superhard alloy materials

Abstract

A cemented carbide body for neutron shielding and a method for producing the same, characterized in that the cemented carbide body contains WC, Fe, and Cr, the Cr being present in an amount of about 1% by mass to about 150% by mass relative to the Fe content, and the cemented carbide body contains WC grains, cementite grains, and dissolved Cr, W, and C in an Fe-based binder matrix material.

Description

Technical Field

[0001] The present disclosure generally relates to cemented carbide materials and blocks containing the same.

Background Art

[0002] In a fusion reactor for nuclear power generation that is currently under intensive development, a protective material against intensive neutron irradiation caused by a fusion process in an extremely high-temperature plasma is required. As a result, high-energy neutrons emitted from the plasma must be slowed (moderated) and captured (absorbed) by the wall of the containment vessel surrounding the plasma. The most suitable material for this is known to be tungsten carbide (WC). However, it is impossible to produce a 100% dense block for a reactor wall from pure tungsten carbide without a metal binder. Furthermore, it is inevitable that the wall material has pores.

[0003] Traditionally, cobalt (Co)-based binders have been used in the manufacture of cemented carbides. However, according to MR Gilbert, T. Eade et al (Waste implications from minor impurities in European DEMO materials. Nuclear Fusion, April 2019, DOI: 10.1088 / 1741-4326 / ab154e), the use of conventional WC-Co cemented carbides required for neutron shielding is problematic because cobalt remains radioactive for extended periods. According to the same document, iron is a remarkably superior binder material in terms of the lifetime of its radioactive isotopes, making WC-Fe cemented carbides preferable for manufacturing the blocks that form the reactor walls required for neutron shielding. However, as is well known (see, for example, B. Uhrenius, H. Pastor, E. Pauty, On the composition of Fe-Ni-Co-WC-based cemented carbides, Int. J Refractory Met Hard Mater. 15(1997)139-149), the two-phase region of the iron-based binder and cemented carbide at 1000°C, i.e., the region where only the carbide phase and the binder phase coexist in equilibrium, is extremely narrow (on the order of less than 0.01 mass%), more than 10 times lower than that of conventional WC-Co cemented carbides. This presents significant difficulties in the manufacture of cemented carbides with iron as the binder. This is because even a slight deviation between the carbon content in the initial WC-Fe classified powder and the carbon content in the sintering furnace atmosphere can lead to the formation of the η phase or free carbon, which are extremely brittle. For this reason, WC-Fe cemented carbides are not manufactured in the cemented carbide industry. This is because it is virtually impossible to manufacture cemented carbide without inclusions of η-phase or free carbon, which make the cemented carbide extremely brittle and unacceptable for the production and brazing of the aforementioned fusion reactor wall blocks. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The main objective of this invention is to overcome the above-mentioned difficulties. [Means for solving the problem]

[0005] The object of the present invention is achieved by alloying the binder phase with a chemical element that maintains radioactivity for a relatively short period of time. As described herein, by adding specific amounts of different chemical elements, particularly chromium powder, to WC-Fe classified powder, it is possible to expand the region of the WC-Fe phase diagram in which only the carbide phase, i.e., WC and cementite, and the metal binder, i.e., the Fe-based binder, exist in equilibrium, and it has surprisingly turned out that this ensures the possibility of manufacturing such cemented carbides on a production scale without major technical difficulties. [Modes for carrying out the invention]

[0006] Accordingly, in a first aspect of the present invention, a cemented carbide body for neutron shielding is provided, the cemented carbide body containing, for example, comprising, consisting of, or essentially consisting of WC, Fe, and Cr, wherein the Cr is present in an amount of 6% by mass or less relative to the Fe content, and the microstructure of the cemented carbide body comprises, consisting of, or essentially consisting of, WC grains, cementite grains, and dissolved Cr, W, and C in an Fe-based binder matrix material.

[0007] As one option, the cemented carbide may contain up to 5% by mass of Si, Ti, V, Ge, Ta, Pb and / or Y, or combinations thereof, relative to the iron content.

[0008] As one option, the cemented carbide body contains up to 50% by mass of Mn relative to its Fe content.

[0009] According to a second aspect of the present invention, a cemented carbide body for neutron shielding is provided, the cemented carbide body contains, for example, WC, Fe, and Cr, comprising, consisting of, or essentially comprising these, wherein the Cr is present in an amount of about 1% to about 150% by mass relative to the Fe content, and the cemented carbide body comprises, consisting of, or essentially comprising WC grains, cementite grains, and dissolved Cr, W, and C in an Fe-based binder matrix material.

[0010] As one option, the aforementioned Cr is present in an amount of approximately 1% to 90% by mass relative to the Fe content.

[0011] As one option, the aforementioned Cr is present in an amount of approximately 1% to 10% by mass relative to the Fe content.

[0012] As one option, the aforementioned Cr is present in an amount of approximately 1% to 6% by mass relative to the Fe content.

[0013] As one option, the aforementioned Cr is present in an amount of approximately 5% to 90% by mass relative to the Fe content.

[0014] As one option, the aforementioned Cr is present in an amount of approximately 5% to 10% by mass relative to the Fe content.

[0015] One option is that the Vickers hardness of the cemented carbide body is at least 15 GPa. The Vickers hardness is measured according to ISO 6507-1:2018 (Metallic materials - Vickers hardness test - Part 1: Test method).

[0016] As one option, the Palmqvist fracture toughness of the cemented carbide material is at least 7 MPa·m 1 / 2 Palmqvist fracture toughness is measured according to ISO 28079:2009 (Hardmetals - Palmqvist toughness test).

[0017] As an option, the cemented carbide body contains less than 0.01% by mass of free carbon. The free carbon referred to in this specification means, for example, carbon in the form of graphite and present in the form of an element in the cemented carbide body.

[0018] As an option, the cemented carbide body substantially does not contain free carbon.

[0019] As an option, the cemented carbide body contains less than 0.01% by mass of η-phase.

[0020] As an option, the cemented carbide body substantially does not contain η-phase.

[0021] As an option, the porosity of the cemented carbide body is less than 1%.

[0022] As an option, the porosity of the cemented carbide body is less than 0.1%.

[0023] As an option, the cemented carbide body is completely dense.

[0024] As an option, the cemented carbide body does not contain voids.

[0025] The characterization of porosity, carbon defects and η-phase content is carried out in accordance with ISO 4499-4:2016 (Hardmetals - Metallographic determination of microstructure - Part 4: Characterisation of porosity, carbon defects and eta-phase content).

[0026] As an option, the cemented carbide body further contains up to a maximum of 5% by mass of Si, Ti, V, Ge, Ta, Pb and / or Y, and combinations thereof, relative to the iron content.

[0027] As one option, the cemented carbide body further contains up to 50% by mass of Mn relative to the Fe content.

[0028] According to a third aspect of the present invention, a method for manufacturing a cemented carbide body as described herein is provided, the method comprising the following steps: A process of grinding together powders of tungsten carbide, iron, and chromium-containing materials; A step of pressing the pulverized powder to form a molded body; A step of sintering the molded body in a vacuum at a temperature of 1300°C or less and for a period of at least 15 minutes; and Steps to cool the sintered body Includes.

[0029] As one option, the method further comprises adding Si, Ti, V, Ge, Ta, Pb, Y and / or Mn in the form of carbides, nitrides, carbonitrides or intermetallic compounds, for example, providing a pulverized powder containing Si, Ti, V, Ge, Ta, Pb, Y and / or Mn in the form of carbides, nitrides, carbonitrides or intermetallic compounds during the pulverization stage.

[0030] According to a fourth aspect of the present invention, a method for manufacturing a cemented carbide body is provided herein, the method comprising the following steps: A process of grinding together powders of tungsten carbide, iron, and chromium-containing materials; A step of pressing the pulverized powder to form a molded body; A step of sintering the molded body in a vacuum; and A step of cooling the sintered body, Includes.

[0031] As one option, the sintering is carried out at a temperature of at least 1200°C.

[0032] As one option, the sintering is carried out at a temperature of 1300°C or less and / or for a period of at least 15 minutes.

[0033] As one option, the sintering is carried out at a temperature of no more than 1500°C.

[0034] As one option, the sintering is carried out at a temperature of approximately 1250°C to 1480°C.

[0035] As one option, the sintering is carried out for at least 15 minutes.

[0036] One option is that the chromium-containing material is chromium carbide or chromium nitride, or includes both.

[0037] One option is that the chromium carbide is Cr3C2.

[0038] As one option, the method further comprises adding Si, Ti, V, Ge, Ta, Pb, Y and / or Mn in the form of carbides, nitrides, carbonitrides or intermetallic compounds, for example, providing a pulverized powder containing Si, Ti, V, Ge, Ta, Pb, Y and / or Mn in the form of carbides, nitrides, carbonitrides or intermetallic compounds during the pulverization stage.

[0039] According to a fifth aspect of the present invention, a block for forming the wall of a nuclear fusion reactor is provided, the block being made of a cemented carbide body as described herein.

[0040] According to a sixth aspect of the present invention, the use of the cemented carbide body described herein in a nuclear fusion reactor is provided. [Brief explanation of the drawing]

[0041] Non-limiting examples illustrating this disclosure will be described with reference to the accompanying drawings: [Figure 1] Figure 1 is an optical microscope image of a cemented carbide body prepared according to Example 1 after etching with Murakami reagent. [Figure 2] Figure 2 is an optical microscope image of a cemented carbide body prepared according to Example 1 after etching with Nital reagent. [Figure 3] Figure 3 is an optical microscope image of a cemented carbide body prepared according to Example 2 after etching with Murakami reagent. [Figure 4] Figure 4 is an optical microscope image of a cemented carbide body prepared according to Example 2 after etching with Nital reagent. [Figure 5] Figure 5 is an optical microscope image of a cemented carbide body prepared according to Example 3 after etching with Murakami reagent. [Figure 6] Figure 6 is an optical microscope image of a cemented carbide body prepared according to Example 3 after etching with Nital reagent. [Figure 7] Figure 7 shows an optical microscope image of a cemented carbide body prepared according to Example 4 after etching with Murakami reagent. [Figure 8] Figure 8 is an optical microscope image of a cemented carbide body prepared according to Example 4 after etching with Nital reagent. [Figure 9] Figure 9 is an optical microscope image of a cemented carbide body prepared according to Example 5 after etching with Murakami reagent. [Figure 10] Figure 10 is an optical microscope image of a cemented carbide body prepared according to Example 5 after etching with Nital reagent. [Figure 11] Figure 11 shows a high-resolution scanning electron microscope image of a cemented carbide body prepared according to Example 5, without etching. [Figure 12] Figure 12 shows a high-resolution scanning electron microscope image of a cemented carbide body prepared according to Comparative Example 1, without etching. [Examples]

[0042] A series of experiments were conducted to determine the optimal range of chromium content. The composition of the lab batches of starting materials is shown in Table 1.

[0043] [Table 1]

[0044] (Example 1) A lab batch of WC-Fe powder (10 kg) was prepared by grinding 500 g of Fe, 30 g of Cr3C2 powder, and 9470 g of WC powder together with 180 g of paraffin wax in 30 kg of WC-Co balls in hexane. The average particle size of the WC powder was approximately 6 μm. The average particle size of the Fe powder was approximately 3 μm, and the average particle size of the Cr3C2 powder was approximately 2 μm. These components were ground together in a ball mill for 30 hours. The ETC (Equivalent Total Carbon) value of this mixture was approximately equal to 5.93 mass%.

[0045] After grinding, the resulting slurry was dried at approximately 90°C, then sieved to obtain classified powder suitable for pressing in a mold. A cylindrical sample with a diameter of 20 mm and a height of 10 mm was pressed from this classified powder and sintered in a Sinter-HIP furnace at 1280°C for 75 minutes (45 minutes in vacuum + 30 minutes sintering under an Ar pressure of 40 Bar).

[0046] As a result of sintering, a completely dense sample was obtained that did not contain η-phase or free carbon inclusions. The microstructure of one such sample after etching with a different reagent is shown in Figures 1 and 2. As seen in Figure 1, the sample etched with Murakami's reagent did not contain η-phase, and as seen in Figure 2, the microstructure contained some cementite, which appeared as white or light gray inclusions after etching with Nital's reagent. It was found that no other carbide phases other than WC and cementite were present in the microstructure, indicating that the added amount of chromium carbide was completely dissolved in the binder phase during liquid-phase sintering. The Vickers hardness of the sample was approximately 15.5 GPa, and the Palm-Qvist fracture toughness was approximately 9 MPa·m 1 / 2It was found that this combination of hardness and fracture toughness is similar to that of conventional WC-Co cemented carbide. See, for example, Roebuck B, Gee MG, Morrell R. Hardmetals - microstructural design, testing and property maps. In: Kneringer G, Roedhammer P, Wildner H, editors. Proceedings of the 15th International Plansee Seminar, Vol. 4. Reutte; 2001. p. 245-66.

[0047] Subsequently, trace amounts (i.e., small amounts) of classified powder were mixed with varying amounts of tungsten metal powder and carbon black, with an average particle size of approximately 0.5 μm, such that the ETC value steadily decreased to 5.8 mass% on one side and gradually increased to 6.1 mass% on the other side, at intervals equal to 0.02 mass%C. Samples obtained from the mixture of classified powders thus were pressed and sintered under the above conditions. A cross-section was then prepared, and the presence of the η phase and free carbon was examined. As a result, it was confirmed that the carbon content range in which the η phase and free carbon were not present in the microstructure was approximately 0.14 mass%, similar to that of conventional WC-Co cemented carbide.

[0048] (Example 2) A sample was prepared in the same manner as in Example 1, except that 50 g of chromium carbide powder was added and the amount of WC was reduced accordingly to form a 10 kg batch. As a result of sintering, a completely dense sample was obtained that did not contain η phase or free carbon inclusions. As seen in Figure 3, the sample etched with Murakami reagent did not contain the η phase, and as seen in Figure 4, the microstructure contained some cementite, which appeared as white or light gray inclusions after etching with Nital reagent. It was found that no other carbide phases other than WC and cementite were present in the microstructure, which was confirmed by XRD testing. The Vickers hardness of the sample was approximately 15.7 GPa, and the Palm-Qvist fracture toughness was approximately 8.4 MPa·m 1 / 2 This value was lower than that of Example 1.

[0049] (Example 3) A sample was prepared in the same manner as in Example 1, except that 80 g of chromium carbide powder was added and the amount of WC was reduced accordingly to make a 10 kg batch. As a result of sintering, a completely dense sample was obtained that did not contain η phase or free carbon inclusions. As seen in Figure 5, the sample etched with Murakami reagent did not contain η phase, and as seen in Figure 6, the microstructure contained some cementite, which appeared as white or light gray inclusions after etching with Nital reagent. This sample is a mixed carbide (Cr,Fe) x C y The sample also contained inclusions, which can be seen as dark inclusions in Figure 6 and were confirmed by XRD testing. These mixed carbide inclusions exhibit the dark brown color typical of Cr-Fe mixed carbides. The Vickers hardness of the sample was approximately 15.9 GPa, and the Palm-Qvist fracture toughness was approximately 7.6 MPa·m 1 / 2 The value was lower than that of Examples 1 and 2. This relatively low fracture toughness value is thought to be related to the presence of Cr-Fe mixed carbide inclusions in the microstructure.

[0050] (Example 4) A sample was prepared in the same manner as in Example 1, except that 150 g of chromium carbide powder was added and the amount of WC was reduced accordingly to form a 10 kg batch. As a result of sintering, a completely dense sample was obtained that did not contain η phase or free carbon inclusions. As seen in Figure 7, the sample etched with Murakami reagent did not contain η phase, and as seen in Figure 8, the microstructure contained a lot of cementite, which appeared as white or light gray inclusions after etching with Nital reagent. The Vickers hardness of the sample was approximately 16.5 GPa, and the Palm-Qvist fracture toughness was approximately 7.4 MPa·m 1 / 2 This value was lower than that of Examples 1 and 2. The relatively low fracture toughness is thought to be related to the fact that almost all of the Fe binder has been converted to cementite.

[0051] (Example 5) A sample was prepared in the same manner as in Example 1, except that 500 g of chromium carbide powder was added and the amount of WC was reduced accordingly to form a 10 kg batch. As a result of sintering, a completely dense sample was obtained that did not contain η phase or free carbon inclusions. As seen in Figure 9, the sample etched with Murakami reagent did not contain η phase, and as seen in Figure 10, the microstructure contained a lot of cementite, which appeared as white or light gray inclusions after etching with Nital reagent. Figure 11 shows an HRSEM image of the microstructure, showing that no voids were present. The Vickers hardness of the sample was approximately 16.5 GPa, and the Palm-Qvist fracture toughness was approximately 7.0 MPa·m 1 / 2 This value was lower than that of Examples 1 and 2. Such a low fracture toughness value is thought to be related to the presence of Cr-Fe mixed carbide inclusions in the microstructure. Although the fracture toughness is lower than that of Examples 1 and 2, it is still sufficiently high, so the composition of Example 5 can be used in the manufacture of molded articles for neutron shielding.

[0052] (Comparative Example 1) Samples were prepared in the same manner as in Example 1, except that 1000g of chromium carbide powder was added and the amount of WC was reduced accordingly to form a 10kg batch. As a result of sintering, a highly porous sample was obtained. Due to the extremely high porosity, the density could not be measured by hydrostatic pressure. A fracture surface of one sample is shown in Figure 12. Such porous samples are not suitable for use in the manufacture of molded products for neutron shielding.

[0053] (Comparative Example 2) A sample was prepared in the same manner as in Example 1, except that 5 g of chromium carbide powder was added and the amount of WC was reduced accordingly to form a 10 kg batch. As a result of sintering, a completely dense sample containing η-phase inclusions was obtained. 0.01 mass% of carbon black was added to the mixture, and the sample was sintered in the same manner as in Example 1. As a result, it was shown that free carbon inclusions were present in the microstructure, and the width of the two-phase region of this alloy was equal to or close to zero; in other words, it was impossible to produce a sample without η-phase and free carbon using this amount of chromium. Such a material is not suitable for use in the manufacture of neutron shielding molded articles.

[0054] Although the present invention has been shown and described with particular reference to various embodiments, it will be understood by those skilled in the art that various modifications in form and detail can be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A cemented carbide body for neutron shielding, wherein the cemented carbide body contains WC, Fe, and Cr, with the Cr present in an amount of 1% to 150% by mass relative to the Fe content, and the cemented carbide body contains WC grains, cementite grains, and molten Cr, W, and C in an Fe-based binder matrix material.

2. The cemented carbide body according to claim 1, wherein the Cr is present in an amount of 1% to 90% by mass relative to the Fe content.

3. The cemented carbide body according to claim 1 or 2, wherein the Cr is present in an amount of 1% to 10% by mass relative to the Fe content.

4. The cemented carbide body according to claim 1, wherein the Cr is present in an amount of 1% to 6% by mass relative to the Fe content.

5. The cemented carbide body according to claim 1, wherein the Vickers hardness is at least 15 GPa.

6. Palmqvist fracture toughness of at least 7 MPa·m １／２ The cemented carbide body according to claim 1.

7. The cemented carbide body according to claim 1, wherein the free carbon content is less than 0.01% by mass.

8. The cemented carbide body according to claim 1, wherein the η phase content is less than 0.01% by mass.

9. The cemented carbide body according to claim 1, wherein the porosity of the cemented carbide body is less than 0.1%.

10. The cemented carbide body according to claim 1, further comprising up to 5% by mass of Si, Ti, V, Ge, Ta, Pb and / or Y, and combinations thereof, relative to the iron content.

11. The cemented carbide body according to claim 1, further comprising up to 50% by mass of Mn relative to the Fe content.

12. A method for manufacturing a cemented carbide body according to claim 1, A process of grinding together powders of tungsten carbide, iron, and chromium-containing materials; A step of pressing the pulverized powder to form a molded body; A step of sintering the molded body under vacuum; Cooling process of the sintered body Methods that include...

13. The method according to claim 12, wherein the sintering is carried out at a temperature of at least 1200°C.

14. The method according to claim 12 or 13, wherein the sintering is carried out at a temperature of at most 1500°C.

15. The method according to claim 12, wherein the sintering is carried out at a temperature of 1250°C to 1480°C.

16. The method according to claim 12, wherein the sintering is carried out for at least 15 minutes.

17. The method according to claim 12, wherein the chromium-containing material is chromium carbide or chromium nitride.

18. The aforementioned chromium carbide is Cr ３ C ２ The method according to claim 17.

19. The method according to claim 18, further comprising adding Si, Ti, V, Ge, Ta, Pb, Y and / or Mn in the form of carbides, nitrides, carbonitrides or intermetallic compounds.

20. A block for forming the wall of a nuclear fusion reactor, characterized in that the block includes the cemented carbide body described in claim 1.

21. Use of the cemented carbide body according to claim 1, for use in a nuclear fusion reactor.

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