Hard material layers with selected thermal conductivity

Abstract

A hard material layer system with a multilayer structure, comprising alternating layers A and B, with A layers having the composition Me.sub.ApAO.sub.nAN.sub.mA in atomic percent and B layers having the composition Me.sub.BpBO.sub.nBN.sub.mB in atomic percent, where the thermal conductivity of the A layers is greater than the thermal conductivity of the B layers. Me.sub.A and Me.sub.B each comprise at least one metal of the group Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Al, p.sub.A indicates the atomic percentage of Me.sub.A and p.sub.B indicates the atomic percentage of Me.sub.B and the following is true: P.sub.A=P.sub.B, n.sub.A indicates the oxygen concentration in the A layers in atomic percent and n.sub.B indicates the oxygen concentration in the B layers in atomic percent and the following is true: n.sub.A<n.sub.B, and m.sub.A indicates the nitrogen concentration in the A layers in atomic percent and m.sub.B indicates the nitrogen concentration in the B layers in atomic percent and the following is true: p.sub.A/(n.sub.A+m.sub.A)=p.sub.B/(n.sub.B+m.sub.B).

Claims

1. A hard material layer system that is deposited onto a substrate surface and has a multilayered layer structure comprising: alternating layers A and B, where the A layers have a composition of Me.sub.ApAO.sub.nAN.sub.mA atomic percent and the B layers have a composition of Me.sub.BpBO.sub.nBN.sub.mB in atomic percent, wherein: a. a thermal conductivity of the A layers is greater than a thermal conductivity of the B layers, b. Me.sub.A and Me.sub.B each comprise at least one metal selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Al, c. p.sub.A indicates an atomic percentage of Me.sub.A and p.sub.B indicates an atomic percentage of Me.sub.B and P.sub.A=P.sub.B, d. n.sub.A indicates an oxygen concentration in the A layers in atomic percent and n.sub.B indicates an oxygen concentration in the B layers in atomic percent and n.sub.A<n.sub.B, e. m.sub.A indicates a nitrogen concentration in the A layers in atomic percent and m.sub.B indicates a nitrogen concentration in the B layers in atomic percent and p.sub.A/(n.sub.A+m.sub.A)=p.sub.B/(n.sub.B+m.sub.B); f. MeA=MeB; and g. 5%n.sub.B30%, and p.sub.A+n.sub.A+m.sub.A=p.sub.B+n.sub.B+m.sub.B=100%.

2. The hard material layer system according to claim 1, wherein Me.sub.A and Me.sub.B each further comprise at least one element selected from the group consisting of Si, B, W, Nb, Y, Mo, and Ni.

3. The hard material layer system according to claim 1, wherein n.sub.A=0%.

4. The hard material layer system according to claim 1, wherein n.sub.A and n.sub.B are selected so that the A layers do not differ significantly from the B layers with regard to the layer hardness and modulus of elasticity.

5. The hard material layer system according to claim 1, wherein a thermal conductivity of the hard material layer system is greater parallel to a substrate surface than the thermal conductivity of the hard material layer system perpendicular to the substrate surface.

6. The hard material layer system according to claim 1, wherein a hardness of the hard material layer system is greater than 20 GPa.

7. The hard material layer system according to claim 1, wherein at least the multilayered layer structure has a cubic structure.

8. The hard material layer system according to claim 1, wherein Me.sub.A and Me.sub.B at least mostly include the metals aluminum and/or titanium or the metals aluminum and/or chromium.

9. The hard material layer system according to claim 1, wherein a concentration ratio in atomic percent of titanium relative to aluminum, i.e. Ti/Al, or of chromium relative to aluminum, i.e. Cr/Al, is less than 1.

10. The hard material layer system according to claim 1, wherein at least one A layer or at least one B layer comprises at least a part of a layer thickness across a graduated oxygen concentration or the hard material layer system has at least one additional hard material layer of the type Me.sub.pO.sub.nN.sub.m where n0, Me=Me.sub.A, and p=P.sub.A or Me=Me.sub.B, and p=p.sub.B, as a top layer, which comprises at least a part of the layer thickness across a graduated oxygen concentration.

11. A component or a cutting tool for chip-removing machining, that is coated with the hard material layer system according to claim 1.

12. A method of using a cutting tool for chip-removing machining comprising using the cutting tool according to claim 11 for the chip-removing machining of hard-to-machine materials comprising Ni- and/or Ti-based alloys.

13. The hard material layer system according to claim 1, wherein n.sub.A and n.sub.B are selected so that the A layers do not differ significantly from the B layers with regard to layer morphology and/or grain size.

14. The hard material layer system according to claim 1, wherein n.sub.A and n.sub.B are selected so that the A layers do not differ significantly from the B layers with regard to phase inventory and/or structural stability.

15. A method for manufacturing a metal oxynitride hard material layer of the type Me.sub.pO.sub.nN.sub.m with a predetermined oxygen-dependent thermal conductivity, i.e. a predetermined oxygen-dependent thermal conductance, the method comprising: a. depositing the Me.sub.pO.sub.nN.sub.m layer in a vacuum coating chamber using physical gas phase deposition from at least one target in a reactive gas-containing atmosphere with a substrate temperature Ts and a coating pressure P onto a substrate surface, b. using nitrogen and oxygen as reactive gases, c. wherein the target contains Me, and d. wherein Me comprises at least one metal selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Al and Me further comprises at least one element selected from the group consisting of Y, Ni, B, and Si, e. controlling an oxygen concentration in the vacuum coating chamber during the deposition of the Me.sub.pO.sub.nN.sub.m layer so that an oxygen concentration value, which has been previously calculated by the correlation ()=.sub.0/(1+.Math.), is maintained so that the predetermined oxygen-dependent thermal conductivity in the Me.sub.pO.sub.nN.sub.m layer is set during the layer deposition, where: i. () is the oxygen-dependent thermal conductivity of a Me.sub.pO.sub.nN.sub.m layer, which is produced while maintaining an oxygen concentration in the vacuum coating chamber during the layer deposition, ii. indicates the oxygen concentration in the vacuum coating chamber during the layer deposition, iii. .sub.0 is the thermal conductivity of a first reference layer Me.sub.p0O.sub.n0N.sub.m0, where n.sub.0=0% and Me.sub.p0O.sub.n0N.sub.m0 is deposited with the same process parameters described above with regard to the deposition of Me.sub.pO.sub.nN.sub.m, but without the use of oxygen as a reactive gas and using only nitrogen instead, iv. is a parameter that includes a scattering cross-section and that is obtained by adapting the above-indicated correlation to experimental data of at least one additional second reference layer Me.sub.p1O.sub.n1N.sub.m1 and one additional third reference layer Me.sub.p2O.sub.n2N.sub.m2, where Me.sub.p1O.sub.n1N.sub.m1 and Me.sub.p2O.sub.n2N.sub.m2 are deposited with the same process parameters described above with regard to the deposition of Me.sub.pO.sub.nN.sub.m, but using different oxygen concentrations in the vacuum coating chamber and Me.sub.p1O.sub.n1N.sub.m1 is deposited using an oxygen concentration in the vacuum coating chamber that results in an oxygen concentration in atomic percent of between 5 and 20% in a layer n.sub.1 while Me.sub.p2O.sub.n2N.sub.m2 is deposited using an oxygen concentration that results in an oxygen concentration in atomic percent of between 20 and 30% in a layer n.sub.2, taking into account that p.sub.0+n.sub.0+m.sub.0=p.sub.1+n.sub.1+m.sub.1=p.sub.2+n.sub.2+m.sub.2=100%, m.sub.1 and m.sub.2 are greater than zero, p.sub.0=p.sub.1=p.sub.2, and p.sub.0/(n.sub.0+m.sub.0)=p.sub.1/(n.sub.1+m.sub.1)=p.sub.2/(n.sub.2+m.sub.2).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 and 2 illustrate the relationship between the oxygen content in the layer and the thermal conductivity of the layer (measured from the layer surface) for the layer systems TiON and CrON.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(2) For these experiments, the layers were deposited using arc evaporation PVD techniques. The substrate temperature and the total pressure in the coating chamber during the coating processes were correspondingly kept constant at approximately 450 C. and 2 Pa. Nitrogen and oxygen were correspondingly used as reactive gases for the deposition of the nitride and oxynitride layers.

(3) For both systems, this relationship can be mathematically described by means of the constant scattering model as demonstrated in FIGS. 1 and 2. This is an indication of the general applicability of this relationship. The addition of O.sub.2 in this case changes the scattering cross-section, i.e. with the addition of O.sub.2, increasing lattice defects are produced, which interfere with the propagation of lattice vibrations (phonons).

(4) The replacement of nitrogen with oxygen in nitrides produces significant disorder in the material structure due to the different radius, different number of valence electrons, and higher electron negativity. Possible defects include empty lattice positions, occupied interstitial positions, lattice dislocations, and lattice distortions. All of these detects have a negative impact on the propagation of phonons in the crystal structure and thus potentially reduce the thermal conductivity of the material. In total, the influence of all defects on the thermal conductivity that an oxygen atom produces on average is referred to as the phonon scattering cross-section of oxygen. As long as the crystal structure of the material does not fundamentally change and no additional oxide phases are produced in addition to the nitride, it is possible to assume the existence of a scattering cross-section that is constant (independent of the oxygen content). This makes it possible to adjust the thermal conductivity by means of the oxygen content. The functional relationship is described by the following equation:
()=.sub.0/(1+.Math.)
where () is the oxygen-dependent thermal conductivity of the material, .sub.0 is the thermal conductivity in the oxygen-free material, indicates the oxygen concentration, and is a parameter that includes the scattering cross-section. In order to find the parameter , a series of samples with different oxygen contents must be produced and the thermal conductivity measured. The adaptation of the function () to the data yields .

(5) Specifically, the present invention proposes using Al-rich AlTiN- and AlCrN-based coatings with controlled contents, preferably in the range from 0-30 at. % O.sub.2, particularly preferably in the range from 3 to 25 at. % O.sub.2, for the chip-removing machining of Ti- and Ni-based alloys, taking into account a combination with other alloy elements such as Si, B, W, Nb, Y, Mo, Ni.

(6) The controlled addition of O.sub.2 is used to optimize these layer systems for specific applications by producing a selected thermal conductivity behavior within the layer. Preferably, the thermal conductivity perpendicular to the layer is minimized (made as low as possible) and the thermal conductivity parallel to the layer is maximized (made as high as possible), i.e. the anisotropy of the thermal conductivity is maximized.

(7) The O.sub.2 concentration should not be so high that the mechanical, chemical, and structural properties of the layer system are significantly changed or negatively influenced.

(8) Preferably, a hardness of the layer system of greater than 20 GPa or even more preferably greater than 30 GPa is achieved.

(9) One embodiment of the present invention is a layer system composed of TiAlNO or CrAlNO, with the oxygen concentration within the layer being graduated in the direction of the layer thickness.

(10) Another embodiment of the present invention is a layer system in which several layers with elevated and reduced oxygen concentrations are deposited in alternating fashion as a multilayer structure.

(11) The use of graduations can be understood as follows: O.sub.2 content is varied perpendicular to the substrate surface in accordance with the requirements.

(12) The use of multilayer systems can be understood as follows: an O.sub.2-rich AlTiN layer follows an O.sub.2-free AlTiN layer in order to thus selectively increase the thermal conductivity parallel to the substrate and decrease it perpendicular to the substrate. The result is an optimized heat dissipation into the chip, i.e. out of the layer/substrate system.

(13) The use of multilayer systems can also be understood as follows: an alternating sequence of AlCrN and AlTiN, respectively with or without O.sub.2, in order to optimize anisotropy in the thermal conductivity in accordance with the above explanations while taking into account a combination with other alloy elements such as Si, B, W, Nb, Y, Mo, and Ni.

(14) In particular, the present invention relates to a method for manufacturing metal oxynitride hard material layers by means of PVD techniques in a vacuum chamber; the hard material layer has a composition of Me.sub.pO.sub.nN.sub.m in atomic percent, where p+n+m=100%, and has a predetermined thermal conductivity: One method according to the present invention can be carried out as follows: a. The metallic elements of the metal oxynitride hard material layer are deposited by means of physical gas phase deposition from at least one target; the target contains Me and Me is at least one metal from the group Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Al and preferably, Me also includes at least one element from the group Y, Ni, B, and Si; and the target is used for the deposition of at least three layers using various processes, but using the same process parameters with the exception of the composition of the reactive gas. b. Nitrogen is used as the reactive gas for the deposition of a first reference layer, which is a metal nitride layer Me.sub.p1O.sub.n1N.sub.m1 with an oxygen concentration in atomic percent of O.sub.2-conc1=n1=0, where the first reference layer is deposited with a constant substrate temperature Ts and a constant overall coating pressure P. c. Nitrogen and oxygen are used as reactive gases for the deposition of a third reference layer, which is a metal oxynitride layer Me.sub.p3O.sub.n3N.sub.m3 with an oxygen concentration in atomic percent of O.sub.2-conc3=n3 of at most 30%, preferably O.sub.2-conc3=is between 20 and 30%, where the third reference layer is deposited with the same constant substrate temperature Ts and the same constant overall coating pressure P as the deposition of the first reference layer and p1=p3 and p1/(m1+n1)=p3/(m3+n3). d. Nitrogen and oxygen are used as reactive gases for the deposition of a second reference layer, which is a metal oxynitride layer Me.sub.p2O.sub.n2N.sub.m2 with an oxygen concentration in atomic percent of O.sub.2-conc2=n2 which is greater than O.sub.2-conc1 and less than O.sub.2-conc3, O.sub.2-conc1 is between 5 and 20%, where the second reference layer is deposited with the same constant substrate temperature Ts and the same constant overall coating pressure P as the deposition of the first and third reference layers and p1=p3=p2 and p1/(m1+n1)=p3/(m3+n3)=p2/(m2+n2). e. The thermal conductivity of the first, second, and third reference layers is measured starting from the layer surface of each layer. f. The measured values of thermal conductivity and oxygen concentration of the first, second, and third reference layers are used to establish a correlation in the following, form:
()=.sub.0/(1+.Math.)
where () is the oxygen-dependent thermal conductivity of the hard material layer system Me-ON. .sub.0 is the thermal conductivity in the first reference layer, indicates the oxygen concentration, and is a parameter that includes the scattering cross-section and that is obtained by adapting the function () to the data. g. The correlation is used to calculate the oxygen concentration in the Me.sub.pO.sub.nN.sub.m hard material layer at which a predetermined thermal conductivity is achieved and a calculation is performed as to the oxygen concentration of the reactive gas at which the coating process must be carried out in step h. h. The Me.sub.pO.sub.nN.sub.m hard material layer with the predetermined thermal conductivity is deposited with the same process parameter as the reference layers with the exception of the oxygen concentration of the reactive gas, which must first be adapted in accordance with the value determined in step g.

(15) The present invention also relates to hard material layer systems that are deposited on substrate surfaces and contain at least one Me.sub.pO.sub.nN.sub.m hard material layer produced according to the method described above.

(16) Preferably, the Me.sub.pO.sub.nN.sub.m hard material layer of a hard material layer system according to the present invention includes a cubic structure and preferably, Me includes at least mostly titanium and aluminum or chromium and aluminum.

(17) Preferably, the concentration ratio in atomic percent of Ti relative to Al, i.e. Ti/Al, or of Cr relative to Al, i.e. Cr/Al, is less than 1.

(18) A particular embodiment of a hard material layer system according to the present invention has a graduated oxygen concentration across at least part of the layer thickness.

(19) A particularly preferred embodiment of a hard material layer system according to the present invention has at least one part of the layer thickness across a multilayer structure, having, alternating layers A with the composition Me.sub.ApAO.sub.nAN.sub.mA and B layers with the composition Me.sub.BpBO.sub.nBN.sub.mB, where Me.sub.A=Me.sub.B, p.sub.A=p.sub.B, n.sub.A<n.sub.B, and p.sub.A/(n.sub.A+m.sub.A)=p.sub.B/(n.sub.B+m.sub.B).

(20) A preferred variant of the above-described embodiment of as hard material layer system is characterized by A layers, where na=0.

(21) Preferably, a hard material layer system according to the present invention is produced so that the thermal conductivity parallel to the substrate surface is greater than the thermal conductivity perpendicular to the substrate surface.

(22) For particular applications, for example for the forming and chip-removing machining of certain materials, the use of a hard material layer system according to the present invention is particularly advantageous if it has a hardness of at least greater than 20 GPa and preferably greater than 30 GPa. Any components and tools can also be provided with a hard material layer system according to the present invention. In particular, coated chip-removing machining tools with a coating according, to the present invention are very promising for chip-removing machining of hard-to-machine materials such as Ni- and Ti-based alloys.

(23) In particular, the present invention relates to: A hard material layer system that is deposited onto a substrate surface and has a multilayered layer structure comprising alternating layers A and B, where the A layers have a composition of Me.sub.ApAO.sub.nAN.sub.mA in atomic percent and the B layers have a composition of Me.sub.BpBO.sub.nBN.sub.mB in atomic percent, where a. the thermal conductivity of the A layers is greater than the thermal conductivity of the B layers. b. Me.sub.A and Me.sub.B each comprise at least one metal from the group Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Al, c. p.sub.A indicates the atomic percentage of Me.sub.A and p.sub.B indicates the atomic percentage of Me.sub.B and the following is true: p.sub.A=p.sub.B, d. n.sub.A indicates the oxygen concentration in the A layers in atomic percent and n.sub.B indicates the oxygen concentration in the B layers in atomic percent and the following is true: n.sub.A<n.sub.B, and e. m.sub.A indicates the nitrogen concentration in the A layers in atomic percent and m.sub.B indicates the nitrogen concentration in the B layers in atomic percent and the following is true: p.sub.A/(n.sub.A+m.sub.A)=p.sub.B/(n.sub.B+m.sub.B). A hard material layer system according to the above-described embodiment, where Me.sub.A and/or Me.sub.B include(s) at least one other element from the group Si, B, W, Nb, Y, Mo, and Ni. A hard material layer system according to one of the above-described embodiments, where Me.sub.A=Me.sub.B. A hard material layer system according to one of the above-described embodiments, where 5%n.sub.B30%, taking into account the fact that p.sub.A+n.sub.A+m.sub.A=p.sub.B+n.sub.B+m.sub.B=100%. A hard material layer system according to one of the above-described embodiments, where n.sub.A=0%.

(24) A hard material layer system according to one of the above-described embodiments, where n.sub.A and n.sub.B are selected so that the A layers do not differ significantly from the B layers with regard to the layer hardness and modulus of elasticity and preferably also with regard to layer morphology and/or grain size and/or phase distribution and/or structural stability.

(25) A hard material layer system according to one of the above-described embodiments, where the thermal conductivity of the hard material layer system is greater parallel to the substrate surface than the thermal conductivity of the hard material layer system perpendicular to the substrate surface. Preferably, the hardness of the hard material layer system is greater than 20 GPa, and more preferably greater than 30 GPa.

(26) A hard material layer system according to one of the above-described embodiments, where at least the multilayered layer structure has a cubic structure.

(27) A hard material layer system according to one of the above-described embodiments, where Me.sub.A and/or Me.sub.B at least mostly include(s) the metals aluminum and/or titanium or the metals aluminum and/or chromium.

(28) A hard material layer system according to one of the above-described embodiments, where the concentration ratio in atomic percent of titanium relative to aluminum, i.e. Ti/l, or of chromium relative to aluminum, i.e. Cr/Al, is less than 1.

(29) A hard material layer system according to one of the above-described embodiments, where at least one A layer or one B layer comprises at least a part of the layer thickness across a graduated oxygen concentration or the hard material layer system has at least one additional hard material layer of the type Me.sub.pO.sub.nN.sub.m where n0, Me=Me.sub.A, and p=p.sub.A or Me=Me.sub.B, and p=p.sub.B, preferably as a top layer, which comprises at least a part of the layer thickness across a graduated oxygen concentration.

(30) A component or tool, preferably a chip-removing machining tool, that is coated with hard material layer system according to one of the above-described embodiments.

(31) The use of a cutting tool for coated chip-removing machining having a hard material layer system according to one of the above-described embodiments for the chip-removing machining of hard-to-machine materials such as Ni- and/or Ti-based alloys.

(32) A method for manufacturing a metal oxynitride hard material layer of the type Me.sub.pO.sub.nN.sub.m with a predetermined oxygen-dependent thermal conductivity, i.e. a predetermined oxygen-dependent thermal conductance, where a. the Me.sub.pO.sub.nN.sub.m layer is deposited in a vacuum coating chamber by means of physical gas phase deposition from at least one target in a reactive gas-containing atmosphere with a substrate temperature Ts and a coating pressure P onto a substrate surface, b. nitrogen and oxygen are used as reactive gases, c. the target contains Me, and d. Me is at least one metal from the group Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Al and Me preferably includes at least one element from the group Y, Ni, B, and Si,
wherein e. the oxygen concentration in the vacuum coating chamber is controlled during the deposition of the Me.sub.pO.sub.nN.sub.m layer so that an oxygen concentration value, which has been previously calculated by means of the correlation ()=.sub.0/(1+.Math.), is maintained so that the predetermined oxygen-dependent thermal conductivity in the Me.sub.pO.sub.nN.sub.m layer is set during the layer deposition, where: i. () is the oxygen-dependent thermal conductivity of a Me.sub.pO.sub.nN.sub.m layer, which is produced while maintaining an oxygen concentration in the vacuum coating chamber during the layer deposition, ii. indicates the oxygen concentration in the vacuum coating chamber during the layer deposition, iii. .sub.0 is the thermal conductivity of a first reference layer Me.sub.p0O.sub.n0N.sub.m0, where n.sub.0=0% and Me.sub.p0O.sub.n0N.sub.m0 is deposited with the same process parameters described above with regard to the deposition of Me.sub.pO.sub.nN.sub.m, but without the use of oxygen as a reactive gas and using only nitrogen instead. iv. is a parameter that includes the scattering cross-section and that is obtained by adapting the above-indicated correlation to experimental data of at least one additional second reference layer Me.sub.p1O.sub.n1N.sub.m1 and one additional third reference layer Me.sub.p2O.sub.n2N.sub.m2, where Me.sub.p1O.sub.n1N.sub.m1 and Me.sub.p2O.sub.n2N.sub.m2 are deposited with the same process parameters described above with regard to the deposition of Me.sub.pO.sub.nN.sub.m, but using different oxygen concentrations in the vacuum coating chamber and preferably Me.sub.p1O.sub.n1N.sub.m1 is deposited using an oxygen concentration in the vacuum coating chamber that results in an oxygen concentration in atomic percent of between 5 and 20% in the layer n.sub.1 while Me.sub.p2O.sub.n2N.sub.m2 is deposited using an oxygen concentration that results in an oxygen concentration in atomic percent of between 20 and 30% in the layer n.sub.2, taking into account the fact that p.sub.0+n.sub.0+m.sub.0=p.sub.1+n.sub.1+m.sub.1=p.sub.2+n.sub.2+m.sub.2=100%, m.sub.1 and m.sub.2 are greater than zero, p.sub.0=p.sub.1=p.sub.2, and p.sub.0/(n.sub.0+m.sub.0)=p.sub.1/(n.sub.1+m.sub.1)=p.sub.2+m.sub.2)

(33) Preferably, the oxygen concentration in the vacuum coating chamber is controlled by adjusting the oxygen flow, particularly during the deposition of the Me.sub.pO.sub.nM.sub.m layer.