Composite material for switchgear

Abstract

Embodiments of the present disclosure relate to a composite material for a switchgear. Comprising hafnium carbide (HfC) and / or zirconium carbide (ZrC) and a preparation method thereof.

Description

Technical Field

[0001] The present invention relates to the field of materials applicable to low-voltage switchgear. Background Art

[0002] Currently, the silver (Ag)-based materials used in low-voltage switchgear are composite materials of silver with graphite (Ag / C), tungsten W (Ag / W), or tungsten carbide WC (Ag / WC), which are used to provide properties such as arc erosion resistance and weldability. During an arc discharge event, these materials are exposed to high temperatures, resulting in undesirable physical, chemical, and / or compositional changes. In the case of Ag / W and Ag / WC, W and WC oxidize to form WO3. WO3 is a strongly adhesive oxide with low electrical conductivity.

[0003] WO3 has a melting point of 1473 °C and a boiling point of 1700 °C. Since the temperature generated during arc discharge is much higher than this temperature, it causes the evaporation of the oxidation products, resulting in compositional changes near the contact surface. This ultimately adversely affects the performance. A part of the oxide that does not observe its boiling temperature remains firmly adhered to the contact surface. This increases the contact resistance and increases the electrical losses during product operation.

[0004] In addition to forming pure oxides, it is also known that tungsten (W) and tungsten carbide (WC) form non-conductive combined oxides with Ag (silver tungstate Ag2WO4). Compared with oxides and carbides, silver tungstate has a very low melting point (580 - 620 °C). The formation of this tungstate further accelerates material loss and changes the electrical properties. This may adversely affect the characteristics of the devices using such materials. Generally, a material is needed that provides a good balance of welding properties (especially the welding properties of closed contacts and the welding properties during manufacturing operations), low erosion during arc discharge, low arc residence time, low contact resistance after arc discharge, and high arc re-ignition voltage.

[0005] The present invention is based on the discovery that a composite material including hafnium carbide (HfC) and / or zirconium carbide (ZrC) can meet these needs. Summary of the Invention

[0006] The present invention provides a composite material including hafnium carbide (HfC) and / or zirconium carbide (ZrC), the composite material having:

[0007] a) a total carbide content greater than 30 wt.-% relative to the total weight of the composite material, the total carbide content being the sum of tungsten carbide, hafnium carbide, zirconium carbide, tantalum carbide, and chromium carbide, and

[0008] b) a combined amount of hafnium carbide and / or zirconium carbide of 0.1 wt.-% to 40 wt.-% relative to the total carbide content, and

[0009] c) Optionally, a metal component of up to 4.0 wt.-% relative to the total weight of the composite material, the metal component being selected from the group of elements consisting of Ni, Co, Cu, Fe, Cr, Mo and mixtures thereof, and

[0010] d) Optionally, nickel (Ni) of up to 18.0 wt.-% relative to the total weight of the composite material

[0011] or additional nickel, and

[0012] e) The balance, silver (Ag) and unavoidable impurities.

[0013] The present invention also provides that the composite material as herein can be obtained by:

[0014] a) Providing

[0015] aa) Hafnium carbide powder (HfC) and / or zirconium carbide powder (ZrC),

[0016] bb) Silver powder (Ag),

[0017] cc) Optionally, tungsten carbide powder (WC),

[0018] dd) Optionally, a metal component in powder form, the metal component being selected from the group of elements consisting of Ni, Co, Cu, Fe, Cr, Mo and mixtures thereof,

[0019] ee) Optionally, nickel (Ni) or additional nickel;

[0020] b) Mixing all the powders provided in step a) to produce a premix,

[0021] c) Optionally sieving the premix and obtaining a sieved premix,

[0022] d) Compacting the premix or the sieved premix to form a green body,

[0023] e) Subjecting the green body to sintering, wherein the sintering is liquid phase sintering (LPS) in a hydrogen atmosphere in the temperature range of 960 to 1300

[0024] °C, preferably in the temperature range of 960 to 1150 °C;

[0025] f) Optionally, subjecting the sintered premix or the sintered sieved premix to repressing and / or hot isostatic pressing (HIP).

[0026] The present invention also provides a method for providing a composite material comprising hafnium carbide (HfC) and / or zirconium carbide (ZrC), the composite material having:

[0027] a) A total carbide content greater than 30 wt.-% relative to the total weight of the composite material, the total carbide content being the sum of tungsten carbide, hafnium carbide, zirconium carbide, tantalum carbide and chromium carbide, and

[0028] b) A combined amount of hafnium carbide and / or zirconium carbide of 0.1 wt.-% to 40 wt.-% relative to the total carbide content, and

[0029] c) Optionally a metal component of at most 4.0 wt.-% relative to the total weight of the composite material, the metal component being selected from the group of elements consisting of Ni, Co, Cu, Fe, Cr, Mo and mixtures thereof, and

[0030] d) Optionally nickel (Ni) of at most 18.0 wt.-% relative to the total weight of the composite material

[0031] or additional nickel

[0032] e) The balance, the balance being silver (Ag) and unavoidable impurities,

[0033] The method comprises the following steps:

[0034] i) Providing

[0035] aa) Hafnium carbide powder (HfC) and / or zirconium carbide powder (ZrC),

[0036] bb) Optionally silver powder (Ag),

[0037] cc) Optionally tungsten carbide powder (WC),

[0038] dd) Optionally a metal component in powder form, the metal component being selected from the group of elements consisting of Ni, Co, Cu, Fe, Cr, Mo and mixtures thereof,

[0039] ee) Optionally, nickel (Ni) or additional nickel of at most 18 wt.-% relative to the total weight of the composite material,

[0040] ii) Mixing all the powders provided in step i) to produce a premix,

[0041] iii) Optionally screening the premix and obtaining the screened premix,

[0042] iv) Compacting the premix or the screened premix to form a green body,

[0043] v) Combining sintering and silver infiltration of the green body in a temperature range of 960 to 1300 °C, preferably 960 to 1150 °C

[0044] vi) Optionally re-pressing and / or hot isostatic pressing (HIP).

[0045] On the other hand, the present invention provides a switching device comprising a composite material as described herein. On the other hand, the present invention relates to the use of a composite material as described herein for a switching device, preferably a low-voltage switching device.

[0046] All aspects regarding the composite material described below also apply to composite materials obtainable by a specific method and to methods for providing a composite material and a switching device.

[0047] The wording "a composite material comprising hafnium carbide (HfC) and / or zirconium carbide (ZrC), the composite material having" is to be understood as meaning "a composite material comprising hafnium carbide (HfC) and / or zirconium carbide (ZrC), the composite material consisting of...".

[0048] The wording "providing hafnium carbide powder (HfC) and / or zirconium carbide powder (ZrC)" also encompasses providing such a mixture by using blended powders.

[0049] The term "total carbide content is the sum of tungsten carbide, hafnium carbide, zirconium carbide, tantalum carbide and chromium carbide" indicates the total weight of tungsten carbide, hafnium carbide, zirconium carbide, tantalum carbide and chromium carbide. This means that the weights of components such as WC, W2C, WTiC, HfC, ZrC, TaC, Cr2C3 need to be added together.

[0050] The terms amount and content are used synonymously. Percentages are given relative to the composite material unless otherwise stated.

[0051] The introduction of hafnium carbide and / or zirconium carbide surprisingly favors properties that can be used in various applications such as contact tips. The oxide layer formed on the HfC grains causes the grains to break into many smaller grains upon cooling. This exposes new, oxide-free surfaces with minimal change in contact resistance for subsequent operation.

[0052] Without wishing to be bound by theory, it is believed that the melting point (2758 °C) and boiling point (5400 °C) of hafnium oxide (HfO2) significantly reduce material loss and / or compositional changes of the contact material due to evaporation under arc discharge relative to tungsten oxide (WO3, Tm = 1473 °C; Tb = 1700 °C). Surprisingly, unlike silver tungstate (Ag2WO4), no silver-hafnium composite oxide seems to form.

[0053] Better arc erosion resistance provides structural stability to the contact material, which further paves the way for reducing the total size of the contact, thus saving costs.

[0054] Preferably, the total carbide content, as the sum of tungsten carbide, hafnium carbide, zirconium carbide, tantalum carbide and chromium carbide, is in the range of 33.0 wt.-% to 60.0 wt.-%, more preferably 36.0 wt.-% to 55.0 wt.-%, and most preferably 38.0 wt.-% to 45.0 wt.-%, all weight percentages being relative to the total weight of the composite material.

[0055] The composite materials described herein preferably have a conductivity (% IACS at 20 °C) of at least 30.0%, more preferably 35.0%, and most preferably at least 40.0%. The conductivity is mainly affected by the total Ag content, where high Ag (content is closely related to lower carbide content) increases the conductivity.

[0056] In a first embodiment, the density of the composite materials described herein is preferably greater than 96.0% of the theoretical density, more preferably greater than 97.0%, and most preferably greater than 98.0%.

[0057] In a second and even more preferred embodiment, the density of the composite materials described herein is preferably greater than 98.0% of the theoretical density, more preferably greater than 98.5%, and most preferably greater than 99.0%. It has surprisingly been found that for a HfC content of at most 25.0 wt.-%, a density above 90.0% of the theoretical density can be achieved upon sintering without additional pressing or hot isostatic pressing. Additional pressing and / or hot isostatic pressing (HIP) allows for even higher densities, especially for values above 98.0% of the theoretical density.

[0058] In a preferred aspect, the composite materials described herein include a metal component in an amount of at most 2.0 wt.-% relative to the total weight of the composite material, the metal component being selected from the group consisting of Ni, Co, Cu, Fe, Cr, Mo, and mixtures thereof. Further preferably, the metal component is present in an amount of 0.5 - 1.5 wt-%. Independently thereof, the metal component is preferably nickel (Ni).

[0059] It may also include a higher amount of nickel (Ni) (also referred to herein as "additional nickel") of at most 18.0 wt.-% as an additional component. If so, the maximum total amount of nickel is 22.0 wt.-%, which is the sum of the maximum amounts of the metal component (nickel) and "additional nickel". Generally, the maximum total amount of nickel is 20.0 wt.-%, which is the sum of the maximum amounts of the metal component (nickel) and "additional nickel".

[0060] In a preferred embodiment, the total amount of nickel in the composite material is 4.0 to 20.0 wt-%, preferably 6.0 - 14.0 wt-%, and most preferably 7.0 - 12.0 wt-%.

[0061] In yet another preferred aspect, the composite material as described herein comprises tungsten carbide (WC) in an amount of at least 32.0 wt.-%, more preferably at least 34 wt.-% and most preferably at least 36 wt.-% relative to the total weight of the composite material. Preferably, the composite material as described herein comprises tungsten carbide (WC) in an amount less than 50.0 wt.-%, more preferably at least 45.0 wt.-% and most preferably at least 43.0 wt.-% relative to the total weight of the composite material.

[0062] Also preferably, the composite material as described herein has one or more of the following characteristics:

[0063] i) A Vickers

[0064] hardness (HV1) greater than 128.0, preferably greater than 135.0 and most preferably greater than 140.0;

[0065] ii) A conductivity ( % IACS at 20 °C) of at least 35.0%, preferably at least 45.0% and most preferably at least 46.0%.

[0066] By increasing the total carbide amount to at least 40.0 wt.-%, a Vickers hardness (HV1) greater than 135.0 can be easily achieved. A higher total carbide amount will further increase the Vickers hardness (HV1). The conductivity is also mainly affected by the amount of total carbide: a lower amount increases the conductivity. A value of 45.0% can be achieved with a total carbide amount of 40.0 wt.-% or lower. The conductivity can be further improved by increasing the sintering temperature during the production of the composite material or by repressing, both of which contribute to obtaining a higher final density.

[0067] When the total carbide amount is in the range of 38.0 to 45.0 wt.-%, a good balance between the Vickers hardness (HV1) and the conductivity ( % IACS at 20 °C) can be achieved. When the composite material is sintered at a relatively high temperature, especially 1100 - 1250 °C, the balance between the Vickers hardness (HV1) and the conductivity ( % IACS at 20 °C) is further improved.

[0068] In a preferred aspect, the present invention provides a composite material which can be obtained by the following steps:

[0069] a) Providing

[0070] aa) Hafnium carbide powder (HfC) and / or zirconium carbide powder (ZrC),

[0071] bb) Silver powder (Ag),

[0072] cc) Optionally tungsten carbide powder (WC),

[0073] dd) A metal component, optionally in powder form, selected from the group of elements consisting of Ni, Co, Cu, Fe, Cr, Mo, and mixtures thereof,

[0074] ee) Optionally nickel, or additional nickel

[0075] b) Mix all the powders provided in step a) to produce a premix,

[0076] c) Optionally screen the premix and obtain the screened premix,

[0077] d) Compact the premix or the screened premix to form a green body,

[0078] e) Subject the green body to sintering, wherein the sintering is liquid phase sintering (LPS) in a hydrogen atmosphere at a temperature in the range of 960 to 1300

[0079] °C, preferably in the range of 960 to 1150 °C.

[0080] f) Optionally, subject the sintered premix or the sintered screened premix to repressing and / or hot isostatic pressing (HIP).

[0081] The composite material obtained in this way is characterized by a unique combination of high theoretical density, excellent hardness, and acceptable electrical conductivity.

[0082] All the preferred aspects described herein regarding the composite material also apply to the composite material obtainable by the above method.

[0083] The present invention also provides a method for providing a composite material including hafnium carbide (HfC) and / or zirconium carbide (ZrC) as described herein. This method is particularly suitable for medium to full-scale preparation of composite materials. In this method, combined sintering and silver infiltration of the green body occur. This combined sintering and silver infiltration method is known in the art and is generally denoted as liquid phase sintering plus silver infiltration. The temperature of liquid phase sintering plus silver infiltration will typically be in the range of 960 °C to 1200 °C, preferably in the range of 960 to 1150 °C. Temperatures significantly higher than 1200 °C are not desirable because cracking of the composite material with internal silver agglomeration occurs. In addition, when a temperature significantly higher than 1200 °C and a low pressure such as below 100 mbar are applied, volatilization and loss of silver occur. All the above aspects regarding the composite material also apply to this method.

[0084] The composite material described herein can be particularly used in switching devices. The present invention thus provides a switching device including the composite material as described herein.

[0085] Furthermore, the present invention relates to the use of the composite materials described herein for switching devices, in particular for low-voltage switching devices. Detailed Embodiments

[0086] A first particularly preferred embodiment is a composite material comprising hafnium carbide (HfC) and / or zirconium carbide (ZrC), the composite material having

[0087] a) a total carbide content of 38.0 to 45.0 wt.-% relative to the total weight of the composite material, the total carbide content being the sum of tungsten carbide, hafnium carbide, zirconium carbide, tantalum carbide and chromium carbide, and

[0088] b) a combined amount of hafnium carbide and / or zirconium carbide of 4.0 wt.-% to 20.0 wt.-% relative to the total carbide content, and

[0089] c) a metal component of 0.5 to 1.5 wt.-% relative to the total weight of the composite material, the metal component being selected from the group of elements consisting of Ni, Co, Cu, Fe, Cr, Mo and mixtures thereof, and preferably the metal component being only Ni, and

[0090] d) the balance, the balance being silver (Ag) and unavoidable impurities.

[0091] Preferably, zirconium carbide is absent in this embodiment.

[0092] A second particularly preferred embodiment is a composite material comprising hafnium carbide (HfC) and / or zirconium carbide (ZrC), the composite material having

[0093] a) a total carbide content of 38.0 to 45.0 wt.-% relative to the total weight of the composite material, the total carbide content being the sum of tungsten carbide, hafnium carbide, zirconium carbide, tantalum carbide and chromium carbide, and

[0094] b) a combined amount of hafnium carbide and / or zirconium carbide of 4.0 wt.-% to 20.0 wt.-% relative to the total carbide content, and

[0095] c) a metal component of at most 4.0 wt.-% relative to the total weight of the composite material, the metal component being selected from the group of elements consisting of Co, Cu, Fe, Cr, Mo and mixtures thereof, and

[0096] d) nickel (Ni) in an amount of 4.0 to 20 wt.-% relative to the total weight of the composite material,

[0097] e) the balance, the balance being silver (Ag) and unavoidable impurities.

[0098] Preferably, zirconium carbide is absent in this embodiment.

[0099] The third particularly preferred embodiment is a composite material comprising hafnium carbide (HfC) and / or zirconium carbide (ZrC), the composite material having

[0100] a) a total carbide content greater than 45.0 to 55.0 wt.-% relative to the total weight of the composite material, the total carbide content being the sum of tungsten carbide, hafnium carbide, zirconium carbide, tantalum carbide and chromium carbide, and

[0101] b) a combined amount of hafnium carbide and / or zirconium carbide of 3.0 wt.-% to 25.0 wt.-% relative to the total carbide content, and

[0102] c) a metal component of 0.5 to 1.5 wt.-% relative to the total weight of the composite material, the metal component being selected from the group of elements consisting of Ni, Co, Cu, Fe, Cr, Mo and mixtures thereof, and preferably the metal component being only Ni, and

[0103] d) the balance, the balance being silver (Ag) and unavoidable impurities.

[0104] Preferably, zirconium carbide is absent in this embodiment.

[0105] The fourth particularly preferred embodiment is a composite material comprising hafnium carbide (HfC) and / or zirconium carbide (ZrC), the composite material having

[0106] a) a total carbide content greater than 45.0 to 55.0 wt.-% relative to the total weight of the composite material, the total carbide content being the sum of tungsten carbide, hafnium carbide, zirconium carbide, tantalum carbide and chromium carbide, and

[0107] b) a combined amount of hafnium carbide and / or zirconium carbide of 3.0 wt.-% to 25.0 wt.-% relative to the total carbide content

[0108] c) a metal component of at most 4.0 wt.-% relative to the total weight of the composite material, the metal component being selected from the group of elements consisting of Co, Cu, Fe, Cr, Mo and mixtures thereof, and preferably the metal component being only Ni, and

[0109] d) nickel (Ni) in an amount of 4.0 to 20 wt.-% relative to the total weight of the composite material

[0110] e) the balance, the balance being silver (Ag) and unavoidable impurities.

[0111] Preferably, zirconium carbide is absent in this embodiment.

[0112] These particularly preferred embodiments can be combined with any of the above aspects as appropriately as possible.

[0113] Experimental section

[0114] Raw materials

[0115] Use commercially available raw materials:

[0116] Ag (d50 < 5 μm)

[0117] WC (d50 < 3 μm)

[0118] Ni (d50 < 5 μm)

[0119] HfC (d50 < 4 μm)

[0120] General procedure

[0121] Prepare reference samples using Ag and WC without adding HfC.

[0122] Prepare some samples without adding any nickel. Most of the samples for measurement include added nickel.

[0123] Weigh the powder components of different formulations in the required proportions.

[0124] Use a mixer with ZrO2 grinding media to mix the powder for 64 hours. After mixing, sieve the powder through a 100-μm sieve to remove large agglomerates. Prepare green compacts by die pressing at 300 MPa. Prepare 8-mm-diameter samples for sintering studies and 26-mm-diameter samples for property measurements.

[0125] Sinter the green compacts in a hydrogen furnace under an H2 gas atmosphere. The solid-state sintering method (SSS), liquid-phase sintering method (LPS), and Ag infiltration liquid-phase sintering method (LPS+I) were studied. The sintering temperature ranged from 950 to 1300 °C. Most of the sintering tests were carried out at a pressure of 20 mbar in the furnace, and several tests were carried out at a pressure of 900 mbar, as shown below. For additional evaluation, for some samples, the Ni content was varied from 1 wt.% to 2 wt.% and 5 wt.%.

[0126] Measurement methods

[0127] Density

[0128] Measure the density of the green compact using a geometric method. Measure the sintered density using the Archimedes technique with ethanol as the displacement medium.

[0129] Microstructure

[0130] Evaluate the microstructure of the samples according to standard metallographic preparation techniques. Perform optical microscopy on several samples, and at the same time, analyze the selected samples using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) to evaluate the elemental microstructure and distribution.

[0131] Vickers hardness (HV1)

[0132] The Vickers hardness (HV1) of the selected composite materials was measured on a polished cross-section. At least 10 measurements were made for each sample.

[0133] Electrical conductivity

[0134] The electrical conductivity was measured on flat samples with a diameter of 26 mm. Three measurements were made on each of the top and bottom surfaces of each sample (a total of 6 measurements per sample).

[0135] Wetting was evaluated by varying the Ni content

[0136] In the first experimental series, Ag64.8HfC34.2Ni1, Ag63.8HfC34.2Ni2 and Ag60.8HfC34.2Ni5 were evaluated. Ag65.8HfC34.2 was used for comparison purposes. Sintering tests were carried out at 1100 °C, 1200 °C and 1300 °C. The sintering experiments were carried out under hydrogen at 20 mbar. Both liquid phase sintering and liquid phase sintering plus silver infiltration were evaluated. Cross-section analysis of the samples indicated the formation of cracks in comparison to Ag65.8HfC34.2 and Ag60.8HfC34.2Ni5. As a result, up to 2 wt.-% of nickel is fully acceptable and beneficial in terms of process selection.

[0137] Evaluation of silver mass loss versus sintering temperature

[0138] Sintering plus silver infiltration using silver foil was evaluated (temperatures 1000, 1050, 1100, 1200, 1300 °C; pressures all under 20 mbar hydrogen). As a result, silver loss up to 1200 °C is acceptable, while excessive silver loss occurs at 1300 °C. It can also be seen that silver loss is lower under 900 mbar hydrogen.

[0139] Experimental run A

[0140] For all formulations of experimental run A, the total carbide content was chosen to be 34.2 wt-%. The HfC content varied from 5% to 100% as a percentage of the total carbide. The Ni content was kept constant at 1 wt.-%, and the compositions studied are listed in Table 1 below. Table 1 also shows the changes in green density. It can be seen that for all compositions except AgWC17.1HfC17.1Ni1(50), the green density > 70% of the theoretical density. Sintering was carried out for 30 minutes at 1000 °C under 20 mbar hydrogen. A number of runs were subjected to sintering for 30 min at 1050 °C under 20 mbar hydrogen and some runs were subjected to sintering for 30 min at 1100 °C and 1200 °C under 20 mbar hydrogen.

[0141]

[0142] *The numbers in parentheses (such as 5, 10, …, 100) indicate the percentage of HfC content in the total carbide.

[0143] **Archimedes density after sintering at 1000 °C for 30 minutes under 20 mbar hydrogen.

[0144] ***Archimedes density after sintering at 1050 °C for 30 minutes under 20 mbar hydrogen

[0145] ****Archimedes density after sintering at 1100 °C for 30 minutes under 20 mbar hydrogen

[0146] In additional experiments, the sintering temperature was further modified to 1150 and 1200 °C. Similar results were obtained.

[0147] For HfC contents of 50 and 75 wt.-% HfC (relative to the total weight of the carbide), silver dewetting problems were observed.

[0148] A uniform microstructure was observed for all samples.

[0149] Experimental run B

[0150] For all formulations of experimental run B, the total carbide content was chosen to be 40.0 wt-%. Due to the observed silver dewetting (in experimental run A), compositions with 50 and 75 wt-% HfC (relative to the total weight of the carbide) were not evaluated.

[0151]

[0152] *The numbers in parentheses (such as 0, 1, 2, 5…, 25) indicate the percentage of HfC content in the total carbide.

[0153] **Archimedes density after sintering at 1000 °C for 30 minutes under 20 mbar hydrogen.

[0154] ***Archimedes density after sintering at 1100 °C for 30 minutes under 20 mbar hydrogen.

[0155] ****Archimedes density after sintering at 1150 °C for 30 minutes under 20 mbar hydrogen.

[0156] When the HfC content (as % of total carbide) was 25%, metal layer presence on the surface was observed for all samples indicating Ag dewetting. No dewetting was observed for any other samples. Samples with 2% HfC content (as % of total carbide) showed formation of several nodules (rough spots) on their surface.

[0157] After sintering at 1100 °C, Ag dewetting was observed when the HfC content (as % of total carbide) was 20% or higher. Similar results were obtained by sintering at 1150 °C.

[0158] Additional experiments were carried out by sintering at 1200 °C. Again, no Ag dewetting was observed for samples containing 20 wt.-% HfC (as percentage of total carbide). A trend of decreasing density was confirmed.

[0159] It can be concluded that a sintering temperature of about 1100 °C results in the highest density.

[0160] The microstructure of all samples appeared homogeneous. Localized Ag dewetting was observed for compositions with 20% and 25% HfC content (as % of total carbide).

[0161] Experimental run C

[0162] For all formulations of experimental run C, the total carbide content was chosen as 50.0 wt-%.

[0163]

[0164] *Numbers in parentheses (such as 5, 10, …, 100) indicate the percentage of HfC content in the total carbide.

[0165] **Archimedes density after sintering at 1000 °C for 30 min under 20 mbar hydrogen.

[0166] ***Archimedes density after sintering at 1100 °C for 30 min under 20 mbar hydrogen.

[0167] ****Archimedes density after sintering at 1150 °C for 30 min under 20 mbar hydrogen.

[0168] No dewetting was observed for any other samples.

[0169] Additional experiments were carried out by sintering at 1200 °C. The trend could be confirmed.

[0170] The microstructure of all samples appeared homogeneous.

[0171] Representative samples from Runs A1 to C5 were also evaluated using SEM / EDS to further verify the microstructure uniformity and the distribution of the composite components.

[0172] Hardness evaluation

[0173] Experiment Carbide content / wt.-% Sintering temperature / °C Hardness (HV1) Run A 34.2 1000 113 34.2 1100 113 34.2 1150 116 34.2 1200 114 Run B 40.0 1000 137 40.0 1100 137 40.0 1150 139 40.0 1200 135 Run C 50.0 1000 181 50.0 1100 180 50.0 1150 177 50.0 1200 171

[0174] The hardness of the composite with a total carbide content of 34.2 wt.-% was very low (average 112 - 114 HV1), independent of the sintering temperature. The hardness of the composite with a total carbide content of 40 wt-% was higher (average 134 - 140 HV1).

[0175] The highest hardness (average 170 - 180 HV1) was obtained for samples with a total carbide content of 50 wt-%. Composites with a 50 wt.-% total carbide content showed significantly higher hardness values than those of the widely used AgWC60 / 40 samples. In summary, the final hardness is affected by the total carbide content and the sintering temperature.

[0176] In yet another additional experimental series, the influence of the HfC content (as a percentage of the total carbide) was evaluated. It was demonstrated that the HfC content had essentially no effect on the final hardness of composites with 34.2 or 40 wt.-% total carbide. In composites with 50 wt.-% carbide, a higher HfC content (as % of the total carbide) led to moderately lower hardness.

[0177] Conductivity evaluation

[0178]

[0179]

[0180] Oxidation evaluation

[0181] The oxidation behavior of AgWC34HfC6Ni1 (Run B, Example B6) was evaluated in an air furnace at 600 °C for 12 hours. Ag59WC40Ni1 and Ag60WC40 were used as reference materials.

[0182]

[0183] Surprisingly, an oxidation improvement was observed relative to the comparative materials.

[0184] Although the present invention has been described in detail and described in the foregoing description, such description is considered to be exemplary rather than restrictive. The present invention is not limited to the disclosed embodiments. In view of the foregoing description, it will be apparent to those skilled in the art that various modifications can be made within the scope of the present invention as defined by the claims.

Claims

1. A composite material comprising hafnium carbide HfC and / or zirconium carbide ZrC, the composite material having: a) a total carbide content of greater than 30 wt.-%, relative to the total weight of the composite material, the total carbide content being the sum of tungsten-containing carbides, hafnium carbide, zirconium carbide, tantalum carbide and chromium carbide, and b) a combined amount of hafnium carbide and / or zirconium carbide of 0.1 wt.-% to 40 wt.-%, relative to the total carbide content, and c) optionally up to 4.0 wt.-% of a metal component, relative to the total weight of the composite material, said metal component being chosen from the group of elements consisting of Ni, Co, Cu, Fe, Cr, Mo and mixtures thereof, and d) optionally up to 18.0 wt.-% nickel or further nickel, relative to said total weight of said composite material, and e) The balance, which is silver (Ag) and unavoidable impurities.

2. The composite material of claim 1, having an electrical conductivity (% IACS at 20°C) of at least 30.0%.

3. The composite material according to claim 1 or 2, having a density greater than 96.0%, preferably greater than 97.0%, most preferably greater than 98.0% of the theoretical density.

4. A composite material according to any one of the preceding claims, wherein the metal component is present. The composite material according to claim 4 , wherein the metal component is nickel (Ni).

6. A composite material according to any one of the preceding claims, wherein the total amount of nickel is i) up to 2.0 wt-%, preferably 0.5 to 1.5 wt-%, all values ​​relative to said total weight of said composite material, or ii) 4.00 wt-% to 20.0 wt-%, preferably 6.0 wt-% to 14.0 wt-%, and most preferably 7.0 wt-% to 12.0 wt-%, all values ​​relative to said total weight of said composite material.

7. A composite material according to any of the preceding claims, wherein the total carbide content is in the range of 33.0 wt.-% to 60.0 wt.-%, preferably in the range of 36.0 wt.-% to 55.0 wt.-% and more preferably in the range of 38.0 wt.-% to 45.0 wt.-%, all weight percentages being relative to the total weight of the composite material.

8. The composite material according to any one of the preceding claims, wherein tungsten carbide WC is present, preferably in an amount of at least 32.0 wt.-%, more preferably at least 34 wt.-%, and most preferably at least 36 wt.-%.

9. A composite material according to any one of the preceding claims, having one or more of the following features: i) a Vickers hardness (HV1) greater than 128.0, preferably greater than 135.0, most preferably greater than 140.0; ii) an electrical conductivity (% IACS at 20°C) of at least 35.0%, preferably at least 45.0% and most preferably at least 46.0%.

10. The composite material according to any of the preceding claims, having a total carbide content of 38.0 wt.-% to 45.0 wt.-%, relative to the total weight of the composite material, the total carbide content being the sum of tungsten-containing carbides, hafnium carbides, zirconium carbides, tantalum carbides and chromium carbides.

11. The composite material according to any one of the preceding claims, obtainable by: a) Provide aa) hafnium carbide powder HfC and / or zirconium carbide powder ZrC, bb) Silver powder Ag, cc) optionally tungsten carbide powder WC, dd) a metal component, optionally in powder form, selected from the group consisting of Ni, Co, Cu, Fe, Cr, Mo and mixtures thereof, ee) optionally nickel or further nickel, b) mixing all the powders provided in step a) to produce a premix, c) optionally sieving the premix and obtaining a sieved premix, d) compacting the premix or the sieved premix to form a green body e) subjecting the green body to sintering, wherein the sintering is liquid phase sintering (LPS) in a hydrogen atmosphere at a temperature range of 960° C. to 1300° C., preferably 960° C. to 1150° C.; f) Optionally, the sintered premix or the sintered screened premix is ​​subjected to re-compacting and / or hot isostatic pressing (HIP).

12. A method for providing a composite material comprising hafnium carbide HfC and / or zirconium carbide ZrC, the composite material having: a) a total carbide content of greater than 30 wt.-%, relative to the total weight of the composite material, the total carbide content being the sum of tungsten-containing carbides, hafnium carbides, zirconium carbides, tantalum carbides and chromium carbides, and b) a combined amount of hafnium carbide and / or zirconium carbide of 0.1 wt.-% to 40 wt.-%, relative to the total carbide content, and c) optionally up to 4.0 wt.-% of a metal component, relative to the total weight of the composite material, said metal component being chosen from the group of elements consisting of Ni, Co, Cu, Fe, Cr, Mo and mixtures thereof, and d) optionally up to 18.0 wt.-% nickel or further nickel, relative to the total weight of the composite material, wherein The balance is silver Ag and unavoidable impurities. The method comprises the following steps: i) Provide aa) hafnium carbide powder HfC and / or zirconium carbide powder ZrC, bb) optionally silver powder Ag, cc) optionally tungsten carbide powder WC, dd) a metal component, optionally in powder form, selected from the group consisting of Ni, Co, Cu, Fe, Cr, Mo and mixtures thereof, ii) mixing all the powders provided in step i) to produce a premix, iii) optionally sieving the premix and obtaining the sieved premix, iv) compacting the premix or the sieved premix to form a green body, v) combined sintering and silver infiltration of the green body at a temperature in the range of 960°C to 1200°C, preferably 960°C to 1150°C, and vi) Optional re-compacting and / or hot isostatic pressing (HIP).

13. A switchgear comprising the composite material according to any one of claims 1 to 11.

14. Use of a composite material according to any one of claims 1 to 11 for a switchgear, preferably a low voltage switchgear.

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