is caused by the action of plasma sputtering continuously;With the increase of the deformation,nitriding layer thickness increase amplitude is not obvious.Friction coefficient of nitriding samples is lower 0.1than that of samples aging 8h under the same temperature and the volume wear rate reduced to 2/5 of the wear rate of aging samples;With the increase of the deformation and the nitriding time,the grinding crack becomes shallow and the wear rate decreases,this phenomenon illustrates that TC4 alloy wear-resisting performance is also improved after 540?nitriding treatment.