Patent Application
20150079416
A compound tool for a high pressure, high temperature system manufactured by fusing together two or several cemented carbide parts having different grades, for example, a compound anvil.
The multi-anvil system or cubic system is the most developed and economical high pressure, high temperature system (HPHT), i.e., least cost per carat, that is used for making HPHT products. Also, service and the maintenance work costs are less than for the corresponding uniaxial V-shape and straight bore systems.
The HPHT cell/capsule is a cube that is compacted from six directions by the controlled movement of the pistons or anvils during the pressing procedure. The HPHT apparatus consists of the six pressing tools/anvils that work in three directions. Two of the anvils are electrical conductors to maintain electrical resistance heating of the HPHT capsule. The anvils are fitted into steel holders without radial pre-stresses. Forces on the anvils during the HPHT process are supplied from the support-plate at the bottom of the anvil and from the HPHT capsule and the gasket at the top-portion.
Cemented carbide pressing tools have been used in large scale/volume HPHT apparatus for many years. The tool set-up with cemented carbide pressing tools is used in uniaxial HPHT pressing system and in the anvils for the multi-axis/cubic system. The punches/anvils are typically made of solid cemented carbide.
The original HPHT tools concept with the punches separated in several parts have been replaced by a solid compound punch/anvil of cemented carbide. The new types of anvils are manufactured in two or several parts with two or several different CC-grades and are sintered together to form a “compound anvil.” Today it is this tool set-up used worldwide in the uniaxial HPHT pressing system and in the anvils for the multi-axis/cubic system.
Known compound anvils have a working layer having a higher hardness and supporting layers having a higher toughness than the working layer. These known anvils have not been an issue with the pressure that is generated in available capsules, however, there is a demand from the market for higher pressure in the cubic HPHT system. New demands of the HPHT process parameters have shown that the existing HPHT tools have got a limited or too low compressive strength to manage a high pressure up to 11 GPa. In such HPHT pressing apparatus systems, several materials interact during high pressure. Design analyses have not shown appropriate results with regards to the rheological properties of the used cemented carbide tools. With known stress-strain relationship of the carbide is it possible to get the true ultimate strength associated with brittle failure.
New demands of the HPHT process parameters have shown that the existing HPHT tools have limited, too low compressive strength to manage a pressure up to 11 GPa. To manage a bigger volume in a high pressure cell with a pressure up to 100-110 kBar (10-11 GPa), new anvils or other HPHT tools will be needed.
In one embodiment, a tool for a high temperature, high pressure apparatus includes a working layer of a first hard metal composition of material and at least one supporting layer of a second hard metal composition of material attached to the working layer. The first hard metal composition of the working layer has a mean linear intercept of less than about 0.4 μm of a binder phase.
In another embodiment, a tool for a high temperature, high pressure apparatus includes a working layer of a first hard metal composition of material. The working layer has a top and bottom surface. At least one supporting layer of a second hard metal composition of material is attached to the working layer. The at least one supporting layer includes an upper portion. An interface region is formed by the bottom surface of the working layer and the upper portion of the at least one supporting layer. The bottom surface and upper portion have a corresponding shape, wherein the bottom surface and upper portion are bonded to form the corresponding shape in the interface region.
In yet another embodiment, a method of forming a compound anvil for a high pressure, high temperature apparatus includes the steps of forming a first member of a first hard metal composition of material. The first hard metal composition of material has a mean linear intercept of less than about 0.4 μm of a binder phase. At least one other member of a second hard metal composition of material is formed. The first and at least one other member are assembled. The two or more members are joined to form a compound anvil.
In still another embodiment, a method of forming a compound anvil for a high pressure, high temperature apparatus includes the steps of forming a working layer of a first hard metal composition of material, the working layer having a top and bottom surface. At least one supporting layer of a second hard metal composition of material is formed, the at least one supporting layer having an upper portion. The working layer and at least one supporting layer are assembled such that the bottom surface of the working layer mates with the upper portion of the at least one supporting layer to form an interface region. The bottom surface and upper portion have a corresponding shape, wherein the bottom surface and upper portion are bonded to form the corresponding shape in the interface region. The working layer and at least one supporting layer are joined to form a compound anvil.
The foregoing summary, as well as the following detailed description of the embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood that the embodiments depicted are not limited to the precise arrangements and instrumentalities shown.
a)-7(c) are illustrations of the stress distributions of embodiments of the compound anvil.
a) and 8(b) are illustrations of the stress distributions of embodiments of the compound anvil.
Referring to
Anvil 10 includes a base 12 and head 14 located adjacent base 12. As shown in
Cemented carbides have a unique combination of high hardness and good toughness. Cemented carbide, as used herein, is defined as a hard, carbide phase, 70 to 97 wt-% of the composite and a metal alloy binder phase. Cemented carbides (CC) include straight grade carbide, which is the basic cemented carbide structure with grades formed by a composition of tungsten carbide and cobalt. P-grades or cubic grades consists of grades containing a significant proportion of γ-phase, (i.e. TiC, TaC, NbC etc.) together with WC and cobalt. Cemented carbide grades could contain grain growth inhibitors in small amounts and types of γ-phase formers. γ-phase formers or elements that tend to partition to the γ-matrix come from group III, IV, V and VI and include V, Cr, Ti, Ta, Nb, Zr. In addition, the cobalt binder phase can be alloyed with or completely replaced by nickel (Ni), chromium (Cr), iron (Fe), molybdenum (Mo) or alloys of these elements.
Cemented carbide grades can be classified according to the binder phase content and WC grain size. Different types of grades have been defined as fine, medium, medium course and coarse. As referred to herein, a fine grade can be defined as a material with a binder content of about 3% to about 20% and a grain size of less than about 1 μm, with nano, ultrafine and submicron fine grades having grain sizes of less than about 0.1 μm, about 0.1 to about 0.5 μm and about 0.5 to about 1 μm, respectively. Medium grades have binder content between about 6 to about 30% and a grain size of about 1 to about 3 μm. Medium coarse and coarse grades have binder contents between about 6 to about 15% and grain sizes above about 3 μm.
The hardness of cemented carbide depends upon the concentration and contiguity of the hard phase. For example, the higher the concentration of tungsten carbide the greater the hardness. Toughness, in turn, depends on the concentration of the binder. The higher the concentration of the binder the greater the toughness. Hence, by varying the composition, the resulting physical and chemical properties can be tailored to ensure maximum resistance to wear, deformation, fracture, corrosion, oxidation and other damaging effects. The available unique composition of cemented carbide also makes it an ideal tool material for HPHT apparatus operating at high pressures
As referred to herein a hard metal composition refers to a composite material normally having a hard phase composed of one or more carbides, nitrides or carbonitrides of tungsten, titanium, chromium, vanadium, tantalum, niobium, or an equivalent material, or a combination thereof, bonded by a binder or metallic phase typically cobalt, nickel, iron, or combinations thereof in varying proportions. Grade refers herein to cemented carbide as described above in one of several proportions and with a certain grain size.
Fine grade cemented carbide material having a WC grain size of less than about 1 μm offer a great challenge to measure grain size. Grain size has been conventionally measured by manual intercept measurements obtained from Electron backscatter diffraction (EBSD) images.
As used herein, grain size is defined as the equivalent circle diameter (ECD) of a hard grain. The ECD is the diameter of a circle with the same area as the grain. To determine average equivalent circle diameter a calculation can be made from the orientation maps generated with high quality EBSD from mounted and polished cross-sections of CC-specimens (
As shown in Table 1 below, for various grades the calculated mean linear intercept (LB) of the cobalt-binder is less than about 0.40 μm. The linear intercept (LB) of the cobalt-binder is an indirect measurement of the volume fraction of cobalt and the WC grain size and can be calculated according to the formula:
LB
Co
=d
WC(0.1+2.0 VCo)
where:
LBCo=arithmetic mean linear intercept in the Co phase
dWC=the Equivalent Circle Diameter of the WC grains
VCo=Volume-% fraction of binder-phase.
Cemented carbide (CC) sample SHM-H is a straight grade of tungsten carbide (WC) and cobalt (Co) with a mean linear intercept calculation of grain size of less than 0.4 μm of the Co binder-phase. A Cobalt binder phase with a linear intercept less than 0.4 μm in a cemented carbide (CC) matrix has a major composition of a face center cubic (FCC) Co-phase. FCC phase metals are usually soft and ductile. Hexagonal closed packed (HCP) metals are less ductile, but stronger. FCC phase metals have more sliding directions than HCP phase metals. Due to the low stacking fault energy (SFE) of cobalt within the Co-binder a formation of a dislocations network can be more easily formed to provide a strain hardening of the binder-phase. This is of outermost importance to withstand the creep of the CC at high HPHT conditions.
Referring again to
Because working layer 20 is the layer that directly applies pressure to the material being pressed by the press, material 22 has a high hardness and high resistance to plastic deformation to ensure that a uniform ultra-high pressure can be applied to the material being pressed. Accordingly, to maintain an increase of the pressure in the HPHT cell to 11 GPa it is important to use a cemented carbide grade that can withstand the plastic deformation without crack formation in this most critical part of the anvil.
To achieve a high hardness, the layer is preferably fabricated from cemented tungsten carbide with a cobalt content of about 8% or less and an average tungsten carbide grain size of less than about 1 micron. For example, H6F, 8UF, 6UF grades can be used for the working layer, or other out CC grades with a CC composition between about 3 to about 10% Cobalt and a WC-grain size between about 0.3 to about 1 μm.
The high hardness makes the working layer brittle and more susceptible to cracking than softer layers. As set forth above, with finer grain size material the FCC phase dominates the Co-binder phase in CC grade with a binder phase intercept of less than about 0.4 μm. Accordingly, working layer 20 has a work hardening/dislocation formation within the CC during the first number of HPHT-runs that will increase the creep resistance and therefore enable the working layer to withstand higher pressure after a running-in period.
Supporting layer 24/base 12 has an upper portion 28. Upper portion 28 of base 12 and bottom surface 18 of head 14 are adjacent to form an interface region 30. As described above, base 12 can be a single supporting layer or a plurality of layers. Material 26 of the base and supporting layers is a soft cemented carbide grade that can manage the high stresses from the head 14 without breakage. Supporting layer can be replaceable to enable the hard working top to be reused.
The at least one supporting layer has a lower hardness than the working layer, with increased toughness for increased crack growth resistance. To achieve this, cemented tungsten carbide with a cobalt content of approximately 10% and an average carbide grain size of less than 1 μm is used. The layer material properties are selected so that the layer can withstand the high stress levels without subjecting the anvil to a substantial decrease in fatigue life.
Referring to
The shape of bottom surface 18 of working layer/head can have a flat (
The carbide grades and the UHP grade used in the anvil have a high heat conductivity to manage an efficient cooling of the HPHT-tools during the HPHT-process. Also, the cemented carbide grades are good electrical conductors to manage the electrical heating possible in the HPHT capsule without heat losses in the anvils.
Thus, the capability of tailoring the compound anvil by use of cemented tungsten carbide layers of different grades allows for the incorporation of a very high hardness layer at the working face of the anvil. This gives the anvil the capability of applying uniform ultra-high pressure. Use of layers allows the incorporation of softer supporting layer(s) to prevent any cracks from traversing the anvil body. Tailoring the compound anvil using the different grades and thicknesses of layers allows for fabrication of a better performing anvil capable of withstanding its operating environment for consistently longer periods than existing anvils.
The corresponding shapes at the interface region between base 12 and head 14 have an impact on stress distribution in the compound anvil. Referring to
This issue for the anvils is the high stresses in the top portion that must manage the rheological properties/creep of the cemented carbide without resulting in fracture. The radius of the anvil also has an impact on stress distribution. Particularly, the distribution of the stresses in the joint of the anvil could be better distributed by making the anvil wider
Stresses can also be significantly by using a finer carbide grade with higher stiffness. Low cycle fatigue (LCF) studies of CC during HPHT conditions has shown a phase-transformation of FCC and BCC phases within the Co-binder to achieve deformation/strain hardening of the binder-phase. A finer grain size CC-material will transform the binder-phase making it easier to maintain a deformation hardening by dislocation formation.
A higher pressure in the HPHT-capsule of a cubic system is possible to maintain by changing the carbide grade to a stiffer grade with less creep at high pressure. The compound anvil concept makes it possible to utilize a stiffer grade with low risk of breakage in the contact area towards the support/back log plate. The fused compound carbide gives favorable compressive stresses in the joint/contact interface surface of the brittle/hard carbide type to resist prematurely failures during the HPHT-processes.
The shape of the fusing joint could be optimized according to size of the anvil and according to the pressing force applied: a compound anvil should have a radius of the convex/concave surface related to the outer diameter of the anvil. For the best performance of a compound anvil with an outer diameter D, the radius of the joint surface should be bigger than D/2 to a flat joint surface. The optimum radius of the top portion regarding favorable distributed stresses from forces applied at the anvil top surface is D/2 for the cubic HPHT-system with a taper angle of 45°. If the radius is smaller shear stresses in the joint volume could result in a cleavage of the anvil/tool. A radius bigger than D/2 to a flat surface gives a favorable stress pattern in the joint.
Referring to
In step 42 a first member or working layer 20 of a first hard metal composition of material is formed. The first hard metal composition of material can be cemented carbide in the form of a tungsten carbide powder with a cobalt alloy binder powder having a high degree of hardness. The carbide and binder powder can be compacted as known, to form the first member or working layer. As described above, the first hard metal composition of material has a mean linear intercept of less than 0.4 μm of a binder phase.
At least one other member of a second hard metal composition of material is formed in step 44. This member can be at least one supporting layer, as described above that is a second cemented carbide material, different from the first cemented carbide of the working layers. As fully set forth previously, the at least one supporting layer has a high degree of toughness. Like, working layer 20, at least one supporting layer 24 can be formed by compacting carbide and binder powders.
In step 46, the first member or working layer 20 and at least one other supporting layer 24 are assembled by mating the bottom surface of the working layer and upper portion of the at least one supporting layer to form the corresponding shape in the interface region. The corresponding shapes can be formed on the members or layers by machining the corresponding surfaces. Moreover, during the assembly step a layer of ultra-hard material, for example, polycrystalline diamond/PCD can be disposed on the top of the working layer as described below.
The working layer and at least one supporting layer are joined to form the compound anvil in step 48. In the embodiment wherein a plurality of supporting layers is provided, the layers can be superimposed upon one another. In one example, two or several compacted layers of the cemented carbide powder (green bodies) are sintered together to a compound product with two different CC-grades. A known method of making powder-metallurgical articles includes making a compaction of two types of CC-powder of different CC-grades that are separated during the filling procedure of the powder pressing tool. After the sintering is the CC-body compound carbide of two CC-grades.
Alternatively, the members or layers can be sintered separately, assembled and then fused together by subjecting the assembled sintered members to a temperature and pressure sufficient to fuse the parts together to form the compound anvil.
Another type of HPHT press commonly used is known as a belt press. As shown in
The techniques described herein may be used for fabricating the cemented tungsten carbide belt and anvils for a belt press. In such an embodiment, the annular working layer 60 of the belt which encounters high pressure is formed of hard material with less toughness. The supporting layers 62 of the belt are formed of somewhat softer, tougher cemented tungsten carbide. For purposes of this method, belts are equivalent to anvils and may be made with multiple layers of the same or differing grades of carbide. Each anvil has a working layer 64 at the tip that enters the hole in the center of the belt for applying high pressure. Supporting layers 66 behind the working layer are truncated cones and are of a softer, tougher material than the working layer.
The cross-section of the die in the axial direction shows a similar stress pattern as the anvils in the cubic HPHT-system. For the dies is it also possible to maintain a favorable stress pattern in the dies from the load applied by the HPHT cell. In this case is an inner-ring with a fine grained CC fused together with an outer ring of a tougher CC to maintain a stiffer HPHT-tool that could withstand the higher stresses with less bore expansion. The punches have a more favorable stress pattern than the corresponding anvils in the cubic system with regard to the pre-stresses at the outer diameter (OD) of the punches. To maintain a pressure up to 11 GPa the anvils must be designed and composed according to the present embodiments.
Referring to the graph of
To get an understanding of the Co-phase transformation with regards to the CC-hardening and the strength an X-ray diffraction analysis (XRD) was performed to quantify the different Co-phases.
The measurements have been performed directly on the polished sample surface. The samples were in an as-sintered condition. To quantify the content of the Co-phases a Rietveld refinement was used in the analysis. From the cobalt composition has only the cubic-Cobalt (phase 1013214) and the hexagonal-Cobalt (phase 311946) been chosen.
Results from the XRD analysis shown in Table 2 demonstrate that fine CC-grades have Fcc/cubic Co-phases in the binder-phase.
Although the present embodiment(s) has been described in relation to particular aspects thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred therefore, that the present embodiment(s) be limited not by the specific disclosure herein, but only by the appended claims.
The present application is related to and claims the benefit of U.S. Provisional Patent Application No. 61/887,409 filed Sep. 13, 2013.
| Number | Date | Country | |
|---|---|---|---|
| 61877409 | Sep 2013 | US |
