COMPONENT

TECHNICAL FIELD

The present disclosure relates to a Hot Isostatic Pressing (HIP) process for manufacturing a component of a hard metal powder by using a capsule of zirconium (Zr) or Zr-alloy.

BACKGROUND

Hot isostatic pressing (HIP) is a known method used for preparing solid articles. Components comprising cemented carbides or cermets (hard metal) are usually difficult to machine. Using HIP near-net- shape techniques to manufacture such components is an attractive alternative as the desired object can be obtained almost without any or with very limited machining. The obtained objects will also have a higher material yield than when manufactured by traditional pressing, green- machining, sintering or post- sintering machining.

However, when HIPdng powders of hard metal, due to the high temperatures used in the process, eta-phase will be formed in the interface between the obtained component and the capsule. Eta-phase is a brittle phase and is detrimental to the strength of the component as it may initiate cracks.

The present disclosure is aiming at solving or at least reducing the above-mentioned problems and furthermore, the present disclosure provides an effective and cost efficient method for producing components of hard metal.

SUMMARY OF THE DISCLOSURE

The present disclosure relates to a process of manufacturing a cemented carbide or cermet component by using a HIP process. The cemented carbide powder or cermet powder used in the process is a free flowing dense or semi-dense powder. The obtained components will have enhanced hardness and wear resistance and will also have a fully dense net- or near net shape.

Hence, the present disclosure relates to the following process for manufacturing a cemented carbide or cermet component comprising the following steps: a) providing spherically shaped granules comprising metallic binder and hard constituents with an organic binder;

b) loading the spherically shaped granules in a furnace chamber;

c) heat-treating the spherically shaped granules in the furnace chamber at a sintering temperature to remove the organic binder and to sinter the hard constituents with the metallic binder and thereby forming bonded spherically shaped sintered granules;

d) unloading the bonded spherically shaped sintered granules from the furnace chamber;

e) milling the bonded spherically shaped sintered granules whereby a powder of spherically shaped cermet or cemented carbide is formed; f) providing a form;

g) filling the form with the powder obtained in step e);

h) evacuating air from the form;

i) sealing the form;

j) subjecting the form to Hot Isostatic Pressing (HIP) at a predetermined temperature, a predetermined pressure and for a predetermined time so that the powder is metallurgically bound and consolidated whereby a solid body is formed;

characterized in that the form is made of zirconium or a zirconium alloy,.

The advantage with the process as defined hereinabove or hereinafter is that when zirconium or a zirconium alloy is used as capsule material, a layer comprising zirconium carbide (ZrC) is formed in the contact interface between the capsule and the cemented carbide or cermet. This carbide layer is dense and has almost no cracks and will therefore prevent most of the interdiffusion between the capsule and the powder. Thus, this ZrC layer will limit the loss of carbon from the cemented carbide or the cermet to the capsule material whereby the chemical balance and stability of the cemented carbide or cermet are maintained and thus the degradation of the cemented carbide or cermet is reduced, thereby , this carbide layer (ZrC) provides conditions to avoid formation of low carbon containing carbides such as e.g. M2C, M6C and M12C. Different grades of the Zr (Zirconium) alloys may be used for capsule material, however it is necessary that the grades comprise the amount of zirconium to allow the above-mentioned carbide layer to be formed. Other aspects, advantages and novel features of the disclosure will become apparent from the following detailed description of the disclosure when considered in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 discloses SEM image of the product according to one embodiment obtained after step c). The magnitude of the image is xlOOO: Figure 2 discloses a SEM image of the powder according to one embodiment obtained after step e);

Figure 3 discloses a SEM image of the micro structure in the component according to one embodiment of the present disclosure;

Figure 4 discloses a SEM image of the microstructure at the interface between the obtained component and the capsule according to one embodiment of the present disclosure. DEFINITIONS

The term "cermet" is herein intended to denote a material comprising a ceramic phase, i.e. hard constituents, and a metallic binder phase.

The term "cemented carbide" is herein intended to denote a material comprising a ceramic phase, i.e. hard constituents, which are selected from WC, TiC, TaC, MoC, , TiN, Ti(C,N) NbC, Mo ₂ C or a mixture thereof and a metallic binder phase, comprising Co, Ni, Fe, Cr, Mo, V or a mixture thereof. The amount of metallic binder is in the range of from 5 to 30 weight , such as of from 10 to 25 weight , such as of from 15 to 20 weight , such as 20 to 25 weight .

The term "granule" refers to the agglomerated state of a mixture that is produced by e.g. spray drying. After sintering, the granules are named "sintered granules" The term "sintering" is a generic term for a process wherein heating under controlled atmosphere is conducted in order to minimize the surface of a particulate system, which mostly is associated with generation of bonds between neighboring particles or granules resulting in the fusion of neighboring particles and minimizing of inter- particle voids.

The term "green body" refers to a body comprising granules that are bonded by organic binder.

The term "solidus" refers to a certain temperature that when being exceeded leads to the inception of liquid phase formation.

The term "about" as used herein is intended to mean +/- 10% of the numerical value. DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to a process for manufacturing a cemented carbide component or cermet comprising the following steps:

a) providing spherically shaped granules comprising metallic binder and hard constituents with an organic binder;

b) loading the spherically shaped granules in a furnace chamber;

c) heat-treating spherically shaped granules in the furnace chamber at a sintering temperature to remove the organic binder and to sinter the hard constituents with the metallic binder and thereby forming bonded spherically shaped sintered granules;

d) unloading the bonded spherically shaped sintered granules from the furnace chamber;

e) milling the bonded spherically shaped sintered granules whereby a powder of spherically shaped cermet or cemented carbide is formed; f) providing a form;

g) filling the form with the powder obtained in step e);

h) evacuating air from the form;

i) sealing the form;

j) subjecting the form to Hot Isostatic Pressing (HIP) at a predetermined temperature, a predetermined pressure and for a predetermined time so that the powder is metallurgically bound and consolidated whereby a solid body is formed;

characterized in that

the form is made of zirconium or a zirconium alloy.

The forming of spherically shaped granules comprising metal, hard constituents and organic binder may be performed by spray drying. The advantage of using spray drying is that the granules will not be exposed to pre-pressing and breaking. The organic binder may for example be PEG (polyethylene glycol). The metallic binder is selected from Cobalt (Co), Nickel (Ni), Iron (Fe), Chromium (Cr), Molybdenium (Mo), Vanadium (V) or a mixture thereof. The hard constituents are selected from WC, TiC, TiN, Ti(C,N), TaC, MoC, Mo ₂ C, NbC or a mixture thereof. According to one embodiment of the present process as defined hereinabove or hereinafter, the metallic binder is selected from Ni, Fe or Co. The step of providing the granules with a spherical shape is important since the subsequent heating process will ideally make the granules to shrink but preserve their original spherical shape. According to one embodiment of the present process as defined hereinabove or hereinafter, the hard constituents and the metallic binder may be in the form of particles which do not contain any organic binder, thus also other methods than spray drying may be used for obtaining the particles.

The step of heat-treating the mixture of spherically shaped granules in the furnace chamber at a sintering temperature is performed in order to remove the organic binder from the spherically shaped granules and to sinter the hard constituents with the metallic binder in each spherically shaped granule whereby the granules will be bound together by the metallic binder and form a friable material. At an initial stage of the sintering, typically even before the sintering temperature has been reached, typically at temperatures of from 200 °C to 700 °C, such as from 200 to 500 °C, the organic binder will evaporate and leave the spherically shaped granules by degassing. As an alternative, hydrogen may also be introduced during the initial step of sintering into the furnace whereby the evaporation of the organic binder will be enhanced. At the sintering temperature, the metallic binder and the hard constituents will sinter and bond. Thus, the sintering performed in the present disclosure is an inter-granule sintering which causes the sintered granules to stick together and thereby form co-sintered granule agglomerates or a sintered cake of the granules. According to one embodiment of the present disclosure, the bonded spherically shaped sintered granules will form a sintered cake meaning that all the spherically shaped granules which have been loaded in the furnace have been loosely bound together by the metallic binder. The sintering is usually performed at temperatures in the range of from 1200 to 1500 °C. The sintering temperature to be used depends on which element(s) is(are) used as metallic binder and also on the amount of metallic binder comprised in the spherically shaped granules. Further, the sintering is usually performed, in vacuum, in a vacuum furnace at pressures of 2 x 10 ^"1 - 2 x 10 ^"4 Bar.

The step of unloading the bonded spherically shaped granules from the furnace chamber may be performed after a cooling step wherein the bonded spherically shaped sintered granules have reached a temperature of about room temperature. The obtained bonded spherically shaped sintered granules, i.e. the granule agglomerates or the sintered cake is milled to a cermet or cemented carbide powder by using a mill, such as a ball mill. The obtained powder is free flowing in order to fill the capsule homogenously and will furthermore be able to flow through a Ford Cup (a 5 mm aperture funnel used for ASTN D1200 viscosity measurement) without stopping, the continuous particle size distribution of the spherically shaped granules size may be in the range of from about 5 to about 500 μιη, such as about 10 to about 200 μιη. A wide granule size distribution may be advantageous in applications such as in HIP, when a capsule is being filled with powder having a wide distribution will obtain a higher packing density compared to a more narrowly distributed granule size. On the other hand, if the free flowing properties are of prime interest for the given application a narrow distribution can be preferred.

In one embodiment of the present disclosure, the heat treatment in the furnace chamber is performed at a sintering temperature above the solidus temperature of the metal in the spherically shaped granules. When the sintering temperature is above the solidus temperature, liquid phase is formed.

In step f), a form is provided which is sealable. According to one embodiment, more than one form may also be provided. Even though, the terms "form" and "capsule" are used herein interchangeably, the term "mould" could be used as well. The form is manufactured from zirconium or a zirconium alloy and may be a manufactured of e.g. sheets or tubes, which are welded together. The form may have any shape. The form may also define a portion of the final component.

In the next step, the powder is poured/filled into the form which is thereafter sealed, for example by welding. Prior to sealing the form, air is evacuated from the form. The air is removed (evacuated) as air contains argon and/or oxygen, which may have negative effect on density, ductility and toughness. The evacuation is usually performed by using vacuum pump(s), thus ensuring the removal of oxygen and argon. According to one embodiment of the present process as defined hereinabove or hereinafter, the capsule may, after the evacuation, be backfilled with a gas such as nitrogen. The filled, evacuated, and thereafter sealed form is then subjected to HIP in a heatable pressure chamber, normally referred to as a Hot Isostatic Pressing-chamber at a predetermined temperature, a predetermined isostatic pressure and a

predetermined time so that said powder particles bond metallurgical to each other and consolidate so that the voids between the powder particles are closed and a solid and dense body is formed, thus a certain shrinkage of the total volume of said powder is obtained which means that the obtained component has a dense structure.

The heating chamber is pressurized with gas, e.g. argon gas, to a predetermined pressure (isostatic pressure) of above 500 bar. Typically the isostatic pressure is of from about 900 to about 1500 bar, such as of from 1000 to 1200 bar.

The heating chamber is heated to a predetermined and suitable temperature allowing said powder particles to metallurgically bond and consolidate and thereby allowing the voids in-between the powder particles to close, whereby a component having a dense structure is obtained. At low temperatures, the consolidation process slows down and the obtained component will contain residual porosity and the

metallurgical bond between said powder particles becomes weaker. Therefore, the predetermined temperature may be above 900°C, such as of from about 900 to about 1350°C, such as about 1100 to about 1350°C. The form is held in the heating chamber at said predetermined pressure and said predetermined temperature for a predetermined time period. The diffusion processes that take place between the powder particles during HIP are time dependent so long times are preferred.

Preferable, the form should be HIP treated for a time period of about 0.5 to about 3 hours, such as about 1 to about 2 hours, such as about 1 hour. However, the size of the component and also the composition of the powder comprising cermet or cemented carbide will determine the preferred time period.

A cermet or cemented carbide component obtained according to the process as defined hereinabove or hereinafter may be used in any product requiring good wear resistant properties and/or high stiffness. Examples of, but not limited to, components which may be manufactured by using the process as defined

hereinabove or hereinafter are hot rolls, pipe wear liners and pump valves. For further illustrating the present disclosure, it is further described by the following non-limiting example.

EXAMPLE

A tungsten carbide grade with 10% Co metallic binder was selected as spherically shaped granules. The spherically shaped granules were made by mixing tungsten carbide powder with cobalt powder and PEG. The obtained mixture was spray dried to produce the spherically shaped granules.

The spherically shaped granules were spread onto graphite trays and placed in a vacuum furnace. The granules were sintered by raising the temperature of the furnace to 1300°C and keeping the furnace at that temperature for 30 minutes under vacuum conditions. Before sintering, the furnace was slowly heated and at 250°C, hydrogen was added to the furnace to aid the removal of organic binder. Vacuum was then applied to the furnace again. Upon cooling, 2 bar pressure of nitrogen was added to the furnace from 900°C. This was to speed up the cooling process.

When the furnace was below 50°C, the trays containing the spherically shaped sintered granules were removed. The spherically shaped sintered granules had adhered together producing a friable 'cake' that could be easily broken apart by hand (See Figure 1). The cakes had a diameter of about 30 cm and were 4 cm thick.

The caked lumps were placed in a ball mill with a half charge of 10 mm diameter tungsten carbide media. The mill was run for 30 minutes without fluid. The resultant powder was passed through a 500μ aperture sieve to remove any residual agglomerates.

The resulting powder from this process was free flowing and had retained the spherical like granule shape of the starting spray dried powder (see figure 2).

The obtained powder was filled in a cylindrical zirconium tube capsule (dimensions OD 25.4 x ID 20.4 x L 120 mm) which was sealed in both ends with zirconium disks. The capsule was evacuated and then backfilled with nitrogen gas before sealing.

The capsule was placed in a HIP equipment and argon gas was used to create the pressure to rise simultaneously with the temperature to finally reach a pressure of 1500 bar and a temperature of 1300°C. The holding time was one hour then the temperature and pressure was reduced to normal pressure and room temperature.

Figure 3 and 4 show the microstructure in the obtained component (Figure 3) and at the interface with the capsule (Figure 4). Figure 3 shows a HIPed compacted cemented carbide granule. The metal binder (1) is pointed out with arrows. Figure 4 shows the interface with the granule, the metal binder (1) is pointed out with arrows and also the reaction zone (2). Further, the wall of the zirconium capsule (3) is also shown. As can be seen from the figures, the cemented carbides particles have been consolidated to form one dense body. In Figure 3, the metal binder (cobalt is the metallic binder) is seen between some of the cemented carbide powder particles. In Figure 4, the area named reaction zone comprises ZrC and as in figure 3, the metal binder (cobalt is the metallic binder) is seen between some of the cemented carbide granules.