ICMCTF2016 Session G3: Innovative Surface Engineering for Advanced Cutting and Forming Tool Applications

It should also be appreciated that our industrial research and development have tackled them for a wide range of materials innovation over the last decades. The present talk will review and summarize the latest understanding of the film deposition method, characterization, mechanical and thermal properties and tribological behavior of coatings. The present talk will review and summarize the latest understanding of the film deposition method, characterization, properties and tribological behavior of coatings. The talk will start with the effect of microstructure and thermal stability on cutting performance of TiN/AlN and TiAlN/AlCrN superlattice coatings using cathodic arc ion plating system. Then we will discuss the effects of residual stress on cutting performance of coated tools. Especially the depth profiles of residual stress have a large impact on cutting performance; however, there are very few studies that describe the influence of depth profiles of residual stress. The talk will end with the introduction of lubricant layer which was deposited on hard coating layers using the hybrid method, where the cathodic arc ion plating method was with unbalanced magnetron sputtering technique. The combination of hard/lubricant coating layers allowed the reduction of friction in the tool-workpiece, reduced cutting force and improved anti-adhesion at the cutting edge. A further direction our study will be several to attempt a development of new tribo-material coated tools.

The worldwide production of plastics increased continuously over the last decades leading to an increasing demand on processing machines for blown film extrusion or sheet film extrusion. During the extrusion process machine components such as extruder screw and extrusion die are exposed to the plastics melt. Additionally, the feed and melting zones of the extruder screws are in contact with solid plastic particles. These tribolocical loads can lead to excessive adhesive and abrasive wear. Besides the maintenance costs due to the wear of the machine components, adhering plastics melt on the extrusion screw and die can degrade and cause defects in the extrudate. Therefore, adhesion and abrasion have a significant impact on machine efficiency and product quality. In this regard, chromium based nitride and oxynitride hard coatings deposited via physical vapor deposition (PVD) offer great potential in order to protect machine components and tools against wear due to their high hardness and chemical stability. In order to produce PVD coatings with increased mechanical properties on complex geometries such as extrusion screws the high power pulsed magnetron sputtering/high power impulse magnetron sputtering (HPPMS/HiPIMS) technology seems to be promising. In this paper Cr-Al-N and Cr-Al-O-N coatings deposited on plasma nitrided steel 34CrAlNi7‑10 (1.8550) by a direct current magnetron sputtering (dcMS)/HPPMS hybrid PVD process are investigated. The Cr/Al ratio and the O content of the coatings were varied. The chemical composition of the bulk and at the surface, morphology and structure were analyzed by means of SEM (scanning electron microscopy), XPS (X-ray photo spectroscopy) and XRD (X-ray diffraction), respectively. Furthermore, high temperature contact angle measurements at the processing temperature of the plastics and tribological tests were conducted in order to analyze the adhesion behavior of the coatings and uncoated steel towards the industrial relevant types of polyamid (PA), polycarbonate (PC) and polypropylene (PP). The tribological behavior of the coatings and uncoated steel against plastic pins at ambient temperature was investigated in a pin-on-disc (PoD) tribometer. Regarding the chemical interactions, the contact zones between the (coated) surfaces and the plastics were analyzed by XPS and Raman spectroscopy. Furthermore, the wear behavior was investigated. The results of the conducted research reveal a correlation between the chemical composition of the coatings and the adhesion towards the investigated plastics.

Wear and oxidation resistant tool coatings are today instrumental in most industrial manufacturing processes. In particular, production of gears is commonly performed by hobbing, using a cylindrical tool with a large number of cutting teeth arranged around the tool body. This process imposes high thermal load on the cutting edges, which is particularly accentuated at high cutting speeds. Optimization of the relevant coating properties for this application can be done by appropriate selection of material systems, incorporation of alloying elements, and through different architectures. Of particular importance are stress state and thermal conductivity of the coating. For evaluation of cutting performance and wear mechanisms, analogy tests are applied, where a single tooth can be tested under conditions replicating those of the hob in the application. Different test conditions will be discussed, which simulate different wear mechanisms. The observed variations in cutting performance and wear behavior will be discussed and correlated with structure and properties of the coatings.

Alumina based CVD thick oxide coating is dominantly used for high speed turning application of high strength cast iron. Use of PVD deposited nitride coating for this application is still minor due to limitation in coating thickness. Since PVD deposited coating is basically in compressive stress as deposited state and spontaneous coating failure can take place once coating thickness excesses typically more than 10um. Previously, we have reported a new cathodic arc source which can substantially reduce the residual stress of the coating and with this new arc source, it is possible to deposit nitride coating up to several tens of microns without failure. In this study, cutting performance was evaluated by using thick TiAlN coating in high speed turning test of cast iron and effect of coating parameter and coating material on wear behavior is investigated.

Thick TiAlN coatings were deposited by the newly developed arc cathode on WC-Co cutting inserts with different edge geometry (edge rounding 15 and 40umR). Wet cutting test was conducted with coated WC-Co cutting insert (MMC SNGA 120408) using ductile cast iron (AISI 80-55-06) at cutting speed 300m/min.

With smaller edge rounding (15umR), amount of flank wear increased almost linearly as the cutting length increased and reached end of tool life (flank wear=300um) at the cutting length of approximately 2.5km. In case of the insert with larger edge rounding, after initial running in process, amount of flank wear stayed constant up to cutting length of 3km then started to increase. Final tool life was 3.5km. We found out that coating at the cutting edge quickly worn out and substrate was exposed for the insert with smaller edge rounding and once substrate was exposed increase of the flank wear was rather quick. Whereas in case of the insert with larger edge rounding, substrate was not exposed until certain cutting length and during that period, flank wear stayed almost constant. Different coating materials were also deposited and subjected to the cutting test. Coatings were AlTiN, TiCrAlN TiCN and AlCrN. Tool life of these coatings was compared with thick TiAlN. Although some of these coating showed smaller wear rate than TiAlN, tool life was not as long as thick TiAlN, because these coatings were highly stressed than TiAlN and there was a limitation in maximum thickness which significantly affected tool life.

Finally a comparison of cutting performance with commercial CVD oxide coating insert was done and Thick TiAlN showed longer tool life compared to commercial CVD coatings in high speed turning of cast iron.

Since its inception, High Power Impulse Magnetron Sputtering (HiPIMS) has developed from a university research tool to an industrial applicable technology. In the field of cutting tools there has been a simultaneous development towards an increasing emphasis on high-precision cutting. Hard HiPIMS coatings with low surface roughness are therefore seen as a promising alternative to the current cathodic arc evaporation coatings. However, there is still a lack of comparative studies on the cutting performance and wear behaviour of industrial HiPIMS and cathodic arc coatings. In this study, the differences in cutting performance of HiPIMS and cathodic arc coatings have been examined and the results explained in terms of coating microstructure and physical properties.

Forces during steel cutting were examined and it was concluded that the surface roughness of the coatings as well as the surface morphology are crucial factors for avoiding early tool breakage and that low cutting forces and increased tool reliability can be obtained with HiPIMS coatings. Furthermore, the HiPIMS coatings also showed superior wear resistance compared to the cathodic arc coatings. These results were explained using a qualitative study on steel turning where the adverse role of droplets in causing uneven wear was highlighted.

From the experimental results, it will be argued that the absence of droplets in HiPIMS coatings, along with a suitable surface morphology, can improve wear resistance as well as increase tool reliability in metal cutting applications.

The influence of tool surface topography on the initiation and build-up of transfer layers in the orthogonal turning of 316L austenitic stainless steel have been studied under well controlled conditions. Tool materials include CVD Ti(C,N)-Al₂O₃-TiN and PVD (Ti,Al)N-(Al,Cr₂)O₃ coated cemented carbide inserts prepared using different grinding and polishing treatments. Post-test characterization of the inserts was performed using high resolution scanning electron microscopy, energy dispersive X-ray spectroscopy and high resolution Auger electron spectroscopy.

The results show that the transfer tendency of work material is strongly affected by the surface topography of the rake face. For both types of inserts, the initial transfer and the build-up of transfer layers are localized to surface irregularities on the rake face. Consequently, an appropriate surface treatment of the cemented carbide substrate before coating deposition and the as-deposited CVD and PVD coating can be used in order to reduce the transfer tendency and the mechanical interaction between the mating surfaces.

Machining of lightweight alloys differs from that of the conventional ferrous alloys because of the strong tendency of most Al, Mg, and Ti alloys to adhere to the cutting tools. To prevent adhesion that reduces the tool life and increase power consumption during machining low-friction carbon based coatings can be applied to tool surfaces. The tribological performances of diamond-like carbon (DLC) coatings and multilayered graphene in mitigating adhesion and reducing friction of lightweight alloys are studied. Sliding contact tests were performed on multilayer graphene (I_G/I_2D > 1) in air (10, 20% and 45% RH) and under a dry N₂ atmosphere against an aluminum alloy (319 Al-Si alloy) and a titanium alloy (Ti-6Al-4V). Progressively lower friction values were observed when the atmospheric humidity was increased, with the lowest coefficient of friction (COF) of 0.10 reached at 45% RH. Tests under a dry N₂ atmosphere consistently produced high COF of about 0.50. Cross-sectional FIB/HR-TEM of transfer layers showed that graphene was transferred to the counterfaces. The transfer layers consisted of an amorphous matrix with graphene layers with d-spacings larger than that of the pristine graphite suggesting an increase in the interlayer lattice spacing to accommodate the dissociated water molecules. Comparisons were made with hydrogenated diamond-like carbon (H-DLC) and polycrystalline diamond (PCD) by considering the running in as well as the steady state COFs. Tribological tests were also performed to simulate the cylinder bore-piston ring contact while measuring the COF of non-hydrogenated DLC (NH-DLC) coatings against aluminum alloys. Current and potential uses DLC coated tools and graphene incorporating lubricants and surfaces in energy-efficient machining and forming of the lightweight automotive components are discussed, including minimum quantity aqueous lubrication (H₂O-MQL) machining, and thermally assisted machining using W-containing DLC (W-DLC) coatings.

The use of a supercritical high pressure cryogenic nitrogen jet (HPCryoN₂Jet) has been recently promoted for materials cutting and surface modifications. The principle of this new technique consists in impacting the material with a low temperature (-160°C) and high velocity (supersonic) nitrogen jet that is naturally recycled in the atmosphere. Thus, in comparison with other processes that often use toxic chemicals, abrasive media and generate waste, the HPCryoN₂Jet is a dry and environmental friendly technology. Depending on the material to be treated and the test parameters such as jet pressure, standoff distance, jet temperature and dwell time, the nitrogen jet technique has been used efficiently for ablating material surfaces [1, 2].

In addition to the ablation / cutting effect, the present work will investigate the potential of HPCryoN₂Jet technique for cleaning / stripping metallic surfaces without using additional abrasive media or chemicals. To this end, the HPCryoN₂Jet technique has been used under dynamic conditions with different processing parameters to remove epoxy paint layers from surfaces of the AISI 316 L stainless steel and E24 low carbon mild steel. Finally, the effectiveness of the process will be discussed and the ablation as well as the cleaning / stripping results will be analyzed.

[1] Laribou, H.; Fressengeas, C., Entemeyer, D., Jeanclaude, V., Pesci, R., Tazibt, A., 2012. Effects of the impact of a low temperature nitrogen jet on metallic surfaces. Proceedings of the royal society A 468, 3601-3619.

[2] A., Tazibt, A., Grosdidier, T., Berrio-Marine, G., Munoz-Cuartas, V.A., Tidu., 2015. Modification, Ablation and Hardening of Metallic Surfaces by a Cryogenic Nitrogen Jet. Procedia Engineering, Vol. 114, 506-513.