【作者】 杨兵；

【导师】 杜勇； 陈利；

【作者基本信息】 中南大学 ， 材料物理与化学， 2014， 博士

【摘要】 摘要：金属切削过程中,涂层刀具表面与工件之间剧烈的摩擦使切削区域的温度急剧上升,因而涂层是否具有良好的热稳定性和高温抗氧化性能是衡量其性能的两个重要指标。由Al替代过渡族金属氮化物MeN (Me=Zr、Ti、Cr等)中部分Me形成的亚稳相MeAlN涂层,因具有高硬度、高熔点和抗氧化性好等优良性能,成为刀具涂层的研究热点。其中,Ti-Al-N和Cr-Al-N涂层相对其它涂层具有更好的高温抗氧化性能,在切削刀具上应用非常广泛。但是,Ti-Al-N涂层在高于1000℃时转变为稳定六方相w-AlN,使其力学性能下降,其抗氧化温度更是低于850℃；Cr-Al-N涂层虽然抗氧化温度高于1000℃但其在900℃以上会发生热分解而使涂层的力学性能下降。随着高速切削加工技术的不断发展,尤其是切削一些难加工材料时,刀具刃口温度达到1000℃以上,这一温度超过了Ti-Al-N和Cr-Al-N涂层的服役温度。因此,开发新的涂层材料、进一步改善涂层刀具的切削性能成为推动高速切削技术发展的关键技术之本论文首先比较目前通用的两种刀具涂层制备技术(阴极弧蒸发和磁控溅射技术)的优劣,确定高效的涂层工艺。在此基础上通过在Ti-Al-N和Cr-Al-N涂层中添加合金元素进一步改善涂层的力学及热性能。本工作所取得的主要研究成果如下：1)相比与磁控溅射沉积涂层的平滑表面,弧蒸发沉积涂层会出现“液滴”缺陷,因而提高了涂层的表面粗糙度。然而,弧蒸发沉积方法由于其沉积粒子高的表面扩散能力,沉积的Ti-Al-N涂层表现出更致密的结构而呈现更好的高温抗氧化性能；低的应力使其热分解温度向低温方向偏移而拥有高的热稳定性；并最终表现出更优异的切削性能。2)Ti-Al-N涂层中添加Si元素促进了w-AlN的形成,涂层表现出硬化效应,Si的加入阻止了Ti-Al-N的热分解过程,因此,Ti-Al-Si-N具有更高的热硬度。Si的加入显著改善了Ti-Al-N涂层的高温抗氧化性能,其高温抗氧化温度由Ti-Al-N的800℃。C提高到1100℃以上。3)Ti-Al-N涂层中添加Cr元素后,产生固溶强化和细晶强化效应,使涂层的硬度由31.2GPa提高到34.4GPa。因此,虽然Cr的加入促进了Ti-Al-N的热分解过程,但是Ti-Al-Cr-N涂层无论是沉积态还是高温退火态的硬度均大于Ti-Al-N涂层的硬度值。另外,Cr的加入将Ti-Al-N的高温抗氧化温度由800℃提高到900℃。4)在高温时Cr-N涂层中Cr—N键发生断裂,逐步释放出N原子,由Cr2N过渡并最终转化为单质Cr。在Cr-N涂层中加入Al,形成的Al-N键增强了N元素的稳定性,从而改善了Cr-N涂层的热稳定性。Al的加入改善了Cr-N的热稳定性,阻止了涂层在高温氧化时的体积收缩,因此,提高了涂层的高温抗氧化性能。5)Cr-Al-N涂层中添加Zr元素显著提升了涂层的热稳定性,其热稳定温度由Cr-Al-N的900℃提高到1100℃；但在高温氧化时,Zr的优先氧化使Cr-Al-N涂层的高温抗氧化性能大大降低。研究表明,在Ti-Al-N和Cr-Al-N涂层中添加合金元素有利于涂层的高温应用。在Ti-Al-N涂层中添加合金元素Cr或Si均可提高涂层的高温抗氧化性能,并分别通过固溶强化和界面强化效应提高涂层的力学性能；Cr-Al-N涂层中添加Zr元素可有效阻止涂层的热分解行为,从而改善涂层的热稳定性。更多还原

【Abstract】 Abstract:The work temperature of machining region rapidly increases due to the friction between coated cutting tools and metal materials during machining. Therefore, the thermal stability and high-temperature oxidation resistance of coating become very important for the coatings applied in cutting tools. Aluminum based ternary transition metal nitrides MeAIN hard coatings (Me=Zr, Ti, Cr, etc.) with cubic structure, where Al substitutes for Me in the MeN based lattice, are in favor for such industrial applications due to their high hardness and melting point together with high oxidation resistance. Among them, Ti-Al-N and Cr-Al-N are the most widely used in cutting tools due to more excellent anti-oxidation performance. However, the hardness of Ti-Al-N coating reduces while exceeding1000℃due to thermal decomposition, and the anti-oxidation temperature of Ti-Al-N coating is below850℃. Although the anti-oxidation temperature exceeds1000℃, the mechanical properties of Cr-Al-N coating decrease due to thermal decomposition above900℃. During severe industrial applications with working temperature reaching or exceeding1000℃, new coating materials with the optimized oxidation resistance and thermal stability are needed.Here, a comparative research on magnetron sputtering and arc evaporation deposition of Ti-Al-N coatings is investigated in order to choose coating technology. And then, an improvement of the properties for Ti-Al-N and Cr-Al-N coatings is achieved by incorporation of the forth alloy elements. This thesis is comprised of the following five parts:1. Evaporated Ti-Al-N coating exhibits the typical growth defects originated form incorporated macro-particles and roughened surface, compared with the non-defect surface of sputtered Ti-Al-N coating. However, high atom mobility of arc evaporation process arising from the high ion to neutral ratio results in a more dense structure, and thus higher oxidation resistance. Simultaneously, the thermal decomposition temperature of evaporated Ti-Al-N coating with low stress shifts to higher temperature, and the coating exhibits better thermal stability. At last, evaporated Ti-Al-N coated tools exhibit better machining performance.2. The alloying with Si into Ti-Al-N coating promotes the growth of w-AIN phase, and the coating behaves hardening behavior. Ti-Al-Si-N coating exhibits higher thermal hardness due to the retarded thermal decomposition process with incorporation of Si into Ti-Al-N. Additionally, addition of Si element significantly improves the oxidation resistance of Ti-Al-N coating. The oxidation temperature of Ti-Al-Si-N coating is elevated to1100℃from800℃of Ti-Al-N coating.3. Incorporation Cr into Ti-Al-N coating results in an increase in hardness from～31.2GPa for Ti-Al-N coating to～34.4GPa due to the solid solution strengthening and decreased grain size. Therefore, Cr-containing coating behaves higher thermal hardness although alloying with Cr promotes the thermal decomposition process. The oxidation temperature of Ti-Al-Cr-N coating is elevated to900℃from800℃of Ti-Al-N coating.4. The N-loss of Cr-N coating at elevated temperature occurs, and thus results in the formation of h-Cr2N and finally Cr due to the instability of Cr—N bond. Addition of Al into Cr-N coating strengthens the stability of N in the CrN phase and thus promotes its thermal stability. Correspondingly, the oxidation resistance of Cr-N coating is improved by incorporation of Al.5. The thermal stability of Cr-Al-N coating is significantly improved with incorporation of Zr, where the thermal decomposition temperature is increased up to1100℃from900℃for Cr-Al-N coating. Nevertheless, alloying with Zr into Cr-Al-N coating leads to a drop in oxidation resistance.The results show that addition of the forth alloy element into Ti-Al-N and Cr-Al-N is beneficial to their application at high temperature. Alloying with Cr and Si into Ti-Al-N coating improves its mechanical and thermal properties. And incorporation of Zr into Cr-Al-N coating retards its thermal decomposition process, and thus improves the thermal stability of Cr-Al-N coatings.更多还原