The present invention relates to a tap drill with enhanced performance, comprising a wear resistance layer of Al-Cr-N and a friction reduction layer deposited atop the wear resistance layer and to a method for producing a tap drill. State of the art

In the document US 9540726 B2 it is proposed to improve performance of drills, in particular of tap drills and micro drills by coating at least the head of the drill. The coating comprises at least one HiPIMS coating that is applied directly onto the drill substrate and which includes at least one layer of at least one nitride and/or carbide and/or oxide, and an amorphous carbon or DLC layer provided on the HiPIMS layer. The HiPIMS coating can be a (AI,Cr)N layer and the DLC layer can be a metalliferous DLC layer. The drill shown in US 9540726 B2 can be used in drilling operations of stainless steel workpieces, however the tool life is relatively short.

Objective of the present invention The objective of the present invention is to provide a coated tap drill and a method for producing a tap drill that may exhibit better performance and relative tool life in drilling operations of stainless steel workpieces in comparison with the state of the art. In particular, better performance in relation to friction reduction and cold-welding reduction properties. Description of the present invention

The objective of the present invention is attained by providing a tap drill comprising a substrate and a coating, wherein the coating is deposited on at least a portion of the substrate comprising the head of the drill, the coating comprising a first layer deposited directly on the substrate and a second layer deposited atop the first layer, wherein the first layer is a wear resistant layer of (AI,Cr)N deposited by HiPIMS and the second layer is a friction reduction layer, characterized in that: · The second layer is a metal carbide layer or a metal-carbide comprising layer deposited by using a physical vapor deposition (PVD) process of the type magnetron sputtering, preferably of the type high-power impulse magnetron sputtering (HiPIMS) method.

HiPIMS methods are also known as HPPMS methods because of the terminology high power pulsed magnetron sputtering.

Coatings produced by sputtering, in particular by HiPIMS show much better performance compared to coatings produced by arc, in particular if arc-deposited coating is without post-treatment.

HiPIMS provides the possibility to produce dense and smooth coatings. Coating like the AICrN+WC/C coating shown in figure 1 can be produced in one deposition run.

Preferably the friction reduction layer being preferably of carbon-containing titanium nitride or titan carbonitride or diamond like carbon doped with tungsten carbide or a tungsten carbide layer.

According to a preferred embodiment of the present invention the metal carbide layer can be a tungsten carbide layer or comprises mostly (more than 50 atomic-%) tungsten carbide, preferably comprises more than 70 atomic-% tungsten carbide, more preferably more than 90 atomic-%.

According to a further preferred embodiment of the present invention the metal carbide layer can be a titanium carbide layer or comprises mostly (more than 50 atomic-%) titanium carbide, preferably comprises more than 70 atomic-% titanium carbide, more preferably more than 90 atomic-%. Preferably the second layer is a tungsten carbide comprising layer of the type WC/C.

The objective of the present invention is attained by providing a method for producing a tap drill according to claim 6.

Preferably the second layer is a tungsten carbide comprising layer of the type WC/C and is deposited by sputtering of WC targets in an atmosphere comprising argon and a carbon- containing gas, preferably acetylene gas.

Preferably Hi PI MS techniques are used for sputtering of the WC targets.

Preferably the second layer is a titanium carbide comprising layer and is deposited by sputtering of Ti orTiC targets in an atmosphere comprising argon and a carbon-containing gas, preferably acetylene gas.

Preferably Hi PI MS techniques are used for sputtering of the Ti of TiC targets.

Figure 1 shows a coating for tap drill according to the present invention.

Figure 2 shows the benefits of the present invention in comparison with the state of the art. Figure 1 shows in the upper part a picture of a tap drill 1 according to the present invention. The tap drill 1 comprises a substrate 2 and a coating 3. The coating 3 is deposited on at least a portion of the substrate 2 comprising the head of the drill 1.

The coating 3 comprises a first layer 4. The first layer 4 is deposited directly on the substrate 2. The coating 3 comprises a second layer 5. The second layer 5 is deposited atop the first layer 4. The first layer 4 is a wear resistant layer of (AI,Cr)N. The first layer 4 is deposited by HiPIMS. The second layer 5 is a friction reducing layer. The second layer 5 is a metal carbide layer or a metal-carbide comprising layer. It can also be preferably of carbon- containing titanium nitride or titan carbonitride or diamond like carbon doped with tungsten or a tungsten carbide layer. The second layer 5 is deposited using physical a vapor deposition (PVD) process, preferably of the type magnetron sputtering, prferably of the type HiPIMS.

This can be seen in figure 2, which shows n a diagram the relative tool life of different coatings and/or depositing methods. The tool life of the Benchmark tool is defined to 100 %. In figure 2 the Benchmark tool has been deposited with TiN. An AICrN coating shows the same tool life of 100 % compared to the Benchmark. An AICrN + TiN coating, which has been deposited by Arc deposition and post-treated in order to reduce roughness shows a tool life of 160 % compared to the Benchmark. A significant tool life increase can be seen. An AICrN + WC/C coating that has been deposited by Arc deposition shows a tool life of 3 % compared to the Benchmark. An AICrN + WC/C coating deposited by HiPIMS deposition shows a tool life of 710 % compared to the Benchmark.

AICrN+TiN coating (deposited by arc plus post-treatment in order to reduce roughness) show significant tool life increase vs. Benchmark. Smooth coating surface has advantage.

Coatings produced by sputtering, in particular by HiPIMS show much better performance compared to coatings produced by arc, in particular if arc-deposited coating is without post-treatment.

HiPIMS provides the possibility to produce dense and smooth coatings. Coating like the AICrN+WC/C coating shown in figure 1 can be produced in one deposition run. ^■ AICrN+Ti(CN) coating shows increase in the tool life. This is actually the main topic for application.

Preferably the first layer 4 is deposited by sputtering of Cr targets in a nitrogen reactive atmosphere (comprising argon and nitrogen or only nitrogen) by using HiPIMS techniques.

According to a preferred embodiment of the present invention, the second layer 5 is a tungsten carbide comprising layer of the type WC/C (WC+C) which can deposited by sputtering of WC targets in an atmosphere comprising argon and a carbon-containing gas, preferably acetylene gas (i.e. preferably in an atmosphere comprising argon and acetylene gas). According to a variant of this preferred embodiment instead of conventional sputtering techniques HiPIMS techniques are used for sputtering of the WC targets.

According to a further preferred embodiment of the present invention, the second layer 5 is a titanium carbide comprising layer which can be deposited by sputtering of Ti or TiC targets in an atmosphere comprising argon and a carbon-containing gas, preferably acetylene gas (i.e. preferably in an atmosphere comprising argon and acetylene gas). According to a variant of this preferred embodiment instead of conventional sputtering techniques HiPIMS techniques are used for sputtering of the Ti or TiC targets.