METHOD FOR MANUFACTURING A WEAR RESISTANT COMPONENT HAVING MECHANICALLY INTERLOCKED CEMENTED CARBIDE BODIES

Abstract

A method for manufacturing a wear resistant component includes the steps of providing a metallic base material and a wear resistant cemented carbide body including an anchoring portion. The wear resistant cemented carbide body is arranged such that the anchoring portion is at least partially enclosed by the metallic base material. The metallic base material and the least one wear resistant cemented carbide body is subjected to Hot Isostatic Pressing (HIP). A layer of Al2O3 or hBN is arranged between the anchoring portion and the metallic base material.

Description

TECHNICAL FIELD

The present invention relates to a method for manufacturing a wear resistant component by Hot Isostatic Pressing according to the preamble of claim 1. The invention also relates to a wear resistant component according to the preamble of claim 15.

BACKGROUND ART

Hot Isostatic Pressing (HIP) is a method which is very suitable for Net Shape manufacturing of individual components. In HIP a capsule which defines the final shape of the component is filled with a metallic powder and subjected to high temperature and pressure whereby the particles of the metallic powder bond metallurgically, intergranular voids are closed and the material is consolidated. The main advantage of the method is that it produces components of final, or close to final, shape having strengths comparable to forged material.

The HIP method may be used for manufacturing wear resistant components. For example, tube bends or impellers for transporting sand or sand/water slurries. The wear resistance of the component may thereby be increased by mixing hard particles, such as tungsten carbide powder, in the metallic powder from which the component is manufactured.

However, a drawback with this approach is that the toughness of the component decreases with increasing amounts of tungsten carbide. This may in turn result in low impact strength of the component. A further drawback is the unnecessary high material cost connected to manufacturing the entire composite component from a mixture of cemented carbide and metallic powder.

To increase the wear resistance of components attempts have been made to integrate cemented carbides bodies in components made of steel or cast iron. Cemented carbide bodies consist of a large portion hard particles and a small binder phase and are thus very resistant to wear.

However, due to formation of brittle phases such as M₆C-phase (a.k.a. eta-phase) and W₂C-phase in the interface between the cemented carbide body and the surrounding steel these attempts have not been successful. The M₆C-phase cracks easily under load and the cracks may propagate into the cemented carbide bodies and cause these to fail with decreased wear resistance of the component as a result.

U.S. Pat. No. 4,764,255 shows a method of integrating cemented carbide drillbits in a cast iron matrix by enclosing the drillbits in a steel cup prior to casting.

EP0169718 shows a roller bit cutter in which hard metallic inserts having an anchor portion are embedded in the core material of the roller bit cutter.

It is an object of the present invention to provide a method which remedies at least one of the above mentioned drawbacks of prior art.

In particular, it is an object of the present invention to provide a method that allows for manufacturing of components having high wear resistance. A further object of the present invention is to provide a method which allows for manufacturing, by Hot Isostatic Pressing, of wear resistant components in which cemented carbide bodies are securely retained with no or very little formation of brittle phases. Yet a further object of the present invention is to provide a method which allows for cost effective manufacturing of wear resistant components.

SUMMARY OF THE INVENTION

According to a first aspect of the invention at least one of the above objects is achieved by a method for manufacturing a wear resistant component (100) comprising the steps:

• • providing a metallic base material (1) and at least one wear resistant cemented carbide body (2), wherein the cemented carbide body (2) comprises a top portion (3) which is adopted to extend over at least a section of the surface of the metallic base material (1) and an anchoring portion (4) which is adopted to be retained mechanically by the metallic base material (1) in the final wear resistant component (100);
  • arranging the wear resistant cemented carbide body (2) such that the top portion (3) extends over at least a section of the surface of the metallic base material (1) and such that the anchoring portion (4) at least partially is enclosed by the metallic base material (1);
  • sealing the arrangement of the wear resistant cemented carbide body (2) and the metallic base material (1);
  • subjecting the metallic base material (1) and the least one wear resistant cemented carbide body (2) to Hot Isostatic Pressing by heating at a predetermined temperature and at a predetermined pressure for a predetermined time period;

characterized in the step of arranging a layer (5) which comprises Al₂O₃ and/or hBN between at least the anchoring portion (4) of the wear resistant cemented carbide body (2) and the metallic base material (1).

Experiments have surprisingly shown that when a layer of Al₂O₃ (alumina) or a layer of hBN (hexagonal boron nitride) is arranged between the wear resistant cemented carbide body and the metallic base material, no metallurgic bonding occurs between the metallic base material and the cemented carbide body. The absence of direct contact and metallurgic bonding between the metallic base material and the cemented carbide body results in that no brittle M₆C-phase is formed between the cemented carbide body and the metallic base material during HIP of the component. This in turn greatly reduces the risk that the cemented carbide body will crack during operation and cause failure of the component. Due to the fact that the cemented carbide body is retained mechanically in the base material of the component it is prevented from being knocked out or pulled away from the component, even under very severe operational conditions.

The reason behind the minimized formation of brittle M₆C-phase may be explained as follows.

The HIP process takes place at high pressures and a high temperature and achieves thereby a metallurgical bond between surfaces of the cemented carbide body and the metallic base material. The metallurgical bond may be described as a flawless interface between the cemented carbide body and the metallic base material free of any pores, oxides or films. The surfaces of the cemented carbide body and base material adhere fully to each other at the interface and essentially form a homogenous body. The forming of the metallurgic bond takes place under various diffusion processes whereby, amongst other things, alloy elements diffuse between the wear resistant body and the metallic base material.

It is believed that under these conditions, the carbides in the surface of the cemented carbide body (e.g. tungsten carbide) dissolves and forms a complex phase, M₆C-phase or eta-phase with alloy elements in the metallic base material.

Further advantages of the inventive method is that it allows for selective wear protection of components. This since only areas which are subjected to wear are provided with cemented carbide bodies. This allows for reduced manufacturing costs.

A further advantage is that the properties, e.g. the mechanical properties, of the component may be tailored to suit a particular application by selecting specific materials for the body of the component and specific materials for the wear resistant cemented carbide bodies.

Further alternatives and embodiments of the present invention are disclosed in the dependent claims and the following detailed description.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows schematically a perspective view of a wear resistant component manufactured with the inventive method.

FIGS. 2a-2d shows schematically wear resistant cemented carbide bodies used in the inventive method.

FIGS. 3a and 3b shows schematically steps of the inventive method according to a first alternative.

FIGS. 4a-4c shows schematically steps of the inventive method according to a second alternative.

FIG. 5 shows schematically a component manufactured according to the first or the second alternative of the inventive method.

FIGS. 6 and 7 shows SEM-pictures of a sample of a component manufactured in a first test with the inventive method using a layer of Al₂O₃.

FIG. 8 shows a SEM-picture of an uncoated cemented carbide reference body used in a second test with the inventive method using a layer of hBN.

FIGS. 9 and 10-12 shows SEM-pictures of samples of components manufactured in a second test with the inventive method using a layer of hBN.

FIG. 13 show a SEM-picture of a sample from a comparative example.

FIG. 14 shows the EDS-analysis of the chemical composition of the reaction phase in the sample of FIG. 13.

FIG. 15 shows a SEM-picture of a sample from a wear resistant component manufactured in a fourth test with the inventive method.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically a wear resistant component 100 manufactured with the inventive method. In FIG. 1, the wear resistant component 100 is a-Grouser bar. However, the wear resistant component could have any form. For example, the wear resistant component may be a pipe, or crushing equipment such as an impact hammer or a crusher tooth, or slurry handling equipment or mineral handling equipment.

The wear resistant component 100 comprises a body 1 which consists of metallic base material. The metallic base material may be any type of metallic material which is suitable to form the main structural body of the component in question. For example, the metallic base material may be a steel alloy, for example an iron based steel alloy, or a nickel based steel alloy or a cobalt based steel alloy. Preferably the metallic base material is a ferritic steel alloy such as a ferritic iron based steel alloy, for example the commercially available steel 410L. Ferritic steels have low coefficient of thermal expansion, which minimizes stress in the metallic base material during cooling from the HIP temperature. Further non-limiting examples of the metallic base material are the steel grades S355JR or S235JR. The metallic base material may also comprise hard particles in order to increase the overall hardness or strength of the component, for example the metallic base material may be Metal Matrix Composite (MMC).

Wear resistant cemented carbide bodies 2 are arranged on a surface of the component which is to be protected against wear, such as protection from abrasive wear, erosive wear, impacts or corrosion. The wear resistant bodies 2 have a top portion 3 which extends over a section of the surface of the body 1 of metallic base material. The cemented carbide bodies 2 further have an anchoring portion 4 which protrudes from the top portion 3. The anchoring portion 4 is enclosed by the metallic base material and is, as will be further described below, due to its design locked mechanically in the metallic base material.

The number and shape of the wear resistant cemented carbide bodies depends on the type and shape of the component 100. Therefore, the component could comprise merely one wear resistant body or several wear resistant bodies such as two wear resistant bodies or any other number, for example 1000 wear resistant bodies.

The inventive method for manufacturing a wear resistant component 100 according to a first embodiment will in the following be described with reference to FIGS. 2a-5.

In a first step, a wear resistant cemented carbide body 2 is provided. FIG. 2a shows schematically a wear resistant body 2 which has a top portion 3 which is adopted to extend over at least a portion of the component in order to protect that portion of the component from wear.

The top portion 3 of the wear resistant cemented carbide body may have any shape suitable for protecting the underlying section of the component from wear.

The top portion may for example be rectangular, or triangular or have any other geometrical form which allows several wear resistant bodies 2 to be placed adjacent each other such that their top portions 3 together form a continuous, unbroken surface. Typically, the upper surface of the top portion 3, i.e. which faces away from the anchoring portion 2 is flat, but depending of the field of application it may have other shapes, such as convex. Also the lower surface of the top portion 3, i.e. that faces the anchoring portion may have any shape, such as flat or convex or concave.

The wear resistant body 2 further comprises at least one anchoring portion 4 which protrudes from the top portion 3. The anchoring portion 4 protrudes from the lower side of the top portion 3 of the wear resistant body. In FIG. 2a, the anchoring portion 4 is in the form of an elongated profile and extends over the entire middle section of the top portion 3. However, it is obvious that the anchoring portion 4 may also only extend over a portion of the top portion 3 of the wear resistant body 2. An advantage with a profile shaped, elongated, anchoring portion is that the anchoring portion is retained very strong in the final component.

FIG. 2b shows an alternative design of the wear resistant body 2. In this case, the anchoring portion 4 is a discrete, protruding element which protrudes like a stem from the center of the lower side of the top portion 3. The advantage thereof is that the top portion 3 covers the entire anchoring portion 4 and thus protects the anchoring portion from wear.

The anchoring portion is designed such that it will be mechanically locked in the consolidated metallic base material after HIP. In general, this may be achieved by designing the anchoring portion 4 so that the cross-section of the upper end of the anchoring portion (i.e. adjacent the top portion 3) is narrower than the cross-section of the lower end of the anchoring portion 4, i.e. distal from the top portion.

However, it is also possible to achieve a mechanical lock by designing the anchoring portion so that the cross-section of the middle of the anchoring portion may be thicker, or narrower than adjacent portions.

In FIG. 2a, the anchoring portion 4 is an elongated drop-shaped profile. In FIG. 2b the discrete anchoring portion 4 is drop-shaped. Both designs thereby achieve a mechanical lock in the final component.

FIGS. 2c and 2d shows alternative designs of the anchoring portion. For example, FIG. 2c, shows an anchoring portion 4, having projections 4b which extends perpendicular from the anchoring portion 4 and parallel with the top portion 3 of the wear resistant body. FIG. 2d shows a design in which the anchoring portion 4 forms a wall around a hollow space under the top portion 3. The bottom end of the wall is undercut.

The wear resistant body 2 is manufactured from sintered cemented carbide. The cemented carbide consist of 75-99%, preferably 90-95%, of hard carbide particles, typically tungsten carbide (WC) and remainder binder phase such as cobalt. However, it may also consist of other carbides, such as TiC and other binder phase such as nickel or combinations of chromium, nickel and cobalt. The high amount of hard particles in the cemented carbide body provides a good wear protection on the surface of the component.

The wear resistant bodies 2 may be manufactured by molding a blend of carbide and binder powders into a green body with a desired shape and subsequently sintering of the green body in a sintering furnace. Sintering may take place at a temperature above the melting point of the binder material, which melts and during solidification cements the hard carbides into a rigid wear resistant body.

Profile shaped elongated wear resistant bodies, such as shown in FIG. 2a, may be formed by uniaxial pressing into a green bodies followed by sintering, thus allowing for effective production.

In a second step (not shown), a metallic base material 1 is provided. In the first alternative of the inventive method, the metallic base material is in the form of a volume of powder, for example a volume of powder having a particle size of 10-250 μm. However, as will be described further below, the metallic base material may also be a forged or a cast body. It is of course possible that the metallic base material is constituted by both powder and forged and/or cast bodies.

In a third step, see FIGS. 3a and 3b, the wear resistant cemented carbide bodies 2 and the metallic base material 1 are arranged such that the top portions 3 of the wear resistant cemented carbide bodies 2 extends over at least a portion of the surface of the metallic base material 1.

Consequently, in the first alternative of the invention, in which the metallic base material at least partially is a powder, a capsule 10 which at least partially defines the shape of the component 100 is provided. The capsule 10, see FIG. 3a, is manufactured from steel sheets that are welded together. The capsule 10 may have any shape, in FIG. 3a the capsule defines the shape of a brick shaped component and has thus a bottom plate 11 and a circumferential wall 12. Wear resistant cemented carbide bodies 2 are placed in the capsule 10 so that the upper surface of the top portion 3 of the wear resistant bodies are supported on the bottom plate 11 of the capsule whereby the anchoring portion 4 protrudes in a direction towards the interior of the capsule.

In a subsequent step, see FIG. 3b the capsule 10 is filled with a powder of a metallic base material 1. The powder 1 thereby encloses the anchoring portion 4 of the wear resistant cemented carbide bodies and embeds the anchoring portions and the lower side of the top portion 3 of the wear resistant cemented carbide bodies 2. It is of course also possible to first fill the capsule with a volume of powder and then placing the wear resistant bodies 2 on the surface of powder volume and pushing the anchoring portion into the powder. The wear resistant bodies can of course be arranged on any surface of the metallic base body.

Subsequently, the capsule is sealed by a lid 13 which is welded to the circumferential wall of the capsule, see FIG. 3b. Prior to HIP, the capsule 13 may be evacuated. Thereby, a vacuum may be drawn through an opening in the capsule (not shown) whereupon the opening is closed and sealed.

According to a second alternative of the inventive method, the metallic base material is a solid metallic body see FIG. 4a. The solid metallic body may for example be a forged solid body, a cast solid body or a solid body manufactured from consolidated metallic powder. The solid body 1 is provided with recesses 15, such as bores formed by drilling and/or milling, on a surface that shall be protected against wear. The wear resistant cemented carbide bodies 2 are arranged such the top portion 3 extends over the surface of the solid body of metallic base material and such that their anchoring portions 4 are inserted into the recesses 15 and thereby enclosed by metallic base material 1, see FIG. 4b. Subsequently, a lid 13 is placed over the wear resistant bodies 2 and welded to the metallic base body 1, see FIG. 4c. It is important to seal the arrangement of metallic base material and wear resistant bodies since the body of metallic material otherwise not will be compacted by the pressure in the HIP-chamber. Prior to HIP, the arrangement of solid metallic material and wear resistant bodies may be evacuated. Thereby, a vacuum may be drawn through an opening (not shown) in the lid 13 whereupon the opening is closed and sealed.

According to the invention, a layer 5 of Al₂O₃ (alumina) or hBN (hexagonal boron nitride) is arranged between at least the anchoring portion 4 and the metallic material which encloses the anchoring portion. Preferably, the layer of Al₂O₃ or hBN also extends between the metallic base material and the lower surface of the top portion 3 of the wear resistant body 2. More preferably, the layer of Al₂O₃ or hBN is arranged between all interfacing surfaces of metallic base material and wear resistant cemented carbide bodies. When the metallic base material is in the form of powder, the layer of Al₂O₃ or hBN is suitably applied on the wear resistant body, see FIG. 3a which shows a layer 5 that is applied on the anchoring portion 4 of the wear resistant cemented carbide body 2. However, when the metallic base material is a solid body, such as forged or cast, the layer of Al₂O₃ or hBN may be applied either on the surfaces of the metallic body or on the wear resistant body 2.

According to a further embodiment, a first layer of Al₂O₃ is applied on the wear resistant body and then a second layer of hBN is applied on top of the Al₂O₃ layer. The advantage thereof is that the Al₂O₃ layer ensures that no metallurgical binding occurs between the wear resistant body and the metallic base material whereas the hBN layer allows for relative motion between the wear resistant body and the metallic base material.

In the case that the metallic base material is a solid body, the two layers may be applied either on the solid body or on the wear resistant body. Alternatively, a layer of Al₂O₃ or hBN is applied on the surface of the wear resistant body 2 and another layer of Al₂O₃ or hBN is applied on the surface of the solid metallic body.

However, preferably the layer or the layers of Al₂O₃ and hBN are applied on the wear resistant body rather than on the solid metallic base material. The reason therefore is that the wear resistant cemented carbide bodies are more formstable during HIP than the metallic base material. So, if the layers of Al₂O₃ and hBN were applied on the metallic material, they could crack due to deformation of the metallic material deform during HIP.

FIG. 4c show schematically a portion of a solid body, in which a layer 5 of Al₂O₃ or hBN has been applied on the surface of the recess 15.

As discussed earlier, the layer of Al₂O₃ or hBN will prevent metallurgical bonding between the wear resistant cemented carbide bodies and the metallic base material and thus also prevent the formation of brittle M₆C-phase.

The layer of Al₂O₃ or hBN may be applied by various methods.

Preferably, Al₂O₃ is applied by CVD (Chemical Vapour Deposition). Being a gas-based coating method, CVD effectively reaches and covers all surfaces of the bodies to be coated. This method is therefor suitable for applying coatings on components with complex geometries. The method also allows for high coating speed and many components may be coated simultaneously. A further advantage with CVD is that dense coatings are achieved and the repeatability is high.

Al₂O₃ may also be applied by plasma spraying, which is a suitable method for coating of large surfaces. It is also possible to apply the layer of Al₂O₃ by PVD (Physical Vapor deposition).

When the layer consists of Al₂O₃, the thickness should be at least 2 μm in order to ensure that interfacing surfaces of wear resistant body and metallic base material does not come in contact with each other. The resistance to metallurgical bonding is believed to increase with increasing layer thickness. However, too thick layers may crack and therefore the thickness of Al₂O₃ layers should be 2 μm-10 μm, preferably 4 μm-8 μm.

In addition to preventing metallurgic bonding, a further advantage of a layer of Al₂O₃ is that Al₂O₃ has good adhesion to the underlying surface and is resistant to mechanical wear which makes components with Al₂O₃ layers easy to handle.

A layer of hBN may be applied by brushing or spraying a suspension of hBN, a binder, such as a solgel and a solvent, such as ethanol or water, onto the wear resistant body. It is also possible to apply the hBN layer onto the wear resistant body by dipping the wear resistant body in the suspension. To achieve a layer of suitable thickness the wear resistant body need to be sprayed, painted or dipped several times. Between each application, the wear resistant body may be allowed to dry for at least 10 minutes in room temperature. The drying time must be adjusted in dependency of the solvent since, for example ethanol, evaporates faster than water. A suitable solution of hBN and solvent is for example MYCRONID® BORON NITRIDE SUSPENSION which is available commercially from ESK Ceramics GmbH & Co. KG. Another type of hBN solution is HeBoCoat 401E which is commercially available from Henze Boron Nitride Products GmbH.

The thickness of the hBN layer depends on the geometry of the component in question and also on the HIP process parameters. However, the thickness should be at least 10 μm in order to ensure that interfacing surfaces of wear resistant body and metallic base material does not come in contact during HIP. However, too thick layers, may result in that the wear resistant bodies are not sufficiently retained in the metallic base material. A further disadvantage with thick layers is that the adhesion of thick layers to the base material is poor. Therefore, the thickness of hBN layers should not exceed 500 μm. For example the minimum thickness of the hBN layer may be 20 μm or 40 μm. The maximum thickness may be 400 μm or 300 μm or 200 μm or 100 μm. According to one example the thickness is 50 μm-80 μm or 50 μm-80 μm.

An additional advantage with a layer of hBN is that due to its low friction coefficient the hBN layer allow relative motion between the metal and the cemented carbide as well as reduce stresses in the interface otherwise arising from the thermal elongation mismatch between the metal and the cemented carbide.

It is also possible to apply an intermediate layer of TiC or TiN on the surface of the wear resistant body prior to application of the layer of Al₂O₃. The intermediate layer may also be a mixture of TiC and TiN. The The layer of TiC and/or TiN may for example be 0.5-10 μm, 2-10 μm or 5-10 μm and increases the adhesion between the cemented carbide and the Al₂O₃ coating.

In a further step, (not shown) the sealed arrangement of metallic base material and wear resistant cemented carbide bodies, are subjected to Hot Isostatic Pressing (HIP) at a predetermined temperature, a predetermined isostatic pressure during a predetermined time so that the metallic base material closes around the anchoring portions of the wear resistant bodies and lock thereby these mechanically in the component. The capsule is thereby placed in a heatable pressure chamber, normally referred to as a Hot Isostatic Pressing-chamber (HIP-chamber).

The heating chamber is pressurized with gas, e.g. argon gas, to an isostatic pressure in excess of 500 bar. Typically the isostatic pressure is 900-1200 bar. The chamber is heated to a temperature which is below the melting point of the metallic base material. The closer the temperature is to the melting point, the higher is the risk for the formation of melted phase and unwanted streaks of brittle carbide. Therefore, the temperature should be as low as possible in the furnace during HIP:ing. However, at low temperatures the diffusion process slows down and the material will contain residual porosity and the metallurgical bond between individual particles or pieces of metallic base material becomes weak. Therefore, the temperature is 900-1150° C., preferably 1000-1150° C. The arrangement of metallic base material and cemented carbide bodies is held in the heating chamber at the predetermined pressure and the predetermined temperature for a predetermined time period. The consolidation processes that take place between the metallic materials during HIP:ing are time dependent so long times are preferred. The HIP time also depends on the dimension of the component, i.e. heavy components require long HIP times. Preferably, HIP is performed during a period of 0.5-3 hours, preferably 1-2 hours, most preferred 1 hour.

During HIP:ing the metallic base material deform plastically around the anchoring portions of the wear resistant bodies and lock thereby these mechanically in the component. Metallic base material which is not coated with Al₂O₃ or hBN bond metallurgically through various diffusion processes and internal voids are closed so that a dense, coherent component is achieved. FIG. 5 shows a HIP:ed component consisting of a solid body 1 of metallic base material and wear resistant bodies that are mechanically locked in the metallic base material.

After HIP:ing the lid and, if present, the capsule may be partly or completely stripped from the consolidated component by e.g. machining, grinding or grit blasting.

Examples

The present invention will in the following be described with reference to two non-limiting concrete examples performed by the inventive method and one comparative example.

In a first test (Test 1), the effect of a coating of alumina (Al₂O₃) on a cemented carbide body was investigated. In a second test (Test 2), the effect of coatings of hexagonal boron nitride (hBN) on cemented carbide bodies was investigated. In a third test (Comparative Test) a non-coated cemented carbide body was embedded in steel powder and HIP:ed.

Test 1—Al₂O₃ Coating on Cemented Carbide

Firstly a cemented carbide test body having a 5 μm thick TiC coating closest to the cemented carbide surface and an outermost 5 μm thick coating of Al₂O₃ was provided. For this purpose a cutting insert was used. The insert had the dimensions 2×2×0.5 (cm). The coatings were applied with CVD.

FIG. 6 shows a Scanning Electron Microscope (SEM) image of the cemented carbide body 2 which consisted of two different types of hard particles 2a and 2b and a binder phase 2c. The chemical composition of the cemented carbide body was determined in the SEM. The first type of hard particles 2a was identified as tungsten carbide. The second type of hard particles 2b consisted of carbides of tungsten, Ti and Nb. The binder phase 2c consisted of mainly cobalt with a small addition of nickel.

The cemented carbide body was embedded in commercially available 410L steel powder in a capsule of steel sheets that had been welded together. The 410L powder had the following composition:

C: 0.023, Si: 0.52, Mn: 0.20; P 0.009, S: 0.008; Cr: 13.0; Ni: 0.27, balance Fe.

The steel powder had the following Sieve analysis according to ASTM-E11:

	Micron:	355	300	212	125	53
	Mesh:	45	50	70	120	270
	% <	100	94	76	47	8

The capsule was sealed by welding and subjected to Hot Isostatic Pressing (HIP) at a temperature of 1150° C., at a pressure of 1000 bar. The capsule was held at this temperature and pressure for two hours and then allowed to cool down with a cooling rate of approximately 3-5° C./min.

After HIP:ing the capsule was cut through the center of the cemented carbide body and samples were taken for analysis. The samples were prepared prepared by polishing for analysis by scanning electron microscopy (SEM) which was performed in a Zeiss EVO 50 VPSEM.

FIG. 7 shows a SEM image of the interface between the surface zone of the cemented carbide body 2 and the surrounding steel matrix 1. The layer closest to the surface of the cemented carbide body is TiC. The outermost layer, 5 is Al₂O₃.

As can be seen in FIG. 7, there is no evidence of metallurgical binding in the interface between the Al₂O₃ layer 5 on the cemented carbide body 2 and the surrounding steel matrix 1. Nor are there any traces of any reaction phase, e.g. M₆C-carbides due to diffusion of elements between the cemented carbide and the steel matrix. A void 6 is clearly visible between the outermost layer of Al₂O₃ and the adjacent steel matrix. The void is approximately 2-3 μm wide and is believed to be formed when the steel matrix and the cemented carbide shrinks during cooling from the HIP temperature.

Test 2—hBN Coating on Cemented Carbide Body

In a second test two cemented carbide cutting inserts were coated with a suspension of hexagonal boron nitride (hBN). The solution used was Mycronide® boron nitride suspension from the company Ceradyne/ESK. The suspension contained a solid content of ≦18% BN in a liquid phase of ethanol and a reactive solgel binder.

Firstly, the chemical composition of the cemented carbide insert in uncoated condition was investigated in the SEM, see FIG. 8. The cemented carbide insert consists of three different phases which were identified as 1a=(W, Ti, Ta)C and 1b=WC and a binder phase. The hard phase particle size was roughly 3 μm and below. The binder phase consisted mainly of cobalt but with an addition of chromium.

The inserts were dipped eight times each in the hBN solution. Between each dipping the inserts were allowed to dry for 30 minutes in room temperature.

The coating on the first insert was hardened at a temperature of 300 for 30 minutes after the final dipping.

The coating on the second insert was not hardened. Instead it was only allowed to dry in room temperature for 30 minutes between each dipping.

Thereafter the two cemented carbide cutting inserts were embedded in 410L steel powder in a capsule and subjected to HIP as described in Test 1. After HIP:ing the capsule was cut through the center of the cemented carbide body and samples from both inserts were taken and prepared for analysis as described in Test 1.

FIG. 9 shows a SEM image of a sample from the first cemented carbide cutting insert. As can be seen in the image there is a black area 6 between the steel matrix 1 and the surface of the cutting insert 2. The black area 6 is hBN which appears in black due to that the SEM image is taken in backscattering mode. As can be seen, the black area 6 is of uniform cross-section and approximately 20 μm thick. On some occasions there are “bridges” between the steel matrix and the surface of the cemented carbide insert. The “bridges” are believed to be formed by steel powder that penetrates through cracks in the hBN coating. The cracks may have been formed due to that the coating becomes brittle during hardening. A reaction zone is formed between steel and cemented carbide at the end of the “bridge”. However, the “bridges” are relatively few and narrow and have therefore no significant negative effect on the mechanical interlocking attachment of the cemented carbide insert in the steel matrix.

FIG. 10 shows a SEM image of a sample from the second cemented carbide cutting insert. Also in this sample there is a black area 6 of hBN between the steel matrix 1 and the cemented carbide insert 2. FIG. 11 is an enlargement of a portion of the image in FIG. 10. FIG. 12 is a 1000 times magnification of FIG. 10, it is clearly visible that no reaction zone has formed where the hBN layer has separated steel powder and cemented carbide insert.

From FIGS. 11 and 12 it is visible that particles of the steel powder have penetrated into the hBN coating during HIP. This is possible, since the hBN coating on the second cutting insert only has been dried in room temperature between applications and therefore is softer than the hardened coating on the first sample.

Test 3—Comparative Test with Uncoated Cemented Carbide Insert

In a third test an uncoated cemented carbide insert was embedded in 410 L steel powder in a capsule and subjected to HIP under the same conditions as the coated inserts in the first and the second tests.

The chemical composition of the uncoated cemented carbide insert was identical to the chemical composition of the inserts used in Test 2.

After HIP:ing the capsule was cut through the center of the uncoated cemented carbide body and samples were taken and prepared for analysis as described in Test 1 and Test 2. FIG. 13 shows a SEM-image of a sample from the HIP:ed uncoated cemented carbide insert.

As can be seen in FIG. 13, the uncoated cemented carbide insert 2 is metallurgically bound to the surrounding 410L steel matrix 1 and a reaction zone 7 of brittle carbide phases is formed in the outermost part of the cemented carbide insert 2. The chemical composition of the reaction phase 7 is shown in FIG. 14.

Test 4—hBN Coating on Cemented Carbide Wear Resistant Body Having a Drop Shaped Anchoring Element.

In a fourth test, a cemented carbide body was embedded in 410 L steel powder and subjected to HIP. The cemented carbide body had a design according to FIG. 2, i.e. it it comprised a flat top portion 3 and a drop-shaped anchoring element 4.

The cemented carbide body was manufactured by sintering of the commercially available cemented carbide grade C15C. Thus comprising 6.6 wt % Co, 7.5 wt % Ni 0.8 wt % chromium carbide and remainder WC.

The cemented carbide body was provided with a hBN coating (HeBoCoat 401 E spray) from the company Henze.

The coated cemented carbide body was embedded in 410 L steel powder in a HIP capsule, which was vacuumed and welded shut. The capsule was subjected to HIP at a temperature of 1150° C. and a pressure of 100 MPa for 2 hours. Thereafter, the capsule was divided into sections by spark maching and the sections were prepared for SEM.

FIG. 15 shows a SEM image of a sample taken from a corner of the flat top portion 3 of the cemented carbide body. It is apparent that the hBN coating has prevented contact between the steel powder 1 and the cemented carbide 3 during HIP. Only in one minor area (encircled) has the steel powder penetrated the hBN layer and caused a metallurgical bond with the cemented carbide.

Claims

1. A method for manufacturing a wear resistant component comprising the steps:

providing a metallic base material and at least one wear resistant cemented carbide body, wherein the cemented carbide body includes a top portion which is arranged to extend over at least a section of the surface of the metallic base material and an anchoring portion which is arranged to be retained mechanically by the metallic base material in the final wear resistant component;

arranging the wear resistant cemented carbide body such that the top portion extends over at least a section of the surface of the metallic base material and such that the anchoring portion at least partially is enclosed by the metallic base material;

sealing the arrangement of the wear resistant cemented carbide body and the metallic base material;

subjecting the metallic base material and the least one wear resistant cemented carbide body to Hot Isostatic Pressing by heating at a predetermined temperature and at a predetermined pressure for a predetermined time period; and

arranging a layer of alumina (Al2O3) or hexagonal boron nitride (hBN) between at least the anchoring portion of the wear resistant cemented carbide body and the metallic base material.

2. The method according to claim 1, wherein the layer is applied on at least the anchoring portion of the wear resistant cemented carbide body.

3. The method according to claim 1, wherein the layer is applied on the metallic base material.

4. The method according to claim 1, wherein the layer consists is made of alumina (Al2O3) or hexagonal boron nitride (hBN).

5. The method according to claim 1, wherein the layer consists is made of Al2O3 and wherein an intermediate layer of Ti is arranged between the Al2O3 layer and the surface of the wear resistant cemented carbide body.

6. The method according to claim 5, wherein the intermediate layer is TiC or TiN or a mixture of TiC and TiN.

7. The method according to claim 4, wherein the layer is made of Al2O3, the thickness of the layer being 2 μm-10 μm.

8. The method according to claim 1, wherein the layer is made of hBN, the layer having a thickness of 10 μm-500 μm.

9. The method according to claim 1, wherein the layer is made of a first layer of Al2O3 and a second layer of hBN.

10. The method according to claim 1, wherein the anchoring portion of the wear resistant cemented carbide body has a drop shaped cross-section.

11. The method according to claim 1, wherein the metallic base material is selected from an iron based alloy, a cobalt based alloy, a nickel based alloy and a Metal Matrix Composite (MMC).

12. The method according to claim 1, wherein the metallic base material is an iron based ferritic steel alloy.

13. The method according to claim 1, wherein the metallic base material is a solid metallic body, the at least one recess being formed in the metallic base material, and the anchoring portion of the wear resistant cemented carbide body being arranged in the recess.

14. The method according to claim 1, wherein the metallic base material is powder, the anchoring portion of the wear resistant cemented carbide body being arranged such that the anchoring portion is at least partially enclosed by the metallic base material powder.

15. A wear resistant component comprising a metallic base material and at least one wear resistant cemented carbide body made by the method according to claim 1.

16. The wear resistant component of claim 15, wherein the layer of Al2O3 or hBN extends along an interface between the cemented carbide body and the metallic base material.

17. The method according to claim 4, wherein the layer is made of Al2O3, the thickness of the layer being 4 μm-8 μm.