Optimization of diamond coated microdrills in aluminum alloy 7075 machining: A case study

Aluminum alloy 7075 is widely used for producing micro-scale heat sinks, micro-fluidic devices, micro-propellers and so on. This paper deals with optimizing microstructure and thickness of diamond coatings on microdrills used in 7075 aluminum alloy machining. Firstly, the friction tests between microcrystalline diamond (MCD), nanocrystalline diamond (NCD) films and aluminum alloy reveal that the stable coefficient of friction (COF) of MCD–aluminum alloy working pair is 0.240, much higher than that of NCD–aluminum alloy working pair (0.072). The decrease of COF is mainly attributed to the lower roughness of NCD films and the presence of more graphite or the non-diamond phases in NCD coatings. Afterwards, comparative cutting tests involving MCD, NCD, diamond-like coating (DLC) and TiAlN coated microdrills show that after drilling 200 holes, NCD coated microdrills exhibit the best cutting performance. Furthermore, NCD coated microdrills with coating thicknesses of 1 μm, 2 μm, 4.5 μm and 7 μm are fabricated and their cutting performance is studied in aluminum alloy machining. The cutting experiments show that the NCD coated microdrill with coating thickness of 4.5 μm shows the best cutting performance, exhibiting not only lowest flank wear and no tool tipping or chipping on the main cutting edges but also the highest quality of drilled holes because of the outstanding adhesive strength and wear resistance of the NCD coating.     

High speed continuous and interrupted dry turning of A390 Aluminum/Silicon Alloy using nanostructured diamond coated WC–6 wt.% cobalt tool inserts by MPCVD

Nanostructured diamond films were grown to a thickness of approximately 35 µm by a 30 kW, 915 MHz, microwave plasma-assisted chemical vapor deposition (MPCVD) on chemically treated WC–6 wt.% Co tool inserts. Rockwell indentation tests were performed to evaluate the adhesion of the films and compared to that of traditional microcrystalline diamond. A series of high speed dry turning tests on high-silicon (18 wt.% Si) aluminum alloy A390 under continuous and interrupted modes were performed and comparisons were carried out to investigate the wear behavior on tool inserts that were uncoated, coated with nanostructured diamond, and commercial PCD (polycrystalline diamond cutter) ones. The tests showed that nanostructured diamond coatings demonstrated excellent durability against the highly abrasive A390 aluminum–silicon alloys in high speed dry turning. Ultra fine grain structure of this coating produces workpiece surface finish comparable or even better than PCD tools in the range we studied. Excellent coating adhesion of nanostructured diamond on WC–6% Co substrates leads to reliable wear behavior. For the first time, we evaluated the performance of nanostructured diamond film coated insert under high speed interrupted turning mode. A “self-cleaning” mechanism was observed which can significantly improve the performance of nanostructured diamond films. Micro-Raman spectra were taken on tested tools to study the wear mechanism of the coating.     

Applicability of DLC and WC/C low friction coatings on Al2O3/TiCN mixed ceramic cutting tools for dry machining of hardened 52100 steel

The present work examines the applicability of DLC and WC/C low friction coatings on Al₂O₃/TiCN based mixed ceramic cutting tools for the dry and hard turning of AISI 52100 steel (62 HRC). The characterization of coated tools reveals that the coatings retain very low values of surface roughness, whereas the DLC coating exhibits much higher microhardness when compared to the WC/C coating. On the other hand, the WC/C coating exhibit a coarse surface morphology virtually due to the tungsten doping. Later, continuous turning tests were executed with the help of coated and uncoated cutting tools under dry cutting conditions, and their performance was investigated in terms of machining forces, cutting temperature and tool wear. Coating delamination by flaking and peeling is quite prominent in the case of both the coatings; however, it is less severe for the WC/C coated tool. The coatings help to reduce machining forces, cutting temperatures and tool wear, but the performance of coated tools converge towards uncoated tool as the cutting speed, and feed rate is increased. Both the coatings prevent the development of cracks near the cutting edge with WC/C coating exhibiting superior wear behavior basically due to its multilayered structure and better thermal stability. Moreover, the tested low friction coatings don't serve as thermal barriers and only the lubrication generated due to graphitization at the chip-tool interface is mostly responsible for the improved machining performance.     

Improvement of structural/tribological properties and milling performances of tungsten carbide cutting tools by bilayer TiAlN/TiSiN and monolayer AlCrSiN ceramic films

In this study, bilayer TiAlN/TiSiN and monolayer AlCrSiN ceramic films were grown on carbide cutting tool material by cathodic arc physical vapor coating (CAPVD) method to improve the structural/tribological properties and milling performances. The ceramic films were applied on cylindrical test samples and carbide end mills. The coated materials' structural, mechanical, and tribological properties were determined via scanning electron microscope (SEM), X-ray diffraction meter (XRD), tribometer, microhardness tester, and optical profilometer. DIN 40CrMnNiMo8-6-4 steel workpieces were machined by using a CNC vertical machining center to determine the actual working performance of the coated and uncoated cutting tools. The wear performance of the cutting tools after machining was determined by measuring the flank wear widths and mass losses. The hardness and adhesion results of the coated sample with bilayer TiAlN/TiSiN were higher than the coated sample with monolayer AlCrSiN. According to the scratch test results, the best adhesion results were obtained for TiAlN/TiSiN coating. The critical load value was determined as about 105 N. As a result, the wear rate value of the TiAlN/TiSiN thin film coated sample was lower. After machining, the mass loss of TiAlN/TiSiN coated tools was lower than AlCrSiN coated tools. In addition, the surface roughness value of the workpiece machined by the cutting tool coated with AlCrSiN was higher than the cutting tool coated with TiAlN/TiSiN.     

Hard machining performance of PVD AlCrN coated Al2O3/TiCN ceramic inserts as a function of thin film thickness

In the present work, AlCrN coating was deposited on Al₂O₃/TiCN ceramic inserts with varying thin film thickness using physical vapor deposition (PVD) technique. The thickness, surface morphology, chemical composition, hardness and adhesion strength of the coating to the substrate were characterized by field-emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), micro-indentations and scratch tests respectively. The machining performance of uncoated and coated tools was investigated in hard turning of AISI 52100 steel (62 HRC) under dry environment. The cutting behavior was analyzed in terms of machining forces, tool temperature, wear, friction and chip morphology. Further, a 3D finite element model with hybrid friction criterion has been adopted to support the experimental findings. The results revealed that coating/substrate adhesion and edge radius were the deciding criteria for the machining performance of coated tools with 3 µm coating thickness tool exhibiting best turning performance on Al₂O₃/TiCN mixed ceramic insert.     

Single-crystal diamond tools formed using a focused ion beam: Tool life enhancement via heat treatment

We describe a technique to improve diamond cutting tools used in nanometer- and micrometer-scale machining and formed via focused-ion-beam (FIB) micromachining. Although FIB irradiation is an effective means of fabricating arbitrary miniature shapes in diamond cutting tools, FIB irradiation induces a non-diamond phase, as well as Ga ion implantation, in the irradiated area. This adversely affects the performance of the ultra-precision machining process, especially in terms of tool life and the quality of the machined surface. To eliminate the affected layer, we applied heat-treatment techniques and investigated the optimum thermal profiles. A temperature of 500 °C applied to the cutting tool provided optimal machining of nickel phosphorus. The tool life was significantly improved, and a tool life similar to that of a non-irradiated diamond tool was obtained. The quality of the machined surface was also improved markedly owing to superior tool wear and adhesion resistance.     

Properties of TiN–Al2O3–TiCN–TiN,TiAlN, and DLC-coated Ti(C,N)-based cermets and their wear behaviors during dry cutting of 7075 aluminum alloys

In the work, TiAlN for physical vapor deposition (PVD), multilayer TiN-Al₂O₃-TiCN-TiN for chemical vapor deposition (CVD), and diamond-like carbon (DLC) for plasma-enhanced chemical vapor deposition (PECVD) were deposited on the cermet inserts. Characteristics and wear behaviors of the three coated cermets during dry cutting of 7075 aluminum alloys were observed. The results show that TiN-Al₂O₃-TiCN-TiN coatings have highest adhesion strength and hardness. At the cutting speed of 1100 r/min, the depth of 0.2 mm, and the feed rate of 0.1 mm/r, the three coated inserts show the best wear-resistant properties. In this case, TiN/Al₂O₃/TiCN/TiN shows the worst wear-resistant properties (value of the flank wear [VBB] = 0.062 mm), while DLC coatings show the most excellent wear-resistant properties (VBB = 0.046 mm). During the cutting of aluminum alloys, which have high plasticity and low melting point, adhesive wear dominate on the flank of the inserts. The thickest coating of TiN/Al₂O₃/TiCN/TiN results in the bluntest cutting edge, which form the most serious adhesive worn zone. For the TiAlN and DLC coatings, due to a smaller cutting force, the two coatings have much better wear resistance. Further, the self-lubricating properties of DLC show excellent effect on protecting the inserts. Thus, the DLC-coated cermets have the best wear-resistant properties. Further, the TiAlN-coated cermets have the widest wear-affected zone while the DLC coating has the narrowest.     

A study of CVD diamond deposition on cemented carbide ball-end milling tools with high cobalt content using amorphous ceramic interlayers

In this paper, CVD diamond coatings are deposited on cemented carbides with 10 wt.% Co using amorphous SiO₂ and amorphous SiC interlayers. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Raman spectrum and X-ray diffraction (XRD) are carried out to characterize the microstructure and composition of as-deposited films. Moreover, the adhesion and cutting performance of as-fabricated diamond coatings are studied. Indentation tests show that the amorphous ceramic interlayers can enhance the adhesion between diamond films and WC–Co substrates. The cutting tests against zirconia indicate that the tools with amorphous ceramic interlayered diamond coatings exhibit improved cutting performance. The amorphous ceramic interlayers can improve the adhesive strength and wear endurance of diamond coatings on WC–10 wt.% Co substrates, which provide a viable way for adherent diamond coatings on cemented carbide tools with high cobalt content.     

Effect of nano-scale texture pretreatment on wear resistance of WC/Co tools with/without TiAlN coated flank-face in dry turning of green Al2O3 ceramics

Advanced ceramics after sintering are almost processed by grinding or non-traditional machining. Nevertheless, these methods are limited by complexity of processing efficiency, tool wear and economic effectiveness. So machining green ceramics before sintering is introduced, it is environmentally friendly, efficient and cheap with high removal rate of materials. During dry turning green ceramics, flank-wear of tools and processing quality of compacts are two main elements to evaluate cutting performance of tools. The processing efficiency and economic effectiveness are mainly effected by the cutting performance of tools. In this paper, polished tool, tool with nano-scale textured flank-face, tool with TiAlN coating deposited on polished flank-face, and tool with TiAlN coating deposited on nano-scale textured flank-face were prepared. Effect of nano-scale texture pretreatment on wear-resistance of WC/Co tools with/without TiAlN coated flank-face was studied in turning of green Al₂O₃ ceramics. Results displayed that nano-scale textures on the flank-face had prominent effects on the enhancement of flank-wear resistance of tools. Relevant mechanisms were explored that nano-scale textures exhibited “derivative cutting” to protect unworn face from abrasion, and nano-scale textures pretreated on the flank-face could enhance the adhesion strength between coating and matrix. These developed tools could also significantly improve the processing quality of machined surfaces.     

TiB2涂层刀具制备及干铣削Ti-6Al-4V磨损行为研究?

由于切削过程中产生高温、刀具粘结与氧化严重,钛合金切削尤其是干切削,一直是刀具行业的重大挑战之一,而在刀具表面添加涂层是提高钛合金切削刀具寿命的有效途径。利用脉冲磁控溅射技术制备了TiB2涂层刀具,以相同基体的无涂层刀具为对照,干铣削Ti-6Al-4V钛合金,切削速度从30~100 m/min变化,研究TiB2涂层刀具的切削性能与失效机理。所制备的TiB2涂层具有(100)择优取向的六方晶体结构,组织致密。涂层硬度可高达4000 HV。切削实验发现,在30 m/min的低速时,TiB2涂层刀具的切削寿命超过无涂层刀具57%之多,当切削速度加倍到60 m/min时,刀具寿命未见下降。当切削速度增加到100 m/min时,TiB2涂层刀具与无涂层刀具切削寿命相当。TiB2涂层刀具表面氧化所产生的B2O3液化膜,起自润滑作用,可充分减少钛合金的粘结,降低摩擦力。因此,在TiB2或B2O3消失之前,TiB2涂层刀具均有良好表现。在100 m/min时,切削高温造成B2O3强烈挥发,且TiB2被氧化为多孔疏松的TiO2,刀具寿命急剧下降到无涂层刀具的水平。     

Micromechanical characterization and dynamic wear study of DC-Arc coated cemented carbide cutting tools for dry titanium turning

The present study investigates the micromechanical properties of ceramic coated WC/Co tools and their influence on wear performance during dry Ti6Al4V turning. Physical and micromechanical characterization have been performed for the evaluation of the PVD coating properties. Higher hardness, elastic modulus, and adhesion strength have been obtained for dual-layer (AlTiN/AlCrN) coated tool than monolayer AlTiN and AlCrN coated tools. Micromechanical properties influence the wear mechanisms in thermally activated and abrasion dominant crater zones. Dual-layer coated tools reduced the flank wear at the corner radius and crater wear by 35–50% and 40%, respectively. Dynamic wear and abrasion-dissolution wear mechanisms have been explored over the tool rake face. Dual-layer coatings have improved wear performance by diminishing delamination, micro-fracturing of WC grains, binder dissolution and fractured interface boundaries.     

A study of diamond film deposition on WC–Co inserts for graphite machining: Effectiveness of SiC interlayers prepared by HFCVD

Thin silicon carbide (SiC) films were deposited from tetramethylsilane/hydrogen gas mixture on Co-cemented tungsten carbide (WC–Co) inserts by using Hot-Filament Chemical Vapour Deposition (HFCVD) technique. Grazing incidence X-Ray Diffraction (XRD) confirmed that the films were composed of cubic silicon carbide (β-SiC) and that small amounts of dicobalt silicide (Co₂Si) were formed. These films were used as interlayers for subsequent CVD of diamond films. XRD and combined Scanning and Transmission Electron Microscopies showed that the binder phase reacted during CVD to form cobalt silicides. However, these intermetallic compounds did not have bad effects on diamond adhesion. Dry turning of graphite was chosen to check the multilayer (SiC + diamond) film performance. For the sake of comparison, machining tests were also carried out under identical conditions using commercial sintered diamond (PCD) inserts and WC–Co diamond coated inserts with no interlayer. The wear mechanism of the tools has been identified and correlated with the criterion used to evaluate the tool life. The results showed that multilayer (SiC + diamond) coatings exhibited the longest tool lives. Therefore, thin SiC interlayers proved to be a new viable alternative and a suitable option for adherent diamond coatings on cemented carbide components and cutting tools.     

Cutting performance of microwave-sintered sub-crystal Al2O3/SiC ceramic tool in dry cutting of hardened steel

Tool life and failure mechanisms of a microwave-sintered sub-crystal Al₂O₃/SiC ceramic tool (AS) in dry turning hardened steel were studied. The AS tool with plane face shows better cutting performance and wear resistance than the commercial ceramic tool SW500 and cemented carbide tool YG8 at both low and high cutting speeds. It's suitable for dry cutting at high speed (210–270 m/min), the cutting distance is 5–8 times longer than that of other two tools. The results indicate that the ceramic tool fabricated by this pressureless sintering technology can satisfy the requirements of high-speed machining. Wear forms of AS tool at low cutting speed are slight crater wear and groove wear, which were mainly caused by abrasion. At high cutting speed, tool failure forms are cater wear, groove wear and slight chipping caused by severe abrasion and adhesion.     

Performance and wear mechanism of spark plasma sintered WC-Based ultrafine cemented carbides tools in dry turning of Ti–6Al–4V

Cutting performance and failure mechanisms of spark plasma sintered (SPS) ultrafine cemented carbides in dry turning Ti–6Al–4V were studied. The tools of UYG8 (WC-8wt%Co) and UYG8V2B10 (WC-8wt%Co-0.2 wt%VC-1.0 wt%cBN) exhibited higher lifetime and better processing quality than the commercial YG8 cemented carbide tool. The cutting distance of UYG-8 and UYG8V2B10 tools are 1.8 and 1.6 times longer than that of YG8, respectively. Cutting-edge breakage was found as the main failure forms of the SPS cemented carbide tools containing low Co content (≤6 wt%), whereas the SPS cemented carbide tools containing high Co content (≥8 wt%) exhibited flank and rake wear as main failure forms caused by abrasion, adhesion, diffusion, and oxidation. UYG8V2B10 tool wear mechanism was affected by cutting speed and depth. Wear mechanisms of UYG8V2B10 tool are mainly adhesive wear and oxidative wear at low cutting speed, but follow adhesive wear and diffusive wear at higher cutting speed. Moreover, with increasing cutting depth, tool failure forms are mainly breakage and chipping, largely induced by high cutting temperature and severe cutting vibration.     

Characterization of TiCN and TiCN/ZrN coatings for cutting tool application

Coating a cutting tool improves wear resistance and prolongs tool life. Coating performance strongly depends on the mechanical and chemical properties of the coating material. In a machining process, the type of selected coating depends on the cutting condition because of the properties of the applied coating material. In addition, many factors, such as coating thickness, composition ratio, sequences of layers in multilayer coatings, and the deposition method influence the performance of a coating. In this study, the mechanical properties of TiCN and TiCN/ZrN were investigated using a ball on disk test. The substrate material made from a carbide-based cutting tool was also developed in-house. The analysis performed shows that the performances of TiCN and TiCN/ZrN coatings were found to be comparable to that of the commercial TiN-coated carbide-based cutting tool. Both the in-house and commercial coated inserts had significantly lower coefficient of friction than uncoated inserts, and the friction coefficient of TiCN coatings was constantly slightly lower than that of TiN coatings. Moreover, the coefficient of friction of the in-house developed TiCN was slightly lower than that of commercial TiN coating. However, the coefficient of friction of the in-house developed uncoated carbide inserts was slightly higher than that of commercial uncoated carbide inserts.     

Enhanced machinability of SiCp/Al composites with laser-induced oxidation assisted milling

In this study, an innovative machining process called laser-induced oxidation assisted milling (LOM) is proposed. A polycrystalline diamond (PCD) cutting tool is applied to machine 55% SiC_p/Al composites. The laser-induced oxidation mechanism is investigated. Under the condition of average laser power of 10 W, laser scanning pitch of 15 μm, laser scanning speed of 6 mm/s and oxygen-rich atmosphere, the effect of laser-induced oxidation is optimal. A loose oxide layer and a sub-layer with the hardness of 160 ± 40 HV are generated where the composition of the oxide layer is mullite (2Al₂O₃·SiO₂). Comparative investigation on the cutting force, surface quality and tool wear are performed. Compared with the conventional milling (CM), the normal force and thrust force of LOM decrease by 39% and 55%, respectively. The reduction of cutting forces is attributed to thermal failure of the interface layer. The dominant surface defects of the machined surface are particle fracture, particle pull-out, matrix tearing and matrix coating. Among the investigated parameters, the minimum surface roughness S_a is 0.37 μm when the feed per tooth and the cutting depth are 0.005 mm/z and 0.2 mm, respectively. The dominant tool wear modes of LOM include diamond spalling and edge chipping. The tool wear modes of CM are diamond spalling, edge chipping, abrasive wear, and adhesive wear. LOM can prolong the tool life and achieve better surface quality under the same cutting length.     

Machining behaviour of silicon nitride tools coated with micro-, submicro- and nanometric HFCVD diamond crystallite sizes

Very smooth CVD diamond films are used as direct coatings on Si₃N₄ tool substrates. By adjusting deposition parameters, namely Ar/H₂ and CH₄/H₂ gas ratios, and substrate temperature, nano- (27 nm) and submicrometric (43 nm) crystallite sized grades were produced in a hot filament reactor. Also, a conventional 5 and 12 μm micrometric grain size types were produced for comparison. Normalized coated inserts were tested for dry turning of WC–25 wt.% Co hardmetal. All the CVD diamond grades endured the hardmetal turning showing slight cratering, having the flank wear as the main wear mode. Their turning performance was distinct, as a consequence of morphology and surface roughness characteristics. Among all the tested tools, the more even surface and the submicrometric grade presented the best behaviour regarding cutting forces, tool wear and workpiece surface finishing. For this coating, the depth-of-cut force attained the lowest value, 150 N, the best combination of wear types (KM = 30 μm, KT = 2 μm and VB = 110 μm) and workpiece surface finishing (Ra = 0.2 μm).     

Microstructure and tribological properties of cubic boron nitride films on Si3N4 inserts via boron-doped diamond buffer layers

Cubic boron nitride (cBN) coatings were deposited on silicon nitride (Si₃N₄) cutting inserts through conductive boron-doped diamond (BDD) buffer layers in an electron cyclotron resonance microwave plasma chemical vapor deposition (ECR MPCVD) system. The adhesion and crystallinity of cBN coatings were systematically characterized, and the influence of doping level of BDD on the phase composition and microstructure of the cBN coatings were studied. The nano-indentation tests showed that the hardness and elastic modulus of the obtained cBN coatings were 78 GPa and 732 GPa, respectively. The tribological properties of the cBN coatings were evaluated by using a ball-on-disc tribometer with Si₃N₄ as the counterpart. The coefficient of the friction and the wear rate of the cBN coatings were estimated to be about 0.17 and 4.1 × 10^− 7 mm³/N m, respectively, which are remarkably lower than those of titanium aluminum nitride (TiAlN) coatings widely used in machining ferrous metal. The results suggest that cBN/BDD coated Si₃N₄ inserts may have great potentials for advanced materials machining.     

Deposition and characterization of diamond coatings on WC-Co cutting tools with W/Al interlayer

A new double interlayer W/Al was developed for chemical vapor deposition (CVD) of diamond coatings on cemented WC-Co cutting tools to enhance diamond nucleation and adhesion. A thin layer of Al directly deposited on WC-Co is used to suppress the interfacial graphitization induced by Co and an additional thin layer of W is used to enhance diamond nucleation. The microstructure and adhesion of diamond coatings grown on the W/Al/WC-Co and, for comparison, on W/WC-Co as well as bare WC-Co were investigated. The results demonstrate that diamond coatings grown on W/Al are continuous and well adhesive. The advantage of the interlayer includes that nano-crystalline diamond can be achieved even under typical microcrystalline diamond growth conditions. In addition, the W/Al interlayer of overall 50–65 nm thickness would cause marginal lost of cutting edge sharpness and mechanical integrity of coated cutting tools.     

Influence of annealing temperature on microstructure evolution of TiAlSiN coating and its tribological behavior against Ti6Al4V alloys

TiAlSiN multicomponent coating, owing to its high hardness and excellent high temperature resistance, was widely used in the cutting field of difficult-to-cut materials such as titanium alloys. For machining titanium alloys, high temperature is easy to gather on the tool chips and deteriorate the cutting tools. Moreover, high temperature will also promote the microstructure evolution and make the wear mechanism more complex. In this paper, TiAlSiN coatings were deposited on cemented carbides and annealed at 400 °C, 600 °C and 800 °C respectively for 60 min in air, followed by reciprocating friction tests against Ti6Al4V counterparts. AFM, SEM, EDS and XPS were applied to investigate the microstructure evolution and tribological behavior of TiAlSiN coating after high temperature annealing. The results demonstrated that the oxidation resistance of TiN phase in TiAlSiN coating was worse than Si₃N₄ and AlN phases. These nitrides can be oxidized to TiO₂, SiO_x and AlO_x under 600 °C, and the depth of oxide layer was increased with the rising annealing temperature, resulting in the coarsened microstructure. The wear mechanisms of as-deposited TiAlSiN coating were oxidation wear and adhesion wear. With the rising annealing temperature, abrasive wear was gradually enhanced. For the TiAlSiN coating annealed at 800 °C, abrasive wear became the dominant wear mechanism.