Study On Microstructure Evolution And Properties Of Cord Deformation Ti-6Al-4V Alloy Under 600℃ Carbonitriding

For the disadvantage of the low hardness and poor abrasion resistance of Ti-6Al-4V alloy,We chose to perform 840℃ solid solution treatment on the alloy in advance,and then carry out rolling deformation.finally,at relatively low temperatures of550℃ and 460℃,the alloy is subjected to different holding time carbonitriding treatment to achieve the purpose of improving the overall performance of the alloy.Metallographic microscope,Scanning Electron Microscope（SEM）,EDS energy spectrum analysis,Transmission Electron Microscopy（TEM）,X-Ray Diffraction analysis（XRD）and Electron Backscatter Diffraction（EBSD）were used to characterize the transformation of deformed microstructure and nitriding microstructure.The performance changes were characterized by friction and wear test and microhardness test.TC4 alloy after solid solution treatment and room temperature cold rolling,the deformation of the sample for structural analysis,the results show that:the interior of the alloy due to solid solution cooling generated by the metastableα,phase andβ,phase,the phase is furture decomposed intoβphase,with the amount of deformation the increase ofβphase content gradually increased and grain refinement become more and more obvious.The EBSD analysis of 0%,30%,50%deformation samples shows that the larger the deformation,the smaller the grain size,the percentage of small angles grain boundary first increased and then decreased,the 0%deformation sample after water cooling produced a large amount of internal residual stress generates dislocations at the grain boundaries.As the deformation increase,the internal dislocation density increases.The texture components of alloys changed with the increase of deformation from approximately transverse texture to transverse texture.After carbonitriding at 550℃ and 460℃,white particles were observed on the surface of the sample by scanning electron microscopy.EDS spectroscopy showed the presence of carbon and nitrogen on the surface.There are not obvious interface between nitrided layer and diffusion layer in the specimen,the carbon and nitrogen elements distributed from the surface of the sample to the heart,and the surface nitrogen and carbon elements are higher than the core carbon and nitrogen elements.The XRD date shows that TiN,TiN_0.3,CTi_0.42V_1.58,AlTi₃（C,N）_0.6.6 and intermetallic compounds are mainly formed in the alloy.EBSD analysis of the 550℃ insulation 22h 0%,30%,50%carbonitriding samples,significant deflection of the texture compared to the deformed sample and significant changes in strength.With the increase of deformation amount,the grain size of the alloy is smaller than that of the deformed sample,the grain boundary at the small angle is obviously reduced,the content ofβ-Ti and TiN is gradually increased,and the alloy reverts to recrystallization and the amount of deformation increases during the carbonitriding process.The greater the degree of recrystallization.These results indcate that the higher the dislocation density of the material under the same carbonitriding process conditions,the smaller the grain size,the more the grain boundary,the closer the crystal texture,and the more hard phases are generated,the better the carbonitriding effect.The alloy hardness is280HV-310HV after cold rolling deformation,both surface hardness or core hardness increased significantly after carbonitriding.550℃ insulation22h50%deformation of the sample hardness increased maximum,the surface hardness reached a maximum of 587HV,the hardness value near the heart is 445HV.The results of friction and wear tests show that the friction coefficient and wear rate of the alloy decrease with the increase of the holding time at the same temperature,and the friction coefficient and the wear rate of the alloy increase with the increase of the deformation.The wear mechanism is mainly based on adhesive wear and abrasive wear.Among the specimens analyzed in this paper,the wear of the deformed specimens at 550℃ for 22h 40%is the most obvious,indicating that the cold deformation combined with low temperature carbonitriding process can improve the overall performance of TC4 alloy.