Ti-Zr-Nb-V alloy and preparation method and application thereof

Abstract

The invention discloses a Ti-Zr-Nb-V alloy and a preparation method and application thereof, and belongs to the technical field of metal materials and preparation thereof. The alloy comprises chemical elements Ti, Zr, Nb, V and O, the atomic percent expression is TiaZrbNbcVdOe, a is larger than or equal to 36 and smaller than or equal to 43, b is larger than or equal to 30 and smaller than or equal to 35, c is larger than or equal to 15 and smaller than or equal to 26, d is larger than or equal to 4 and smaller than or equal to 11, e is larger than or equal to 0.8 and smaller than or equal to 2, and a + b + c + d + e = 100. The prepared TiaZrbNbcVdOe alloy has high strength, low density and good corrosion resistance, the alloy density rho is smaller than or equal to 6.5 g / cm < 3 >, the tensile strength reaches 1081 MPa or above, the yield strength reaches 1058 MPa or above, the percentage elongation after fracture exceeds 17.6%, and therefore the series of alloy has good application prospects in electric power fitting materials.

Description

Technical Field

[0001] This invention relates to the field of metallic materials and their preparation technology, and in particular to a Ti-Zr-Nb-V alloy, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In power transmission systems, fittings, as key metal components connecting and assembling various devices, play a vital role in ensuring the safe and stable operation of the power system, guaranteeing efficient power transmission, and supporting grid scalability. With the continuous growth of electricity demand and the upgrading and transformation of transmission lines, more stringent requirements are being placed on the comprehensive performance of fitting materials.

[0004] Currently, commonly used power fitting materials are mainly iron and aluminum. While iron fittings hold an important position in the power industry, they suffer from high density, poor corrosion resistance, and high hysteresis and eddy current losses, limiting their application in scenarios with high requirements for weight, loss, and corrosion resistance. Aluminum fittings, although low in density, have relatively low strength and cannot provide sufficient support and fixation under high stress or heavy load conditions, making them unsuitable for complex operating conditions. Furthermore, during service, fittings are subjected to alternating loads and exposed to outdoor environments, making them susceptible to corrosion from rain, dust, wind, snow, and other natural factors, leading to frequent corrosion failures. Therefore, developing a new fitting material that combines high strength, low density, and good corrosion resistance is urgently needed. Summary of the Invention

[0005] In view of this, the present invention provides a Ti-Zr-Nb-V alloy, its preparation method, and its application. The Ti alloy provided by the present invention... a Zr b Nb c V d O e The alloy has high strength, low density and good corrosion resistance.

[0006] In a first aspect, the present invention provides a Ti-Zr-Nb-V alloy, wherein the alloy contains the chemical elements Ti, Zr, Nb, V and O, and the atomic percentage expression is Ti a Zr b Nb c V d O e, where: 36≤a≤43, 30≤b≤35, 15≤c≤26, 4≤d≤11, 0.8≤e≤2, and a+b+c+d+e=100.

[0007] Preferably, the atomic percentage ratio of Ti to Zr is 1.1:0.9.

[0008] In a second aspect, the present invention also provides a method for preparing the Ti-Zr-Nb-V alloy described in the first aspect, comprising the following steps: Weigh each raw material, perform electric arc melting on each raw material, and after homogenization treatment, obtain the alloy material.

[0009] Preferably, titanium blocks, zirconium blocks, niobium blocks, vanadium blocks and titanium dioxide with a purity of 99.95 wt% or higher are used as raw materials, and each raw material is weighed according to the atomic percentage expressed in the expression.

[0010] Preferably, the prepared raw materials are piled in the furnace in order of melting point from highest to lowest, a vacuum is drawn, a protective atmosphere is introduced, and the furnace is repeatedly melted by electric arc.

[0011] Preferably, the vacuum is evacuated to 3×10 -3 Pa ~ 5.5×10 -3 Pa, then backflush argon gas to 0.05 MPa.

[0012] Preferably, the temperature of each melting is 2100℃ ~ 2300℃, the melting voltage is 10~15V, the melting current is 300~350A, and the melting is repeated 6~8 times.

[0013] Preferably, the homogenization process includes: holding the alloy ingot obtained from smelting at 1100℃~1300℃ for 20~40 minutes, and then cooling it.

[0014] Preferably, the homogenization treatment further includes a plastic processing treatment, firstly, warm rolling at 550℃~600℃ until the thickness is reduced by 40%~60%, then hot rolling at 750℃~850℃ until the thickness is reduced by 80%~90%, and then air cooling. The plastic processing also includes a final heat treatment, which involves holding at 600℃~900℃ for 5~15 minutes and then cooling.

[0015] In a third aspect, the present invention also provides the application of the Ti-Zr-Nb-V alloy described in the first aspect or the Ti-Zr-Nb-V alloy prepared by the preparation method described in the second aspect in power fitting materials.

[0016] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) This invention selects low-density, high-melting-point refractory elements Ti, Zr, Nb, and V as the main components and dops them with non-metallic element O to obtain a low-density refractory multi-principal-element alloy with an alloy density ρ≤6.5g / cm³. This composition design enables the alloy to meet the lightweight requirements of power fittings while also providing a basis for coping with complex service environments. Moreover, by controlling the atomic ratio of O and subsequent thermomechanical processing, an alloy that maintains a single BCC disordered solid solution structure can be obtained. This structure is conducive to the alloy exhibiting excellent comprehensive performance and provides a material basis for meeting the harsh service environments in the field of power fittings.

[0017] (2) The alloy composition obtained by the present invention can be expressed as Ti in terms of atomic percentage. a Zr b Nb c V d O e Where: 36≤a≤43, 30≤b≤35, 15≤c≤26, 4≤d≤11, 0.8≤e≤2, and a+b+c+d+e=100. Through precise control of the atomic ratios of each element and thermomechanical processing, it not only possesses low density but also exhibits extremely excellent comprehensive mechanical properties, with tensile strength exceeding 1081MPa and yield strength exceeding 1058MPa. This allows it to withstand the high stresses experienced by power fittings during operation, ensuring structural stability under complex working conditions. The elongation after fracture exceeds 17.6%, indicating good plasticity, which is beneficial for subsequent processing and deformation, enabling large-size fabrication to meet the production needs of power fittings of different specifications.

[0018] (3) The alloy of the present invention benefits from the unique high entropy effect of multi-principal alloys, which promotes the formation of a single-phase solid solution structure, thereby eliminating the microcouple coupling between the constituent phases. In addition, the synergistic effect of the multi-components enhances the continuity and self-healing ability of the passivation film through the dynamic redistribution of elements during the film formation and regeneration process, and has excellent corrosion resistance. Attached Figure Description

[0019] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0020] Figure 1 Ti provided in Example 1 37 Zr 30 Nb 26 XRD pattern of V5O2 alloy; Figure 2 Ti provided in Example 1 37 Zr 30 Nb 26 Microscopic morphology images of V5O2 alloy; Figure 3 Ti provided in Example 1 37 Zr 30 Nb 26 Room temperature tensile stress-strain curve of V5O2 alloy; Figure 4 Ti provided in Example 1 37 Zr 30 Nb 26 Potentiodynamic polarization curves of V5O2 alloy under simulated seawater environment. Detailed Implementation

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] This invention provides a Ti-Zr-Nb-V alloy, wherein the alloy contains the chemical elements Ti, Zr, Nb, V and O, and the atomic percentage expression is Ti a Zr b Nb c V d O e , where: 36≤a≤43, 30≤b≤35, 15≤c≤26, 4≤d≤11, 0.8≤e≤2, and a+b+c+d+e=100.

[0023] The elements Ti, Zr, Nb, and V themselves possess low density characteristics, resulting in an overall alloy density ρ ≤ 6.5 g / cm³, which meets the requirements for lightweight hardware. The alloy structure formed with Ti, Zr, Nb, and V elements exhibits high strength properties. As strong solid solution strengthening elements, Nb and V cause lattice distortion due to the difference in atomic radii between them and the matrix elements Ti and Zr, increasing the resistance to dislocation movement. Simultaneously, O element, embedded atomically in the BCC lattice interstices, further exacerbates lattice distortion, contributing to an increase in the alloy's yield strength. Ti, Zr, Nb, and V elements readily form a dense oxide film on the alloy surface, enhancing the continuity of the passivation film through multi-component synergistic effects, thus improving the alloy's corrosion resistance.

[0024] In this invention, the atomic percentage ratio of Ti to Zr is 1.1:0.9. This ratio achieves an optimal balance in atomic size. Zr atoms are relatively large, while Ti and Nb atoms are smaller. By slightly increasing the Ti content compared to Zr, the average atomic radius of the alloy can be moderately reduced, mitigating excessive lattice distortion caused by Zr atoms. This fine-tuning helps stabilize the body-centered cubic (BCC) crystal structure, prevents the formation of other harmful phases, and thus optimizes the overall stability and comprehensive mechanical properties of the alloy. This invention also provides a method for preparing the Ti-Zr-Nb-V alloy described above, comprising the following steps: Weigh each raw material, perform electric arc melting on each raw material, and after homogenization treatment, obtain the alloy material.

[0025] In this invention, titanium blocks, zirconium blocks, niobium blocks, vanadium blocks, and titanium dioxide with a purity of 99.95 wt% or higher are used as raw materials, and each raw material is weighed according to the atomic percentages expressed in the formula. High-purity raw materials ensure a purer chemical composition of the alloy and reduce the adverse effects of impurities on the alloy's properties. In this invention, the prepared raw materials are stacked in a furnace in order of decreasing melting point, a vacuum is drawn, a protective atmosphere is introduced, and the furnace is repeatedly melted by electric arc. The protective atmosphere is high-purity argon or helium.

[0026] Arranging materials by melting point ensures that high-melting-point elements melt preferentially and diffuse fully, guaranteeing that all raw materials are fully melted. Vacuuming removes O2 and H2O from the furnace chamber, while introducing a protective atmosphere isolates air and prevents active metals such as Ti, Zr, and V from oxidizing at high temperatures.

[0027] In this invention, a vacuum of 3 × 10⁻⁶ is applied. -3 Pa ~ 5.5×10 -3 Pa, then backflush argon gas to 0.05 MPa.

[0028] In this invention, the temperature of each melting is 2100℃ ~ 2300℃, the melting voltage is 10~15V, the melting current is 300~350A, and the melting is repeated 6~8 times.

[0029] In this invention, the homogenization treatment includes: holding the alloy ingot obtained from smelting at 1100℃~1300℃ for 20~40 minutes, and then cooling it. Holding the alloy ingot at 1100℃~1300℃ for 20~40 minutes allows the atoms in the alloy to diffuse and rearrange. During this process, the internal stress and compositional inhomogeneity of the alloy are eliminated, defects at grain boundaries are reduced, and the crystal structure is more stable, which is beneficial to improving the mechanical properties and corrosion resistance of the alloy.

[0030] In this invention, the homogenization treatment further includes plastic processing, firstly, warm rolling at 550℃~600℃ until the thickness is reduced by 40%~60%, then hot rolling at 750℃~850℃ until the thickness is reduced by 80%~90%, and then air cooling. The plastic processing also includes a final heat treatment, which involves holding at 600℃~900℃ for 5~15 minutes and then cooling.

[0031] During warm rolling, the alloy's grains are elongated and fragmented, generating numerous dislocations. The movement and interaction of these dislocations contribute to improving the alloy's strength and hardness. Furthermore, warm rolling improves the alloy's surface quality and reduces surface defects. During hot rolling, the alloy's grains recrystallize, forming new equiaxed grains. This new equiaxed grain structure helps improve the alloy's toughness and plasticity, while also enhancing its corrosion resistance. Final heat treatment further eliminates internal stresses generated during plastic processing, stabilizing the alloy's microstructure.

[0032] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] Example 1 This embodiment Ti a Zr b Nb c V d O e The atomic percentages of Ti, Zr, Nb, V, and O in the alloy are 37:30:26:5:2, and the specific preparation steps are as follows: Titanium blocks, zirconium blocks, niobium blocks, vanadium blocks, and titanium dioxide particles with a purity of ≥99.95wt% were weighed and proportioned according to atomic percentage.

[0034] When melting alloys using a vacuum electric arc furnace, the raw materials are stacked in a water-cooled copper crucible in order of their melting point from highest to lowest. The titanium block with the lowest melting point is placed at the bottom, followed by zirconium blocks, vanadium blocks, and niobium blocks at the top. Titanium dioxide, being relatively small, is placed at the very bottom to prevent it from being blown away.

[0035] Evacuate to a vacuum level of 3×10 -3At a pressure of Pa, argon gas is backflushed to 0.05 Pa, and melting begins. Before melting the alloy, a Ti alloy ingot is first melted to absorb residual oxygen in the vacuum arc furnace. During alloy melting, the temperature is 2100℃, the voltage is 10V, and the current is 300A. Melting requires flipping the ingot and is performed at least six times, with each pass lasting two minutes, to ensure uniform composition. An alloy ingot is then obtained.

[0036] The alloy ingot obtained from the smelting was held at 1200℃ for 30 minutes, followed by water quenching. Then, it was warm rolled at 550℃ until the thickness was reduced by 50%, then hot rolled at 800℃ until the thickness was reduced by 85%, air-cooled, and finally held at 800℃ for 10 minutes, followed by water quenching to obtain Ti. 37 Zr 30 Nb 26 V5O2 alloy.

[0037] Measurement of room temperature mechanical properties and microstructure characterization of the lightweight alloy provided in Example 1: Figure 1 Ti provided in Example 1 37 Zr 30 Nb 26 The XRD pattern of the V5O2 alloy indicates that the prepared alloy has a single-phase BCC crystal structure.

[0038] Figure 2 Ti provided in Example 1 37 Zr 30 Nb 26 Microscopic morphology images of V5O2 alloy show that Ti 37 Zr 30 Nb 26 The V5O2 alloy has an equiaxed crystal structure with a grain size of approximately 38 μm.

[0039] Figure 3 Ti provided in Example 1 37 Zr 30 Nb 26 The room temperature tensile stress-strain curve of V5O2 alloy shows that the alloy has high yield strength while maintaining good plasticity.

[0040] The corrosion resistance was tested using a three-electrode test method, with the sample as the working electrode, a platinum sheet as the counter electrode, and saturated calomel as the reference electrode. Figure 4 Ti provided in Example 1 37 Zr 30 Nb 26 The potentiodynamic polarization curves of V5O2 alloy under simulated seawater environment show that Example 1 has better corrosion resistance than 316L stainless steel.

[0041] Example 2 This embodiment Ti a Zr b Nb c V d O e The atomic percentages of Ti, Zr, Nb, V, and O in the alloy are 38:33:20:7.5:1.5, and the specific preparation steps are as follows: Titanium blocks, zirconium blocks, niobium blocks, vanadium blocks, and titanium dioxide particles with a purity of ≥99.95wt% were weighed and proportioned according to atomic percentage.

[0042] When melting alloys using a vacuum electric arc furnace, the raw materials are stacked in a water-cooled copper crucible in order of their melting point from highest to lowest. The titanium block with the lowest melting point is placed at the bottom, followed by zirconium blocks, vanadium blocks, and niobium blocks at the top. Titanium dioxide, being relatively small, is placed at the very bottom to prevent it from being blown away.

[0043] Evacuate to a vacuum level of 3×10 -3 At a pressure of Pa, argon gas is backflushed to 0.05 Pa, and melting begins. Before melting the alloy, a Ti alloy ingot is first melted to absorb residual oxygen in the vacuum arc furnace. During alloy melting, the temperature is 2200℃, the voltage is 15V, and the current is 330A. Melting requires flipping the ingot and is performed at least six times, with each pass lasting two minutes, to ensure uniform composition. An alloy ingot is then obtained.

[0044] The alloy ingot obtained from the smelting was held at 1300℃ for 35 minutes, followed by water quenching. Then, it was warm rolled at 600℃ until the thickness was reduced by 55%, then hot rolled at 750℃ until the thickness was reduced by 80%, air-cooled, and finally held at 600℃ for 15 minutes, followed by water quenching to obtain Ti. 38 Zr 33 Nb 20 V 7.5 O 1.5 alloy.

[0045] Example 3 This embodiment Ti a Zr b Nb c V d O e The atomic percentages of Ti, Zr, Nb, V, and O in the alloy are 42:34:15:8:1, and the specific preparation steps are as follows: Titanium blocks, zirconium blocks, niobium blocks, vanadium blocks, and titanium dioxide particles with a purity of ≥99.95wt% were weighed and proportioned according to atomic percentage.

[0046] When melting alloys using a vacuum electric arc furnace, the raw materials are stacked in a water-cooled copper crucible in order of their melting point from highest to lowest. The titanium block with the lowest melting point is placed at the bottom, followed by zirconium blocks, vanadium blocks, and niobium blocks at the top. Titanium dioxide, being relatively small, is placed at the very bottom to prevent it from being blown away.

[0047] Evacuate to a vacuum level of 3×10 -3 At a pressure of Pa, argon gas is backflushed to 0.05 Pa, and melting begins. Before melting the alloy, a Ti alloy ingot is first melted to absorb residual oxygen in the vacuum arc furnace. During alloy melting, the temperature is 2100℃, the voltage is 10V, and the current is 300A. Melting requires flipping the ingot and is performed at least six times, with each pass lasting two minutes, to ensure uniform composition. An alloy ingot is then obtained.

[0048] The alloy ingot obtained from the smelting was held at 1100℃ for 40 minutes, followed by water quenching. Then, it was warm rolled at 570℃ until the thickness was reduced by 45%, then hot rolled at 770℃ until the thickness was reduced by 90%, air-cooled, and finally held at 650℃ for 10 minutes, followed by water quenching to obtain Ti. 42 Zr 34 Nb 15 V8O1 alloy.

[0049] Example 4 This embodiment Ti a Zr b Nb c V d O e The atomic percentages of Ti, Zr, Nb, V, and O in the alloy are 36:32:22.2:8:1.8, and the specific preparation steps are as follows: Titanium blocks, zirconium blocks, niobium blocks, vanadium blocks, and titanium dioxide particles with a purity of ≥99.95wt% were weighed and proportioned according to atomic percentage.

[0050] When melting alloys using a vacuum electric arc furnace, the raw materials are stacked in a water-cooled copper crucible in order of their melting point from highest to lowest. The titanium block with the lowest melting point is placed at the bottom, followed by zirconium blocks, vanadium blocks, and niobium blocks at the top. Titanium dioxide, being relatively small, is placed at the very bottom to prevent it from being blown away.

[0051] Evacuate to a vacuum level of 3×10 -3 At a pressure of Pa, argon gas is backflushed to 0.05 Pa, and melting begins. Before melting the alloy, a Ti alloy ingot is first melted to absorb residual oxygen in the vacuum arc furnace. During alloy melting, the temperature is 2300℃, the voltage is 13V, and the current is 300A. Melting requires flipping the ingot and is performed at least seven times, with each melt lasting two minutes, to ensure uniform composition. An alloy ingot is then obtained.

[0052] The alloy ingot obtained from the smelting was held at 1200℃ for 25 minutes, followed by water quenching. Then, it was warm rolled at 570℃ until the thickness was reduced by 60%, then hot rolled at 850℃ until the thickness was reduced by 85%, air-cooled, and finally held at 700℃ for 10 minutes, followed by water quenching to obtain Ti. 36 Zr 32 Nb 22.2 V8O 1.8 alloy.

[0053] Comparative Example 1 The difference between this comparative example and Example 1 is that no titanium dioxide particles are added in this comparative example, while the rest is the same as in Example 1.

[0054] Comparative Example 2 The difference between this comparative example and Example 1 is that no vanadium block is added in this comparative example, while the rest is the same as in Example 1.

[0055] Comparative Example 3 The difference between this comparative example and Example 1 is that the atomic percentages of Ti, Zr, Nb, V, and O in this comparative example are 50:20:17:11:2, while the other aspects are the same as in Example 1.

[0056] Comparative Example 4 The difference between this comparative example and Example 1 is that the atomic percentages of Ti, Zr, Nb, V, and O in this comparative example are 45:40:5:3:7, while the other aspects are the same as in Example 1.

[0057] Comparative Example 5 The difference between this comparative example and Example 1 is that the atomic percentages of Ti, Zr, Nb, V, and O in this comparative example are 25:25:35:10:5, while the other aspects are the same as in Example 1.

[0058] All the above samples were tested for mechanical properties under the same conditions according to GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test at room temperature". The experimental results of each sample are shown in Table 1.

[0059] Table 1 Mechanical Properties

[0060] As can be seen from Table 1, the alloy of the present invention has excellent comprehensive mechanical properties. The tensile strength of the alloy reaches more than 1081 MPa, the yield strength of the alloy reaches more than 1058 MPa, and the elongation after fracture exceeds 17.6%.

[0061] In Comparative Examples 1 and 2, changing the elemental composition of the alloy significantly reduced both its tensile strength and yield strength. In Comparative Examples 3, 4, and 5, changing the atomic percentage of each element in the alloy significantly reduced the properties of each phase. Therefore, by using the preferred high-entropy alloy composition and atomic percentage of this invention, the tensile strength, yield strength, and elongation after fracture properties can be coordinated to achieve optimal results.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A Ti-Zr-Nb-V alloy, characterized in that, The alloy contains the chemical elements Ti, Zr, Nb, V, and O, with the atomic percentage expression being Ti. a Zr b Nb c V d O e , where: 36≤a≤43, 30≤b≤35, 15≤c≤26, 4≤d≤11, 0.8≤e≤2, and a+b+c+d+e=100.

2. The Ti-Zr-Nb-V alloy as described in claim 1, characterized in that, The atomic percentage ratio of Ti to Zr is 1.1:0.

9.

3. A method for preparing a Ti-Zr-Nb-V alloy as described in any one of claims 1-2, characterized in that, Includes the following steps: Weigh each raw material, perform electric arc melting on each raw material, and after homogenization treatment, obtain the alloy material.

4. The preparation method according to claim 3, characterized in that, Titanium blocks, zirconium blocks, niobium blocks, vanadium blocks, and titanium dioxide with a purity of 99.95 wt% or higher were used as raw materials, and each raw material was weighed according to the atomic percentage expressed in the formula.

5. The preparation method according to claim 3, characterized in that, The prepared raw materials are piled in the furnace in order of their melting point from highest to lowest. A vacuum is drawn, a protective atmosphere is introduced, and the furnace is repeatedly melted by electric arc.

6. The preparation method according to claim 5, characterized in that, Vacuum up to 3×10 -3 Pa ~ 5.5×10 -3 Pa, then backflush argon gas to 0.05 MPa.

7. The preparation method according to claim 5, characterized in that, The temperature for each melting is 2100℃ ~ 2300℃, the voltage for melting is 10~15V, the current for melting is 300~350A, and the melting is repeated 6~8 times.

8. The preparation method according to claim 3, characterized in that, The homogenization process includes: holding the alloy ingot obtained from smelting at 1100℃~1300℃ for 20~40 minutes, and then cooling it.

9. The preparation method according to claim 3, characterized in that, The homogenization process also includes plastic processing, firstly, warm rolling at 550℃~600℃ until the thickness is reduced by 40%~60%, then hot rolling at 750℃~850℃ until the thickness is reduced by 80%~90%, and then air cooling. The plastic processing also includes a final heat treatment, which involves holding at 600℃~900℃ for 5~15 minutes and then cooling.

10. The application of a Ti-Zr-Nb-V alloy as described in any one of claims 1-2 or a Ti-Zr-Nb-V alloy prepared by the preparation method described in any one of claims 3-8 in power fitting materials.

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