Brittleness and fatigue effect of mono- and multi-layer PVD films on the cutting performance of coated cemented carbide inserts

The effect of brittleness and fatigue of mono- and multi-layer PVD films on coated tools cutting performance is introduced. Cemented carbide inserts were coated to the same overall film thickness with various numbers of layers. Nanoindentations were conducted to evaluate the hardness of the diverse coating structures. The film brittleness and fatigue were characterized by nano- and macro-impact tests respectively. The coated inserts’ wear behaviour was investigated in milling hardened steel. The attained results revealed the coatings’ brittleness and fatigue endurance enhancement by increasing the number of film's layers. This increase leads simultaneously to the coated tool life improvement.     

The effect of substrate pretreatments and HPPMS-deposited adhesive interlayers’ materials on the cutting performance of coated cemented carbide inserts

High power pulsed magnetron sputtering (HPPMS), substrate pretreatments and adhesive interlayers can enhance tool life significantly. In the conducted research, TiAlN PVD-films and W-, Ti- or Cr-adhesive nanointerlayers were deposited by HPPMS on different superficially treated hardmetal inserts. The mechanical properties of the coatings were determined via nanoindentations and mathematical analysis. Additionally, inclined impact tests and milling investigations were performed to examine the substrate pretreatment and interlayer effects on film adhesion and wear behaviour. The results reveal that HPPMS jointly with an appropriate substrate pretreatment and a Cr-nanointerlayer lead to significant adhesion and cutting performance improvement.     

CVD diamond coatings on geometrically complex cutting tools

The manufacturing of chemical vapour deposition (CVD) diamond coated shaft type cutting tools is demanding due to the complex design of the cutting edges and the cobalt content of the cemented carbide. The influencing parameters of substrate, pre-treatment and diamond film on the tool cutting performance are discussed. The optimised manufacturing route of CVD diamond coated thread milling drills is identified with the use of material and tribological tests. Following the optimised production of the tools, the thread milling drills 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.     

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.     

硼掺杂梯度对硬质合金金刚石涂层的影响

为提高硬质合金刀具上金刚石涂层的结合性能,采用热丝化学气相沉积法在YG 8硬质合金基体上沉积高、低梯度硼掺杂微米金刚石（high gradient boron-doped micron crystal diamond, HGBMCD;low gradient boron-doped micron crystal diamond, LGBMCD）涂层和无硼掺杂的微米金刚石（micrometer crystal diamond, MCD）涂层,探究沉积过程中硼掺杂浓度的梯度大小对金刚石涂层的形核和生长性能的影响。结果表明:随着硼的掺入,金刚石的形核密度增大,生长6 h后的金刚石晶粒更均匀细小,其中LGBMCD的晶粒尺寸大部分在2～3 μm;而石墨相在梯度硼掺杂金刚石涂层中的生长会被抑制,HGBMCD中I_Dia/I_G高达14.65,残余应力仅为–0.255 GPa,且Co₂B、CoB等硼钴化合物含量随硼掺杂梯度的减小而增大;金刚石涂层的残余应力因硼的掺入逐渐从压应力转变成拉应力,残余应力大小先减小后增大;洛氏压痕显示,随着硼的掺入,金刚石涂层的结合性能提高,LGBMCD的结合性能最好,在1 470 N下可达到HF2级。因此,适当的硼掺杂梯度有利于提高金刚石涂层的质量和结合性能。      

Face milling of the EN AB-43300 aluminum alloy by PVD- and CVD-coated cemented carbide inserts

Two commercially available WC-6Co cemented carbide substrates (Extramet EMT100 and Pramet H10), were industrially coated with PVD TiB₂ or CVD diamond. Subsequently, the coated inserts were submitted to dry sliding tests (slider on cylinder contact geometry) against the aluminum alloy EN AB-43300, for preliminary performance ranking and identification of basic wear mechanisms. The best substrate/coating combination (CVD-Diamond coated Extramet EMT100) was then tested in face milling EN AB-43300 with milling tool characterized by two different geometries (A and B), using PCD inserts as a reference for comparison. In milling tests, the influence of both insert geometry and cutting fluid feed rate were taken into account. The geometry of the tool was identified as the main parameter in influencing the tool performance. In particular, in the case of the A geometry, the relative flank wear of CVD coated tools increased abruptly during the test due coating detachment, whilst with the B geometry no catastrophic failure of the CVD coated insert was observed. The influence of Cutting Fluid Feed Rate (CFFR) also changed with tool geometry: in particular, with the B geometry, which allowed to obtain the best results with the CVD coated inserts, a decrease of CFFR from 100 to 25% did not affect significantly the wear resistance of CVD-coated inserts and allowed to maintain the roughness of the workpiece (R_a) below 0.6 μm, notwithstanding a slightly increased tendency towards the formation of Al-based transfer layers.     

渗硼+两步处理硬质合金微米-纳米金刚石复合涂层工具研究

研究了固体粉末渗硼＋碱酸两步预处理硬质合金基体的表面组织、形貌、粗糙度。实施优化的微米．纳米为0．1402μm金刚石复合涂层沉积工艺，得到表面平整、光滑、平均粗糙度的优质金刚石复合涂层。该涂层与基体附着力高，压痕测试其临界载荷大于1500N，金刚石复合涂层刀具加工ZAlSi12合金试验表明其切削寿命是无涂层刀具的41倍。     

Thermal stresses in diamond coatings and their influence on coating wear and failure

Thermal stresses in diamond coatings deposited onto cemented carbide substrates are calculated using the finite element method. The thermo-elastic stress fields for some coating-substrate geometries are presented. The results are compared with experimental data on the tribological behaviour of diamond coatings. Residual stresses can explain many of the observed patterns of coating wear and failure. A model for the abrasive wear of brittle coatings under large compressive biaxial stresses is described. These stresses prevent cracks initiated at the surface to propagate towards the interface and may promote crack paths parallel to the interface, thus causing the formation of a smooth coating surface. Once the smooth appearance is reached it will become extremely hard to initiate and propagate cracks into the coating and consequently the wear rate becomes very low. Thus, large compressive residual stresses increase the already high wear resistance of diamond coatings. When diamond coatings are deposited onto substrate edges, intense concentrations of normal and shear stresses may lead to coating failure by interfacial spalling. These stresses are lowered by increasing the ratio r/h, where r is the edge radius and h is the coating thickness.     

Adhesion analysis and dry machining performance of CVD diamond coatings deposited on surface modified WC-Co turning inserts

This paper investigates the effects of different surface pretreatments on the adhesion and performance of CVD diamond coated WC-Co turning inserts for the dry machining of high silicon aluminum alloys. Different interfacial characteristics between the diamond coatings and the modified WC-Co substrate were obtained by the use of two different chemical etchings and a CrN/Cr interlayer, with the aim to produce an adherent diamond coating by increasing the interlocking effect of the diamond film, and halting the catalytic effect of the cobalt present on the cemented carbide tool. A systematic study is analyzed in terms of the initial cutting tool surface modifications, the deposition and characterization of microcrystalline diamond coatings deposited by HFCVD synthesis, the estimation of the resulting diamond adhesion by Rockwell indentations and Raman spectroscopy, and finally, the evaluation of the dry machining performance of the diamond coated tools on A390 aluminum alloys. The experiments show that chemical etching methods exceed the effect of the CrN/Cr interlayer in increasing the diamond coating adhesion under dry cutting operations. This work provided new insights about optimizing the surface characteristics of cemented carbides to produce adherent diamond coatings in the dry cutting manufacturing chain of high silicon aluminum alloys.     

Direct manufacturing of diamond composite coatings onto silicon wafers and heat transfer performance

This paper reveals new insights on how to achieve direct deposition of functional materials onto silicon wafers for cooling purposes. Manufacturing heat spreaders directly onto a microprocessor will negate the need for Thermal Interface Materials (TIMs) which often account for the highest resistances in a typical CPU thermal circuit. In this work we demonstrate that Cold Spray can be tailored to directly print onto a silicon wafer with a layered structure of aluminum, copper and diamond. The thermal performance of the copper/diamond coating was also separately measured using an in-house testing apparatus showing heat-transfer enhancements in agreement with theoretical predictions.     

Oxygen-shielded ultrasonic vibration cutting to suppress the chemical wear of diamond tools

Ultrasonic vibration has been applied to reduce intense chemical tool wear in ultra-precision diamond cutting of steel and other alloys since a few decades ago. But still, its tool wear suppression mechanisms have not been fully understood. In this paper, the effect of oxygen in suppression of diamond tool wear for ultrasonic vibration cutting is investigated. Experimental results show that the wearing rate is reduced by applying oxygen shielding to the cutting zone in comparison with air and argon. Scientific explanations are also provided for the observed phenomenon through low-pressure metal oxidation experiments and X-ray photoelectron spectroscopy surface analyses.     

酸浸+等离子体刻蚀YG6微米-纳米金刚石复合涂层工具研究

金刚石涂层工具一直是金刚石膜工具应用研究的主流.制约其产业化的主要因素是涂层的附着力低和微晶金刚石涂层工具的加工精度差.通过对衬底的有效预处理和CVD沉积过程控制的研究,开发在硬质合金基体上沉积高结合强度、低粗糙度的金刚石涂层新技术,对于实现CVD金刚石涂层刀具高效、高精度切削加工具有重要意义.对旨在提高金刚石涂层附着力的预处理技术,本文探索了将酸蚀脱钴+等离子体刻蚀处理衬底法.利用优化的沉积工艺,在酸浸+等离子刻蚀处理的YG6刀片上沉积的两层金刚石复合膜表面粗糙度为0.13μm,附着力压痕测试临界载荷大于1500N.金刚石涂层工具的切削加工性能明显高于无涂层硬质合金工具.在加工ZAlSi12合金时,单层和两层金刚石涂层车刀片的切削寿命分别是无涂层车刀片切削寿命的21倍和28倍.     

酸浸＋等离子体刻蚀YC6微米-纳米金刚石复合涂层工具研究

金刚石涂层工具一直是金刚石膜工具应用研究的主流。制约其产业化的主要因素是涂层的附着力低和微晶金刚石涂层工具的加工精度差。通过对衬底的有效预处理和CVD沉积过程控制的研究，开发在硬质合金基体上沉积高结合强度、低粗糙度的金刚石涂层新技术，对于实现CVD金刚石涂层刀具高效、高精度切削加工具有重要意义。对旨在提高金刚石涂层附着力的预处理技术，本文探索了将酸蚀脱钴＋等离子体刻蚀处理衬底法。利用优化的沉积工艺，在酸浸＋等离子刻蚀处理的YG6刀片上沉积的两层金刚石复合膜表面粗糙度为0．13μm，附着力压痕测试临界载荷大于1500N。金刚百涂层工具的切削加工性能明显高予无涂层硬质合金工具。在加工ZAlSi12合金时，单层和两层金刚石涂层车刀片的切削寿命分别是无涂层车刀片切削寿命的21倍和28倍。     

Influence of Ar ion etching on the surface topography of cemented carbide cutting inserts

In situ substrate cleaning by ion etching prior to physical vapor deposition of hard coatings alters topography and composition of the surface to be coated. Within this work, the influence of Ar ion etching on the surface topography of cemented carbide cutting inserts with different geometries was investigated. The surface of cutting inserts before and after ion etching was evaluated by different scanning electron microscopy techniques to illuminate the effect of ion etching on both, the cutting edges and the flat surface. Additionally, profilometric measurements were carried out to determine changes of the surface roughness and to quantify the removed material by measuring the step height between the etched and un-etched surface. Surface roughness and thickness of the removed layer increased with etching time at constant bias voltage, while the applied voltage had only a minor influence. In addition, energy-dispersive X-ray spectroscopy mappings indicated changes of the surface composition by ion etching due to preferential sputtering of the cobalt binder phase.     

Study on morphologies and structures of diamond films synthesized on cemented carbide substrates

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Development of micro milling tool made of single crystalline diamond for ceramic cutting

In order to machine micro aspheric ceramic molds precisely and efficiently, micro milling tools made of single crystalline diamond (SCD) are developed. Many cutting edges are fabricated 3-dimensionally on the edge of a cylindrical SCD by a laser beam. Flat binderless tungsten carbide mold was cut with the developed tool to evaluate the tool wear rate and its life. Some micro aspheric molds of tungsten carbide were cut with the tool at a rotational speed of 50,000 min⁻¹. The molds were cut in the ductile mode. The form accuracy obtained was about 100 nm P–V and the surface roughness 12 nm R_z.     

化学脱钴对硬质合金沉积金刚石薄膜的影响

采用HFCVD系统,以CH4和H2为反应气体,分别在YG3、YG6、YG10、YG13硬质合金上沉积了金刚石薄膜,研究了化学脱钴处理对不同钴含量硬质合金沉积金刚石薄膜的影响.通过对105个样品的实验结果进行统计分析发现,YG3所得金刚石薄膜样品具有足够结合强度的比例为89%;而YG6、YG10 和YG13所得样品的相应值分别为24%、7%和0%.相反,YG3、YG6、YG10 和YG13所得金刚石薄膜严重破坏的比例分别为0%、64%、72%和79%.研究表明,化学腐蚀脱钴处理能够解决金刚石涂层形核率低的问题,但难以解决高钴硬质合金的附着性差的问题.     

Mechanical and structural properties of multilayer c-BN coatings on cemented carbide cutting tools

Multilayer cubic boron nitride (c-BN) coatings represent a new deposition method that can improve adhesion on metal substrates. The multilayer c-BN system in this study consisted of a TiAlN interlayer (2– 3.5 μm), boron carbide (~ 1 μm), and a c-BN (~ 2 μm) gradient layer. This multilayer c-BN structure, exceeding 5 μm in thickness, showed outstanding adhesion in atmospheric conditions even with high residual stress. Compared to monolayer c-BN coatings, the multilayer c-BN films had lower elastic moduli, and their critical loads were twice as high. The adhesion of the multilayer c-BN system was significantly improved because of the induced stress relaxation.     

Face milling of the EN AB-43300 aluminum alloy by PVD- and CVD-coated cemented carbide inserts

Two commercially available WC-6Co cemented carbide substrates (Extramet EMT100 and Pramet H10), were industrially coated with PVD TiB₂ or CVD diamond. Subsequently, the coated inserts were submitted to dry sliding tests (slider on cylinder contact geometry) against the aluminum alloy EN AB-43300, for preliminary performance ranking and identification of basic wear mechanisms. The best substrate/coating combination (CVD-Diamond coated Extramet EMT100) was then tested in face milling EN AB-43300 with milling tool characterized by two different geometries (A and B), using PCD inserts as a reference for comparison. In milling tests, the influence of both insert geometry and cutting fluid feed rate were taken into account. The geometry of the tool was identified as the main parameter in influencing the tool performance. In particular, in the case of the A geometry, the relative flank wear of CVD coated tools increased abruptly during the test due coating detachment, whilst with the B geometry no catastrophic failure of the CVD coated insert was observed. The influence of Cutting Fluid Feed Rate (CFFR) also changed with tool geometry: in particular, with the B geometry, which allowed to obtain the best results with the CVD coated inserts, a decrease of CFFR from 100 to 25% did not affect significantly the wear resistance of CVD-coated inserts and allowed to maintain the roughness of the workpiece (R_a) below 0.6 μm, notwithstanding a slightly increased tendency towards the formation of Al-based transfer layers.