Wear mechanisms of PVD-coated cutting tools during continuous turning of Ti-6Al-4V alloy

The aim of this study was to investigate the damage of cutting tools coated by physical vapor deposition (PVD) during the continuous turning of a titanium alloy. The investigation utilized scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), and transmission electron microscopy (TEM). It was found that a TiN coating on the tool wore faster than an uncoated cemented carbide tool. The damage mode of the coating on the rake face was fracture without plastic deformation. Additionally, there was a pattern to the crystal orientation relationship at some of the interfaces between the adhered workpiece material and the TiN coating. The crystal orientation relationship presumably produced a strong bond between the adhered material and the coating. The coating damage was thus caused by the force exerted by the adhered materials on the grain boundary on the damaged coating surface. A comparison of the tool damages during the machining of Ti-6Al-4V alloy and alloy 718 suggested that the damage of the coating depended on the interfacial strength between the adhered material and the coating, as well as the strength of the adhered material at a high temperature. Hence, to prevent the damage of the tool during the machining of a titanium alloy, it is preferable to use a ductile material (e.g., cemented carbide) rather than a brittle material (e.g., ceramic).     

不同涂层刀具切削淬硬H13钢加工性能研究

为了研究不同涂层刀具切削淬硬H13钢的切削性能,进行了多层Ti化合物涂层、TiAlN涂层以及MTTiCN厚Al_2O_3TiN涂层材料刀具车削加工淬硬H13钢试验,分析了不同的涂层材料刀具与切削力、切削温度、涂层刀具磨损以及刀具寿命的关系。研究得出:多层Ti化合物涂层刀具受到三个方向的力都大于其它两种涂层的刀具,而且切削温度最高;用TiAlN涂层刀具切削时温度最低;切削过程中三种刀具后刀面磨损程度不同,发现多层Ti化合物涂层刀具磨损最为严重,寿命最短;MT-TiCN厚Al_2O_3Ti N涂层材料刀具比多层Ti化合物涂层刀具寿命长30%;TiAlN涂层刀具的切削寿命最长比多层Ti化合物涂层刀具寿命长45%。     

High-Speed Machining of Malleable Cast Iron by Various Cutting Tools Coated by Physical Vapor Deposition

The coating material of a tool directly affects the efficiency and cost of machining malleable cast iron.However,the machining adaptability of various coating materials to malleable cast iron has been insufficiently researched.In this paper,turning tests were conducted on cemented carbide tools with different coatings(a thick TiN/TiAlN coating,a thin TiN/TiAlN coating,and a nanocomposite(nc)TiAlSiN coating).All coatings were applied by physical vapor deposi-tion.In a comparative study of chip morphology,cutting force,cutting temperature,specific cutting energy,tool wear,and surface roughness,this study analyzed the cutting characteristics of the tools coated with various materials,and established the relationship between the cutting parameters and machining objectives.The results showed that in malleable cast iron machining,the coating material significantly affects the cutting performance of the tool.Among the three tools,the nc-TiAlSiN-coated carbide tool achieved the minimum cutting force,the lowest cutting tempera-ture,least tool wear,longest tool life,and best surface quality.Moreover,in comparisons between cemented-carbide and compacted-graphite cast iron machined under the same conditions,the wear mechanism of the coated tools was found to depend on the cast iron being machined.Therefore,the performance requirements of a tool depend on multiple factors,and selecting an appropriately coated tool for a particular cast iron material is essential.     

Wear behavior of adaptive nano-multilayered AlTiN/MexN PVD coatings during machining of aerospace alloys

Machining of aerospace materials is one of the major challenges of modern manufacturing. Application of nano-multilayered AlTiN/Me_xN PVD coatings (where Me_x is a transition metal of V-VI groups of periodic table) to cemented carbide tooling results in a significant tool life improvement under conditions of cutting hard to machine alloys such as Ni-based Inconel 718 superalloy and Ti-based TiAl6V4 alloy. Microhardness and coefficient of friction of the coatings were measured during this experiment. Investigations of the coated tool life, wear behavior, chip formation (chip type and undersurface morphology) for cutting tools with nano-multilayered PVD coating were also performed. Morphology of worn tools has been studied using SEM and EDX. This study will show that metallurgical design of the nano-multilayered coating should be tailored to its application. To achieve better tool life when machining Inconel 781, adaptive nano-multilayered AlTiN/MoN coating is recommended, whereas a AlTiN/VN coating is better suited to machining TiAl6V4 alloy. A driving force behind selecting these coatings was a noticeably lower coefficient of friction at elevated temperatures.     

Cutting forces and wear in dry machining of Inconel 718 with coated carbide tools

In the machining of heat resistant super alloys used in aeronautical applications and classified as difficult-to-machine materials, the consumption of cooling lubricant during the machining operations is very important. The associated costs of coolant acquisition, use, disposal and washing the machined components are significant, up to four times the cost of consumable tooling used in the cutting operations. To reduce the costs of production and to make the processes environmentally safe, the goal of the aeronautical manufacturers is to move toward dry cutting by eliminating or minimising cutting fluids. This goal can be achieved by using coated carbide tools at high cutting speeds. To achieve this goal, different coated tools and different cutting conditions were tested in dry conditions. The elementary orthogonal cutting process was chosen, the cutting and feed cutting forces components were measured and the cutting force ratio calculated. This ratio is shown to be as an interesting indicator of tool wear. The tool wear mechanisms tool were analysed by using white light interferometer and scanning electron microscopy coupled to an energy-dispersive X-ray spectroscopy EDS-system. The EDS was very useful to analyse the elements deposited on the cutting tool faces. The ability of the different coatings to increase the carbide tool performance were analysed, the main wear modes were depicted. An optimisation of the cutting conditions was finally proposed and the efficiency of the coatings was shown. The results coming from uncoated tools were compared with those obtained with coated tools under the same conditions of machining. At the end, a choice of coatings is proposed and an extension of this study to an industrial machining operation is presented for future developments.     

Specimen preparation by ion beam slope cutting for characterization of ductile damage by scanning electron microscopy

To investigate ductile damage in parts made by cold sheet‐bulk metal forming a suited specimen preparation is required to observe the microstructure and defects such as voids by electron microscopy. By means of ion beam slope cutting both a targeted material removal can be applied and mechanical or thermal influences during preparation avoided. In combination with scanning electron microscopy this method allows to examine voids in the submicron range and thus to analyze early stages of ductile damage. In addition, a relief structure is formed by the selectivity of the ion bombardment, which depends on grain orientation and microstructural defects. The formation of these relief structures is studied using scanning electron microscopy and electron backscatter diffraction and the use of this side effect to interpret the microstructural mechanisms of voids formation by plastic deformation is discussed. A comprehensive investigation of the suitability of ion beam milling to analyze ductile damage is given at the examples of a ferritic deep drawing steel and a dual phase steel. Microsc. Res. Tech. 79:321–327, 2016. © 2016 Wiley Periodicals, Inc.     

On the wear of PVD-coated HSS hobs in dry gear cutting

A hob is an advanced gear cutting tool usually made of homogenous high-speed steel (HSS) and coated by physical vapour deposition (PVD). It is designed for regrinding and recoating many times. However, hobs of today suffer from unpredictable wear making it difficult to schedule when they should be taken out for reconditioning. This investigation is aimed to contribute to the fundamental knowledge of the wear mechanisms and wear propagation of hobs used in dry gear cutting. Two AlCrN-coated hobs, used in actual gear cutting, were investigated by scanning electron microscopy (SEM) to study the tool topography, light optical microscopy (LOM) to study metallographic cross-sections and by X-ray photoelectron spectroscopy (XPS) for surface analyses.It is concluded that the high potential of PVD-coated HSS as tool material is not taken full advantage of. The main reason is a combination of a poor surface preparation prior to coating and excessively high compressive residual stresses, making parts of the coating detach along the edge line even on unused cutting teeth. During cutting, the high intrinsic stresses in combination with droplets and defects in the coating facilitated its fragmentation through decohesion and detachment. Simultaneously, the rake face is gradually covered by a thin oxide layer dominated by Fe, Cr and Mn in about equal amounts, and also with a significant content of Si. It is believed but not proved that this layer is beneficial.To improve service life and reliability of gear cutting hobs, precautions should be taken for the grinding–polishing preparation prior to PVD-coating to ensure a smooth substrate free from burning damage and other defects. Also, the edge radius and coating thickness has to be matched with the magnitude of compressive residual stresses in the coating.     

PVD涂层硬质合金钻头钻削SKD61模具钢试验的研究

涂层技术在切削刀具中得到越来越广泛的应用,性能优异的涂层可以显著改善刀具表面性能,提高其高温硬度、隔热性能、热稳定性及冲击韧性,从而可大幅度提高刀具的切削速度和寿命。基于常见的钻削加工方式以及难加工材料SKD61模具钢,采用应用广泛的刀具涂层工艺PVD(物理气相沉积)涂层,进行了系统的切削试验。分别从切削力、加工表面质量、切屑变形机理等方面,对不同涂层刀具的切削性能做出了对比分析和基于试验结果的合理判断。     

Study on cutting forces and experiment of MoS2/Zr-coated cemented carbide tool

MoS₂/Zr composite films were deposited on the cemented carbide YT14 (WC+14%TiC+6%Co) by medium-frequency magnetron sputtered coupled with multi-arc ion plating techniques. The thickness, micro-hardness, and coating/substrate adhesion strength of the coatings were tested. Surface morphologies of the composite coatings, as well as wear features, were investigated by scanning electron microscopy. Dry machining tests on hardened steel were carried out with the coated tool and uncoated YT15 tool. The variation of cutting forces for 45# hardened steel was tested by the Kistler force tester. The result shows that the cutting forces of coated tool were decreased by 25–30%, and flank wear resistance was improved by 30–35% in comparison with the uncoated YT15 tool. Through the analysis of cutting force distribution theory, the lower mean shear stress on the MoS₂/Zr-coated tool face leads to the decrease of cutting force and increase of tool wear resistance.     

Microstructural characterization of plasma sprayed Ln2Zr2O7 thermal barrier coatings by electron microscopy methods

The presented article characterized microstructural aspects of thermal barrier coatings (TBCs) analysis using methods of electron microscopy such as electron backscatter diffraction (EBSD), transmission/scanning electron microscopy (S/TEM), and TEM. The analyzed TBC system is based on gadolinium zirconate deposited by air plasma spraying method, and additionally, it was subjected to an oxidation test for 500 hr at a temperature of 1,100°C. Moreover, the morphological characterization of feedstock powder was showed. EBSD analysis revealed the inhomogeneity of feedstock materials in the form of complex phase composition. In the case of deposited coating, this method was used to characterize the crystallite size of zirconate coating and phase composition of thermally grown oxide zone. S/TEM and TEM analysis showed morphological details of this zone but not revealed such phase as perovskite oxide of GdAlO₃ type.     

Nano-scale multilayered-composite coatings for the cutting tools

In machining, the tool life is one of the limiting criteria in the process; therefore, the development of wear-resistant material for the cutting tools is imperative. This paper presents a methodological approach to the design of nano-scale multilayered-composite coatings for cutting tools. A plasma-enhanced technology of filtered cathodic vacuum-arc deposition is used to coat the tools, which significantly extends the operational life of the cutting tools. Here, a three-layered architecture of coatings is proposed and each layer has a specific function. The engineered structural layers allowed for optimum combination of a high adhesion strength with the tool substrate and a minimum adhesion of the work material to the tool surface. The coating process is presented here alongside with the technological role of the layers. A study of the effect of the developed nano-scale multilayer composite coatings on the rates of tool wear was undertaken, and results were compared with the wear rates of uncoated and standard coatings. The results of a wide range experimental work are given in terms of flank wear and tool life for various machining conditions.     

ZrN涂层YT15硬质合金刀具的制备及切削性能

采用中频磁控溅射和电弧离子镀相结合的方法,在YT15硬质合金刀片上制备了三种ZrN涂层,测试了涂层的物理性能,并通过切削试验研究了不同ZrN涂层对YT15硬质合金刀具切削性能的影响,并与无涂层刀具的切削效果进行了对比。结果表明:ZrN涂层的硬度较YT15硬质合金刀具的提高了12 GPa;三种涂层刀具中,有锆过渡层的ZrN涂层刀具降低了切削过程中刀具的切削力,使刀具的耐磨损性能得到提高。     

干切削刀具的设计理论研究

在分析干切削加工特点的基础上,提出了干切削加工对刀具的要求,并对国内外干切削加工刀具的研究进展作了综合归纳与评述,阐明了各种方式的优缺点,指出了干切削加工刀具研究中的值得重视的发展方向。     

陶瓷涂层刀具切削灰铸铁的试验研究

为了探究陶瓷涂层刀具涂层材质、基体材质对切削性能的影响,试验采用四种陶瓷涂层刀具连续干切削灰铸铁,测试了切削力和切削温度的变化情况以及后刀面的磨损量和已加工表面的粗糙度。结果表明,在刀具基体同为Si_3N_4的条件下,涂层材质为Ti N/Al_2O_3/Ti C的刀具比Ti N/Al_2O_3的切削性能好;在涂层材质同为Ti N的条件下,刀具基体Al_2O_3/Ti CN比Al_2O_3/Ti C的切削性能好。研究发现:四种陶瓷涂层刀具前刀面磨损形式均为微崩刃和月牙洼,后刀面磨损形式均为磨粒磨损和粘着磨损,涂层的磨损形式均为剥落和扩散磨损。     

钛合金铣削加工的PVD涂层适应性研究

利用电弧法沉积制备Al Cr N、Al Cr Si N、Al Cr N/Ti Al N、Al Cr N/Ti Si N四种用于钛合金切削加工涂层,研究了涂层的基本特性及切削使用效果。结果表明,Al Cr N涂层呈柱状生长,通过添加Si等元素或采用多层交替沉积有利于形成细化晶粒组织,提升涂层纳米硬度。切削试验表明,在低速铣削钛合金TC4时,Al Cr N/Ti Al N复合涂层表现最好。在较高速铣削时,四种涂层的刀具表现性能接近。     

Minimization of focused ion beam damage in nanostructured polymer thin films

Focused ion beam (FIB) instruments have proven to be an invaluable tool for transmission electron microscopy (TEM) sample preparation. FIBs enable relatively easy and site-specific cross-sectioning of different classes of materials. However, damage mechanisms due to ion bombardment and possible beam heating effects in materials limit the usefulness of FIBs. Materials with adequate heat conductivity do not suffer from beam heating during FIB preparation, and artifacts in materials such as metals and ceramics are primarily limited to defect generation and Ga implantation. However, in materials such as polymers or biological structures, where heat conductivity is low, beam heating can also be a problem. In order to examine FIB damage in polymers we have undertaken a systematic study by exposing sections of a PS-b-PMMA block copolymer to the ion beam at varying beam currents and sample temperatures. The sections were then examined by TEM and scanning electron microscopy (SEM) and analyzed using electron energy loss spectroscopy (EELS). Our empirical results show beam heating in polymers due to FIB preparation can be limited by maintaining a low beam current (≤100 pA) during milling.     

Microstructural analysis of a FeAl/quasicrystal-based composite prepared using a focused ion beam miller

A composite consisting of a brittle multiphase matrix containing both an Al-based quasicrystalline phase (ψ) and an ordered body centred cubic phase (β) and a relatively ductile ordered body centred cubic intermetallic FeAl phase has been developed as an abrasive wear-resistant coating material. It is applied as a 500 μm thick layer onto stainless steel substrates through plasma spray processing. The microstructure of such materials can be readily examined by optical and scanning electron microscopy, but the inherent difficulty of preparing transmission electron microscope (TEM) samples has inhibited higher resolution studies. However, the relatively recent development of the focused ion beam (FIB) miller as a tool in materials science provides a method ideal for the preparation of TEM specimens of these materials. In this study a coating consisting of a mixture of an Al–Cu–Fe based quasicrystal and FeAl+Cr was deposited on to a 304 stainless steel substrate. TEM specimens were prepared using a FIB and subjected to detailed microstructural characterization. The structure consisted of elongated bands of a FeAl phase about 100 nm in width and several micrometres in length, which enclosed more equiaxed regions about 1 μm in diameter that consisted of fine mixtures of quasicrystal and two Al-Fe-Cu phases isostructurally related to FeAl.     

高速切削刀具磨损寿命的研究

分析了高速切削时刀具的磨损形态 ,综述了各种高速切削刀具材料 (包括陶瓷刀具、立方氮化硼刀具、金刚石刀具、金属陶瓷刀具和涂层刀具 )高速切削时的磨损机理 ,讨论了高速切削铸铁、淬硬钢和镍基合金时刀具的磨损寿命。     

Effect of mechanical pre-treatments in the behaviour of nanostructured PVD-coated tools in turning

As a consequence of the lack of characterization of advanced physical vapour deposition (PVD) coatings in the scope of turning, a methodology is presented to evaluate the performance of nanostructured coated tools in the scope of difficult to machine materials turning in particular are austenitic stainless steels. A main aspect of this research is the evaluation of different mechanical pre-treatments before PVD coating in cutting tools. In a first stage, four advanced PVD coatings were analyzed prior to studying the effect of pre-treatments. This stage allowed to identify the nanostructured AlTiSiN coating, commercial denomination nACo, as the one with the best performance for turning austenitic stainless steel. Once the best coating is identified in a second stage, the influence of drag-grinding and microblasting mechanical substrate pre-treatments was analyzed with regard to the performance of coated tools. Several aspects were considered: geometric modification of cutting edge, coating adhesion, substrate roughness and machining performance. The performance of the mentioned coatings was evaluated through wear tests. The machined material was AISI 304L and machining operation was cylindrical turning. Each test started up using a new edge. Results showed that drag-grinding pre-treatment leads to improved coating adhesion and, therefore, in the performance of the tool. Therefore, combination of nACo coating with drag-grinding pre-treatment offers a good solution for difficult to machine metals.