body

Abstract

The present disclosure provides an assembly for neutron shielding comprising a cemented carbide body which comprises W, Fe, V, Cr and C, wherein the Cr is present in an amount from approximately 1 wt.% to approximately 6 wt.% with respect to the Fe content, and wherein the V is present in an amount from approximately 0.5 wt.% to approximately 2.5 wt.% with respect to the Fe content, a method of making the cemented carbide body, use of the assembly as neutron shielding in a fusion nuclear reactor, and a fusion nuclear reactor comprising the assembly.

Description

[0001] BODY

[0002] FIELD OF THE INVENTION

[0003] This disclosure relates generally to an assembly for neutron shielding comprising a cemented carbide body and the use of the assembly as neutron shielding in fusion nuclear reactors.

[0004] BACKGROUND

[0005] Fusion nuclear reactors for fusion power plants, which are presently under intensive development, need materials for protection against intensive neutron irradiation caused by the nuclear fusion processes in an extremely high-temperature plasma. The resulting high-energy neutrons emitted from the plasma must be slowed (moderated) and captured (absorbed) in the walls of the containment vessel surrounding the plasma. The most suitable material for this is known to be tungsten carbide (WC). Nevertheless, it is impossible to produce 100% dense blocks for the reactor walls from pure tungsten carbide not containing any metallic binder. Furthermore, any porosity in the wall material must avoided.

[0006] Conventionally, cobalt (Co) based binders are employed for the fabrication of cemented carbides, however, the employment of conventional WC-Co cemented carbides for neutron shielding is problematic as cobalt remains radioactive for a long time after exposure. Iron is known to be a significantly better binder material with respect to life of its radioactive isotopes than cobalt, and therefore WC-Fe cemented carbides are preferred for the fabrication of the blocks forming the reactor walls needed for neutron shielding. However, it is well-known that the two-phase region, i.e. the region in which only the carbide phase, namely WC, and binder phase coexist in the equilibrium, for cemented carbides with iron-based binders at 1000°C is very narrow (of the order of 0.01 wt.% or less), which is more than 10 times lower in comparison to that of conventional WC-Co cemented carbides. This causes significant difficulties in the production of cemented carbide with iron binders, since very insignificant deviations in the carbon content in the initial WC-Fe graded powder and in the atmosphere of sintering furnaces lead to the formation of either q-phase or free carbon, which result in deteriorated mechanical properties. Because of this, WC-Fe cemented carbides are not commonly fabricated in the cemented carbide industry, as it is hardly possible to produce them without inclusions of q-phase, free carbon, and / or mixed carbide phases, which make them very brittle and unacceptable for fabricating and brazing the abovementioned blocks for the fusion nuclear reactor walls.

[0007] It is a major objective of the invention to overcome the difficulty mentioned above.

[0008] SUMMARY

[0009] In a first aspect of the invention, there is provided an assembly for neutron shielding comprising a cemented carbide body comprising W, Fe, V, Cr and C, wherein the Cr is present in an amount from approximately 1 wt.% to approximately 6 wt.% with respect to the Fe content, and wherein the is present in an amount from approximately 0.5 wt.% to approximately 2.5 wt.% with respect to the Fe content.

[0010] As an option, the Cr is present in an amount from approximately 2 wt.% to approximately 6 wt.% with respect to the Fe content, for example in an amount of from approximately 3 wt.% to approximately 6 wt.% with respect to the Fe content, for example in an amount of from approximately 4 wt.% to approximately 6 wt.% with respect to the Fe content, for example in an amount of from approximately 5 wt.% to approximately 6 wt.% with respect to the Fe content.

[0011] As an option, the is present in an amount of from approximately 0.5 wt.% to 2 wt.% with respect to the Fe content, for example from approximately 1 wt.% to approximately 2 wt.% with respect to the Fe content, for example from approximately 1.5 wt.% to approximately 2 wt.% with respect to the Fe content.

[0012] As an option, the cemented carbide body comprises one or more throughholes each of which is configured to receive a cooling tube. As an option, the assembly further comprises one or more cooling tubes inserted through the one or more throughholes.

[0013] As an option, the cooling tube is formed of steel.

[0014] As an option, the cemented carbide body is a block for forming a wall of a fusion nuclear reactor.

[0015] As an option, the cemented carbide body consists of or consists essentially of W, Fe, V, Cr and C and inevitable impurities.

[0016] As an option, the cemented carbide body is substantially free of Co.

[0017] As an option, the cemented carbide body is substantially free of Ni.

[0018] As an option, the cemented carbide body is substantially free of Ni and Co.

[0019] As an option, the cemented carbide body is substantially free of free C. By free C (i.e. free carbon) herein it is meant carbon in the cemented carbide body that is present in elemental form, for example in the form of graphite.

[0020] As an option, the cemented carbide body comprises less than 0.01 wt.% free carbon.

[0021] As an option, substantially all the C present in the cemented carbide body is in the form of C dissolved in the binder, WC, and FesC. FesC is also known as cementite.

[0022] As an option, substantially all the C present in the cemented carbide body is in the form of C dissolved in the binder and WC.

[0023] As an option, the cemented carbide body is substantially free of q-phase.

[0024] As an option, the cemented carbide body comprises less than 0.01 wt.% q-phase. As an option, the cemented carbide body is substantially free of carbide phases other than WC and FesC. As an option, the cemented carbide body is substantially free of carbide phases other than WC and cementite. As an option, the cemented carbide body is substantially free of carbide phases other than WC.

[0025] As an option, the porosity of the cemented carbide body is less than 0.1%.

[0026] As an option, the cemented carbide body is fully dense.

[0027] As an option, the cemented carbide body is free of porosity.

[0028] Characterization of porosity, carbon defects and q-phase content is performed according to ISO 4499-4:2016 (Hardmetals — Metallographic determination of microstructure — Part 4: Characterisation of porosity, carbon defects and eta-phase content).

[0029] As an option, the cemented carbide body has a Vickers Hardness of at least 15 GPa. Vickers Hardness is measured according to ISO 6507-1 :2018 (Metallic materials — Vickers hardness test — Part 1 : Test method).

[0030] As an option, the cemented carbide body has a Palmquist fracture toughness of at least 9 MPa m’ / 2. Palmquist fracture toughness is measured according to ISO 28079:2009 (Hardmetals — Palmqvist toughness test).

[0031] As an option, the Equivalent Total Carbon (ETC) value with respect to WC of the cemented carbide body is from approximately 6.2 wt.% to approximately 6.8 wt.%, for example from approximately 6.3 wt.% to approximately 6.8 wt.%, for example from approximately 6.2 wt.% to approximately 6.5 wt.%.

[0032] As an option, the Equivalent Total Carbon (ETC) value with respect to WC of the cemented carbide body is from approximately 6.2 wt.% to approximately 6.8 wt.%, for example from approximately 6.3 wt.% to approximately 6.8 wt.%, for example from approximately 6.2 wt.% to approximately 6.5 wt.%. As an option, the Equivalent Total Carbon (ETC) value with respect to WC of the cemented carbide body is from approximately 5.8 wt.% to approximately 6.8 wt.%, for example from approximately 5.9 wt.% to approximately 6.5 wt.%, for example from approximately 5.9 wt.% to approximately 6.4 wt.%, for example from approximately 5.9 wt.% to approximately 6.1 wt.%.

[0033] The equivalent total carbon (ETC) in a mixture is the content of carbon in the mixture, the content being in excess of the carbon included in WC, expressed as a proportion of carbon in the whole mixture.

[0034] As an option, the cemented carbide body consists or consists essentially of WC grains, a Fe-based binder matrix material with dissolved Cr, W, and C, and unavoidable impurities.

[0035] As an option, the cemented carbide body consists or consists essentially of WC grains, Fe3C grains, a Fe-based binder matrix material with dissolved Cr, W, and C, and unavoidable impurities.

[0036] As an option, the cemented carbide body consists or consists essentially of WC grains, cementite grains, a Fe-based binder matrix material with dissolved Cr, W, and C, and unavoidable impurities.

[0037] As an option, the cemented carbide body consists or consists essentially of WC grains, a Fe-based binder matrix material with dissolved Cr, W, V, C and N, and unavoidable impurities.

[0038] As an option, the cemented carbide body consists or consists essentially of WC grains, Fe3C grains, a Fe-based binder matrix material with dissolved Cr, W, V, C and N, and unavoidable impurities.

[0039] As an option, the cemented carbide body consists or consists essentially of WC grains, cementite grains, a Fe-based binder matrix material with dissolved Cr, W, V, C and N, and unavoidable impurities. As an option, the cemented carbide body consists or consists essentially of WC grains, a Fe-based binder matrix material with dissolved Cr, W, V, and N, and unavoidable impurities.

[0040] As an option, the cemented carbide body consists or consists essentially of WC grains, FesC grains, a Fe-based binder matrix material with dissolved Cr, W, V, and N, and unavoidable impurities.

[0041] As an option, the cemented carbide body consists or consists essentially of WC grains, cementite grains, a Fe-based binder matrix material with dissolved Cr, W, V, and N, and unavoidable impurities.

[0042] As an option, the cemented carbide body comprises from approximately 1 wt.% to approximately 10 wt.% Fe.

[0043] As an option, the cemented carbide body comprises from approximately 1 wt.% to approximately 7 wt.% Fe.

[0044] As an option, the cemented carbide body comprises from approximately 90 wt.% to approximately 98 wt.% WC, for example from approximately 75 wt.% to approximately 95 wt.% WC, for example from approximately 80 wt.% to approximately 95 wt.% WC, for example from approximately 85 wt.% to approximately 95 wt.% WC, for example from approximately 90 wt.% to approximately 95 wt.% WC.

[0045] As an option, the cemented carbide body consists of from 1 wt.% to 10 wt.% Fe, from 0.01 wt.% to 0.6 wt.% Cr, from 0.005 wt.% to 0.25 wt.% V, from 90 wt.% to 98 wt.% WC, remainder C and inevitable impurities.

[0046] As an option, the cemented carbide body consists of from 1 wt.% to 7 wt.% Fe, from 0.01 wt.% to 0.42 wt.% Cr, from 0.005 wt.% to 0.175 wt.% V, from 90 wt.% to 98 wt.% WC, remainder C and inevitable impurities. As an option, the cemented carbide body consists of from 1 wt.% to 10 wt.% Fe, from 0.01 wt.% to 0.6 wt.% Cr, from 0.005 wt.% to 0.25 wt.% V, from 90 wt.% to 98 wt.% WC, remainder N and inevitable impurities.

[0047] As an option, the cemented carbide body consists of from 1 wt.% to 7 wt.% Fe, from 0.01 wt.% to 0.42 wt.% Cr, from 0.005 wt.% to 0.175 wt.% V, from 90 wt.% to 98 wt.% WC, remainder N and inevitable impurities.

[0048] As an option, the cemented carbide body consists of from 1 wt.% to 10 wt.% Fe, from 0.01 wt.% to 0.6 wt.% Cr, from 0.005 wt.% to 0.25 wt.% V, from 90 wt.% to 98 wt.% WC, remainder N and / or C and inevitable impurities.

[0049] As an option, the cemented carbide body consists of from 1 wt.% to 7 wt.% Fe, from 0.01 wt.% to 0.42 wt.% Cr, from 0.005 wt.% to 0.175 wt.% V, from 90 wt.% to 98 wt.% WC, remainder N and / or C and inevitable impurities.

[0050] As used herein, the assembly for neutron shielding may refer to the cemented carbide body alone, or it may refer to the combination of the cemented carbide body with the above-mentioned cooling tubes or any other desired components.

[0051] According to a second aspect of the invention, there is provided a method of making the cemented carbide body or an assembly as described herein, the method comprising: milling together powders of tungsten carbide, iron, a chromium containing material and a vanadium containing material; pressing the milled powders to form a green body; sintering the green body to form a sintered body; and cooling the sintered body.

[0052] As an option, the method further comprises pre-sintering the green body at a temperature of from approximately 600°C to approximately 1100°C for a duration of from approximately 5 minutes to approximately 360 minutes. As an option, the pre-sintering is performed under vacuum.

[0053] As an option, the method further comprises mechanical treatment of the pre-sintered green body by turning, milling and / or boring to obtain a green body comprising one or more throughholes each of which is configured to receive a cooling tube.

[0054] As an option, the sintering is at a temperature of from approximately 1250°C to approximately 1480°C and for a duration of at least 15 minutes.

[0055] As an option, the sintering is performed for a duration of at least 15 minutes, or at least 30 minutes, or at least 45 minutes, or at least 60 minutes, or at least 75 minutes, or at least 90 minutes, or at least 120 minutes, or at least 150 minutes, or at least 180 minutes, or at least 210 minutes, or at least 240 minutes, or at least 270 minutes, or at least 300 minutes, or at least 330 minutes.

[0056] As an option, the sintering is performed for a duration of no more than 360 minutes, or no more than 330 minutes, or no more than 300 minutes, or no more than 270 minutes, or no more than 240 minutes, or no more than 210 minutes, or no more than 180 minutes, or no more than 150 minutes, or no more than 120 minutes, or no more than 90 minutes, or no more than 75 minutes, or no more than 60 minutes, or no more than 45 minutes, or no more than 30 minutes.

[0057] As an option, the sintering is performed for from approximately 15 minutes to approximately 360 minutes, for example from approximately 15 minutes to approximately 300 minutes, for example from approximately 30 minutes to approximately 240 minutes, for example from approximately 45 minutes to approximately 180 minutes, for example from approximately 60 minutes to approximately 120 minutes, for example from approximately 75 minutes to approximately 90 minutes.

[0058] As an option, the sintering is performed in a vacuum.

[0059] As an option, the sintering is performed in an inert atmosphere, for example in an argon atmosphere. As an option, cooling the sintered body is performed in an argon atmosphere.

[0060] As an option, the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately O.rc / min to approximately 3°C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0061] As an option, the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1oC / min to approximately 2°C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0062] As an option, the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1oC / min to approximately 1 °C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0063] As an option, the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1 °C / min to approximately 1 ,0°C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0064] As an option, the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1 °C / min to approximately 0.8°C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0065] As an option, the chromium containing material is chromium is Cr3C2.

[0066] As an option, the chromium containing material is CrN.

[0067] As an option, the vanadium containing compound is VC.

[0068] As an option, the vanadium containing compound is VN.

[0069] According to a third aspect of the invention, there is provided a use of the assembly as defined herein as neutron shielding in a fusion nuclear reactor. According to a fourth aspect of the invention, there is provided a use of two or more assemblies as defined herein as neutron shielding in a fusion nuclear reactor.

[0070] According to a fifth aspect of the invention, there is provided a use of a plurality of assemblies as defined herein as neutron shielding in a fusion nuclear reactor.

[0071] According to a sixth aspect of the invention, there is provided a fusion nuclear reactor comprising the assembly as described herein.

[0072] As an option, the fusion nuclear reactor comprises at least two assemblies as defined herein.

[0073] As an option, the fusion nuclear reactor comprises a plurality of assemblies as described herein.

[0074] BRIEF DESCRIPTION OF THE DRAWINGS

[0075] A non-limiting example to illustrate the present disclosure is described with reference to the accompanying drawings, in which:

[0076] Figure 1 is a schematic representation of an assembly for neutron shielding according to an embodiment of the invention;

[0077] Figure 2 is a schematic representation of an assembly for neutron shielding according to an embodiment of the invention which comprises a cooling tube;

[0078] Figure 3 is a flow diagram showing exemplary steps to make a cemented carbide body according to an embodiment of the invention;

[0079] Figure 4 is a flow diagram showing exemplary steps to make a cemented carbide body according to another embodiment of the invention; Figure 5 is a light microscopy image obtained at a magnification of x 1000 of the cemented carbide body made in accordance with Example 1 after etching in the Murakami reagent;

[0080] Figure 6 is a light microscopy image obtained at a magnification of x 1000 of the cemented carbide body made in accordance with Example 1 after etching in the Nital reagent;

[0081] Figure 7 is a light microscopy image obtained at a magnification of x 1000 of the cemented carbide body made in accordance with Comparative Example 1 after etching in the Murakami reagent;

[0082] Figure 8 is a light microscopy image obtained at a magnification of x 1000 of the cemented carbide body made in accordance with Comparative Example 1 after etching in the Nital reagent;

[0083] Figure 9 is a light microscopy image obtained at a magnification of x 1000 of the cemented carbide body made in accordance with Comparative Example 2 after etching in the Nital reagent; and

[0084] Figure 10 is a light microscopy image obtained at a magnification of x 1000 of the cemented carbide body made in accordance with Comparative Example 2 after etching in the Nital reagent.

[0085] DETAILED DESCRIPTION

[0086] The objective of the present invention is achieved by alloying the binder phase with chemical elements that remain radioactive for a relatively short time. It has been surprisingly found out that additions of particular amounts (with respect to the Fe content) of powders of chromium and vanadium containing materials to WC-Fe graded powders as described herein allows broadening of the region of W-C-Fe phase diagram in which only WC and cementite carbide phases and a metallic binder, i.e. Fe- based binder, are present in the equilibrium thus ensuring the possibility of fabricating such cemented carbides on a production scale without significant technological difficulties. This facilitates the production of Co-free cemented tungsten carbides with high hardness and high fracture toughness, ideal for use in neutron shielding applications, such as in nuclear fusion reactors.

[0087] An assembly for neutron shielding in the form of a block 1 is represented schematically in Figure 1. Block 1 comprises a cemented carbide body. In this particular embodiment, the block 1 further comprises a throughhole 2 configured to receive a cooling tube and is thus particularly suited for use in the wall of a nuclear fusion reactor. However, the throughhole 2 is entirely optional, and the exact shape or configuration of the block can be adapted depending on the intended application.

[0088] A cooling tube 3, which may be formed of steel, for example, can be inserted through the throughhole 2 to provide the assembly for neutron shielding as depicted in Figure 2. The size of the cooling tube 3 can be adapted to the particular application in which it is intended to be used.

[0089] In another embodiment (not shown), each block 1 may comprise more than one throughhole 2. For example, each block 1 may comprise two, three, four, five, six, seven, eight, nine or ten throughholes and a corresponding number of cooling tubes may be inserted therethrough to form the assembly for neutron shielding.

[0090] In some embodiments, the composition of the cemented carbide body is homogeneous through its thickness, while in other embodiments, the composition of the cemented carbide body varies through the thickness of the cemented carbide body. In some embodiments, a plasma-facing side of the cemented carbide body comprises a lower proportion of a neutron absorbing material than a non-plasma facing side of the cemented carbide body.

[0091] The cemented carbide body which forms block 1 can be formed using the method outlined in Figure 3, which has the following steps: 51. Mill together powders of tungsten carbide, iron, a chromium containing material and a vanadium containing material.

[0092] Milling can be performed by any standard method. For example, the milling step may be performed by attrition milling using an attritor or ball milling using a ball mill, e.g. ball milling using tungsten carbide milling balls. The milling is typically a wet milling process, i.e. in which the powder is dispersed in a solvent and which produces a slurry comprising the milled powders. Milling is typically performed in an organic solvent to form a slurry of the milled powders in said solvent. The organic solvent may be selected from the group consisting of hexane, ethanol, toluene, acetone and mixtures thereof. An organic wax may be dispersed or dissolved the solvent, typically a paraffin wax. The slurry is then dried to form a graded powder mixture. Drying may be followed by granulation. For example, spray-granulation of the slurry may be performed to form granules of the powder mixture for pressing to form the green body.

[0093] 52. Press the milled powders to form a green body.

[0094] The graded powder mixture is then pressed to form a green body. The pressing may be, for example, cold isostatic pressing. In some embodiments, different grades of powder can be placed in different parts of the press so as to form a green body with a varied composition across its thickness.

[0095] 53. Sinter the green body to form a sintered body.

[0096] After pressing, the green body is then sintered to form a sintered cemented carbide body. Sintering may be performed either under vacuum or under a protective atmosphere, such as argon. Alternatively, a first sintering step may be performed under vacuum, followed by a second sintering step performed under an inert, for example argon, atmosphere.

[0097] S4. Cool the sintered body.

[0098] The sintered body is then cooled from the sintering temperature to room temperature. Another method which may be used to form the cemented carbide body of the invention is shown in Figure 4. This method comprises further and optional steps S2A and S2B.

[0099] S2A. Pre-sinter the green body at a temperature of from approximately 600°C to approximately 1100°C for a duration of from approximately 5 minutes to approximately 360 minutes.

[0100] The pre-sintering may be performed under vacuum.

[0101] S2B. Mechanically treat the pre-sintered green body by turning, milling and / or boring to obtain a green body comprising one or more throughholes each of which is configured to receive a cooling tube.

[0102] While step S2B is here specifically directed at forming the block 1 of Figure 1 , the person skilled in the art will understand that any mechanical treatment can be substituted or added here in order to arrive at the requisite shape of cemented carbide body for the intended application.

[0103] As noted in Figure 4, and as may equally be applied to the method of Figure 3, the sintering step S3 is performed at a temperature of from approximately 1250°C to approximately 1480°C and for a duration of at least 15 minutes, for example up to 330 minutes, to form a sintered body.

[0104] As noted in Figure 4, and as may equally be applied to the method of Figure 3, the cooling step S4 may be performed as follows: the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1 °C / min to approximately 1 ,0°C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0105] It has been found that when the sintered body is initially cooled at a relatively slow rate the formation of unwanted free carbon inclusions and eta-phase inclusions (which reduce the fracture toughness and hardness of the material) in the WC-Fe-Cr-V cemented carbide body can be eliminated. However, when initial cooling is rapid, such inclusions are observed. It is therefore advantageous to perform the cooling step S4 as set out in Figure 4.

[0106] A steel tube may be inserted into the or each throughhole of a block of the cemented carbide body by shrink fitting. For example, a steel tube may be cooled in liquid nitrogen in order to shrink it, and then inserted into a throughhole of the cemented carbide body while the steel tube still has a temperature close to that of liquid nitrogen. The resulting assembly is then heated to room temperature, which leads to expansion of the tube and its shrink fitting into the block.

[0107] The cemented carbide body as described herein may be used for neutron shielding. The cemented carbide body may form part of an assembly for neutron shielding as described herein. For example, blocks comprising or consisting of the cemented carbide body as described herein may be used as neutron shielding in a central column for a nuclear fusion reactor. The central column would comprise one or more blocks as described herein and a core of superconducting material, wherein the one or more blocks are arranged to protect the superconducting material from heating and damage by neutrons. When used as neutron shielding in a central column for a nuclear fusion reactor, in particular a tokamak nuclear fusion reactor such as a spherical tokamak nuclear fusion reactor, the blocks may be shaped and / or arranged such that the conductive cemented carbide body forms a solenoid for the initiation of plasma within the reactor, for example as shown in WO 2018 / 197846 A1 , the entire contents of which are hereby incorporated by reference.

[0108] The assembly for neutron shielding or block as described herein may also be used in a divertor for a nuclear fusion reactor.

[0109] EXAMPLES

[0110] Example 1

[0111] A lab batch of a WC-Fe-Cr-V powder (10 kg) was made by milling 500 g Fe + 30 g Cr3C2+ 10 g VC + 20 g carbon black + 50 g paraffin wax and remainder WC powder with a mean grain size of about 6 pm and carbon content of nearly 6.13 wt.%. The Fe powder had a mean grain size of around 3 pm, the Cr3C2powder had a mean grain size of about 2 pm and the VC powder had a mean grain size of about 1 pm. The Cr content was 5.2 wt.% with respect to the Fe content and the V content was 1 .6 wt.% with respect to the Fe content. These components were milled together with 30 kg cemented carbide balls in hexane in a ball-mill for 24 hrs. The ETC (Equivalent Total Carbon) value of this mixture with respect to WC was equal to about 6.4 wt.%.

[0112] After milling, the resultant slurry was dried at a temperature of around 90°C followed by sieving, which provided a graded powder suitable for pressing in dies and wet isostatic pressing. Two types of samples were produced from the graded powder. Small cylindrical samples of 10 mm in diameter and 5 mm in height were pressed from the graded powder by use of mechanical pressing in a die at a pressure of 50 N / mm2. A large cylindrical sample of nearly 100 mm in diameter and 50 mm in height was pressed by use of cold isostatic pressing, also known as ‘wet-bag pressing’, in an elastic mould (rubber bag) sealed with a lid. The assembly obtained in such a way was placed in a cylindrical pressure vessel filled with a pressure water-based liquid, which was closed, and sealed by a threaded lid followed by application of a pressure of 200 MPa built up by a hydraulic pump. After releasing the pressure, the block was removed from the pressure vessel followed by opening the lid and removal of the carbide green block from the elastic mould. The green block was afterwards subjected to pre-sintering in a vacuum at 1000°C for 1 h to achieve a certain strength and toughness of the block needed for its mechanical treatment (turning, milling, and drilling). The block basal surfaces were subjected to milling to obtain parallel and flat surfaces and a throughhole was drilled in the middle of the block.

[0113] The small cylindrical sample and the green pre-sintered and mechanically treated block were sintered in a Sinter-HIP furnace at a temperature of 1420°C for 75 min (45 min vacuum + 30 min sintering under Ar pressure of 40 Bar) followed by cooling down to a temperature of 1100°C at a cooling rate of 0.5 degrees per minute; afterwards, the colling rate was uncontrolled.

[0114] As a result of the sintering process, fully dense samples not containing porosity, inclusions of q-phase and free carbon were obtained. The microstructure of one of such samples after etching in different reagents is shown in Figures 5 and 6. As can be seen in Figure 5, the sample subjected to etching in the Murakami reagent does not show the presence of q-phase, and as can be seen in Figure 6, the microstructure comprises some cementite, which is visible as bright-grey inclusions after etching in the Nital reagent. No other carbide phases except for WC and cementite were found to be present in the microstructure, indicating that the added amounts of chromium carbide and vanadium carbide completely dissolved in the binder phase during liquidphase sintering. The sample was found to have a value of Vickers hardness of about 15 GPa and a value of Palmquist fracture toughness of about 10 MPa m’ / 2. The combination of hardness and fracture toughness is close to that for conventional WC- Co cemented carbides.

[0115] The sintered block was subjected to grinding the basal and side surfaces as well as the throughhole surface. As a result, the diameter of the throughhole became equal to 10 mm + / - 3 pm.

[0116] A steel tube with an external diameter of 10 mm for cooling the cemented carbide block was cleaned in alcohol. The steel tube was immersed in liquid nitrogen for 20 min resulting in its shrinkage. Afterwards, the steel tube at a temperature close to that of liquid nitrogen was inserted into the throughhole of the carbide block followed by its warming up to room temperature, which leads to its expansion and shrink fitting. As a result, a very good contact between the steel tube and the throughhole of the carbide block was achieved. This cemented carbide block fitted with a steel tube is suitable for use in the wall of a nuclear fusion reactor.

[0117] Comparative Example 1

[0118] The small green samples described in Example 1 were sintered in a Sinter-HIP furnace at a temperature of 1420°C for 75 min (45 min vacuum + 30 min sintering under Ar pressure of 40 Bar) followed by cooling down to a temperature of 1100°C together with the furnace at a cooling rate of nearly 5 degrees per minute. As a result, the microstructure of the samples comprised inclusions of free carbon shown in Figure 7 and inclusions of q-phase clearly visible after etching the Murakami reagent as shown in Figure 8. This indicates that the microstructure formation in this case occurred according to the metastable crystallisation mode, which is in some cases typical for cemented carbides of the W-Co-C system or cemented carbides of some other systems, for example the W-C-Co-Re system.

[0119] As expected, the mechanical properties of such cemented carbide samples degraded, so that Vickers hardness was equal to about 14.5 GPa and fracture toughness was nearly 7.5 MPa m’ / 2. This demonstrates the importance of cooling the cemented carbide body to 1100°C at a sufficiently slow rate in order to obtain a cemented carbide body which is free of inclusions of free carbon and q-phase.

[0120] Comparative Example 2

[0121] Cemented carbide samples were produced according to the method detailed in Example 1 , but instead of 30 g Cr3C2+ 10 g VC according to Example 1 , 40 g Cr3C2and 20 g VC were added to the powder mixture. The Cr content was therefore 6.9 wt.% with respect to the Fe content and the V content was 3.2 wt.% with respect to the Fe content. Figures 9 and 10 show the microstructure of the cemented carbide according to Comparative Example 2 after etching in the Murakami reagent and Nital reagent, respectively. Inclusions of a third carbide phase, i.e. in addition to cementite and tungsten carbide, which is a mixed carbide of Fe, Cr, W and V are indicated by arrows in Figure 9. This mixed carbide phase is brittle. The mechanical properties of these cemented carbide samples were inferior to those of Example 1 , in that Vickers hardness was 14.7 GPa and the fracture toughness was 8.5 MPa m’ / 2. This demonstrates the importance of using amounts of V and Cr within the ranges specified above in order to obtain a material with sufficient strength for fabrication of blocks for use in a nuclear fusion reactor.

[0122] While this invention has been particularly shown and described with reference to various embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS1 . An assembly for neutron shielding comprising a cemented carbide body which comprises W, Fe, V, Cr and C, wherein the Cr is present in an amount from approximately 1 wt.% to approximately 6 wt.% with respect to the Fe content, and wherein the is present in an amount from approximately 0.5 wt.% to approximately 2.5 wt.% with respect to the Fe content.

2. The assembly according to claim 1 , wherein the cemented carbide body comprises one or more throughholes each of which is configured to receive a cooling tube.

3. The assembly according to claim 2, further comprising one or more cooling tubes inserted through the one or more throughholes, optionally wherein the cooling tube is formed of steel.

4. The assembly according to any preceding claim, wherein the cemented carbide body is a block for forming a wall of a fusion nuclear reactor.

5. The assembly according to any preceding claim, wherein the cemented carbide body consists of or consists essentially of W, Fe, V, Cr and C and inevitable impurities.

6. The assembly according to any preceding claim, wherein the cemented carbide body is substantially free of Co and / or Ni.

7. The assembly according to any preceding claim, wherein the cemented carbide body is substantially free of free C.

8. The assembly according to any preceding claim, wherein substantially all the C present in the cemented carbide body is in the form of C dissolved in the binder, WC, and Fe3C.

9. The assembly according to any preceding claim, wherein the cemented carbide body is substantially free of q-phase.

10. The assembly according to any preceding claim, wherein the cemented carbide body is substantially free of carbide phases other than WC and Fe3C.

11. The assembly according to any preceding claim, wherein the porosity of the cemented carbide body is less than 0.1 %.

12. The assembly according to any preceding claim, wherein the cemented carbide body has a Vickers Hardness of at least 15 GPa.

13. The assembly according to any preceding claim, wherein the cemented carbide body has a Palmquist fracture toughness of at least 9 MPa m’ / 214. The assembly according to any preceding claim, wherein the cemented carbide body has an Equivalent Total Carbon (ETC) value with respect to WC of the cemented carbide body of from approximately 5.9 wt.% to approximately 6.8 wt.%.

15. The assembly according to any preceding claim, wherein the cemented carbide body consists of WC grains, Fe3C grains, a Fe-based binder matrix material with dissolved Cr, W, V and C, and unavoidable impurities.

16. The assembly according to any preceding claim, wherein the cemented carbide body comprises from approximately 1 wt.% to approximately 10 wt.% Fe.

17. The assembly according to any preceding claim, wherein the cemented carbide body comprises from approximately 90 wt.% to approximately 98 wt.% WC.

18. The assembly according to any preceding claim, wherein the cemented carbide body consists of from 1 wt.% to 10 wt.% Fe, from 0.01 wt.% to 0.6 wt.% Cr, from 0.005 wt.% to 0.25 wt.% V, from 90 wt.% to 98 wt.% WC, remainder N and / or C and inevitable impurities.

19. A method of making the cemented carbide body as defined in any preceding claim, the method comprising:milling together powders of tungsten carbide, iron, a chromium containing material and a vanadium containing material; pressing the milled powders to form a green body; sintering the green body to form a sintered body; and cooling the sintered body.

20. The method according to claim 19, further comprising pre-sintering the green body at a temperature of from approximately 600°C to approximately 1100°C for a duration of approximately 5 minutes to approximately 360 minutes.21 . The method according to claim 20, further comprising mechanical treatment of the pre-sintered green body by turning, milling and / or boring to obtain a green body comprising one or more throughholes each of which is configured to receive a cooling tube.

22. The method according to any one of claims 19 to 21 , wherein the sintering is at a temperature of from approximately 1250°C to approximately 1480°C and for a duration of at least 15 minutes.

23. The method according to any one of claims 19 to 22, wherein the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1 °C / min to approximately 1 °C / min, and then cooling the sintered body to room temperature at an uncontrolled rate.

24. The method according to any one of claims 19 to 23, wherein the chromium containing material is Cr3C2.

25. The method according to any one of claims 19 to 24, wherein the vanadium containing material is VC.

26. The method according to any one of claims 19 to 23, wherein the chromium containing material is CrN and / or the vanadium containing material is VN.

27. Use of the assembly according to any one of claims 1 to 18 as neutron shielding in a fusion nuclear reactor.

28. A fusion nuclear reactor comprising the assembly according to any one of claims 1 to 18.

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