Study On Pulsed Carbon Ion Carbonitriding Of Cold Deformed Ti-6Al-4V Alloy At 500℃

The surface modification is usually used to improve Ti-6A1-4V alloy’ s wear resistance,obtaining a stable performance of the hardened layer by carbonitriding is the most cost-effective mean,conventional Ti-6Al-4V alloy carbonitriding treatment need to be carried out at high temperatures,while under high temperature conditions,the oxidation reaction is likely to influence the modification effect.In this paper,Ti-6A1-4V alloy solution treatment and cold rolling at room temperature deformation,and then pulsing plasma carbonitriding treatment at a relative low temperature conditions,500 ℃,in order to form a stable layer on the Ti-6A1-4V alloy.Whereas,Ti-6A1-4V alloy aging temperature range can be precipitated phase to improve the substrate hardness.The changes of Ti-6A1-4V alloy microstructure,can be analyzed by scanning electron microscopy,energy dispersive spectroscopy and X-ray diffraction.Hardness test and friction and wear test were carried out to measure the effect of Ti-6A1-4V alloy was improvedAccording to the organization data,it can be seen that the surface permeation layer of Ti-6A1-4V alloy after carbonitriding is dark yellow,which consists of two parts,the surface of it is bright white,called TiN layer.The inner layer was dark gray,mainly composed of TiN,Ti2N and TiC phase.Additional,the carbon nanotransformed Ti-6A1-4V alloy matrix is mainly composed of a-Ti,while the existence of part of the titanium nitride and carbide.With the increased amount of deformation,the content of TiN in the infiltration layer decreases with the increased of Ti2N,with the increasing depth of the infiltration layer.The longer time lasting,the higher nitrides,carbides and a phase contains.Through the performance data,it can be seen that the surface hardness of Ti-6A1-4V alloy is up to 628HV after carbonitriding treatment,which improved nearly 300HV and 2000HV relatively.The hardness of the alloy section changes from the boundary to the center,gradually reduced,since the effect of aging to strengthen the heart hardness is higher than the untreated Ti-6A1-4V alloy hardness.With the increase of deformation,the hardness of the alloy is increased but the amplitude is slighter.With the increase of the holding time,the hardness of the alloy increases gradually.Compared with Ti-6A1-4V alloy treated with nitriding and aging alone,the friction coefficient and volume wear rate of Ti-6A1-4V alloy were decreased to a certain extent.The wear behavior of Ti-6A1-4V specimen with the short duration of carbon tetrafiltration and the short holding time is mainly due to adhesive wear.The wear behavior of Ti-6Al-4V specimen with long holding time is mainly abrasive wear,with slight adhesive wear.Compared with the untreated sample,the friction coefficient of Ti-6A1-4V alloy decreases with the increase of the holding time.The friction coefficient and the volume wear rate of Ti-6Al-4V alloy are decreasing.The results show that defects such as solid solution treatment and dislocation of deformation of cold rolling are used as diffusion channels,so that carbonitriding of Ti-6A1-4V alloy can be achieved at a low temperature,titanium nitride and carbide-based hardening layer are formed on the surface,improving the friction and wear properties of the alloy.At the same time,some Intermetallic compounds are generated inside the matrix,and the distribution gradient of N and C in the alloy matrix has a gradient of distribution,resulting in a gradient of the hardness of the alloy matrix and a regular hardness gradient.