Medium Temperature CVD Alpha Alumina Coating

Abstract

The present invention relates to a method for manufacturing a coated cutting tool for chip-forming metal machining, consisting of a substrate of cemented carbide, cermet or cubic boron nitride based ceramic material and a single or multi-layer wear-resistant hard coating, the layer of the hard coating comprising at least one alpha (α) phase Al2O3 coating layer deposited by chemical vapor deposition (CVD) with an average thickness in the range of 1 μm to 20 μm, wherein the deposition of the alpha phase Al2O3 coating layer is carried out at a temperature in the range of 600-900 °C using a process gas composition, as introduced into the CVD reactor, comprising or consisting of AlCl3, H2O, H2 and optionally HCl, and / or a sulfur source selected from H2S, SF6, SO2 and SO3, in which the volume ratio of H2O / AlCl3 is in the range of 0.5-2.5 and the volume ratio of H2 / AlCl3 is in the range of 200-3000.

Description

[Technical field]

[0001] The present invention relates to a surface-coated cutting tool consisting of a substrate body and a hard coating deposited on the substrate by a CVD process, the hard coating comprising at least one dense, hard Al2O3 layer in pure or predominantly pure alpha phase (α-phase) deposited by a "medium temperature" CVD (MT-CVD) process in the range of about 600-900° C. The present invention further relates to a method for depositing such an α-Al2O3 layer at moderate temperatures by CVD.

[0002] The cutting tool coating of the present invention has excellent wear and spallation resistance in continuous and intermittent high speed metal cutting. [Background technology]

[0003] For the past few decades, cutting tools of various substrate body materials such as cemented carbide, cermet, cubic boron nitride, etc. coated with different types of hard layers such as TiC, TiN, TiCN, TiAlN, and Al2O3 have been commercially available. Such tool coatings are generally built up by several hard layers in a multi-layer structure. The sequence and thickness of the individual layers are carefully selected to suit different cutting applications and workpiece materials.

[0004] Tool coatings are most frequently deposited by chemical vapor deposition (CVD) or physical vapor deposition (PVD) techniques. Both CVD and PVD have advantages and disadvantages relative to each other, resulting in different microstructural, physical and mechanical coating properties, and therefore both techniques provide valuable coatings. One essential difference between these techniques is based on the difference in deposition temperature. PVD deposition is carried out at temperatures of about 450-700 °C and is carried out under ion bombardment, which results in high compressive stresses in the coating and no cooling cracks. In contrast, CVD for the deposition of hard tool coatings is carried out at high temperatures of about 880-1100 °C. Due to this high deposition temperature and the mismatch of the thermal expansion coefficients between the deposited coating material and the substrate material, such as cemented carbide, CVD produces coatings with cooling cracks and tensile stresses. These process differences make CVD-coated tools more brittle than PVD-coated tools and, as a result, have poor toughness behavior.

[0005] However, CVD techniques are suitable and advantageous for the deposition of many excellent hardness and wear resistance coating materials, such as Al2O3, ZrO2, and various Ti and TiAl compounds (e.g., Ti(C,N), TiAl(C,N)). The microstructure and therefore the properties of these coatings can be altered by changing the deposition conditions. If the standard CVD deposition temperature could be significantly reduced, it would be expected that the coatings would have better toughness and other improved properties.

[0006] The application of the MT-CVD ("medium temperature" CVD) technique in the tool industry has significantly improved the toughness behavior and performance of CVD-coated tools. The MT-CVD technique works at deposition temperatures in the range of about 700-900 °C and is well established to deposit Ti(C,N) layers from a gas mixture containing TiCl4, CH3CN, and H2.

[0007] Modern tool coatings must contain at least one polycrystalline layer of Al2O3 to achieve high wear resistance, hardness, etc. It is well known that Al2O3 crystallizes in several different phases, including α, κ, γ, δ, and θ. The most common CVD deposition temperatures for Al2O3 are in the range of 980-1050 °C. At these temperatures, both metastable κ-Al2O3 and stable α-Al2O3, or a mixture of them, can be produced. In some cases, the θ phase can also be present in small amounts.

[0008] However, the high temperatures typically used for deposition of Al2O3 can lead to embrittlement of the substrate and / or decomposition of thermodynamically metastable materials, such as TiAlN, in layers beneath the Al2O3 deposition. It would therefore be desirable to be able to deposit high quality Al2O3 layers, especially single-phase stable α-Al2O3 layers, by a CVD process at low temperatures in the range of MT-CVD processes to avoid the disadvantages associated with high temperature CVD deposition, not only to the deposited Al2O3 layer itself, but also to the layers and substrate beneath it.

[0009] There have been various attempts to deposit Al2O3 by CVD at low temperatures, but currently no suitable and economically feasible process is known for the low-temperature CVD deposition of a single-phase stable α-Al2O3 layer on cutting tools.

[0010] EP 1947213 describes a process for depositing α-Al2O3 at temperatures ranging from about 625 to 800 °C. Al2O3 deposition requires the pre-deposition of an underlying oxygen-rich TiCNO layer, which must be further treated with an oxygen-containing gas mixture before the subsequent Al2O3 deposition can take place. The Al2O3 deposition process requires high concentrations of CO2 and a sulfur dopant such as H2S. If the oxygen treatment step is omitted, predominantly amorphous or metastable phases of Al2O3 are formed.

[0011] The deposition of the underlying TiCNO layer can be done at 450-600 °C using PVD techniques or at 1000-1050 °C using CVD techniques. If CVD is used, the necessary oxygen treatment step for the TiCNO layer before the start of the Al2O3 deposition is also done at high temperatures of about 1000 °C or higher. Therefore, one of two different deposition techniques must be applied, PVD and CVD, with the associated need to provide two apparatus and to move the sample between completely different coating devices. Also, if one or more additional CVD layers are deposited under the TiCNO layer, as described in some embodiments of EP 1947213 A1, not one but multiple transfers of the sample from CVD to PVD and back to the CVD apparatus are required. Alternatively, to deposit the TiCNO layer and perform the oxidation step, high temperature CVD must be applied, with all the drawbacks of high temperature treatment for the substrate and / or further underlying layers of the multilayer coating.

[0012] The subsequent Al2O3 deposition process is carried out by CVD using a reactant gas composition of AlCl3, CO2, H2, H2S, and preferably HCl at a process pressure of 40-300 mbar and a temperature of 625-800 °C, which results in a very high CO2 concentration of around 16-40 vol.% of the reactant gas composition.

[0013] EP 3505282 describes a cutting tool with a multilayer hard CVD coating, including an underlayer of Ti and Al composite nitride or composite carbonitride (Ti,Al)(C,N), an adhesion layer, and an overlayer of α-Al2O3. The authors discovered that when an α-Al2O3 layer is directly deposited on a (Ti,Al)(C,N) underlayer under typical CVD conditions at about 1000°C, phase separation of AlN occurs in the (Ti,Al)(C,N) layer, and the (Ti,Al)(C,N) layer does not have sufficient hardness. On the other hand, when an α-Al2O3 layer is formed on the surface of a (Ti,Al)(C,N) layer at a low temperature range of 700°C to 900°C, amorphous Al2O3 is formed on the outermost surface of the (Ti,Al)(C,N) layer, and the adhesion strength between the (Ti,Al)(C,N) layer and the α-Al2O3 layer is not sufficient.

[0014] The authors found that the adhesion strength between the (Ti,Al)(C,N) layer and the α-Al2O3 layer can be improved by providing a TiCN adhesion layer with increased oxygen content near the surface in contact with the α-Al2O3 overlayer, which can then be formed at relatively low temperatures in the range of 800-900 °C, process pressures of 5-15 kPa, using a reactant gas composition of AlCl3, CO2, H2, and HCl during the nucleation stage, with additional amounts of H2S during layer growth.

[0015] Connelly, R. et al., “Development of moderate temperature CVD Al2O3coating”, International Journal of Refractory Metals & Hard Materials 23 (2005) 317-321, describe further attempts to lower the CVD deposition temperature of Al2O3 to the moderate temperature range of about 700-900°C for economic reasons, allowing MT-CVD deposition of an intermediate Ti(C,N) coating with Al2O3 within the same temperature range.

[0016] Al2O3 deposition from AlCl3 requires H2O as an oxygen donor, which in the standard prior art is generated in situ by the CVD process in the water-gas shift reaction from H2+CO2→H2O+CO. Connelly, R. et al. investigated additional water sources in this reaction such as NO+H2, NO2+H2, CHOOH, and H2O2, and the thermodynamics and kinetics of these systems at various temperatures between 700 and 950 °C. Thermodynamic calculations identified the NO+H2 and HCOOH systems as the most potential oxygen donor sources to form alumina in the medium temperature range of 700-950 °C. The authors demonstrate that the AlCl3+CHOOH+H2 system can be used to deposit dense, uniform, and adherent alumina coatings on TiC and TiCN coated cemented carbide cutting tools at 870 °C. XRD analysis showed that the deposited Al2O3 coating contained alpha and kappa phases.

[0017] Funk, R. et al., “Coating of Cemented Carbide Cutting Tools with Alumina by Chemical Vapor Deposition”, J, Electrochem. Soc., Vol. 123, No. 2, pp. 285-289, compares a standard prior art process in which H2O is provided in addition to AlCl3 by water-gas shift reaction from H2+CO2 (the “H2-CO2 process”) with a process in which H2O is directly introduced (the “H2O process”) over a wide temperature range on uncoated and TiC, TiN, or Cr precoated cemented carbide substrates. The authors show that the deposition rate of alumina decreased with increasing deposition temperature (600-1000°C) for the H2O process at 5 Torr, whereas the deposition rate increased with increasing deposition temperature (750-1100°C) for the H2-CO2 process at 50 Torr. Adhesion of substrates pre-coated with TiC and TiN was found to be better than that of uncoated cemented carbide, whereas non-adherent deposits were formed on substrates pre-coated with Cr. In the standard H2-CO2 process, the coating contained α-Al2O3 in the temperature range 850-1100 °C, but nothing was said about the modification, quality, phase purity, or microstructural, physical or mechanical properties of the deposits produced in the H2O process.

[0018] Mantyla et al., Proc. 5th EuroCVD, June 17-20, 1985, have also investigated the deposition behavior of Al2O3 in the temperature range 250-1000 °C, using CVD layers to densify the surface of porous plasma sprayed Al2O3 by directly introducing H2O gas in reaction with AlCl3 to increase the deposition rate ("H2O process"). However, coatings deposited at 250-500 °C were predominantly amorphous, the amount of amorphous phase decreased with increasing temperature, crystalline Al2O3 was obtained only at temperatures above 750-800 °C, and stable α-Al2O3 was obtained only at 1000 °C.

[0019] Similar work was carried out by Schachner et al., Ber. Dt. Keram. Ges. 49 / 3 (1972), 76-80, who directly introduced H2O and hydrolyzed AlCl3 in a CVD reaction carried out in the temperature range of 200-500 °C. However, only amorphous Al2O3 was obtained, as confirmed by the subsequent work of Mantyla et al. Summary of the Invention

[0020] The object of the present invention was to provide an improved and economical process for the low-temperature CVD deposition of alpha-phase Al2O3 coating layers with good crystallinity, high hardness and density. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention provides a new method for manufacturing a coated cutting tool for chip-forming metal machining, consisting of a substrate of cemented carbide, cermet or cubic boron nitride based or other ceramic material and a single or multi-layer wear-resistant hard coating, the hard coating layer comprising at least one alpha (α) phase Al2O3 coating layer deposited by chemical vapor deposition (CVD) with an average thickness in the range of 1 μm to 20 μm, the deposition of the alpha phase Al2O3 coating layer comprising: - At temperatures in the range of 600-900°C, using a process gas composition as introduced into the CVD reactor, comprising or consisting of AlCl3, H2O, H2, and optionally HCl, and / or a sulfur source selected from H2S, SF6, SO2, and SO3, wherein the process gas composition introduced into the CVD reactor comprises: - The volume ratio of H2O / AlCl3 is in the range of 0.5 to 2.5, and - The volume ratio of H2 / AlCl3 is in the range of 200-3000.

[0022] The process of the present invention overcomes several deficiencies of the prior art and allows for the deposition and controlled growth of pure or nearly pure alpha phase Al2O3 coating layers with good crystallinity, high hardness and high density at relatively low temperatures.

[0023] Standard H2-CO2 processes for depositing α-Al2O3 require high temperatures, on the order of 1000°C or higher, which can embrittle the substrate and decompose thermodynamically metastable materials in layers below the Al2O3 deposition. The process of the present invention overcomes this drawback of high temperature deposition. Also, while known H2O processes can deposit Al2O3 at temperatures as low as 250°C, none of the prior art H2O processes were suitable for depositing pure or nearly pure alpha-phase Al2O3 of the quality obtained with the process of the present invention. Prior art H2O processes either did not obtain alpha-phase Al2O3 at all, or only a certain amount of α-Al2O3 mixed with a large amount of other unfavorable phases such as gamma or theta phases, and / or amorphous Al2O3. The process of the present invention allows the deposition of pure or nearly pure high quality α-Al2O3 without the adverse effects of too high a deposition temperature on the underlying material.

[0024] In the process of the invention, the deposition of the alpha-phase Al2O3 coating layer is carried out at a temperature in the range of 600-900 °C. Below 600 °C, no alpha-phase Al2O3 or alpha phase mixed with large amounts of other unfavourable phases is observed, and a layer with poor crystallinity and poor adhesion is obtained. At temperatures above 900 °C, the degradation effects on the underlying unstable or metastable material become too great. In one embodiment of the invention, the deposition of the alpha-phase Al2O3 coating layer is carried out at a temperature in the range of 600-850 °C. At temperatures below 850 °C, the risk of phase transformation of the underlying material and the deposition of a porous Al2O3 layer due to gas-phase reactions is further reduced.

[0025] Surprisingly, it has been found that this can be achieved in a H2O process at relatively low deposition temperatures when the process gas composition as introduced into the CVD reactor has a H2O / AlCl3 ratio in the range of 0.5-2.5, while at the same time the H2 / AlCl3 ratio is in the range of 200-3000.

[0026] If the H2O / AlCl3 ratio is too low, below 0.5, a pure or nearly pure alpha phase will not be obtained and / or the deposition rate will be so slow that it will make the process economically unfeasible.

[0027] When the H2O / AlCl3 ratio exceeds 2.5, even when the H2 / AlCl3 ratio is in the range of 200-3000, no alpha phase is deposited, and only gamma phase Al2O3 is deposited.

[0028] If the H2 / AlCl3 ratio is too low, below 200, no alpha phase Al2O3 is deposited, only gamma phase or a mixture of gamma and theta phases are deposited, and in some cases a poorly or non-adherent powder layer is obtained, even with a H2O / AlCl3 ratio in the range of 0.5-2.5.

[0029] If the H2 / AlCl3 ratio is too high, above 3000, then a pure or nearly pure alpha phase will not be obtained and / or the process will become economically unfeasible due to excessively slow deposition rates or the need to technically handle very large H2 flow rates.

[0030] Therefore, to enable deposition and controlled growth of an α-Al2O3 coating layer with good crystallinity, high hardness, and high density at the relatively low deposition temperature of the present invention, both reactant gas conditions, i.e., H2O / AlCl3 ratio of 0.5-2.5 and H2 / AlCl3 ratio of 200-3000, need to be met simultaneously.

[0031] The process of the invention makes it possible to deposit α-Al2O3 coating layers even on substrates and / or further layers below that are unstable or have low stability or are susceptible to embrittlement or other adverse changes at high temperatures, while at the same time providing a deposition rate that is sufficiently high to make the production of wear-resistant layers several micrometers thick economically viable.

[0032] The process of the present invention is compatible with commonly used industrial CVD equipment designs and allows the deposition of the α-Al2O3 coating layer to be performed in the same deposition run as further coating layers of a multi-layer coating structure, making mass production of coated cutting tools cost and time efficient without the need for separate manufacturing steps such as intermediate PVD depositions.

[0033] The α-Al2O3 coating layer produced by the process of the present invention exhibits high crystallinity, high hardness, and high density, resulting in good wear resistance and mechanical properties.

[0034] Compared to conventional processes that deposit α-Al2O3 coating layers at high temperatures, the process of the present invention operates at significantly lower temperatures, resulting in less energy consumption and potentially lower production costs.

[0035] In a preferred embodiment of the present invention, the deposition of the alpha-phase Al2O3 coating layer is carried out at a total pressure in the range of 3 to 50 mbar, or 3 to 30 mbar, or 3 to 20 mbar, or 3 to 15 mbar.

[0036] Too low a total pressure can slow down the deposition rate, and may require significant technical and financial resources to generate the process vacuum while evacuating corrosive precursors and by-products.

[0037] If the total pressure is too high, a pure or nearly pure alpha phase will not be obtained, and furthermore, if the partial pressure of the reactive gas is too high, undesirable gas phase reactions may occur and a dense layer may not form.

[0038] In another preferred embodiment of the present invention, in the deposition of an alpha-phase Al2O3 coating layer in the process gas composition as it is introduced into the CVD reactor, the ratio of H2O / AlCl3 is in the range of 0.7 to 2.0, or in the range of 0.8 to 1.5. It has been observed that this range of H2O / AlCl3 ratio can improve the uniformity of the coating thickness distribution in the reactor.

[0039] In another preferred embodiment of the present invention, in the deposition of an alpha-phase Al2O3 coating layer in the process gas composition when introduced into a CVD reactor, the ratio of H2 / AlCl3 is >500, or >800, or >1200, or >1400, or >1600.

[0040] It was observed that a higher H2 / AlCl3 ratio could further improve the purity of the alpha-phase Al2O3 deposition and lead to a more uniform coating thickness profile in the reactor.

[0041] In another preferred embodiment of the invention, in the deposition of an alpha-phase Al2O3 coating layer, the process gas composition as introduced into the CVD reactor consists of AlCl3, HO, and H2, or the process gas composition additionally comprises a sulfur source, preferably H2S, in an amount of up to 2% by volume of the process gas.

[0042] In a preferred embodiment of the invention, the process gas composition when introduced into the CVD reactor does not contain additional HCl. However, the invention includes embodiments in which, for deposition of an alpha-phase Al2O3 coating layer, the process gas composition when introduced into the CVD reactor additionally contains HCl in the process gas in an amount up to 10 times the volumetric amount of AlCl3.

[0043] In a preferred embodiment of the invention, the deposition process comprises the deposition of a further layer under the alpha-phase Al2O3 coating layer, i.e. the deposition of a multi-layer structure. The further layer preferably comprises one or more Ti and / or Ti+Al compound layers selected from carbides, nitrides, oxides, carbonitrides and oxycarbonitrides. The further layer comprising the further Ti and / or Ti+Al compound layer may be suitable for improving the adhesion of the coating and / or for promoting a preferred crystal orientation or texture of the α-Al2O3 coating layer and / or the further layer and / or for contributing to and improving the wear resistance of the entire coating structure.

[0044] In one preferred example, the layer deposited under the alpha-phase Al2O3 coating layer includes a layer sequence of a titanium nitride (TiN) underlayer, followed by one or more subsequent layers selected from titanium carbonitride (TiCN), titanium aluminum carbonitride (TiAlCN) and titanium aluminum nitride (TiAlN), and optionally followed by a tie layer immediately under the alpha-phase Al2O3 coating layer according to the invention, which tie layer preferably includes titanium carbonitride (TiCN) or titanium aluminum carbonitride (TiAlCN). In one embodiment of the present invention, the tie layer includes TiCN or TiAlCN in an oxidation state near or immediately under the transition region to the alpha-phase Al2O3 coating layer, which is achieved by depositing a TiCNO or TiAlCNO sublayer or by carrying out an oxidation step on the TiCN or TiAlCN of the tie layer before the deposition of the alpha-phase Al2O3 coating layer. Providing an oxidation state can further improve the adhesion of the alpha-phase Al2O3 coating layer.

[0045] In one embodiment of the present invention, the deposition process comprises an oxidation step prior to the deposition of the alpha-phase Al2O3 coating layer. Preferably, the oxidation step is applied to the Ti and / or Ti+Al compound layer deposited underneath the Al2O3 coating layer. It has been found that the application of an oxidation step can be suitable for improving the adhesion of the subsequently deposited alpha-phase Al2O3 coating layer.

[0046] Preferably, the oxidation step is carried out in the presence of HO as the oxidizing agent for a time period of about 2 to 20 minutes, preferably about 3 to 15 minutes. In one embodiment, the temperature of the oxidation step is about the same as or ±50° C. as the temperature applied for the deposition of the alpha-phase AlO coating layer.

[0047] The present invention also includes a surface-coated cutting tool for chip-forming metal machining consisting of a substrate of cemented carbide, cermet, or cubic boron nitride based ceramic material and a single or multi-layer wear-resistant hard-coating, the layers of the hard-coating comprising at least one alpha (α) phase Al2O3 coating layer deposited by a chemical vapor deposition (CVD) process as defined herein.

[0048] The cutting tool of the present invention differs from cutting tools having at least one alpha (α) phase Al2O3 coating layer conventionally manufactured at high temperatures in that the substrate and / or further layers under the Al2O3 coating layer are not subject to structural changes and degradation due to high temperature deposition or processing steps. Thus, the cutting tool of the present invention can exhibit improved mechanical properties and wear resistance due to the deposition process of the present invention. Furthermore, since the process of the present invention is carried out at a significantly lower temperature, the cutting tool of the present invention can be manufactured at a lower cost and with less resource consumption than a comparable cutting tool having at least one α-Al2O3 coating layer conventionally manufactured at high temperatures.

[0049] In one embodiment of the surface coated cutting tool of the present invention, at least one alpha phase Al2O3 coating layer deposited by the process of the present invention has a Vickers hardness HV0.01 of >2000HV, or >2300HV.

[0050] In another embodiment of the invention, the wear resistant hard coating of the surface coated cutting tool further comprises one or more Ti and / or Ti+Al compound layers under the alpha phase Al2O3 coating layer, the Ti and / or Ti+Al compound layers being selected from carbides, nitrides, oxides, carbonitrides, and oxycarbonitrides.

[0051] Materials and Methods X-ray diffraction (XRD) measurements X-ray diffraction measurements were performed on a GE Sensing and Inspection Technologies XRD3003 PTS diffractometer using CuKα radiation. The X-ray tube was operated at 40 kV and 40 mA with a point focus. On the primary side, parallel beam optics using a polycapillary collimator lens with a fixed size measurement aperture was used, and the irradiated area of ​​the sample was defined in such a way that leakage of the X-ray beam onto the coated side of the sample was avoided. On the secondary side, a parallel plate collimator with a divergence angle of 0.4° and a 25 μm thick NiKβ filter were used. Depending on the layer thickness, diffraction measurements to identify the Al2O3 phase were performed by 2θ scans at a constant incidence angle of ω = 1° or by symmetric θ-2θ scans with 0.04° increments in the angular range of 15° ≤ 2θ ≤ 90°.

[0052] Microhardness measurements The microhardness was measured by Vickers hardness testing. For this purpose, a diamond pyramid (interface angle 136°, Vickers pyramid) was pressed into the layer with a defined test load. In accordance with DIN EN ISO 4516, a smooth calotte grind was used for the test. A smooth surface is necessary to minimize the influence of the surface on the measurement. The indenter is placed in the outer area of ​​the coating, ensuring that the indenter depth is less than 1 / 10 of the layer thickness. The diagonal of the indenter residual mark was measured optically. Indentations and measurements were carried out using an MHT-10 (Anton Paar) mounted on an optical microscope. The hardness was calculated by the software using the average of the two diagonal lengths according to the following formula (F is the test load and d is the average diagonal length): TIFF2024543491000001.tif14170

[0053] Carrot grinding Carrot grinding was used to evaluate the thickness and adhesion of the coating. Inserts were placed on an inclined magnetic holder of a ball cratering device. Spherical carrots were ground into the coating and into the substrate material by a 30 mm rotating steel ball wetted with a drop of 3 μm aqueous diamond suspension (Struers, DP-Lubricant Green) and driven by a drive shaft at >500 rpm. The grinding process was stopped when the diameter of the carrot on the substrate material reached approximately 600-1100 μm. Thickness measurements, taking into account the shape of the carrot, were performed with dedicated software using optical microscopy (LOM).

[0054] “A” Adhesion "A" adhesion defines the adhesion of the α-Al2O3 layer to the underlying layer. "A" adhesion was assessed by LOM observation of polished carrot ground surfaces and visually classified on a scale of 1.0 (= perfect adhesion) to 3.0 (= no adhesion). The criteria for "A" adhesion at the layer / sublayer interface are as follows: A=1: No or negligible delamination is observed at the interface, and the interface line remains intact. A=2: Small peeling can be observed at the interface, and about 51-80% of the entire interface line is not deteriorated. A=3: Large or continuous peeling is observed at the interface, and 50-100% of the interface line of the carrot is deteriorated.

[0055] Cutting test (milling) In this specification, the coated cutting tool is tested at a cutting strength of 785N / mm 2 Tested in a milling operation on 42CrMo4 steel with a tensile strength of: cutting speed v c :180m / min Cutting feed rate, f: 0.2mm / revolution Cutting depth, a p :3mm Cutting width,a e :98mm Radial overhang,u e :5mm Number of teeth: 1 Insert shape: SPHW120408 (No cutting fluid)

[0056] CVD Coating The CVD coatings of the examples presented herein below were applied onto WC-co-based cemented carbide cutting tool substrates. Two different types of CVD equipment were used in the examples herein: a laboratory-scale CVD equipment and an industrial-scale CVD equipment.

[0057] The amount of gas fed to the reactor is ml n / min (standard milliliters / min), l nThe flow rates were controlled by mass flow control units adjusted to flow rates in standard liters per minute (standard liters per minute) or standard cubic centimeters per minute (sccm). All of these refer to conditions of 0° C. and 1.013 bar (absolute) according to technical data provided by the manufacturer (Bronkhorst). The volume of evaporated H2O was controlled and converted to sccm as described below. AlCl3 was generated and evaporated in situ using the technical and industrially common technique of chlorinating Al pellets with HCl gas at high temperature. The literature on thermal CVD of aluminum oxide usually reasonably assumes that the chlorination reaction Al+3HCl→AlCl3+1.5H2 proceeds almost instantaneously and quantitatively, producing only monomeric aluminum trichloride molecules. The process gas compositions and volume ratios given herein take into account the flow rates of AlCl3 and H2 as appropriate.

[0058] In the apparatus and embodiments described herein, the process gas mixture is introduced into the reactor through two separate gas inlets: AlCl3, optionally additional HCl and / or sulfur-containing gas, and H2 are fed through one inlet, and H2O and the remaining H2 are fed through another inlet. However, the invention is not limited to the reactor design and the particular configuration of the gas delivery system.

[0059] Apparatus "A" is a laboratory-scale horizontal-flow hot-wall CVD reactor made of Inconel with an inner diameter of 79 mm, horizontal length of 800 mm, and internal volume of about 6 liters. The substrate temperature is controlled by a K-type thermocouple. Reactant gases are introduced into the reaction zone by separate gas inlets. Apparatus A was used for the preparation of Al2O3 coatings by CVD in some of the inventive and comparative examples described below. In the H2O evaporator of this apparatus, water was evaporated by bubbling H2 carrier gas into liquid water at controlled pressure and temperature. The evaporated H2O gas flow rate (in sccm) is calculated as follows: TIFF2024543491000002.tif14170 formula, v(H2O) = H2O gas flow rate [ml / min] = H2O gas flow rate [sccm] p(H2O) = vapor pressure of H2O [Torr] p = normal pressure 760 [Torr] p v = Pressure inside the evaporator [Torr] R = Universal molar gas constant 62.32 [l Torr mol -1 K -1 ] T0=Reference temperature 273.15[K] V m = Molar volume 22.4 [l mol -1 ] V (carrier gas) = ​​gas flow of carrier gas introduced into the evaporator [ml / min] It is.

[0060] Apparatus "B" is an industrial-sized radial-flow CVD coating chamber with an inner reactor height of 1580 mm, inner reactor diameter of 500 mm, and internal volume of about 300 liters. Reactant gases were fed into the reactor through a central gas inlet pipe and introduced into the reaction zone through openings distributed along the inlet pipe, providing an essentially radial gas flow over the substrate body. Apparatus B was used to prepare Al2O3 coatings by CVD in some of the inventive and comparative examples described below. In the H2O evaporator of this apparatus, water was evaporated by spraying liquid water into a stream of H2 carrier gas at 100°C under reduced pressure. The evaporation rate was controlled by a liquid mass flow controller calibrated in g / h. The molar mass of H2O and the volume of an ideal gas at normal conditions of 0°C and 1.013 bar (absolute) were used to calculate the gas volumetric flow rate in sccm therefrom.

[0061] The volumetric ratios of the process gas compositions introduced into the reactor refer to the gas flow rates in sccm mentioned above.

[0062] Unless otherwise stated, in the examples herein, the reactors were filled with inserts to nearly full capacity, the sample inserts to be investigated were distributed at different locations within the reactor, and the remaining sample locations within the reactor were filled with "scrap" inserts to simulate as closely as possible the full-scale deposition conditions and volume usage within each reactor. EXAMPLES

[0063] deposition In the inventive examples I1-I16 prepared herein, and comparative examples C1-C13 and CWG1, the substrate was precoated with an approximately 0.6 μm thick TiN base layer and an approximately 5.4 μm thick TiCN layer prior to Al2O3 deposition using Apparatus B. The process parameters and reactant gases for this deposition are shown in Table 1. The deposition of TiN and TiCN prior to Al2O3 deposition was all performed under the same process conditions and with the same apparatus, allowing the examples to be compared with respect to changes in Al2O3 deposition conditions.

[0064] The process parameters and reactant gases for deposition of the Al2O3 layer in inventive examples I1-I16 and comparative examples C1-C13 and CWG1 are shown in Table 2. In some of the inventive examples and comparative examples (where indicated), an oxidation step was applied to the TiCN layer before deposition of Al2O3. The oxidation was performed with a fixed H2O flow rate of 12 sccm for Apparatus A and 1333 sccm for Apparatus B, for the time and temperature shown in Table 2 under "Oxidation Time" and "Oxidation Temperature", respectively.

[0065] In comparative examples CWG1 and CWG2, the water gas shift reaction from H2+CO2→H2O+CO was applied to deposit the Al2O3 layer. The layer sequence, process parameters, and reaction gases introduced into the reactor for comparative example CWG1 are included in Tables 1 and 2, and the layer sequence, process parameters, and reaction gases for comparative example CWG2 (prepared in apparatus B) are shown in Table 3.

[0066] Table 4 shows the measured parameters of the Al2O3 layers of the examples (I1 to I16) of the present invention and the comparative examples (C1 to C13, CWG1 and CWG2).

[0067] Table 5 shows the cutting test results of the examples of the present invention and the comparative examples. In each example, four cutting blades were used in the milling test. The milling was interrupted when the milling path reached 800 mm, 1600 mm, 3200 mm, 4800 mm, and 5600 mm, and the wear traces, flank wear width (Vb), maximum flank wear width (Vb max ), and the number of comb cracks (comb cracks). Each cutting edge was evaluated for maximum flank wear width Vb max The wear resistance of the cutting edge of each variation was poorest, and the wear resistance of the cutting edge was 0.30 mm. ,max It was shown that the milling length to reach >0.30 mm was the shortest, and the wear width was the largest when some cutting edges exceeded 0.3 mm at the same measurement interval. TIFF2024543491000003.tif37170

[0068] When depositing the TiCN layer on the TiN base layer, the gas flows of TiCl4 and CH3CN started at the same rates as for the TiN base layer (TiCl4 = 1670 sccm; CH3CN = 0 sccm) and were each linearly and continuously increased at 5000 sccm / min to the values ​​shown in Table 1. TIFF2024543491000004.tif251170TIFF2024543491000005.tif250170TIFF2024543491000006.tif250170 TIFF2024543491000007.tif230170TIFF2024543491000008.tif221170TIFF2024543491000009.tif241170

Claims

1. 1. A method for manufacturing a coated cutting tool for chip-forming metal machining, consisting of a substrate of cemented carbide, cermet or cubic boron nitride based ceramic material and a single or multi-layer wear-resistant hard coating, wherein said layer of said hard coating is at least one alpha (α) phase Al2O3 deposited by chemical vapor deposition (CVD) with an average thickness ranging from 1 μm to 20 μm. ２ O ３ The coating layer includes alpha phase Al ２ O ３ The deposition of the coating layer - at a temperature in the range of 600 to 900 ° C, - AlCl ３ , H ２ O, H ２ , and optionally HCl, and / or H ２ S, SF ６ , S.O. ２ , and SO ３ using a process gas composition when introduced into a CVD reactor comprising or consisting of a sulfur source selected from It is carried out, In the process gas composition as introduced into the CVD reactor: - H ２ O / AlCl ３ The volume ratio of is in the range of 0.5 to 2.5, and - H ２ / AlCl ３ The volume ratio is in the range of 200 to 3000. A method for producing a coated cutting tool for chip-forming metal machining.

2. Alpha phase Al ２ O ３ The method of claim 1, wherein the deposition of the coating layer is carried out at a total pressure in the range of 3 to 50 mbar, or 3 to 30 mbar, or 3 to 20 mbar, or 3 to 15 mbar.

3. Alpha phase Al in the process gas composition as it is introduced into the CVD reactor ２ O ３ In the deposition of the coating layer, H ２ O / AlCl ３ 2. The method of claim 1, wherein the ratio of is in the range of 0.7 to 2.0, or in the range of 0.8 to 1.

5.

4. Alpha phase Al in the process gas composition as it is introduced into the CVD reactor ２ O ３ In the deposition of the coating layer, H ２ / AlCl ３ 2. The method of claim 1, wherein the ratio of is >500, or >800, or >1200, or >1400, or >1600.

5. Alpha phase Al ２ O ３ In the deposition of the coating layer, the process gas composition as introduced into the CVD reactor is AlCl ３ , H ２ O and H ２ or the treat gas composition additionally comprises a sulfur source, preferably H ２ 10. The method of claim 1, wherein S is present in an amount of up to 2% by volume of the process gas.

6. Alpha phase Al ２ O ３ In the deposition of the coating layer, the process gas composition as introduced into the CVD reactor additionally contains HCl and AlCl in the process gas. ３ 10. The method of claim 1, wherein the amount of the hydroxybenzoate is 10 times or less by volume.

7. The deposition process produces alpha phase Al ２ O ３ 2. The method of claim 1, comprising depositing one or more Ti compound layers beneath the coating layer, wherein the Ti and / or Ti+Al compound layers are selected from carbides, nitrides, oxides, carbonitrides, and oxycarbonitrides.

8. The deposition process produces alpha phase Al ２ O ３ The method of claim 1 , including an oxidation step prior to deposition of the coating layer.

9. Alpha phase Al ２ O ３ The method of claim 1, wherein the deposition of the coating layer is carried out at a temperature in the range of 600 to 850°C, or in the range of 650 to 800°C.

10. 10. A surface-coated cutting tool for chip-forming metal machining, consisting of a substrate of cemented carbide, cermet or cubic boron nitride based ceramic material and a single or multi-layer wear-resistant hard coating, wherein the layer of the hard coating is at least one alpha (α) phase Al deposited by the chemical vapor deposition (CVD) process according to any one of claims 1 to 9. ２ O ３ A surface-coated cutting tool comprising a coating layer.

11. At least one alpha phase Al ２ O ３ 11. The surface-coated cutting tool of claim 10, wherein the coating layer has a Vickers hardness HV0.01 of >2000 HV, or >2300 HV.

12. The wear-resistant hard coating is made of alpha phase Al ２ O ３ 11. The surface-coated cutting tool of claim 10, further comprising one or more Ti compound layers beneath the coating layer, wherein the Ti and / or Ti+Al compound layers are selected from carbides, nitrides, oxides, carbonitrides, and oxycarbonitrides.