Ternary TM-diboride coating films

Abstract

The present invention relates to coatings comprising or consisting of one or more ternary TM-diboride coating films. The ternary TM-diboride coating films showing exceptionally high phase stability and mechanical properties, even at high temperatures or even after exposition to high temperatures.

Claims

1. A coated substrate comprising a substrate surface coated with a coating comprising at least one ternary TM-diboride coating film, wherein the at least one ternary TM-diboride coating film comprises two different transition metals, and the at least one ternary TM-diboride coating film has a chemical composition described by the formula W.sub.1-xTa.sub.xB.sub.2-z, or by the formula V.sub.1-xW.sub.xB.sub.2 with 0.05≤x≤0.45 and −0.03≤z≤0.03, wherein the coefficients correspond to mol fractions.

2. The coated substrate according to claim 1, wherein a first of the two transition metals is tungsten, tantalum or vanadium.

3. The coated substrate according to claim 2, wherein a second of the two transition metals is tungsten, tantalum or vanadium.

4. The coated substrate according to claim 1, wherein a chemical composition of the at least one ternary TM-diboride coating film is described by the formula W.sub.1-xTa.sub.xB.sub.2-z, or by the formula V.sub.1-xW.sub.xB.sub.2 with 0.05≤x≤0.26.

5. The coated substrate according to claim 1, wherein a singular ternary phase of diboride of each of the two transition metals is present in the at least one ternary TM-diboride coating film.

6. The coated substrate according to claim 4, wherein a singular α-phase of diboride of each of the two transition metals is present in the at least one ternary TM-diboride coating film.

7. A method for producing the coated substrate according to claim 2, comprising preparing ternary W.sub.1-xTa.sub.xB.sub.2-z coating films by sputtering targets comprising tungsten diboride, WB.sub.2, and tantalum diboride, TaB.sub.2, respectively, in an argon-containing atmosphere in an interior of a vacuum chamber comprising at least one substrate to be coated for depositing the at least one ternary TM-diboride coating film on the substrate surface, or preparing V.sub.1-xW.sub.xB.sub.2 thin films by sputtering targets comprising vanadium diboride, VB.sub.2, and tungsten boride, W.sub.2B.sub.5-x, respectively, in an argon-containing atmosphere in an interior of a vacuum chamber comprising at least one substrate to be coated for depositing the at least one ternary TM-diboride coating film on the substrate surface.

8. The coated substrate according to claim 1, wherein the coated substrate is a forming tool or a cutting tool or a component.

9. The coated substrate according to claim 1, wherein the coated substrate is a part of a forming tool or a cutting tool or a component.

10. The coated substrate according to claim 1, wherein a hardness of the at least one ternary TM-diboride stays higher than 30 GPa measured by nanoindentation after annealing during 1 hour at a temperature between 800° C. and 1400° C. in vacuum atmosphere.

11. The coated substrate according to claim 2, wherein a hardness of the at least one ternary TM-diboride undergoes an age hardening effect during annealing during 1 hour at a temperature between 800° C. and 1400° C. in vacuum atmosphere.

Description

FIGURE CAPTIONS

(1) FIG. 1: Illustrations of crystallization with SG-191 (AlB.sub.2 prototype) and crystallization with SG-194 (W.sub.2B.sub.5 prototype), respectively; (a) Concept of α-WB.sub.2-z phase stabilization due to alloying with metastable α-TaB.sub.2-z; (b) Comparison on the energy of formation, E.sub.f, of the ternary W.sub.1-xTa.sub.xB.sub.2 in relation to their Ta content. The full lines correspond to perfect structures, whereas the dashed lines correspond to the boron-defected crystals. Schottky-defects (vacancy concentration of 10 at. %) for the binary systems are labeled with triangular symbols. The red and green symbols correspond to the ω- and α-structure, respectively.

(2) FIG. 2: (a) Structural evolution of the as deposited W1-xTa.sub.xB.sub.2-z powdered coating materials with increasing Ta content (x=0, 0.07, 0.14, 0.26, 0.40). The 2Θ peak positions for standardized α-WB2 (α=3.020 Å, c=3.050 Å) [34] and α-TaB2 (α=3.098 Å, c=3.227 Å) [35] are indicated with filled and opened hexagonal symbols, respectively. Stress free lattice parameters (a and c) of the single-phased coatings (annealed at Ta=800° C. for 16 h in vacuum to ensure stress free states which are actually in excellent agreement to the as deposited values) with increasing Ta content are presented in (b) and (c), respectively.

(3) FIG. 3: Structural evolution of the W1-xTa.sub.xB2-z (x=0, 0.07, 0.14, 0.26) coating powders with increasing annealing temperatures. The 2Θ peak positions for standardized α-WB2 (a=3.020 Å, c=3.050 Å) [34], ω-W2B5-z (a=2.983 Å, c=13.879 Å) [36] and t-WB (α=3.117 Å, c=16.910 Å) [37] are indicated with full green and open red hexagonal symbols, as well as black filled squares, respectively.

(4) FIG. 4: (a) Boron content of the selected compositions analyzed by elastic recoil detection analysis (ERDA). (b) Change in lattice parameter c and a (c) obtained from DFT. The filled blue squares indicate the data obtained for a perfect (non-defected) cell. The blue half-filled and open symbols indicate the change in lattice parameter for metal and boron defected structures, respectively. The ocher symbols indicate the experimental data. The grey area represents the change in lattice parameter a and c, for the boron-defected cells achieving the experimental composition by DFT.

(5) FIG. 5: Behavior of hardness of the W.sub.1-xTa.sub.xB.sub.2 coating films with increasing temperature measured by nanoindentation after annealing of the coated samples at 800° C., 1000° C., 1200° C. and 1400° C., respectively.

(6) FIG. 6: Behavior of Young's modulus of the W.sub.1-xTa.sub.xB.sub.2 coating films with increasing temperature measured by nanoindentation after annealing of the coated samples at 800° C., 1000° C., 1200° C. and 1400° C., respectively.

(7) FIG. 7: Fracture Toughness (KIC) of W.sub.1-xTa.sub.xB.sub.2-z coating films.

(8) The figure shows the fracture toughness values as a result of micromechanical bending tests for single-phased α-WB1.78 (59.3 at. % B), α-W.sub.0.93Ta.sub.0.07B1.76 (58.6 at. % B), α-W.sub.0.86Ta.sub.0.14B1.83 (61.1 at. % B), and α-W.sub.0.74Ta.sub.0.26B1.87 (62.3 at. % B). It can be clearly seen, that the data reveals a decreasing tendency (˜ from 3.7 to 3 MPam-½) with increasing tantalum content. A maximum KIC value of 3.8±0.5 GPam-½ was determined for the W0.93Ta0.07B1.76 material composition but simultaneously reveals the highest error bar. Comparing the KIC values of coatings with recently published fracture toughness results obtained for TiAlN[35] and TiN[36] it can clearly be seen, that it can be improved by 130 or 200%, respectively. The values of fracture toughness shown in FIG. 7 regarding TiB2 thin films are obtained from the literature.

(9) FIGS. 5 and 6 show the hardness and Young's modulus (elastic modulus) measured by nanoindentation after annealing of samples coated with WB.sub.2, W.sub.0.8Ta.sub.0.2B.sub.2, W.sub.0.2Ta.sub.0.8B.sub.2 and TaB.sub.2. Vacuum annealing was conducted in each case (at each respective annealing temperature).

(10) Exceptional high hardness values up to 1400° C. for all coatings were measured. Superhardness (corresponding to hardness values above 40 GPa) was observed by both W.sub.0.8Ta.sub.0.2B.sub.2 and W.sub.0.2Ta.sub.0.8B.sub.2 coating films even after annealing at 1200° C.

(11) The oxidation resistance and thermal behavior, which are essential to ensure high performance in different applications were analyzed.

(12) Analysis of the structure and mechanical properties of the inventive coating films reveals the potential of this material combination, by reaching superhardness level and allowing for phase transformation induced toughening effects.

(13) FIG. 7 shows the fracture toughness values as a result of micromechanical bending tests for single-phased α-WB1.78 (59.3 at. % B), α-W0.93Ta0.07B1.76 (58.6 at. % B), α-W0.86Ta0.14B1.83 (61.1 at. % B), and α-W0.74Ta0.26B1.87 (62.3 at. % B). It can be clearly seen, that the data reveals a decreasing tendency (˜ from 3.7 to 3 MPam-½) with increasing tantalum content. A maximum KIC value of 3.8±0.5 GPam-½ was determined for the W0.93Ta0.07B1.76 material composition but simultaneously reveals the highest error bar. Comparing the KIC values of the inventive coatings with recently published fracture toughness results obtained for TiAlN[39] and TiN[40] it can clearly be seen, that it can be improved by 130 or 200%, respectively. Unfortunately, TiB2 thin films—in terms of fracture toughness—is rather poor investigated and a single value of 0.6 MPam-½ can be compared to the obtained data. Moreover, no details on the measurement setup can be given [37].

(14) FIG. 8: (a) Crystal structure and the corresponding lattice constants calculated via DFT for VB.sub.2 and WB.sub.2 when crystallizing in either the AlB.sub.2-(α-prototype) (a) or W.sub.2B.sub.5-x-prototype (ω-prototype) (b). (c) Energy of formation, E.sub.f, as well as (d) lattice constant as a function of the vacancy concentration (also considering Schottky-defects) for VB.sub.2 and WB.sub.2. In (d) full symbols denote to the lattice constant a, whereas open symbols refer to c.

(15) FIG. 9: Cross-sectional transmission electron microscopy (TEM) studies including selected area electron diffraction patterns (SAED) of surface and substrate near regions from as-deposited (a) VB.sub.2, (b) V.sub.0.95W.sub.0.05B.sub.2, (c) V.sub.0.87W.sub.0.13B.sub.2, and (d) V.sub.0.79W.sub.0.21B.sub.2. The green dashed lines within the SAED patterns represent the diffraction rings when simply using Vegard's linear approximation for solid solutions between VB.sub.2 and WB.sub.2.

(16) FIG. 10: (a) Hardness (H), (b) indentation modulus (E), and (c) residual stresses (σ) of our as-deposited single phased V.sub.1-xW.sub.xB.sub.2 coatings with x32 0, 0.05, 0.13, and 0.21. The stresses are obtained by curvature measurements of coated Si substrates whereas the indentation experiments were conducted on coated sapphire substrates.

(17) FIG. 11: (a) Hardness (H) and (b) indentation modulus (E) of our V.sub.0.95W.sub.0.05B.sub.2 (yellow circular symbols), V.sub.0.87W.sub.0.13B.sub.2 (grey hexagonal symbols), and V.sub.0.69W.sub.0.21B.sub.2 (green cubic symbols) after vacuum-annealing for 1 h at T.sub.a.

(18) FIG. 12: Cross-sectional transmission electron microscopy (TEM) studies of V.sub.0.69W.sub.0.21B.sub.2 after annealing at Ta=1000° C. (a) and 1400° C. (b), with corresponding higher resolution images (c, and d, after Ta=1000 and 1400° C.), and an FFT of FIG. 12(d) in (d-1).

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