Method of making a coated cutting tool and cutting tool thereof

This application claims priority to Sweden Application No. SE 0702866-5 filed Dec. 21, 2007, which is incorporated by reference herein.

The present invention relates to a method of making a coated cutting tool comprising depositing one or more metallic interlayers in-between deposition of two non-metallic, functional layers. Before each deposition of a metal interlayer, an ion etching step of the non-metallic functional layer is performed. The cutting tools made according to the method of the present invention will exhibit superior life time due to an increased toughness, thus showing better ability to withstand changes in load. In addition, this invention facilitates deposition of thicker PVD coatings without the risk of spalling along the edge line, hence thicker coatings with better flank wear resistance can be deposited.

In general, the life time of a cutting tool is significantly prolonged if a coating is deposited onto its surface. Most cutting tools today are coated with PVD or CVD coatings like Ti(C,N), TiN, (Ti,Al)N, (Ti,Si)N, (Al,Cr)N or Al₂O₃. PVD coatings have several attractive properties compared to CVD coatings, for instance a residual compressive stress in the as-deposited state, no cooling cracks and finer grained coatings.

However, the PVD coatings usually have to be quite thin, since thicker PVD coatings may cause spalling, frittering, so-called edge-line spalling and flaking, either spontaneously, usually around the edge line, or during machining. Since thicker coatings in many applications lead to a longer tool life due to an increased wear resistance, CVD coatings are usually chosen for those applications.

Unfortunately, PVD-coatings, especially arc deposited, suffer from the existence of so-called macros or droplets, which exists as small spheres on the surface of the coating or, buried inside the coating. During the deposition of the coating, these droplets can shadow the incoming flux of charged metal ions, thus creating voids in the coating in the immediate surroundings of the droplet. Due to the subsequent diminished adhesion between the droplet and the coating, the droplet can fall out either during the deposition process or immediately afterwards or even during machining. This may result in an inferior coating quality, with voids, pores or even, in extreme cases, holes straight down to the substrate.

Thicker coatings also have the advantage that the maximum temperature that the substrate is exposed to decreases. A lower substrate temperature decreases the risk of plastic deformation of the cutting edge. Thicker coatings allow for higher cutting forces without initializing plastic substrate deformation.

In the business of cutting tools there is a growing demand for thicker PVD coatings experiencing both the advantages in wear resistance of a thicker coating combined with the toughness of a PVD coating.

Ion etching is a common initial step in the beginning of all kinds of deposition processes. The substrate is usually ion etched prior to deposition to remove surface contaminants and native oxides and nitrides. However, few attempts have been done to use ion etching as an intermediate step.

Depositing metallic layers with PVD techniques is also an established technology in PVD-processes. It is well-known that depositing a metallic layer directly onto the surface of the substrate before depositing the rest of the coating can in some cases enhance adhesion of the coating.

EP 0756019 describes a method of making a PVD-coating for material deforming tools used in punching operations. A PVD-layer composed of (Ti,Al)N, (Ti,Al,Y)N or (Ti,Al,Cr)N or any multilayer thereof is deposited. The surface is then mechanically treated e.g. with sand blasting or metal ion etching to remove any droplets and to achieve a smooth surface. A second, low-friction, PVD coating consisting of MoS₂ is then deposited on top.

U.S. Pat. No. 3,755,866 describes an insert comprising two non-metallic interlayers deposited on top of each other. One layer consists of a fine-grained member of the group consisting of TiC, TaC, ZrC, HfC, VC and NbC. The other layer consists of at least one fine grained member of the group consisting of WC, MoC and CrC. These two layers may or may not be separated by a metallic layer consisting of Co, Ni or Fe. The metallic layer is between 0.1 and 2.0 μm.

EP1136585 describes a self-lubricating coating, consisting of small droplets of metal or other soft material in an otherwise hard coating. Thus, a coating with lower levels of friction is created. The coating is deposited in a sequence consisting of: deposition of a nitride/carbide, followed by ion etching in Ar atmosphere. During the ion etching step a thin metal foil is bombarded with Ar ions, and small metal droplets are emitted. This coating thus consists of layers with small droplets of metal in an otherwise hard coating of a nitride or carbide.

JP2002-103122A describes hard-anodic-oxidation-coatings covering small diameter tools, where the coating consist of an inner Ti layer, followed by a TiCN-layer, an intermediate metallic TiAl-layer and finally covered by an outer TiAlCN-layer.

EP1553210 A1 discloses a method of depositing α-Al₂O₃ layers by PVD technique. In one embodiment, a substrate possibly provided with a primary coating is ion bombarded with either gas ions or metal ions, followed by oxidation of the bombarded surface and finally deposition of a α-Al₂O₃ layer. When metal ions are used for the bombardment, metal ions are implanted into the surface.

It is an object of the present invention to provide a method of making a coated cutting tool having a PVD-coating with improved edge toughness.

It is another object of the present invention to provide a method of making a coated cutting tool having thicker PVD-coatings without increasing the risk of spalling, frittering, so-called edge-line spalling and flaking thus obtaining a tool with an increased tool life.

It is another object of the present invention to provide a method of making a coated cutting tool having better flank wear resistance.

It is another object of the present invention to provide a coated cutting tool made according to the method of the invention having the benefits disclosed above.

In one aspect of the invention, there is provided a method of making a coated cutting tool comprising providing a substrate and coating said substrate with a coating process which comprises at least one sequence comprising the steps of: depositing a non-metallic, functional layer or layer system, subjecting the surface of said non-metallic layer or layer system to an ion etching step, and depositing at least one metallic interlayer.

In another aspect of the invention, there is provided a cutting tool made by the above-described process.