Patent Application
20170203368
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.
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.
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:
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.
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
In a first step, a wear resistant cemented carbide body 2 is provided.
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
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
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
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
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
In a subsequent step, see
Subsequently, the capsule is sealed by a lid 13 which is welded to the circumferential wall of the capsule, see
According to a second alternative of the inventive method, the metallic base material is a solid metallic body see
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
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.
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.
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.
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.
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:
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.
As can be seen in
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
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.
From
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.
As can be seen in
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
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13175106.7 | Jul 2013 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/064153 | 7/3/2014 | WO | 00 |
