Patent Application
20100151260
The invention relates to a method of coating a hard-metal or cermet substrate by means of physical vapor deposition (PVD).
This invention also relates to a coated hard-metal or cermet body.
Hard-metal or cermet bodies having a wide variety of compositions have been proposed for many applications. The substrate composition is adjusted depending on the purpose of the application, special emphasis for example being placed on extreme hardness, resistance to temperature fluctuations or wear resistance, the latter particularly for tools used in chip-producing machining. In certain cases, also coated substrates whose coating was made of one or more layers have been successfully applied. Coating materials include carbides, nitrides, carbonitrides, oxicarbonitrides, oxinitrides or oxides of the metals of the IVa to VIa groups of the periodic table or aluminum compounds, such as Al2O3 and TiAlN. For coating substrates, in particular physical or chemical vapor deposition methods are used. In general, physical vapor deposition (PVD) methods have the advantage that the coating can be applied at low temperatures. According to the prior art, the substrates are ground prior to the PVD process. Substrates left with rough substrate surfaces (which is to say in the sintered state) practically have no residual compressive or tensile stress. As a result of the grinding operation, residual compressive stress is produced in the surface of the substrate, ranging between −200 and −1200 MPa for hard-metal. Due to the high-energy procedure employed for introducing the layer-forming components (ions) into the layers, PVD layers always have residual compressive stress ranging between about −1800 and −4000 MPa. The difference in the residual compressive stresses between the coating and substrate for ground substrates is therefore smaller than for substrates left in the sintered state. The difference in the residual stresses between the substrate and coating causes shearing stresses, which negatively impact the adhesion of the coating. For this reason, non-ground substrates coated by means of PVD have poorer cutting performance.
It is the object of the present invention to improve the service life of PVD-coated substrates.
In order to attain this object, a method according to claim 1 and/or the substrate according to claim 9 are proposed.
Further developments of the inventions are described in the dependent claims 2 to 8 and 10.
The core idea of the present invention is that the fully sintered substrate made of a hard-metal or a cermet, without further intermediate treatment before the PVD process, is subjected to a blasting treatment using a particulate blasting agent until the residual stress in the zone of the substrate close to the surface is at least substantially equal to the residual stress present in the single or first PVD layer applied.
Surprisingly, it was found that an adjustment of the residual stress of the substrate in the regions close to the substrate surface to the known residual compressive stress of a PVD layer brings about a considerable improvement in the service life. Using a blasting method, which is known in principle, the regions close to the surface are compacted, resulting in an increase in the residual compressive stress. By adjusting this residual compressive stress to the known residual compressive stress of the first or single PVD layer applied, the cutting performance was improved.
Preferably, a blasting agent comprising particles is used, the particles having a maximum diameter of 600 μm, preferably of no more than 150 μm, and in particular between 15 and 100 μm. The substrate, which according to a further development of the invention is treated using a dry blasting method, is preferably subjected to at least substantially spherical blasting agents or such blasting agents that have a rounded particulate shape. Possible blasting agents are in particular atomized jets, cast iron granules, heavy metal powders or alloys produced thereof, glass, corundum, hard-metal granules and/or fracture-resistant ceramics.
Furthermore, the blasting agent or agents are preferably directed at the substrate by means of compressed air with a pressure of at least 1.0×105 to 10×105 Pa, preferably 1.5×105 to 3.5×105 Pa.
It is particularly advantageous to blast the substrate with blasting-agent particles that are projected perpendicularly at the surface thereof.
The blasting treatment of the above-described type has been successfully applied in particular in conjunction with a subsequent PVD coating, comprising carbides, nitrides, carbonitrides, oxides or oxicarbonitrides of the elements of the IVa to VIa groups of the periodic table or Al2O3, AlTiN or AlN. The thickness of the individual layers preferably ranged between 0.1 μm and 10 μm with an overall thickness (in the case of multilayer coatings) of no more than 20 μm.
Accordingly, the object is attained by the coated hard-metal or cermet body according to claim 9, for which the advantages as described above apply.
A hard-metal or cermet body coated in this way is in particular made into a cutting tool for drilling, milling or turning operations.
In a concrete embodiment, indexable inserts were coated with an AlTiN coating, which was applied by means of PVD at 350° to 600° (coating temperature). While the tools, which were coated after sintering without further treatment or after only a grinding treatment, had to be replaced after only a short time due to wear, the service life of corresponding tools having the same configuration, which were processed by the inventive method, namely a blasting treatment lasting between 10 and 60 seconds, after sintering, was considerably improved. This is due to the fact that the PVD layers exhibited residual compressive stress in the range of −1.5 to 3.5 GPa as measured according to the SIN2-_ method, compared to residual tensile stress or very small residual compressive stress in the boundary regions of the substrate close to the surface of no more than 100 MPa, in absolute terms. If, however, as a result of the blasting treatment, particularly using a dry blasting method with round granules of 50 μm and 100 μm, the residual compressive stress of the region of the substrate close to the surface is raised to the residual compressive stress depending on the coating material and the PVD parameters (up to +/−10%), this increase in the residual compressive stress results in considerably improved wear resistance of the tools.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 002 371.4 | Jan 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE2006/001943 | 11/7/2006 | WO | 00 | 7/16/2008 |
