【摘要】 为解决TC4钛合金难加工及传统TiAlN涂层刀具易失效的问题，以粉末冶金法制备WC-6Co超细硬质合金基体，采用PVD分别沉积TiAlN与NbN/TiAlN涂层，系统对比无涂层基体与两种涂层刀具的微观组织与切削性能，SEM显示两种涂层均呈致密柱状晶。在v_c=80 m·min^-1,f=0.08 mm·r^-1,a_p=0.5 mm条件下开展TC4切削实验，TiAlN涂层刀片因Ti元素亲和作用在18 min后急剧失效，无涂层刀片在24 min失效，而NbN表层有效阻隔元素扩散，使NbN/TiAlN涂层刀片在30 min失效且磨损平稳。结果表明，NbN/TiAlN涂层可显著提高硬质合金刀具的耐磨性与寿命，为钛合金高效切削刀具设计提供新思路。更多还原

【Abstract】 Objectives:As a key material in aerospace and other fields,TC4 titanium alloy is difficult to machine due to its small deformation coefficient,high cutting temperature,severe work hardening,and strong chemical affinity.Traditional TiAlN-coated tools are prone to adhesive wear and rapid failure due to Ti element affinity and diffusion,restricting the efficient production of related industries.This study aims to systematically compare the microstructures and cutting performances of cemented carbide tools with different coatings,clarify the improvement effect of optimized coating structures on tool wear resistance and service life,and provide technical support and new ideas for the design of high-efficiency cutting tools for titanium alloys.Methods:WC-6Co ultra-fine cemented carbide substrates are prepared by powder metallurgy,including mixing,72-hour ball milling,sieving,granulation,pressing,and sintering at 1 430 ℃ for 1 hour.After pretreatment such as passivation and ultrasonic cleaning,Ti AlN coating(Ti₅₀Al₅₀ target,deposition time 70 minutes) and NbN/TiAlN composite coating(Ti₅₀Al₅₀ target deposition for 70 minutes+Nb target deposition for 20 minutes) are deposited on the substrates by PVD technology.Scanning electron microscopy（SEM） is used to observe the microstructures of the substrate and coatings.Vickers hardness tester,Archimedes method,and atomic force microscopy（AFM） are employed to test the mechanical properties,density of the substrate,and 3D topography and roughness of the coatings,respectively.TC4 titanium alloy with ф60 mm × 220 mm is used as the workpiece,and cutting experiments are carried out under the conditions of cutting speed v_c=80 m·min^-1,feed rate f=0.08 mm·r^-1,and cutting depth a_p=0.5 mm.Tool failure is judged according to ISO 3685 standard(flank wear width VB>0.3 mm,maximum wear VB_max>0.6 mm,or tool tip chipping).The flank wear amount is recorded every 3 minutes,and the wear morphology and composition changes of failed tools are characterized by SEM and elemental analysis.Results:Microstructure:Both coatings exhibited dense columnar crystal structures.The TiAlN coating has a thickness of 1.60 μm,a furrow-like surface,and a roughness Ra 14.1 nm.The total thickness of the NbN/TiAlN coating is 2.71 μm（TiAlN layer 2.03 μm+NbN layer 0.68 μm）.The NbN layer grows epitaxially along the TiAlN layer（the misfit degree of their FCC structures is≤3.8%）,with a peak-valley surface and a roughness Ra 25.9 nm.The substrate has a Vickers hardness of HV₃₀ 2 066.35 and a density of 98.80%,meeting the requirements of TC4 machining.Cutting performance:The TiAlN-coated inserts fail sharply at 18 minutes due to the affinity of Ti elements,with adhesive wear accompanied by diffusion wear as the main wear forms,and high content of TC4 workpiece elements is detected on the flank.The uncoated inserts fail at 24 minutes,mainly suffering from groove wear and adhesive wear.The NbN/TiAlN-coated inserts fail after 30 minutes with stable wear due to the effective blocking of element diffusion by the surface NbN layer,which is divided into three stages:Initial wear（0-6 min）,normal wear（6-21 min）,and severe wear（21-30 min）.The main wear forms are groove wear and slight adhesive wear,with no obvious element diffusion.Conclusions:The NbN/TiAlN composite coating significantly improves the wear resistance and service life of cemented carbide tools through its dense epitaxial growth structure and element diffusion barrier effect,and its cutting performance is superior to that of single TiAlN-coated tools and uncoated tools.Due to the affinity between TiAlN coating and Ti elements in TC4,the service life of TiAlN-coated tools is even lower than that of uncoated tools,making them unsuitable for highdemand TC4 cutting scenarios.This study clarifies the optimization mechanism of composite coating structures on tool cutting performance,provides a practical tool design scheme for solving the difficult machining problem of titanium alloy,and can be applied to the high-efficiency cutting of titanium alloy in aerospace and other fields.更多还原