Analysis of the manufacturing chain of CVD diamond coated shaft type cutting tools

Hypereutectic aluminium silicon alloys, e.g. casted AlSi17Cu4Mg, are commonly used in the automotive and aeronautical industries. These alloys consist of hard, abrasive silicon particles in a soft aluminium matrix and thus place high mechanical loads on the tool during machining processes. Polycrystalline Diamond or CVD (chemical vapour deposition) diamond based cutting tools can be used for the high speed machining of these alloys due to their high hardness and wear resistance. Diamond thin film coatings of different film morphologies are commonly applied on cemented carbide tools using Hot Filament CVD. The distinguishing characteristic to other coatings is utmost hardness resulting in high resistance to abrasion, low tendency to adhesion and low friction coefficient. The manufacturing of CVD diamond coated shaft type cutting tools is challenging due to the complex design of the cutting edges and the demanding stress behaviour during tool application. The influencing parameters of substrate type, chemical and mechanical substrate pre-treatment as well as diamond film modification on the tool cutting performance are discussed. The manufacturing route of CVD diamond coated thread milling drills is analysed with the use of material and tribological tests. The complex thread manufacturing tools are then applied in the machining of AlSi17Cu4Mg, whereby the tool performance is characterised with respect to their wear behaviour, the process forces and temperatures as well as the workpiece quality.     

Process and engineering benefits of sputter-ion-plated titanium nitride coatings

Titanium nitride (TiN) coatings are established in the metal cutting and metal forming industries where they enhance the operating lives of tools and offer substantial gains in productivity. Several technologies for physical vapour deposition (PVD) of TiN have been developed. Coatings, which are usually 1 – 3 μm thick, are hard, chemically inert and create low friction against mating materials.This paper concentrates on a particular PVD technology called sputter ion plating (SIP). An outline is given of the equipment and the salient features of the process; emphasis is placed on the capability to coat large mixed workloads on stationary fixtures with uniform high quality layers of TiN.The main theme of the paper is to illustrate the engineering benefits of SIP TiN coatings by reference to a number of case histories. Applications include tooling used for metal cutting, metal forming, slitting and punching; applications are also included where the performances of bearings and fasteners are improved.     

化学气相沉积制备硬质合金刀具涂层研究进展

化学气相沉积技术(CVD)广泛应用于硬质耐磨涂层的生产中,该类涂层可大大提高硬质合金工具的耐磨性和寿命。综述了CVD涂层技术在硬质合金切削刀具中的应用研究进展,首先介绍了CVD涂层技术的原理及其发展历程;其次阐述了模拟计算方法(相图计算、流体力学计算、第一性原理计算、相场模拟、机器学习等)在CVD涂层中的应用;再次介绍了CVD涂层的沉积实验及结构和性能表征方法;最后列举了几种典型的硬质合金刀具用CVD涂层,以期为高性能涂层的智能设计、智能集成和智能研发提供新的思路:即把多尺度计算模拟、科学数据库和关键实验集成到硬质涂层开发的全过程中,通过对成分-工艺-结构-性能进行关联分析,将耐磨涂层的研发由传统经验或者半经验方式提升到科学的微结构智能设计上,以实现基体与涂层微结构调控和性能的协同优化,获得最佳的综合性能。     

Challenges for exploitation of physical vapour deposition in metal cutting

Abstract

The physical vapour deposition of hard coatings on cutting tools is an emerging technology with the capability of generating many different coatings with complex microstructures which have the potential for exploitation in a wide variety of applications. A current drawback to the cost effective exploitation of such coatings is the lack of knowledge concerning some aspects of chip formation and the tribological interactions occurring at the chip tool interface. This paper takes a step back to overview some of the materials science aspects of these issues and looks at the temperature profiles generated beneath uncoated and coated cutting tools in simple turning experiments. It is demonstrated that such experiments can lead to a clearer understanding of chip tool interactions and assist in the cost effective exploitation of speciality physical vapour deposition coatings designed for fitness for purpose.     

硬质合金工具强电流直流伸展弧等离子体CVD金刚石涂层的均匀性研究

采用自行研制的强电流直流伸展电弧等离子体CVD设备对真空渗硼预处理的YG6刀片进行了金刚石涂层沉积，并对放于有效沉积区域不同位置沉积出的金刚石涂层刀片以及刀片自身不同位置之表面涂层的形貌、厚度、质量进行了分析、研究。结果表明：(1)、硬质合金工具强电流直流伸展弧等离子体CVD金刚石涂层的组织、形貌、厚度、质量都是均匀一致的。(2)、利用强电流直流伸展电弧等离子体CVD设备可进行硬质合金金刚石涂层的批量沉积。     

Industrial applications of superhard nanocomposite coatings

Recent progress in the development and industrialization of superhard and tough nanocomposite coatings, which consist of hard transition metal nitride nanocrystals “glued together” by about 1 monolayer of silicon nitride, is summarized and documented by selected illustrative examples. It is shown that already the presently available superhard nanocomposites applied on machining, stamping and forming tools significantly increase their lifetime and the cutting speed, and consequently also the overall productivity of the machining operations. Further improvement of the presently available and newly developed nanocomposite coatings will push the machining technology towards new horizons. Besides of the superhard nanocomposites, also medium hard, but very tough thick coatings with low internal stress applied to forming tools increase their lifetime by at least one order of magnitude.     

Structure and physicomechanical properties of NbN-based protective nanocomposite coatings: A review

This review summarizes the present-day achievements in the study of the structure and properties of protective nanocomposite coatings based on NbN, NbAlN, and NbSiN prepared by a variety of modern deposition techniques. It is shown that a change in deposition parameters has a significant effect on the phase composition of the coatings. Depending on the magnitude of negative potential on the substrate, the pressure of nitrogen or a nitrogen–argon mixture in the chamber, and the substrate temperature, it is possible to obtain coatings containing different phases, such as NbN and SiN_x (Si₃N₄), AlN, and NbAl₂N. It is found that, in the case of formation of the ε-NbN phase, the coatings become very hard; their hardness achieves values on the order of 53 GPa. At the same time, they remain thermally stable at temperatures of up to 600°C, chemically inert, and resistant to wear. The effect of the nanograin size, the volume fraction of boundaries and interfaces, and the point defect concentration on the physicomechanical properties of these coatings is described. Niobium nitride-based coatings can be used in superconducting systems and single-photon detectors; they are capable of operating under the action of strong magnetic fields of up to 20 T; they can be used in integrated logic circuits and applied as protective coatings of machine parts, edges of cutting tools, etc.     

沉积温度对硬质合金金刚石涂层附着力影响的研究

采用压痕实验、扫描电镜与激光Raman光谱分析,实验研究了酸浸硬质合金基底上金刚石涂层的附着力随沉积温度的变化.结果表明,涂层质量随沉积温度降低而显著恶化,涂层应力则随沉积温度提高而上升.从提高涂层附着力的角度考虑,存在一个最佳沉积温度.在较低的沉积温度下,涂层自身的质量较低、力学性能较差,在载荷作用下易于破坏.提高沉积温度,涂层自身的质量可得到改善,但基底中的钴向基底表面扩散的倾向加大,而且热应力增大,会严重降低涂层与基底的附着力.除硬质合金基底的预处理工艺外,沉积工艺对金刚石涂层的组织、性能以及附着力均有重要影响.     

Tribological properties of thin hard coatings: demands and evaluation

Thin hard coatings are currently being used in a large number of tribological applications. Some important examples are tools for metal cutting and forming, and machine elements like sliding bearings, seals, valves, etc. The present paper deals with the problems of identifying the limiting factors in given tribological applications of coating composites, and how to experimentally determine their tribological responsse, with special attention given to wear.

As a means for coating development, the intricate relations between coating deposition parameters and the triboological response of the coated composite are indicated by a flow chart of relevant coating and substrate properties. It is demonstrated how the general characteristics (topography, composition, microstructure, etc.) and fundamental properties (chemical, thermal, mechanical, etc.) of coating and substrate combine to generate the tribological properties (resistance against abrasion, erosion, sliding wear, etc.), which given the tribological loading, determines the tribological response in terms of friction and wear.

A number of different test methods for tribological evaluation of coating composites are presented together with illustrative examples. The test range from four-point bending for evaluating coating fracture strength, to designated tribological tests to determine the resistance against abrsion, particle erosion, and sliding wear.     

The Properties and Applications of MoS_2/Ti Composite Coatings in Dry Cutting and Forming

MOLYBDENUM DISULFIDE COATIGS have beensuccessfully used in vacuum and aerospaceenvironments in the past30years.In recent years,theapplication of MoS2coatings in ambient or high humidenvironments has been drawing increasing attentions.The main obstacle to the use of MoS coating inambient conditions is its sensitivity to humidity.Fig.1shows the cases that may degrade the humidityresistance of MoSx coatings,such as the columnarstructure,low density,edge orientation of the coatings;and…     

高能量密度脉冲等离子体制备高硬耐磨TiN涂层

用高能量密度脉冲等离子体于室温下在硬质合金刀具上成功淀积了高硬耐磨TiN涂层．实验结果表明，涂层与基体有强的结合力，纳米划痕实验临界载荷达90mN以上；TiN涂层具有很高的硬度和Young’s模量，分别达27和450GPa以上．涂层刀具切削实验表明，刀具可用于硬度高达HRC58-62的CrVVMn钢切削，且磨损量较低，寿命长．     

The effect of the multi-layer surface coating of carbide inserts on the cutting forces in turning operations

In this paper, the effects of the multi-layer hard surface coating of cutting tools on the cutting forces in steel turning are presented and discussed, based on an experimental investigation with different commercially available carbide inserts and tool geometries over a range of cutting conditions. The cutting forces when turning with surface coated carbide inserts are assessed and compared qualitatively and quantitatively with those for uncoated tools. It is shown that hard surface coatings reduce the cutting forces, although the reduction is marginal under lighter cutting conditions. The cutting force characteristics for surface coated tools are also discussed and shown to have similar trends to those of uncoated tools.     

超硬纳微米 PVD 涂层技术在刀具领域的应用及研究进展

介绍了物理气相沉积(PVD)技术的原理、特点和真空蒸镀、溅射镀和离子镀之间的优缺点,从二元涂层、多元涂层、多层涂层和纳米多层复合涂层等4种类别上介绍了PVD涂层技术在切削刀具上的广泛应用。在查阅和整理大量文献资料的基础上,也结合笔者多年从事PVD技术的研究与应用心得,从提高切削刀具的寿命这一重要角度出发,阐述了国内外超硬纳微米PVD涂层技术在切削刀具应用领域的研究进展,并对多元涂层、多层涂层及涂层的纳米化也进行了较为详细地论述。切削刀具表面采用物理气相沉积涂层技术能使刀具获得优异的综合性能,从而显著提高切削刀具的使用寿命,降低生产成本,大幅提高机械加工效率。最后展望了物理气相沉积涂层技术未来将在超硬切削(包括模具钢、淬硬钢等硬度超过HRC55以上的铣削加工)、难加工材料切削(包括高温合金、钛合金、不锈钢等)、石墨和碳纤维等复合材料加工和有色金属的高速切削加工(包括铝合金、铜合金、镍等)的广泛应用。     

Applications of Cr-Based Metal Nitride Hard Coatings Using Multi-Magnetron Sputtering Sources and Elemental Metal Targets

METAL NITRIDE or carbide coatings on cutting toolsare effective ways of improving tool performance.Thedriving force for high productivity and precision inmetal machining has led to the requirement of acontinual improvement of conventional hard coatings.It is necessary that those attractive properties of hardcoatings could be simultaneously retained.Highhardness resists abrasive wear.High chemical orthermal stability reduces dissolution wear andmaintains physical properties at a high tempe…     

Hard and wear-resistant titanium nitride coatings for cemented carbide cutting tools by pulsed high energy density plasma

Hard and wear-resistant titanium nitride coatings were deposited by pulsed high energy density plasma technique on cemented carbide cutting tools at ambient temperature. The coating thickness was measured by an optical profiler and surface Auger microprobe. The elemental and phase compositions and distribution of the coatings were determined by Auger microprobe, x-photon electron spectroscope, and X-ray diffractometer. The microstructures of the coatings were observed by scanning electron microscope and the roughness of the sample surface was measured by an optical profiler. The mechanical properties of the coatings were determined by nanoindentation and nanoscratch tests. The tribological properties were evaluated by the cutting performances of the coated tools applied in turning hardened CrWMn steel under industrial conditions. The structural and mechanical properties of the coatings were found to depend strongly on deposition conditions. Under optimized deposition conditions, the adhesive strength of TiN film to the substrate was satisfactory with the highest critical load up to more than 90 mN. The TiN films possess very high values of nanohardness and Young’s modulus, which are near to 27 GPa and 450 GPa, respectively. The wear resistance and edge life of the cemented carbide tools were improved dramatically because of the deposition of titanium nitride coatings.     

An effort to enhance adhesion of diamond coatings to cemented carbide substrates by introducing Si onto the interface

For diamond-coated cemented carbide cutting tools, adhesion of the coatings remains to be a problem. This problem originates from the fact that the adhesion mechanism of the coating–substrate system is mechanical in nature and hence the adhesion of the coatings is ordinarily weak. As an effort to improve adhesion of diamond coatings to the substrates, Si was introduced into the diamond chemical vapor deposition (CVD) process, in order to produce a chemically active glue interface between the diamond coatings and the substrates. Preliminary results showed that by introducing a nontoxic precursor, octamethylcyclotetrasiloxane (D₄), and under normal microwave plasma CVD conditions, Si could be made concentrating onto the interface, benefiting the improvement in adhesion of the diamond coatings.     

Advantages of nanocomposite coatings deposited by high power pulse magnetron sputtering technology

Recent advantages in PVD coatings for cutting tools enable high speed and dry machining with superior cutting parameters in commercial manufacturing sectors. For this reason hard coatings with high oxidation resistance and thermal stability are used for economically justifiable machining. In this regard nc-(Ti,Al)N/a-Si₃N₄ films were sputtered on tungsten carbide cutting tools and WC/Co samples by using the high power pulse magnetron sputtering (HPPMS) technology. Coating composition, microstructure and applied properties were investigated by using X-ray diffraction, scanning electron microscope and nanoindentation. The hardness value was about 29 GPa for a Si content of 3.3 at.%. The grain size was about 6 nm. As this study focuses on the thickness uniformity of the coatings, SEM pictures of the cross-section have been taken around the cutting edge to determine the deposition rate and the film growth. The coatings morphology has been compared to middle frequency and direct current sputtered nanocomposite (Ti,Al,Si)N films. The results demonstrate the enhanced HPPMS coatings properties, including a denser structure, a smoother surface and a favourable thickness uniformity.     

Nanocrystalline diamond coating tools for machining high-strength Al alloys

Diamond coating tools have been increasingly used for machining advanced materials. Recently, a microwave plasma-assisted chemical vapor deposition (CVD) technology was developed to produce diamond coatings which consist of nano-diamond crystals embedded into a hard amorphous diamond-like carbon matrix. In this study, the nanocrystalline diamond (NCD) coating tools were evaluated in machining high-strength aluminum (Al) alloy. The conventional CVD microcrystalline diamond coating (MCD) tools and PCD tools were also tested for performance comparisons. In addition, stress distributions in diamond coating tools, after deposition and during machining, were analyzed using a 2D finite element (FE) thermomechanical model.

The results show that catastrophic failures, reached in all except one machining conditions, limit the NCD tool life, which is primarily affected by the cutting speed. In addition, coating delamination in the worn NCD tools is clearly evident from scanning electron microscopy (SEM) and force monitoring in machining can capture the delamination incident. At a high feed, coating delamination may extend to the rake face. Furthermore, SEM observations of coating failure boundaries show intimate coating-substrate contact. Though the NCD tools are inferior to the PCD tools, they substantially outperform the MCD tools, which failed by premature delamination. The diamond coating tools can have high residual stresses from the deposition and stresses at the cutting edge are highly augmented. Further machining loading causes the stress reversal pattern which seems to correlate with the tool wear severity.     

Surface modification of 6150 steel substrates for the deposition of thick and adherent diamond-like carbon coatings

Because of the high residual compressive stress normally accompanying the growth of diamond-like carbon (DLC) coatings and the large mismatch in the thermal expansion coefficient between DLC and steel, it is difficult to grow DLC coatings much thicker than 0.25 μm on steels. This paper describes our attempt to overcome this thickness limitation by a sequence of carbonitriding, carburizing and equilibration pre-treatments of the steel surface, followed by DLC coating deposition, all conducted within the same deposition system without breaking vacuum. These pre-treatments resulted in a surface with a graded composition and hardness profile. Such a graded interface is expected to reduce the interfacial energy, decrease thermal mismatch between the coating and the substrate, and thus improve coating adhesion. X-ray diffraction revealed the formation of various hard carbide and nitride phases. Raman spectroscopy showed that the modified steel surface just before DLC deposition exhibits local carbon bonding characteristics similar to DLC. Pulsed dc plasma-enhanced chemical vapor deposition was used to deposit one-micron thick DLC on these steel surfaces. The coating hardness was ~ 18-19 GPa. Its adhesion on the steel substrate was measured by scratch testing and was found to be comparable to thick, adherent DLC coatings deposited by other methods.     

Thermally Sprayed Coatings as Effective Tool Surfaces in Sheet Metal Forming Applications

Two approaches to produce wear-resistant effective surfaces for deep drawing tools by thermal arc wire spraying of hard materials are presented. Arc wire spraying is a very economic coating technique due to a high deposition rate. The coated surface is very rough compared to that of conventional sheet metal forming tools. In the first approach, the coated surface is smoothed in a subsequent CNC-based incremental roller burnishing process. In this process, the surface asperities on the surface are flattened, and the roughness is significantly reduced. In the second approach, the hard material coatings are not sprayed directly on the tool but on a negative mould. Afterward, the rough “as-sprayed” side of the coating is backfilled with a polymer. The bonded hard metal shell is removed from the negative mould and acts as the surface of the hybrid sheet metal forming tool. Sheet metal forming experiments using tools based on these two approaches demonstrate that they are suitable to form high-strength steels. Owing to a conventional body of steel or cast iron, the first approach is suitable for large batch sizes. The application of the second approach lies within the range of small up to medium batch size productions.