【作者】 陈利；

【导师】 杜勇； Paul H.Mayrhofer；

【作者基本信息】 中南大学 ， 材料学， 2009， 博士

【摘要】 Ti-Al-N涂层具有优良的高温抗氧化性能和力学性能成为目前应用最普遍的刀具涂层材料,其晶体结构和力学性能在很大程度上取决于涂层中的Al含量,当Al含量超过TiN的固溶度时,立方相（c）Ti-Al-N向六方（h）转化而使其力学性能显著降低。因此,Ti-Al-N涂层中Al含量的控制显得尤为重要。但是,现在普遍采用的溅射沉积技术制备的涂层成分经常会偏离靶材成分,涂层成分的精确控制难度很大。近来,Ti-Al-N涂层的热稳定性能受到越来越多的关注,亚稳的c-TiAlN在高温（约1000℃）时会向其稳定相c-TiN和h-AlN转化,从而导致涂层失效。然而,h-AlN的形成需要经过调幅分解析出c-AlN作为过渡相才能实现,调幅分解的发生引起涂层的时效硬化现象的发生。到目前为止,Ti-Al-N涂层的时效硬化现象的研究还不够深入,特别是其应用基本上还没有涉及。在实际切削应用中,尤其是对于干式高速切削,切削区域的温度经常高于Ti-Al-N的热分解温度（约1000℃）。为了抑制Ti-Al-N涂层的高温分解过程,在Ti-Al-N涂层中添加第四组元以提高涂层的力学性能和热稳定性已成为目前刀具涂层的前沿研究领域。本论文从溅射过程中Ti、Al原子的不同丢失情况出发,揭示了各种沉积条件下沉积的Ti-Al-N涂层的组成和结构的变化机理。Ti-Al-N基涂层的热稳定性为本论文的另一研究重点。本论文首次详细研究了不同Al含量、不同晶体结构的Ti-Al-N涂层的时效硬化现象,并深入地研究了Ti-Al-N涂层的时效硬化在切削刀具上的应用。本研究还发现:通过Si、Zr元素的加入形成的Ti-Al-X-N四元涂层改善了涂层的热稳定性和力学性能。在此基础上对Ti-Al-Si-N涂层的微结构进行了改进,成功地实现了其在工业上的应用。所取得的主要研究成果如下:1.应用角度、散射丢失机理详细地分析了反应溅射Ti_0.5Al_0.5复合靶材制备Ti-Al-N涂层时不同氮化靶材表面的Ti、Al原子丢失情况,并在此基础上研究了各种沉积条件下制备的Ti-Al-N涂层的成分与微结构的变化。本研究为溅射沉积Ti-Al-N涂层的组成控制提供了系统的理论指导,使Ti-Al-N涂层成分的精确控制成为可能。本研究还表明:在涂层制备过程中,通过调整沉积参数来减小沉积原子的表面扩散能力有利于提高Al在c-TiAlN涂层中的固溶度。2.Ti-Al-N涂层的热分解过程需先经过调幅分解析出亚稳相的c-AlN相作为过渡,然后再转变为稳定的h-AlN相,调幅分解的发生伴随着时效硬化的出现。Ti-Al-N涂层的调幅分解与时效硬化效应与涂层中的Al含量密切相关。高的Al含量会驱使调幅分解与时效硬化在低温区间出现,同时涂层的失效温度也相应的在低温区出现。Ti-Al-N涂层的时效硬化特性为热处理Ti-Al-N涂层刀片并改善其切削性能提供了可能。热处理后的时效硬化改善了涂层的车削性能。但对于铣削加工,合适的热处理工艺则显得尤为重要。通过在700-800℃温度区间快速冷却,而在其它温度区间缓慢冷却,可在增加涂层硬度的同时,减少热处理过程对硬质合金的韧性及涂层与基体的结合强度的影响,从而改善了涂层刀片的铣削性能。3.Ti-Al-N涂层中添加Si形成的nc-Ti_1-xAl_xN/a-Si₃N₄纳米晶复合结构大幅改善了涂层的硬度和热稳定性能。nc-Ti_1-xAl_xN/a-Si₃N₄的热分解过程也会发生调幅分解,从而引起时效硬化。(Ti_0.45Al_0.55)_0.93Si_0.07在1100℃高温时仍能维持高硬度值～42.4GPa。4.Zr元素的加入在降低Ti-Al-N涂层时效硬化的起始温度的同时,还可提高c-AlN向h-AlN的转变温度。因而在Ti-Al-N体系中加入Zr可改善涂层的热稳定性、延长了其时效硬化温度区间,从而有利于涂层的高温应用。5.研究Ti-Al-N与Ti-Al-Si-N在切削刀具上的应用,并通过多层界面结构进一步改善了其切削性能,实现这两种涂层的产业化应用。TiN/TiAlN多层涂层的界面强化作用增加了涂层的硬度并改善了涂层与基体之间的结。因而无论是车削还是铣削加工,多层涂层都表现出比TiN、Ti-Al-N单层涂层更好的切削性能。nc-Ti_1-xAl_xN/a-Si₃N₄纳米晶复合结构改善了涂层的耐磨性与热稳定性,因而提高了其车削性能。然而,nc-Ti_1-xAl_xN/a-Si₃N₄涂层与基体低的结合强度、高的内应力及脆性使其铣削性能下降。通过结构设计制备的TiAlN-TiAlSiN双层和TiAlN/TiAlSiN多层涂层刀片不仅可以降低涂层内应力,而且还增加了涂层与基体的结合强度。低的内应力和高的结合强度有利于改善涂层刀片的铣削性能。特别是TiAlN/TiAlSiN多层涂层刀片在不降低车削性能的前提下,大幅度改善了涂层刀片铣削性能。更多还原

【Abstract】 Ti-Al-N coatings have become the most widely used coating for dry machining due to their high temperature oxidation resistance and excellent mechanical peroperties.The chemical composition of Ti-Al-N coatings basically determines their structure and properties.For Al contents exceeding the cubic solid solubility,a mixed cubic-NaCl and hexagonal-ZnS（h-AlN） structure is formed,which results in reduced coating properties.The Al content of Ti-Al-N coatings has a significant effect on their structure and properties.The composition of the coating deposited using sputtering technology can deviate from that of the corresponding target,which makes it difficult to control the composition of sputtered film.Recently,increasing attention has been concentrated on the thermal stability of Ti-Al-N coatings.The transformation of（c） TiAlN into the c-TiN and c-AlN at elevated temperature of～1000℃results in a drop of mechanical properties.However,this transformation involves an intermediate step of c-AlN by spiondal decomposition,and concomitant increase of the hardness occurs.Nevertheless,there is only limited information on the age-hardening of Ti-Al-N coatings so far,especially for its industrial application.The cutting temperature during high speed and dry cutting exceeds the decomposition temperature（～1000℃） of Ti-Al-N.Therefore,a considerable effort was done by alloying Ti-Al-N based coatings with several elements to improve their mechanical properties and thermal stability.Here,we study the compositional and structural evolution of sputtered Ti-Al-N coatings with different deposition parameters allowing for the different loss states of sputtered Ti,and Al atoms.Additionally,the thermal stability and age-hardening of Ti-Al-N coatings with variable Al content and structure are investigated.Furthermore,we also focus on the age-hardening application of Ti-Al-N coatings on cutting application.The incorporation of Si and Zr into Ti-Al-N coatings significantly improves their mechanical properties and thermal stability.And the commercial process of Ti-Al-Si-N coatings after adjustment of their structure is realized.This thesis is comprised of the following five parts:1.The different poisoning state of the Ti and Al particles of Ti_0.5Al_0.5 target in addition to scattering and angular losses causes a significant compositional and structural modification during preparation of Ti-Al-N with different deposition parameters.This mechanism makes it possible to compositional control of sputtered Ti-Al-N.The decreased surface-diffusion process of deposited atoms by adjustment of deposition parameters allows for the higher Al solid solution in TiN.2.The decomposition of Ti-Al-N coating into the stable phases c-TiN and h-AlN involves an intermediate step associated with the formation step of c-AlN.Ti-Al-N coating undergoes spinodal decomposition with the formation of nm-sized cubic TiN and AlN domains resulting in an increase of hardness.The spiondal decomposition and age-hardening of Ti-Al-N coating have an affinity with Al content,where Ti-Al-N coating with higher Al content permits the occurrence of spiondal decomposition and failure at lower temperature.The turning and milling performance of coated inserts can be optimized by a post-deposition annealing treatment, where the coating undergoes age-hardening,combined with a cooling condition allowing for high cohesion and fracture toughness of the cemented carbide.The latter is essential during milling.The improvement during milling is only obtained if the cooling after annealing at 900℃is performed in three steps.The temperature is decreased from 900 to 800℃by a vacuum furnace cooling,from 800 to 700℃by Ar-flow cooling, and further to RT again vacuum furnace cooling.3.The higher hardness and improved thermal stability are obtained by incorporation of Si into Ti-Al-N coatings due to the formation of special three-dimensional net structure consisting of nanocrystalline（nc） TiAlN encapsulated in an amorphous（a） Si₃N₄ matrix phase.Such a strucutre hinders the generation of h-AlN during high temperature annealing.The spiondal decomposition of nc-TiAlN/a-Si₃N₄ coatings also causes the age-hardening,where the hardness of～42.4 GPa after annealing of (Ti_0.45Al_0.55)₀.93 Si_0.07 coatings at 1100℃is acquired.4.Ti-Al-N coatings alloyed with Zr significantly improve the thermal stability,where Ti-Al-Zr-N coatings allow the occurrence of spiondal decomposition at lower temperature and also retard the decomposition of h-AlN at higher temperature.The incorporation of Zr into Ti-Al-N coatings widens the temperature region of age-hardening and is benefit to its high temperature application.5.The application of Ti-Al-N and Ti-Al-Si-N coatings on cutting tools is investigated.The performance of coated tools is further improved by multilayer structure,and thus realizes the commercial process.The interfaces of TiN/TiAlN multilayers increase the hardness and improve the cohesion strength with substrate.Therefore,the TiN/TiAlN multilayer coated inserts behaves better turning and milling performances compared to TiN and Ti-Al-N coated inserts.The turning performance of nc-TiAlN/a-Si₃N₄ coated inserts can be increased due to the higher hardness and improved thermal stability, However,a decrease in milling properties is obtained owe to their higher stress,brittleness and worse adhesion between coating and substrate.The structural adjustment of Ti-Al-Si-N coating into TiAlN-TiAlSiN bilayer and TiAlN/TiAlSiN multilayer coatings further improves the machining performance including both turning and milling.更多还原