| The progress of tool technology is of great significance to the development of machining.In order to obtain a higher tool life,tool coating technology has been paid more attention by the industry.TiAlN coating has been widely used in the machining of difficult-to-machine materials due to its high surface hardness,good chemical stability,wear resistance and heat resistance.Facing the difficulties of high cutting force,high cutting temperature and severe work hardening when machining difficult-to-machine materials,TiAIN coated tools still need to be further strengthened to ensure tool life.Cryogenic treatment can improve the wear resistance of coated cutting tools.In recent years,it has been gradually applied to the post-treatment process of tool enhancement.However,the research on the cryogenic treatment strengthening mechanism of TiAIN coated cemented carbide tools is not thorough and comprehensive.The optimal cryogenic treatment process of TiAIN coated tools is not given.Cryogenic treatment experiment was carried out in order to solve the above problems.This paper took the cryogenic treatment of PVD TiAIN coated tools as the research object The microstructure evolution mechanism and mechanical property changes of TiAlN coated carbide tools before and after cryogenic treatment were studied by means of microscopic observation,phase analysis and mechanical property test.Through the cutting tool life test of TiAIN coated tools before and after the cryogenic treatment,the strengthening effect of the cryogenic treatment process on TiAIN coated tools was evaluated,and the cryogenic treatment process parameters to improve the tool life were optimized.Firstly,the experiment platform of cryogenic treatment was built,and the cryogenic treatment parameters of cryogenic temperature and holding time were selected as the experimental variables to carry out the cryogenic treatment experiment on TiAIN coated cutting tools.After observing and analyzing the microstructure of TiAIN coated tools before and after cryogenic treatment,it was found that cryogenic treatment promoted the formation of ? phase carbide in the cemented carbide substrate of coated tools.The quantitative analysis of the content of ? phase in cemented carbide substrate by image recognition technology showed that the content of ? phase carbide in cemented carbide substrate increased significantly after cryogenic treatment.The volume fraction of ? phase carbide increased from 3.58%to 11.94%after cryogenic treatment at-190? for 24 hours.The decrease of cryogenic temperature and the extension of holding time were beneficial to the formation of ?phase carbide,and the effect of cryogenic temperature on ? phase content was more significant than that of holding time.In addition,the cryogenic treatment promoted the martensite transformation of Co phase in the cemented carbide substrate.The phase transition from ??Co to ?-Co was promoted by very low temperature of cryogenic treatment,and the amount of ?-Co increased with the decrease of cryogenic temperature.Then,the mechanical properties such as the hardness of cemented carbide substrate,the microhardness of TiAlN coating and the bonding strength of coating and substrate were selected to study the influence of different cryogenic parameters on the mechanical properties of TiAIN coating tools.After cryogenic treatment,the hardness of cemented carbide substrate was improved significantly,but the microhardness of TiAlN coating had no obvious change.The hardness of cemented carbide substrate was positively correlated with the content of ? phase and the degree of Co phase transformation.The lower the cryogenic temperature was,the higher the hardness value of the substrate was.When the cryogenic temperatures were-110? and-150?,the hardness of the substrate increased with the prolongation of the holding time.However,when the cryogenic temperature was-190?,the hardness of the substrate increased with the prolongation of the holding time firstly,reaching the maximum value of 2169N/mm2 in 24h,and then tended to be stable.In addition,the increase of ? phase content and hardness of cemented carbide substrate was beneficial to the improvement of bonding strength of coating and substrate.Finally,the tool life test of turning GH4169 was carried out,the influence of cryogenic treatment on the cutting performance of TiAlN coated tool was analyzed and the strengthening effect of cryogenic treatment on TiAIN coated tool was comprehensively evaluated.The experimental results showed that cryogenic treatment improved the tool life of TiAIN coated tools significantly.The tool life was 34.8%longer than that without cryogenic treatment after 24 hours of cryogenic treatment at-190?.The cryogenic temperature of-190? and holding time of 24h were the optimal combination of cryogenic parameters to improve the tool life of TiAIN coated tools. |
PDF Full Text Request