STIENS DIRK (DE)
GARDECKA ALEKSANDRA (DE)
JANSSEN WIEBKE (DE)
MANNS THORSTEN (DE)
FRAUNHOFER GES FORSCHUNG (DE)
US3836392A | 1974-09-17 | |||
US3914473A | 1975-10-21 | |||
US3885063A | 1975-05-20 |
C L A I M S 1. A process 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-layered or multi-layered wear resistant hard coating, the layers of the hard coating comprise at least one alpha (α) phase Al2O3 coating layer being deposited by chemical vapour deposition (CVD) at an average thickness in the range from 1 μm to 20 μm, wherein the deposition of the alpha phase Al2O3 coating layer is carried out - at a temperature in the temperature range from 600 to 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 in the process gas composition, as introduced into the CVD reactor, - the volume ratio of H2O / AlCl3 is in the range from 0.5 to 2.5, and - the volume ratio of H2 / AlCl3 is in the range from 200 to 3000. 2. The process of claim 1, wherein the deposition of the alpha phase Al2O3 coating layer is carried out at a total pressure in the range from 3 to 50 mbar, or from 3 to 30 mbar, or from 3 to 20 mbar, or from 3 to 15 mbar. 3. The process of any of the preceding claims, wherein in the deposition of the alpha phase Al2O3 coating layer in the process gas composition, as introduced into the CVD reactor, the ratio of H2O / AlCl3 is in the range from 0.7 to 2.0, or in the range from 0.8 to 1.5. 4. The process of any of the preceding claims, wherein in the deposition of the alpha phase Al2O3 coating layer in the process gas composition, as introduced into the CVD reactor, the ratio of H2 / AlCl3 is > 500, or > 800, or > 1200, or > 1400, or > 1600. 5. The process of any of the preceding claims, wherein in the deposition of the alpha phase Al2O3 coating layer the process gas composition, as introduced into the CVD reactor, consists of AlCl3, H2O and H2, or the process gas composition additionally contains a sulfur source, preferably H2S, in an amount of up to 2 vol.-% of the process gas. 6. The process of any of the preceding claims, wherein in the deposition of the alpha phase Al2O3 coating layer the process gas composition, as introduced into the CVD reactor, additionally contains HCl in an amount of not more than 10 times the volume amount of AlCl3 in the process gas. 7. The process of any of the preceding claims, wherein the deposition process includes the deposition of one or more Ti compound layers underneath the alpha phase Al2O3 coating layer, the Ti and/or Ti+Al compound layers being selected from carbides, nitrides, oxides, carbonitrides and oxicarbonitrides. 8. The process of any of the preceding claims, wherein the deposition process includes an oxidation step prior to the deposition of the alpha phase Al2O3 coating layer. 9. The process of any of the preceding claims, wherein the deposition of the alpha phase Al2O3 coating layer is carried out at a temperature in the temperature range from 600 to 850°C or at a temperature in the temperature range from 650 to 800°C. 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-layered or multi-layered wear resistant hard coating, wherein the layers of the hard coating comprising at least one alpha (α) phase Al2O3 coating layer being deposited by the chemical vapour deposition (CVD) process as defined in any of the preceding claims. 11. The surface-coated cutting tool of claim 10, wherein the at least one alpha phase Al2O3 coating layer has a Vickers hardness HV0.01 of > 2000 HV, or > 2300 HV. 12. The surface-coated cutting tool of claim 10 or 11, wherein the wear resistant hard coating further comprises one or more Ti compound layers underneath the alpha phase Al2O3 coating layer, the Ti and/or Ti+Al compound layers being selected from carbides, nitrides, oxides, carbonitrides and oxicarbonitrides. |
It was observed that a higher ratio of H 2 1 AICI3 may further improve the purity of the alpha phase AI2O3 deposition and a more homogeneous coating thickness profile within the reactor.
In another preferred embodiment of the present invention in the deposition of the alpha phase AI2O3 coating layer the process gas composition, as introduced into the CVD reactor, consists of AICI3, H 2 O and H 2 , or the process gas composition additionally contains a sulfur source, preferably H2S, in an amount of up to 2 vol.-% of the process gas.
In a preferred embodiment of the present invention the process gas composition, as introduced into the CVD reactor, contains no additional HCI. However, the invention includes embodiments, wherein in the deposition of the alpha phase AI2O3 coating layer the process gas composition, as introduced into the CVD reactor, additionally contains HCI in an amount of not more than 10 times the volume amount of AICI3 in the process gas.
In a preferred embodiment of the present invention the deposition process includes the deposition of further layers underneath the alpha phase AI2O3 coating layer, i.e. the deposition of a multi-layer structure. The further layers preferably include one or more Ti and/or Ti+AI compound layers being selected from carbides, nitrides, oxides, carbonitrides and oxicarbonitrides. The further layers, including the further Ti and/or Ti+AI compound layers, may be suitable to improve adhesion of the coating and/or promote a preferred crystallographic orientation or texture of the 0AI2O3 coating layer and/or of further layers and/or contribute and improve the wear resistance of the entire coating structure.
In one preferred example the layers deposited underneath the alpha phase AI2O3 coating layer include a layer sequence of a titanium nitride (TiN) lower layer, followed by one or more subsequent layers selected from titanium carbonitride (TiCN), titanium aluminium carbonitride (TiAICN) and titanium aluminium nitride (TiAIN), optionally followed by a bonding layer immediately underneath the alpha phase AI2O3 coating layer according to the invention, which bonding layer preferably includes titanium carbonitride (TiCN) or titanium aluminium carbonitride (TiAICN). In an embodiment of the invention, the bonding layer includes an oxidized state of the TiCN or TiAICN near the transition region to or immediately underneath the alpha phase AI2O3 coating layer, which either depositing a TiCNO or TiAICNO sub-layer or by carrying out an oxidation step to the TiCN or TiAICN of the bonding layer prior to the deposition of the alpha phase AI2O3 coating layer. The provision of the oxidized state may further improve the adhesion of the alpha phase AI2O3 coating layer. In an embodiment of the invention the deposition process includes an oxidation step prior to the deposition of the alpha phase AI2O3 coating layer. Preferably, the oxidation step is applied to a Ti and/or Ti+AI compound layer deposited underneath the AI2O3 coating layer. It was found that the application of an oxidation step may be suitable to improve the adhesion of the subsequently deposited alpha phase AI2O3 coating layer.
Preferably the oxidation step is carried out in the presence of H 2 O as oxidizing agent for a time of about 2 to 20 min, preferably, about 3 to 15 min. In one embodiment the temperature of the oxidation step is about the same as or plus/minus 50°C of the temperature applied for the deposition of the alpha phase AI2O3 coating layer.
The present invention also includes the 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-layered or multi-layered wear resistant hard coating, wherein the layers of the hard coating comprising at least one alpha (a) phase AI2O3 coating layer being deposited by the chemical vapour deposition (CVD) process as defined herein.
The inventive cutting tool of the present invention distinguishes from cutting tools having at least one conventionally produced alpha (a) phase AI2O3 coating layer at high temperature in that the substrate and/or further layers underneath the AI2O3 coating layer have not undergone structural changes and deteriorations due to a high temperature deposition or treatment step. Therefore, the inventive cutting tool may, due to the inventive deposition process, exhibit improved mechanical properties and wear resistance. Furthermore, since the process of the present invention is carried out at significantly lower temperatures, the cutting tool of the present invention can be produced at lower costs and less consumption of resources than comparable cutting tools having at least one a-ALOs coating layer conventionally produced at high temperature.
In an embodiment of the surface-coated cutting tool of the invention the at least one alpha phase AI 2 C>3 coating layer deposited by the inventive process has a Vickers hardness HV0.01 of > 2000 HV, or > 2300 HV.
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+AI compound layers underneath the alpha phase AI2O3 coating layer, the Ti and/or Ti+AI compound layers being selected from carbides, nitrides, oxides, carbonitrides and oxicarbonitrides. MATERIALS and METHODS
X-ray diffraction (XRD) measurements
X-ray diffraction measurements were performed in a XRD3003 PTS diffractometer of GE Sensing and Inspection Technologies using CuKa-radiation. The X-ray tube was run in point focus at 40 kV and 40 mA. A parallel beam optic using a polycapillary collimating lens with a measuring aperture of fixed size was used on the primary side whereby the irradiated area of the sample was defined in such manner that a spillover of the X-ray beam over the coated face of the sample was avoided. On the secondary side a parallel plate collimator with a divergence of 0.4° and a 25 pm thick NiK0 filter was used. Depending on the layer thicknesses, diffraction measurements for identification of the AI2O3 phase were either performed by 20 scans at constant incidence angle of w = 1°, or by symmetrical 0-20 scans within the angle range of 15° < 20 < 90° with increments of 0.04°.
Microhardness Measurements
The microhardness was measured with the Vickers hardness test. For this purpose, a diamond pyramid (with interfacial angle of 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 surface effects on measurement. The indenter is placed in the outer area of the coating to ensure that the indention depth is lower than 1/10 of the layer thickness. The diagonals of the indenter’s remaining impression were measured optically. An MHT-10 (Anton Paar) installed on a light microscope was used to perform the indentation and measurements. The hardness was calculated by software using the average of the two diagonal lengths according to following equation (F is the test load and d is the average of diagonal lengths):
Calotte Grinding
Calotte grinding was used to assess coating thickness and adhesion. The insert was placed on an inclined magnetic holder of the ball cratering set-up. A spherical calotte was ground in the coating and substrate material by a rotating 30 mm steel ball wetted with a drop of 3 pm water-based diamond suspension (Struers, DP-Lubricant Green) and driven by a driving shaft at > 500 rpm. The grinding process was stopped when the calotte diameter in the substrate material reached approx. 600-1100 pm. The thickness measurements taking into account the geometry of the calottes were done by a dedicated software using light optical microscopy (LOM). “A” adhesion “A” adhesion defines the adhesion of the α-Al 2 O 3 layer to the underlying layer. “A” adhesion was assessed by LOM observation on polished calotte ground surfaces and visually classified on a scale from 1.0 (= perfect adhesion) to 3.0 (= no adhesion). The criteria for “A” adhesion at the interfaces of layers / sublayers are as follows: A = 1: no or neglectable breakouts are observable at the interfaces, the interface line is intact. A = 2: minor breakouts can be observed at the interface, about 51-80 % of the total interface line are without deterioration. A = 3: mayor breakouts or a continuous delamination are observable at the interface, 50 – 100 % of the interface line in the calotte are deteriorated. Cutting tests (Milling) Coated cutting tools were tested herein in a milling operation in 42CrMo4 steel having a tensile strength of 785 N/mm 2 using the following cutting data: Cutting speed v c : 180 m/min Cutting feed, f: 0.2 mm/revolution Depth of cut, a p : 3 mm Width of cut, a e : 98 mm Radial overhang, ue: 5 mm No. of teeth: 1 Insert geometry: SPHW120408 (no cutting fluid) CVD coatings The CVD coatings of the examples given herein below were done on WC-Co-based cemented carbide cutting tool substrates. In the examples herein, two different types of CVD equipment were used, lab scale and industrial scale CVD equipment. Volumes of gases fed into the reactor were controlled by mass flow control units calibrated tolows in ml n /min (normal milliliter per minute), l n /min (normal liter per minute) or sccm standard cubic centimeter per minute) which according to the technical data given by the manufacturer (Bronkhorst) all refer to conditions of 0°C and 1.013 bar(abs.). The volume of evaporated H 2 O was controlled and converted into units of sccm as described below. AlCl 3 was generated in situ and evaporated using the technically and industrially commonechnique of chlorinating Al pellets with HCl gas at elevated temperatures. As usual in publications of thermal CVD of aluminum oxide, it is reasonably assumed that the chlorination reaction Al + 3 HCl Æ AlCl 3 + 1.5 H 2 proceeds almost instantaneously and quantitatively, yielding only the monomer molecule of aluminum trichloride. Process gas compositions and volume ratios given herein take AlCl 3 and H 2 flows into account accordingly. n the equipment and working examples described herein, the process gas mixture isntroduced into the reactor by two separate gas inlets. AlCl 3 , optionally additional HCl and/or sulfur containing gases and H 2 are fed in through one, H 2 O and remainder of H 2 through another inlet. However, the present invention is not limited to specific setups of reactor design and gas feeding systems. Equipment “A” is a lab-scale horizontal flow hot wall CVD reactor made of Inconel and having an inner diameter of 79 mm, a horizontal length of 800 mm and an inner volume of approximately 6 litres. The substrate temperature is controlled by a type K thermocouple. Reaction gases are introduced by separate gas inlets into the reaction zone. Equipment A was used for the preparation of CVD Al 2 O 3 coatings of some of the inventive working examples and comparative examples described below. In the H 2 O evaporator of this equipment, water was evaporated by bubbling H2 carrier gas through liquid water at controlled pressure and temperature. The evaporated H 2 O gas flow in sccm is calculated asollows: wherein v(H 2 O)= gas flow of H 2 O [ml/min] = gas flow of H 2 O [sccm] p(H 2 O)= vapor pressure of H 2 O [Torr] p= normal pressure 760 [Torr] v= pressure in evaporator [Torr] R= universal molar gas constant 62.32 [l Torr mol -1 K -1 ] 0= reference temperature 273.15 [K] m= molar volume 22.4 [l mol -1 ] (carrier cas)= gas stream carrier gas introduced into the evaporator [ml/min] quipment “B” is an industrial sized radial flow CVD coating chamber with an inner reactor eight of 1580 mm, an inner reactor diameter of 500 mm and an inner volume of pproximately 300 litres. The reaction gas was fed into the reactor through a central gas inlet ipe and introduced into the reaction zone through openings distributed along the inlet pipeo provide an essentially radial gas flow over the substrate bodies. Equipment B was used forhe preparation of CVD Al 2 O 3 coatings of some of the inventive working examples and omparative examples described below. In the H 2 O evaporator of this equipment, water was vaporated by spraying liquid water into a H 2 carrier gas stream at 100 °C under reduced ressure. The evaporated amount was controlled by a liquid mass flow controller calibratedo units of g/h from which the gas volume flow in sccm is calculated using the molar mass of H 2 O and ideal gas volume at normal conditions 0°C and 1.013 bar(abs.). olume ratios of the process gas composition as introduced into the reactor refer to the forementioned gas flows in sccm. not otherwise indicated, in the examples herein, the reactor was filled with inserts up to bout its full capacity, whereby sample inserts to be investigated were distributed at various ifferent positions within the reactor, and the remaining sample positions within the reactor were filled with “scrap” inserts to simulate, as close as possible, full scale deposition onditions and volume usage within the respective reactor. XAMPLES Depositions or the inventive examples I1 to I16 and comparative examples C1 to C13 and CWG1 prepared herein, prior to the deposition of the Al 2 O 3 , the substrates were pre-coated with an about 0.6 μm thick TiN base layer and an about 5.4 μm thick TiCN layer using equipment B. The process parameters and reaction gases for this deposition are indicated in table 1. The depositions of TiN and TiCN prior to the deposition of the AI2O3 were all carried out under the same process conditions and in the same equipment to make the examples comparable with respect to variations of the AI2O3 deposition conditions.
The process parameters and reaction gases for the deposition of AI2O3 layers in inventive examples 11 to 116 and comparative examples C1 to C13 and CWG1 are indicated in table 2. In some of the inventive and comparative examples (if indicated) an oxidation step was applied to the TiCN layer prior to the deposition of the AI2O3. Oxidations in equipment A were carried out at fixed H 2 O flows of 12 seem and in equipment B at fixed H 2 O flows of 1333 seem for a time and at a temperature as indicated in table 2 under “Ox-Time” and “Ox- Temp”, respectively.
In the comparative examples CWG1 and CWG2 the AI2O3 layer was deposited applying the the water-gas shift reaction from H2 + CO2 --> H2O + CO. The layer sequences, process parameters and reaction gases introduced into the reactor for comparative example CWG1 are included in tables 1 and 2, whereas layer sequences, process parameters and reaction gases for comparative example CWG2 (prepared in equipment B) are indicated in table 3.
Table 4 shows the measured parameters of the AI2O3 layer of the inventive examples (11 to 116) and the comparative examples (C1 to C13, CWG1 and CWG2).
Table 5 shows cutting test results of inventive and comparative examples. For each example, four cutting edges were used in the milling test. The milling operation was interrupted after milling paths of 800 mm, 1600 mm, 3200 mm, 4800 mm and 5600 mm to evaluate the wear marks, which were flank wear width (Vb), maximum flank wear width (Vb max ) and number of comb cracks (comb cracks). Each cutting edge was used until a maximum flank wear width Vbmax of > 0.30 mm was reached. Table 5 lists the wear data for the cutting edge of each variant, which showed the poorest wear resistance, i.e. with the shortest milling length to reach Vb max* 0.30 mm, and had the largest wear width in case several edges exceeded 0.3 mm at the same interval of measurement.
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