Hard-coated body and method for production thereof

Technical field

0001The invention relates to hard material coated bodies with a single or multi-layer coating system comprising at least one Ti_1-xAl_xN-hard material layer, and a method for its production. The coating according to the invention can be used in particular for tools made of steel, hard metals, cermets, and ceramics, such as drills, milling cutters, and indexable inserts. The bodies coated according to the invention exhibit improved wear resistance and oxidation resistance.

State of the art

0002The production of wear protection layers in certain areas of the Ti-Al-N material system is according to the<patcit id="pcit0001" dnum="WO03085152A2"><text>WO 03/085152 A2</text></patcit> It is possible to produce monophase TiAlN coatings with the NaCl structure at AlN contents of up to 67%. These coatings, produced by PVD, have lattice constants a_FCC between 0.412 nm and 0.424 nm (<nplcit id="ncit0001" npl-type="s"><text>R. Cremer, M. Witthaut, A. von Richthofen, D. Neuschütz, Fresenius J. Anal. Chem. 361 (1998) 642-645</text></nplcit>). Such cubic TiAlN coatings possess relatively high hardness and wear resistance. However, at AlN contents > 67%, a mixture of cubic and hexagonal TiAlN forms, and at an AlN content > 75%, only the softer and less wear-resistant hexagonal wurtzite structure is formed.

0003It is also known that the oxidation resistance of cubic TiAlN coatings increases with increasing AlN content (<nplcit id="ncit0002" npl-type="s"><text>M. Kawate, A. Kimura, T. Suzuki, Surface and Coatings Technology 165 (2003) 163-167</text></nplcit>). However, the scientific literature on TiAlN production by PVD suggests that above 750°C practically no single-phase cubic TiAlN layers with a high AlN content can be formed, or that in the case of Ti_1-xAl_xN-phases with x > 0.75 always have the hexagonal wurtzite structure (<nplcit id="ncit0003" npl-type="s"><text>K. Kutschej, PH Mayrhofer, M. Kathrein, C. Michotte, P. Polcik, C. Mitterer, Proc. 16th Int. Plansee Seminar, May 30 - June 03, 2005, Reutte, Austria, Vol. 2, pp. 774 - 788</text></nplcit>).

0004It has also been found that plasma CVD can produce single-phase Ti_1-xAl_xN-hard coatings with x up to 0.9 can be produced (<nplcit id="ncit0004" npl-type="s"><text>R. Prange, Diss. RTHW Aachen, 1999, Progress Reports VDI, 2000, Series 5, No. 576</text></nplcit> as well as <nplcit id="ncit0005" npl-type="s"><text>O. Kyrylov et al., Surface and Coating Techn. 151-152 (2002) 359-364</text></nplcit>). However, the disadvantages are the insufficient homogeneity of the layer composition and the relatively high chlorine content in the layer. Furthermore, the process is complicated and time-consuming.

0005According to<patcit id="pcit0002" dnum="JP2001341008A"><text>JP 2001 341008 A</text></patcit> A titanium-aluminum nitrate-coated tool is known, consisting of a tool body and a single or multi-layer coating layer of titanium-aluminum nitrate which contains at least titanium, aluminum and nitrogen, wherein the crystal structure of the titanium-aluminum nitrate layer is a cubic structure, the titanium-aluminum nitrate layer has a tensile residual stress and the chloride content of the titanium-aluminum nitrate layer is 0.01 to 2 mass%. However, the incorporation of aluminum into the cubic TiAIN crystal lattice is limited. The lattice constant for this TiAIN layer, determined from the (111) reflection, is given as 0.41358 nm.

0006For the production of the well-known Ti_1-xAl_xN-hard coatings are applied using state-of-the-art PVD or plasma CVD processes, which are operated at temperatures below 700°C (<nplcit id="ncit0006" npl-type="s"><text>A. Hörling, L. Hultman, M. Oden, J. Sjölen, L. Karlsson, J. Vac. Sci. Technol. A 20 (2002)5, 1815 - 1823</text></nplcit> as well as <nplcit id="ncit0007" npl-type="s"><text>D. Heim, R. Hochreiter, Surface and Coatings Technology 98 (1998) 1553 - 1556</text></nplcit>). A disadvantage of these processes is that the coating of complex component geometries is difficult. PVD is a highly directional process, and plasma CVD requires high plasma homogeneity, as the plasma power density has a direct influence on the Ti/Al atomic ratio of the layer. With the PVD processes, which are almost exclusively used industrially, it is not possible to deposit single-phase cubic Ti_1-xAl_xTo produce N-layers with x > 0.75.

0007Since cubic TiAlN layers are a metastable structure, production with conventional CVD processes at high temperatures ≥ 1000°C is in principle not possible, because at temperatures above 1000°C a mixture of TiN and hexagonal AIN is formed.

0008According to the<patcit id="pcit0003" dnum="US6238739B1"><text>US 6,238,739 B1</text></patcit> It is also known that by a thermal CVD process without plasma support Ti_1-xAl_xN-layers with x between 0.1 and 0.6 are available in the temperature range between 550°C and 650°C when a gas mixture of aluminum and titanium chlorides and NH₃ and H₂ The disadvantage of this special thermal CVD process is also the limitation to a layer stoichiometry x ≤ 0.6 and the restriction to temperatures below 650°C. The low coating temperature leads to high chlorine contents in the layer of up to 12 at.%, which are harmful for the application (<nplcit id="ncit0008" npl-type="s"><text>S. Anderbouhr, V. Ghetta, E. Blanquet, C. Chabrol, F. Schuster, C. Bernard, R. Madar, Surface and Coatings Technology 115 (1999) 103 -110</text></nplcit>).

Disclosure of the invention

0009The invention is based on the object of hard-coated bodies with a single or multi-layer coating system comprising at least one Ti_1-xAl_xN-hard material layer to achieve significantly improved wear resistance and oxidation resistance.

0010This problem is solved with the features of the patent claims.

0011The hard-coated bodies according to the invention are characterized in that they are coated with at least one Ti layer produced by CVD without plasma excitation._1-xAl_xN-hard material layer, which is a single-phase layer in the cubic NaCl structure with a stoichiometry coefficient x > 0.75 to x = 0.93 and a lattice constant a_FCC between 0.412 nm and 0.405 nm. Further features of this Ti_1-xAl_xN-hard coatings are that their chlorine content is in the range between only 0.05 and 0.9 at.% and the hardness value of the Ti_1-xAl_xN-hard material layer(s) is in the range of 2500 HV to 3800 HV.

0012Advantageously, the chlorine content of the Ti_1-xAl_xN-hard material layer(s) in the range of only 0.1 to 0.5 at.% and the oxygen content in the range of 0.1 to 5 at.%.

0013The layer present on the bodies according to the invention has a high hardness between 2500 HV and 3800 HV and a significantly improved oxidation resistance compared to the prior art, which is achieved by the high AIN content in the cubic Ti_1-xAl_xN-phase, a previously unattained combination of hardness and oxidation resistance, which results in very good wear resistance, especially at high temperatures.

0014For the production of the bodies, the invention includes a method which is characterized in that the bodies are coated in a reactor at temperatures in the range of 700°C to 900°C by means of CVD without plasma excitation, wherein titanium halides, aluminum halides and reactive nitrogen compounds are used as precursors, which are mixed at elevated temperature.

0015According to the invention, reactive nitrogen compounds that can be used are NH₃ and/or N₂H₄ be used.

0016The precursors are advantageously mixed in the reactor immediately before the deposition zone.

0017According to the invention, the mixing of the precursors is carried out at temperatures in the range of 150°C to 900°C.

0018The coating is advantageously applied at pressures in the range of 10² Pa to 10⁵ Pa carried out.

0019The method according to the invention makes it possible to produce a relatively simple thermal CVD process at temperatures between 700°C and 900°C and pressures between 10² Pa and 10⁵ Pa Ti_1-xAl_xN-layers with the NaCl structure. This process can be used to produce both the previously known Ti_1-xAl_xN-layer compositions with x < 0.75 as well as the novel compositions with x > 0.75 are available, which cannot be produced using any other process. This process allows for the homogeneous coating of even complex component geometries.

Embodiments of the invention

0020The invention is explained in more detail below using exemplary embodiments.

Example 1

0021On WC/Co carbide inserts, a Ti_1-xAl_xN-layer is deposited using the thermal CVD process according to the invention. For this purpose, a gas mixture of 20 ml/min AlCl₃, 3.5 ml/min TiCl₄, 1400 ml/min H₂, 400 ml/min of argon at a temperature of 800°C and a pressure of 1 kPa.

0022A second gas supply is used to supply a mixture of 100 ml/min NH₃ and 200 ml/min N₂ into the reactor. The two gas streams are mixed at a distance of 10 cm in front of the substrate carrier. After a coating time of 30 minutes, a gray-black layer with a thickness of 6 µm is obtained.

0023By means of the X-ray thin film analysis carried out in grazing incidence, only the cubic Ti_1-xAl_xN-phase found (see X-ray diffractogram<figref idref="f0001">Fig. 1</figref>).

0024The determined lattice constant is a_FCC = 0.4085 nm. The Ti:Al atomic ratio, determined by WDX, is 0.107. The chlorine and oxygen contents, also determined, are 0.1 at.% for Cl and 2.0 at.% for O.

0025Calculating the stoichiometry coefficient yields x = 0.90. Using a Vickers indenter, the hardness of the coating is measured at 3070 HV[0.05]. The Ti_1-xAl_xN-layer is oxidation resistant in air up to 1000°C.

Example 2

(Comparison example)

0026On indexable inserts made of Si₃N₄-Cutting ceramics, a 1 µm thick titanium nitride layer is first applied using a known standard CVD process at 950°C. A gray-black layer is then deposited using the CVD process according to the invention, using the gas mixture described in Example 1, a pressure of 1 kPa, and a temperature of 850°C.

0027X-ray thin film analysis shows that a heterogeneous mixture of Ti_1-xAl_xN with the NaCl structure and AlN with the wurtzite structure. In the X-ray diffractogram of<figref idref="f0001">Fig. 2</figref> are the reflections of the cubic Ti_1-xAl_xN is denoted by c and that of hexagonal AlN (wurtzite structure) by h. The proportion of cubic Ti_1-xAl_xN predominates in the layer.

0028The determined lattice constant of the cubic phase is a_FCC = 0.4075 nm. The second, hexagonal AlN phase has lattice constants of a = 0.3107 nm and c = 0.4956 nm. The hardness of the layer, determined by Vickers indenter, is 3150 HV[0.01]. The two-phase Ti_1-xAl_xN-layer is oxidation resistant in air up to 1050°C.