SE518151C2 - Multilayer coated cutting tool - Google Patents

Abstract

The present invention relates to a cutting tool comprising a body (1) of a sintered cemented carbide or cermet, ceramic or high speed steel on which, at least on the functioning parts of the surface of the body, a thin, adherent, hard and wear resistant coating (2) is applied. The coating comprises a laminar structure of refractory compounds in a polycrystalline, repetitive form: (MLX/Al2O3) lambda (MLX/Al2O3) lambda / (MLX/Al2O3) lambda / (MLX/Al2O3) lambda /... where the alternating sublayers consist of metal nitrides (or carbides) and crystalline alumina (4) of the alpha( alpha )- and/or the gamma( gamma ) phase, preferably of metal nitrides and crystalline alumina of the gamma phase. The metal elements in the layers MLX (3) are selected from Ti, Nb, Hf, V, Ta, Mo, Zr, Cr, W and Al. The repeat period lambda (5) is essentially constant through the entire multilayered structure, and larger than 3 nm but smaller than 100 nm. The total thickness of said multilayered coating is larger than 0.5 mu m but smaller than 20 mu m.

Description

The coating such as microstructure / grain size, hardness, stress state, cohesion and adhesion to the underlying substrate varies depending on the particular PVD method. An improvement in the wear resistance or edge integrity of a PVD-coated cutting tool used in a special machining operation can thus be implemented by optimizing one or more of the above-mentioned properties.

In addition, new developments of the existing PVD techniques through the introduction of unbalanced magnetrons in reactive sputtering (S. Kadlec, J.

A8 (3), (1990), 1318.) cored arc in cathodic arc coating (H. Curtins in Surface and 76/77, (1995), 632 and K. Akari et al in Surface and Coatings Technology, 43/44 , (1990), 312.) better control of the coating process and an additional pre- Musil and W.-D. Munz and J. Vac. Sci. Techn. or introduction of a controlled and / or felt-Coating Technology, resulting in an improvement in the internal properties of the coating material.

With the invention of the PVD bipolar pulsed DMS technique which is shown in DD 252 205 and DE 195 18 779, a wide range of possibilities for coating (Double Magnetron Sputtering) was opened with insulating layers such as Al 2 O 3 and in addition this method has made it possible to precipitate crystalline Al2O3 layers at substrate temperatures in the range of 500 to 800 ° C. Al2O3 exists in several different phases such as the a (alpha), K (kappa) and X (chi) called the "a-series" with the hcp (hexagonal densely packed) 0 (theta), n (eta) and 5 (delta) cubic) sera in CVD coatings precipitated on cemented carbide at conventional 1000-1050 OC, tastable kappa phase but sometimes also has the metastable theta stacking of the oxygen atoms, and iy (gamma), called the "y-series" with fcc (surface-centered stacking of the oxygen atoms. most common Algb fa- CVD temperatures, the stable alpha and me phase are observed.According to DE 195 18 779, DMS sputtering technology is capable of precipitating and producing high quality, well adherent, crystalline α-Al 2 H thin films at substrate temperatures less than 800 ° C. "α-Al 2 O 3" gamma (y) phase from the "y series" of Al 2 O 3 polymorphs. Compared to the time layer may in part also contain more known plasma-assisted coating techniques such as PACVD as described in DE 42 09 975, the new, pulsed DMS sputtering coating method has the decisive, important advantage of no contaminants, such as halogen atoms, e.g. are enclosed in the Al fl b coating. Conventional cutting tool materials such as cemented carbide consist of at least one hard metallic compound and a binder phase, (CO), the compound, e.g. tungsten carbide (WC), is in the range 1-5 pm. usually cobalt where the grain size of the hard New developments have predicted improved tool properties in durability, impact strength, heat hardness by using tool materials based on ultrafine microstructure using (LE McCandlish, 1 pp. 119- Similar predictions have been made for ceramics of nanostructured WC-Co powder as raw material BH Kear and BK Kim, 124, 1992). tool materials for example for silicon nitride / carbide based (Si3N4 / SiC) equivalent nanocomposites based on alumina. and Nanostructured Materials VOL. nanocomposite ceramics and, for Al2O3-based ceramics, With nanocomposite nitride / carbide and alumina hard coating materials, is meant a multilayer coating where the thickness of (or carbide) is in the nanometer range between 3 and 100 nm, preferably between each individual nitride nitric and alumina 3 and 20 nm. Since there is a certain periodicity or repetition period of metal nitride / carbide and alumina layers in order, these nanoscale, multilayer coatings have been given the generic name "superlattice" films. By repetition period is meant the thickness of two adjacent metal nitride / carbide and alumina layers. Many of the binary nitride superlattice coatings with metal elements from Ti, Nb, V and Ta, on both single and polycrystalline substrates have shown an improved hardness for a particular repetition period usually in the range of 3-10 nm.

GB-A-2 048 960 discloses a composite body, for use as a wear part or as a cutting insert in a cutting tool, comprising a substrate with one or more surface layers of hard material free from binder phase. The thickness of each such surface layer is 1 to 50 μm and one of the layers is composed of a plurality of individual layers each having a thickness of 0.02 to 0.1 μm.

According to the present invention, there is a cutting tool for metalworking such as turning (threading and parting), milling and drilling comprising a body of a hard cemented carbide alloy or cermet on top of which a durable, multilayer coating has been deposited. The shape of the cutting tool comprises indexable inserts as well as shank tools such as drills, end mills, etc .. More specifically, the coated tool comprises a substrate of sintered cemented carbide or a cermet, preferably of at least one metal vessel 10 15 20 25 30 35 40 s1§151 bite in a metal binder phase, or a ceramic body. The substrate may also comprise a high speed steel alloy. Said substrates may also be precoated with a thin single or multilayer of TiN, TiC, TiCN or TiAlN with a thickness in the micrometer range according to the prior art. The coated cutting tool of the present invention exhibits improved wear resistance and toughness properties over prior art tools used for machining steel or cast iron. Said coating, which is well bonded to the substrate, comprises a laminar, multilayer structure of metal nitrides (or - carbides) and crystalline alumina of alpha (a) and / or gamma (y) phase, preferably of metal nitrides and crystalline γ-Al 2 O @ has a thickness between 0.5 and 20 μm, preferably between 1 and 10 μm, preferably between 2 and 6 μm. In the multilayer coating structure (MLX / Al2O fl i / (MLX / Al2O fl i / (MLX / Al2O fl¿ / (MLX / Al2O fl x /......... .. are the alternating layers MLX and Al2O3 where MLX comprises a metal nitride or a metal carbide with metal elements M and L selected (Ti), (Nb), hafnium (Hf), vanadium (V), tantalum (Mo), zirconium (Zr), chromium (Cr), tungsten (W) aluminum (Al), and in said coating if the repetition period Ä i (see Fig. 1) from titanium niobium (Ta), molybdenum or (MLX / Al2O fl¿ is substantially constant throughout the multilayer structure and in addition the repetition period is greater than 3 nm but less than 100 nm, repetition period refers to the thickness of the layers MLX + Al 2 O 3, i.e. of preferably less than 50 nm, preferably less than 25 nm With two adjacent nanolayers Preferred examples of the structure of the nano-multilayer coating described above are, for example, for M = L, TiN / Al 2 O 3 / TiN / Alzoa / TiN / AlZOB / TiN /.... .. or for LiM, TiAlN / Al2O3 / TiAlN / Al2O3 / TiAlN / Al2O3 / TiAlN /..._.

Fig. 1 shows a substrate 1 coated with a laminar, multilayer nitride / carbide and alumina coating 2 with the individual (or carbide) layers MLX 3 and the individual alumina layers 4 and the repetition period Ä 5, the thickness of each metal nitride metal nitride / carbide layer and alumina layer are substantially constant throughout the multilayer coating.

The laminar coatings above show a columnar growth pattern with no or very little porosity at the grain boundaries.

The coatings also have a significant waviness in the sublayers which is due to the surface fineness of the substrate.

For a cutting tool for metalworking, several advantages of the present invention are obtained with nanostructured lamella coatings deposited on substrates of hard, refractory materials such as cemented carbide, ceramics and ceramics. Ex. In a lamellar coating of (MLx / Alzogx / (MLx / Alzø fl v. the observation improves the hardness of the coating, leads to an increased abrasive wear resistance of the cutting edge, while the second observation less internal stress in the coating, gives an increased ability to absorb stresses on the cutting edge during a machining operation.In addition, the invented coating gives the cutting edges of the tool has an extremely smooth surface which, compared with previously known coated tools, leads to a better surface finish even of the machined workpiece.

The laminar, nanostructured coatings of the present invention can be deposited on a cemented carbide or cermet substrate by either CVD or PVD technology, preferably by the PVD bipolar pulsed double magnetron sputtering (DMS) technology, by successively forming individual sublayers on the tool substrate at a substrate temperature of 450-700 ° C, preferably 550-650 ° C, by turning on and off separate magnetron systems.

Claims (4)

10 15 20 518151 Claim 9 Cutting tool comprising a body of sintered cemented carbide or cermet on which at least on the active parts thereof a thin, adhesive, hard and durable coating is deposited, characterized in that the coating comprises a laminar, multilayer structure of refractory compounds in polycrystalline, repetitive form, (MLX / Al2O fl Ä / (MLX / Al fl h) Ä / (MLX / Al2O fl Ä / (MLX / Al2O fl L / ..... where the alternating sublayers are MLX and Al2O3, the MLX layers comprising a metal nitride or a metal carbide with the metal elements M and L selected from Ti, Nb, Hf, V, Ta, Cr, W and Al, the Algh sublayers consist of crystalline Al fl h of gamma (y) phase and Mo, Zr, the repetition period Ä is substantially constant throughout the multilayer structure and greater than 3 nm but less than 25 nm and that the total thickness of the multilayer coating is greater than 0.5 μm but less than 20 μm. Cutting tool according to claim 1, characterized in that the MLX sublayers are composed of metal nitrides. 3. A cutting tool according to claim 2, characterized in that the sublayers of metal nitrides consist of TiAlN and TiN, preferably TiAlN. 4. A cutting tool according to any one of the preceding claims, characterized in that the coating has a total thickness of 1 to 10 μm, preferably 2 to 6 μm.