Manufacturing process of tungsten carbide parts and material obtained based on SPS sintering of tungsten carbide

Abstract

The invention relates to a material obtained by SPS sintering comprising pure tungsten carbide characterized in that the material: - comprises at least one type of homogeneous tungsten carbide grains, each of the grain types having a predetermined grain microstructure, - is free of binder, - has a toughness of between 8 and 17 MPa-m1 / 2 and / or a hardness of between 1500 and 2700 (Vickers hardness HV). The invention also relates to a method for manufacturing a material based on pure tungsten carbide characterized by the following steps: - Using or grinding a powder having at least one type of tungsten carbide grains until grains having a predetermined grain size and a predetermined form factor are obtained, - Sintering using an SPS sintering method. Abstract figure: Fig. 1

Description

Title of the invention: Method for manufacturing tungsten carbide parts and material obtained based on SPS sintering of tungsten carbide TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the manufacture of tungsten carbide parts by sintering, in particular the manufacture of parts having particular mechanical properties of hardness and toughness. STATE OF THE ART

[0002] A manufacturing method is known from the prior art in which the cobalt material is added to tungsten carbide in order to increase the toughness of a material. Document CN108624772 discloses the mixture of tungsten carbide with, in particular, cobalt and vanadium carbide. The disadvantage of mixtures is that they are relatively expensive.

[0003] It is thus desirable to propose a material having a hardness and toughness equivalent to or greater than those of the state of the art. THE INVENTION

[0004] To this end, and according to a first aspect, the invention proposes a material obtained by SPS sintering comprising pure tungsten carbide characterized in that the material: - comprises at least one type of homogeneous tungsten carbide grains, each of the types of grains having a predetermined grain microstructure, - is free of binder, - has a toughness of between 8 and 17 MPa (the length being a length), and / or a hardness between 1500 and 2700 (Vickers hardness HV).

[0005] The proposed material offers both greater toughness and / or hardness compared to prior art materials, while limiting costs thanks in particular to the absence of mixing material such as cobalt.

[0006] Preferably, the toughness is measured by the method known as the Palmquist method.

[0007] For the above and for the remainder of the description, the following terms are understood to mean:

[0008] - SPS sintering, acronym for “Spark Plasma Sintering”, a sintering process under pressure based on the densification of a powder sample by applying mechanical stress associated with the passage of a pulsed current to heat the sample; for example a sintering method related to hot isostatic pressing but using the Joule effect to heat the pre-compacted powder in a hollow cylindrical crucible between two graphite electrodes under an inert atmosphere or under vacuum, the whole being subjected to a pressure of several megapascals under the action of a hydraulic press. A direct or alternating current of several kiloamperes, pulsed or not, is applied between the electrodes with a voltage of a few volts. ;

[0009] - pure, in particular relating to a tungsten carbide powder, a powder comprising at least 95% tungsten carbide, advantageously at least 96% tungsten carbide, advantageously at least 97% tungsten carbide, advantageously at least 98% tungsten carbide, advantageously at least 99% tungsten carbide, or preferably comprising 99.9% tungsten carbide;

[0010] - binder, any material making it possible to improve densification and / or properties final mechanics giving mechanical cohesion to the final part, for example cobalt material or another sintering agent;

[0011] - grain size, the grain size distribution characterized by the values dlO, d90, d50 in order to quantify the dispersion of this grain size distribution,

[0012] - crystallite size, each grain being able to have crystallites, the size is relating to coherent crystallographic domains and which is measured by techniques such as SEM, TEM, etc.;

[0013] - form factor, the ratio between two characteristic lengths, each length extending in a determined direction, said characteristic lengths having a non-zero angle with respect to each other, for example an angle of 90 degrees;

[0014] - atomization or atomizing, in particular concerning a powder, a method of transformation of a metal ingot into spherical powder by melting and projecting the metal drops under gas flow to make them spherical,

[0015] - spheroidization, or spheroidizing, in particular concerning a powder, a method of transforming an angular ground metal powder by fusion, most often assisted by plasma, to make it spherical.

[0016] Furthermore, toughness means the ability of a material to resist the propagation of a crack. Hardness means the resistance of one material to being marked by another.

[0017] Each grain type has a predetermined grain size, a predetermined crystallite size, and a predetermined shape factor.

[0018] The predetermined grain microstructure may have the following characteristics: - Particle size distribution: d50 being between 0.1 and 100 pm, - Crystallite size: 20 to 1000 nm, - Form factor: between 1 and 5 (spherical to angular, without being cylindrical).

[0019] According to one embodiment, a type of grain has the following characteristics: d50 equal or substantially equal to 1 micrometer and a crystallite size equal to 130 nm plus or minus 30 nm. This combination of values makes it possible to obtain a high toughness / high hardness ratio, for example approximately 2700HV.

[0020] According to another embodiment, a type of grain has the following characteristics: d50 equal or substantially equal to 80 micrometers and a crystallite size equal to 30 nm plus or minus 15 nm. This combination of values makes it possible to obtain an average toughness / average hardness ratio, for example approximately 1800HV.

[0021] One embodiment consists of using a monomodal particle size distribution before grinding of between 0.1 and 100 micrometers (pm).

[0022] According to another embodiment, the powders have a bimodal distribution before grinding with d50 values separated by a decade, typically 0.1pm and Ipm or Ipm and lOpm or lOpm and lOOpm. This bimodal distribution may be separated by 2 decades, typically 0.1 and lOpm or 1 and lOOpm.

[0023] According to yet another embodiment, the distribution is trimodal with d50 separated by a decade, typically O.lpm, Ipm and lOpm. These examples are obviously non-limiting.

[0024] In one embodiment, the powder is used as is, raw from the supplier. For example, this powder may have a d50 value, in particular a grain diameter of less than 100 micrometers, preferably less than 50 micrometers, preferably less than 15 micrometers.

[0025] In a preferred embodiment, the powder is ground in order to refine the size of the crystallites (coherent crystallographic domains) which is different from the particle size distribution. Thus, after grinding, there is a reduction in the size of the crystallites, but not necessarily a reduction in the size of the grains.

[0026] Preferably, the size of the crystallites is between 20 and 1000 nanometers (nm). Preferably, the size of the crystallites is between 20 and 100 nm. Finally, preferably, the size of the crystallites is between 20 and 50 nm. In one embodiment, it is possible to combine several crystallite sizes.

[0027] Preferably, the material comprises at least two types of tungsten carbide grains. Each of the at least two types of grains has characteristics cited above; the at least two types of grains being different from each other.

[0028] Preferably, the material is free of cobalt, niobium carbide, vanadium carbide, titanium carbide, or the like.

[0029] According to a second aspect, the invention provides a part comprising a material, or made of a material, according to one or more of the characteristics of the first aspect. A part is a mechanical part, for example cutting tools for machining.

[0030] According to a third aspect, the invention proposes a method for manufacturing a material or part based on pure tungsten carbide comprising the following steps: - using a powder comprising at least one type of tungsten carbide grains having a predetermined grain size, a predetermined crystallite size and a predetermined form factor, - sinter using an SPS sintering process.

[0031] According to one embodiment, the powder comprising at least one type of tungsten carbide grains is ground until grains having a predetermined grain size, a predetermined crystallite size and a predetermined form factor are obtained.

[0032] Preferably, the powder comprises at least two types of tungsten carbide grains, each type having a predetermined grain size, a predetermined crystallite size and a predetermined form factor.

[0033] According to one embodiment, each type of grain is ground separately. Preferably, each type of tungsten carbide grain is ground separately before mixing them.

[0034] One embodiment consists of grinding the base powder whether mono or multimodal. In this embodiment, the final particle size distribution is refined and refocused or, in the case of multimodal distributions, the elimination of this multiple character. The gap between d10 and d90 is reduced around d50. The particle size distribution is finer around the target d50 value.

[0035] In another embodiment, at least two powders of different characteristics are ground separately in order to generate different particle size and crystallite size distributions and then are mixed in order to design a specific powder making it possible to obtain improved final properties.

[0036] Grinding makes it possible to obtain a powder which will have “final” properties in terms of geometry, form factor, crystallite size. Grinding also makes it possible in certain cases to form active sites on the surface of the powder which promote and improve sintering behavior.

[0037] According to one embodiment, the method further comprises a step of selecting at least one mode of atomization of the powder, or at least one mode of spheroidization of the powder.

[0038] Description of the figure

[0039] [Fig-1] [Fig. 1] represents a graph showing the hardness on the abscissa and the toughness on the ordinate, icons in the shape of a triangle and a circle representing the results of the prior art, areas surrounded by the graph indicating the results obtained thanks to the present invention.

[0040] While the prior art proposes materials having a hardness of between 1400 and 1900 HV and / or a toughness of between 7 and about 12 MPa-ml / 2, the invention makes it possible, in addition to propose new embodiments, to obtain tungsten carbide materials having a higher hardness, in particular up to 2700HV and / or a higher toughness, in particular up to 17 MPa-ml / 2, see for example the DS zones in [Fig.l].

Claims

Claims

1. Material obtained by SPS sintering comprising pure tungsten carbide characterized in that the material: - comprises at least one type of homogeneous tungsten carbide grains, each of the grain types having the following characteristics: particle size distribution: d50 being between 0.1 and 100 pm, crystallite size between 20 and 1000 nm, shape factor between 1 and 5 spherical to angular, without being cylindrical, - is free of binder, - has a toughness between 8 and 17 MPa-ml / 2 and / or a hardness between 1500 and 2700 (Vickers hardness HV).

2. Material according to claim 1, characterized in that it comprises at least two types of tungsten carbide grains.

3. Material according to claim 1, characterized in that it is free of cobalt, niobium carbide, vanadium carbide, titanium carbide.

4. Part comprising a material according to one of the preceding claims.

5. Method for manufacturing a material based on pure tungsten carbide characterized by the following steps: - Use a powder comprising at least one type of tungsten carbide grains having the following characteristics: particle size distribution: d50 being between 0.1 and 100 pm, crystallite size between 20 and 1000 nm, form factor between 1 and 5 spherical to angular, without being cylindrical, - Sinter using an SPS sintering process.

6. Manufacturing method according to the preceding claim, characterized in that the powder comprising at least one type of tungsten carbide grains is ground until grains having a predetermined grain size, a predetermined crystallite size and a predetermined form factor are obtained.

7. A manufacturing method according to claim 5 or 6, characterized in that the powder comprises at least two types of tungsten carbide grains, each type having a predetermined grain size, a predetermined crystallite size and a predetermined form factor.

8. Manufacturing method according to the preceding claim, characterized in that each type of tungsten carbide grains is ground separately before mixing them.

9. Manufacturing method according to one of claims 5 to 8, characterized in that it further comprises a step of selecting at least one method of atomizing the powder, or at least one method of spheroidizing the powder.

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