DK144415B - PROCEDURE FOR MANUFACTURING A MATERIAL CONTAINING CUBIC BORN NITRID - Google Patents

Description

144415

The invention relates to a process for the preparation of a material containing cubic boron nitride, whereby hexagonal boron nitride in the presence of a catalyst in the form of an aluminum alloy and under pressure and temperatures whereby cubic boron nitride 5 is stable is converted to cubic boron nitride.

A process for converting hexagonal boron nitride (hexagonal BN) to cubic boron nitride (CBN) using at least one catalyst selected from the group consisting of alkali metals, alkaline earth metals, lead, antimony, tin and nitrides of these metals, is described in the description to the United States Patent No. 2,947,617.

The use of Fe ^ AI and certain silver cadmium alloys as catalysts in the conversion of hexagonal BN to CBN is discussed in "Synthesis of Cubic Boron Nitride" by Saito et al. (Yogyo-Kyokai Shi, 15 vol. 78, no. 893).

According to the present invention, there is provided a process of the kind set forth in the introduction, and this method is characterized in that at least one aluminum and cobalt, nickel or manganese alloy is used as catalyst and that the hexagonal boron nitride is in contact with a lot of sintered carbide or sintered carbide powder.

The invention is based on the recognition that by using a catalyst consisting of at least one alloy of aluminum and cobalt, nickel or manganese and under pressure and temperatures whereby 25 cubic boron nitride is stable, both a conversion of hexagonal boron nitride to cubic boron nitride can be achieved. as an in situ formation of a composite of cubic boron nitride and sintered carbide with a very solid band of CBN carbide. For example, in situ formation of a tool insert consisting of a thin CBN layer is integrally bonded with a solid carbide support.

The invention will now be described in more detail with reference to the drawing, in which: 1 shows an example of a high pressure, high temperature apparatus suitable for use in the practice of the present invention; FIG. 2 is a sectional view of a filling composition embodiment for use in the apparatus of FIG. 1 for the preparation of a tool in batch; U4415 2 FIG. Figure 3 is a three-dimensional view showing a composite CBN / cemented carbide machine tool insert; 4 am. a sectional view through the insert of Figure 3 either along line X-X or along line Y-Y; 5 and 6 are both three-dimensional images of composite CBN / sintered carbide machine tool inserts made in accordance with the present invention; and FIGS. 7 is a sectional view showing a combined liner / filling composition for use in the manufacture of the structures shown in Figures 3, 5 and 6.

A preferred form of a high pressure, high temperature apparatus in which the present invention can be practiced is disclosed in the disclosure to U.S.A. No. 2,941,248 and are broadly shown in Figure 1.

The apparatus 10 comprises a pair of cemented tungsten carbide pistons 11 and 11 'and an intermediate belt or die portion 12 of the same material. The die portion 12 comprises an opening 13 in which a reaction vessel 14. is provided. non-conducting pyrophyllite parts 16 and 17 and an intermediate metal gasket 18.

A preferred form of reaction vessel 14 comprises a hollow salt cylinder 19. The cylinder 19 may be of other material, such as talc, which a) does not convert during high pressure, high temperature operation to a stronger, stiffer state (such as by phase conversion and / or compression), and which b) is largely free of volume discontinuities that occur when using high temperatures and pressures, e.g. occurs in association with pyrophyllite and porous alumina. Materials that meet the criteria set forth in the description to U.S.A. Patent No. 3,030,662 (column 1, line 59 to column 2, line 2) is suitable for the manufacture of cylinder 19.

A graphite electrical resistance heating tube 20 is located concentrically within and adjacent to the cylinder 19. In the graphite heating tube 20, a cylindrical salt liner 21 is again concentrically disposed. The ends of the liner 21 are provided with salt plugs 22, 22 'which are arranged top and bottom respectively. As will be described in more detail below, the liner may have a cylindrical hollow core for accommodating a large filling composition containing the sub-assemblies, or the liner may consist of a variety of mold compositions arranged in a stack to produce multiple composite tool inserts. eg. as shown in FIG. 3, 5 and 6.

Electrically conductive metal end disks 23 and 23 'are used at each end of the cylinder 19 to provide electrical connection to the graphite heating tube 20. Adjacent each disc 23, 23' is an end cap assembly 24 and 24 ', each comprising a pyrophyllite plug or disc 25 which is surrounded by an electric conductive ring 26.

Operating modes utilizing both high pressure and high temperatures in the present apparatus are well known to those skilled in the art. The above mention relates only to a high pressure high temperature apparatus. Various other apparatus capable of providing the necessary pressures and temperatures can be used in the present invention.

EXAMPLE I

A Mo cylinder (0.05 mm thick x 6.4 mm in diameter) was loaded with a mixture of powders (0.050 g hexagonal BN, 0.003 g Al and 0.014 g WC) and a Co-disc (0.034 g), and it was then covered with a Mo disk (0.05 mm thick). The composition was then simultaneously subjected to a pressure of 54 kb and a temperature of 1550 ° C for 70 minutes. All the hexagonal BN was transformed into CBN, forming 25 a hard, strong mass of entwined columnar crystals.

EXAMPLE II

A Zr cylinder (0.05 mm thick x 6.4 mm in diameter) closed at the top with a Mo lid disc (0.05 mm thick) was used as the containment means. Two separate layers of hexagonal BN separated by a layer (1.3 mm thick) of quality "883 Carboloy" (93% WC, 6%

Co) sintered carbide was placed in the enclosure. An Al-ring (0.13 mm thick, 4.8 mm internal diameter, 6.2 mm outer diameter) was placed in contact with the upper layer of hexagonal BN and in contact with the adjacent surface of the carbide layer. A few small chunks of Al (total weight 0.004 g of such size that the material can pass a net of 23 meshes per cm) were placed in contact with the lower hexagonal BN and in contact with the adjacent surface of the carbide layer. The composition was simultaneously subjected to a pressure of 54 kb and a temperature of 1500 ° C for 60 minutes. It was found that a large central patch of CBN appeared on the upper surface of the carbide layer within the Al ring. This mass was polished and examined; The CBN crystals were fused together and their crystal character was dendritic. The wear test groove had a depth 5 of 0.009 mm. Lumps of polycrystalline CBN also appeared on the lower surface of the sintered carbide layer at the sites where the Al lumps were located.

The amount of aluminum in the starting material can range from approx. 2 to approx. 40% by weight of the hexagonal BN, while the amount of 10. the alloy metal (nickel, cobalt, manganese) can range from approx. 4 to approx.

100% by weight of the hexagonal BN. The amount of these alloying metals remaining in the consolidated CBN as the base material will vary depending on the pressure and time of the high pressure and high temperature state. In all cases, the amount of aluminum as well as alloy metal atoms in the compressed CBN will be greater than approx. 1% by weight CBN. Prefabricated aluminum alloys can, of course, be used instead of separate in situ alloy discs.

Pure aluminum or pure Co, Ni or Mn have been found not to act as a catalyst alone in the conversion of hexagonal BN to CBN.

Figure 2 shows an arrangement in which the present invention is used in the preparation of a plurality of disc or pill shaped composite products (sintered carbide substrate having a layer of sintered 25 CBN formed over it and bonded thereto). The filling composition 40 is not indicated on the same scale as Figure 1, but it corresponds to the volume 31 of the apparatus shown in Figure 1.

The filling composition 40 shown consists of a cylindrical sleeve 41 of shielding metal to prevent ingress of 30 and remove oxygen. The shielding metal is selected from the group consisting of zirconium, titanium, tantalum, tungsten and molybdenum. Inside the cylindrical shield metal sleeve 41 are arranged a series of subassemblies separated by discs 42 made of a material such as that used for the cylinder. 19. The sub-compositions are protected above and below by means of shielding discs 43 made of titanium, zirconium, molybdenum, tantalum or tungsten. Each sub-assembly thus protected on all sides consists of a larger mass 44 and a smaller mass 46 as well as metal discs 47,48. Each mass 5 UU15 46 consists for a large part of hexagonal BN. The nature and size of the crystals developed by the hexagonal BN can be changed by mixing CBN particles (e.g., 1-10 microns) or "Carbo-loy" carbide powders (1-5 microns) in the hexagonal BN . The hexagonal BN is preferably treated to remove oxygen from it.

Each mass 44 consists of a sintered carbide disk, preferably made of a mixture of tungsten carbide powder and cobalt powder.

If desired, sinterable carbide powder can be used, in which case the sintered carbide is prepared in situ during preparation of the CBN / sintered carbide composition.

As shown, one of the metal discs 47, 48 is of aluminum, and the other disc is of cobalt, nickel or manganese. By subjecting these sub-compositions to simultaneous pressures and temperatures in the cubic boron nitride-stable region of the boron nitride phase diagram, the hexagonal BN is transformed into CBN, forming a compact wear mass that is an integral part of a sintered carbide support block for this.

When substantially pure hexagonal BN alone is used for the mass 46 20, the CBN crystals forming a layer bonded to the sintered carbide tend to take the form of slender dendrites having a diameter of approx. 10-20 microns and a length p in approx. 50-100 microns. Where the CBN crystals thus formed are not interlocked due to their dendritic nature, the 25 crystals are strongly bonded by metal from the discs 47, 48 and from the mass 44.

The appearance of a polished portion of a CBN compact mass, in which the crystals are developed in situ as in accordance with the present invention, differs from a polished portion of a CBN compact mass 30 made from pre-prepared CBN crystals. In the first case, the crystals appear as crystals that are predominantly oblong in a single direction (columnar) and may also have branching projections (dendritic). In the latter case, the crystals are more block shaped. Thus, in the first case, the ratio of length 35 to width of the crystals is substantially greater than 1.5: 1, while in the latter case the ratio of length to width is substantially less than 1.4: 1.

When finely divided, hard crystalline material (e.g., CBN, WC, A ^ and, SigN ^, etc.), a) stays firm at the pressures and temperatures employed, and b) has a thermal expansion coefficient approximately corresponds to the value of CBN, mixed with hexagonal BN in the presence of sintered carbide or sintered carbide powder to form the mass 46, the growth of the CBN crystals developed is in the 2-10 micrometer range (largest dimension) and they have a tend to be pillar-shaped or block-shaped. The crystalline mass is void-free, the spaces between the CBN crystals being filled with metal and / or crystalline fingodets when used. Bonding of the crystals to each other and to the sintered carbide is predominantly due to metal from the alloying constituents of slices 47, 48 and from the mass 44 and sintered carbide powder when used.

Composite products have been prepared from a cobalt-containing carbide, although the arrangement thereof is not shown in the drawing, using a sub-composition consisting of a sintered carbide disc with a thin aluminum (or aluminum alloy) layer or disc in contact with the top surface, this combination of materials being covered with a mass of hexagonal BN, with no additional catalyst metal present. It was found that cobalt from the sintered carbide was made available in a sufficient quantity in connection with the aluminum layer or disc to supply the necessary catalyst alloy system. Similarly, powdered carbide powder mixture (carbide plus sintering agent) may be used in connection with this arrangement in place of the pre-sintered carbide.

In the case of the sub-composition shown in FIG. 2, cobalt from mass 44 becomes available at the interface between mass 44 and the CBN crystals formed in mass 46, entering a complex matrix system providing excellent bonding between the CBN formed and the sintered carbide.

The direct bonding relationship formed in situ between the newly formed CBN material of very high strength and the substantially greater mass of underlying rigid support material avoids any need for the insertion of any bonding layer therebetween, such as e.g. that resulting from brazing or brazing. By providing a rigid non-yielding support material in direct contact with the CBN-rich machining edge area, the occurrence of fractures in the CBN material is greatly reduced and the attachment of the composite product to another body, e.g. a tool's shaft is lightened.

144415 7

Composite products made according to the present invention are sometimes randomly interrupted during decompression of the reaction vessel to remove the product. This type of fracture occurs in a direction substantially perpendicular to the vertical axis of the filling composition. In the case of the composite products made with the sub-compositions of FIG. 2, the interface between the CBN and the sintered carbide lies in this same direction. The high quality of bonding at this interface is seen by the fact that the breakage usually occurs through the CBN layer. Only 10 rarely did fracture occur at the interface, and in these cases the fracture surface was irregular as it passes through the CBN and through the sintered carbide, as well as along the interface. Thus, the interface is generally stronger than the tensile strength of the CBN crystals.

Microscopic (300X) examination of the polished edges of composite products formed for tool inserts has revealed the causes of this unusually strong interface bonding.

By "good bonding" the CBN grains at the interface (at 300X magnification) are found either to be in direct contact with the sintered 20 carbide or that a thin reaction layer is disposed between the CBN grains and the sintered carbide. Any reaction layer present is less than 10 microns thick, which shows that in any case, there is minimal bursting and attack on the sintered carbide structure. The interface is void free and 25 is irregular in the micrometer scale ratio (1-100µ) due to the CBN being pressed into the sintered carbide and / or due to the movement of plastic deformed sintered carbide into the spaces between adjacent CBNs. crystals. This type and quality of interlocked interface is clearly unattainable by soldering a pre-made CBN compact mass to a sintered carbide disk.

In the manufacture of tool inserts by the present method, the filling composition 40 is placed in the apparatus 10 which is applied to pressure and the system is then heated. The temperatures used range from approx. 1300-1600 ° C for 35 periods of more than 3 minutes to sinter the carbide / cobalt mixture while simultaneously subjecting the system to very high pressures, e.g. of the order of 50 kilobars to ensure thermodynamically stable conditions for the formation of CBN from hexagonal BN. At 1300 ° C the minimum pressure should be approx. 40 kb and at 1600 ° C the minimum pressure should be approx. 50 kb.

The carbide powder used either to produce a 5 pre-sintered mass 44 or as the mass itself 44 is preferably a tungsten carbide mold powder (mixture of carbide powder and cobalt powder) commercially available with particle sizes from 1 to 5 micrometers. The tungsten carbide can, if desired, be replaced in whole or in part by either biting titanium carbide and tantalum carbide. Since there has been some use of nickel and iron in the bonding of carbides, the material for providing the metal bond in the cemented carbide can be selected within the group consisting of cobalt, nickel, iron and mixtures thereof.

However, cobalt is preferred as the metal bonding material.

15 Aluminum alloys of Co and Ni act as catalyst solvents for CBN synthesis in the manufacture of the CBN / sintered carbide composite products for tools. The composition of carbide mold powders useful in the practice of the present invention may consist of mixtures containing about 20%. 75-97% by weight carbide and approx. 3-25% by weight of cobalt.

In the following examples, referring to the results of a wear test, this test consisted of pressing a rod of "Rene 41" (nickel-based super alloy) having a diameter of 3.2 mm rotating at a speed of 2000 rpm. per minute against the 25 CBN layer on the CBN / sintered carbide composition. The depth of the wear groove provided in the CBN layer was measured and recorded.

EXAMPLE III

A Mo cylinder (6.4 mm diameter) was filled with a mixture of 30 "jet-milled" CBN crystals (1-10µ, 0.017g), hexagonal BN (0.050g) and NiAI3 (30µ particles, 0.013g) under a slab (thickness 1.3 mm) of quality "883 Carboloy" sintered carbide. Prior to filling the Mo cylinder, the above mixture was heated in NH 2 at 820 ° C for 1 hour. At the same time, the composition was subjected to a pressure of 55 kb 35 and a temperature of 1550 ° C for 69 minutes. A composite product was formed, and in the mass attached to the carbide disk, it was found that an intimate mixture of metal and CBN grain was provided. The CBN grains were mainly smaller than 40 micrometers. The composite product could provide good polishing. The wear test groove had a depth of 0.023 mm.

U4Å15 9

EXAMPLE IV

A Mo cylinder (0.05 mm thick x 6.4 mm in diameter) was filled with a mixture of powders consisting of hexagonal BN (0.051 g) 2 grade "883 Carboloy" powder (0, Q33g), aluminum (0.005 g) and nickel (0.010 g) under a slice (thickness 1.3 mm) of quality "883 Carboloy" sintered carbide. At the same time, the composition was subjected to a pressure of 54 kb and a temperature of 1500 ° C for 124 minutes. A composite body was obtained in which a strong mass of CBN grain ^ had been formed and the spm was well bonded to the carbide disk. The CBN grains tended to be columnar but much smaller than in experiments lacking the carbide powder addition. The CBN grains were strongly retained in a metal matrix. The wear test groove had a depth of 0.013 mm.

15

EXAMPLE V

A Zr cylinder (0.05 mm thick x 8.9 mm in diameter) was filled with a powdery mixture of hexagonal BN (0.100g) and NiAlg (0.02Qg) over which a disc (2.9 mm thick) 2Q of quality "883 Carboil" sintered carbide. Prior to insertion into the Zr cylinder, the powdered mixture had been cold pressed on pill form and heated in NHg at 900 ° C for 1 hour.

At the same time, the composition was subjected to a pressure of 54 kb and a temperature of 1500 ° C for 62 minutes. It was found that "c" had developed small lumps of CBN on the carbide disk from the hexagonal BN / NiAlg mixture.

EXAMPLE VI

A Mo cylinder (0.05 mm thick x 6.4 mm in diameter) was charged 2q with a powdery mixture (capable of passing a mesh of 128 meshes per cm) consisting of hexagonal BN (0.050 g), Co (0.012 g), W (0.003g), Al (0.003g) under a slice (1.3 mm thick) of quality "883 Carboloy" sintered carbide. The composition was simultaneously subjected to a pressure of 54 kb and a temperature of 1460 ° C for 120 minutes. A sintered strong composite mass was obtained which polished well.

The CBN portion consisted of small grains (e.g., less than 30 microns) of CBN with thin metal layers between them. The wear test groove had a depth of 0.010 mm).

14441B

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EXAMPLE VII

Εη Mo cylinder (8.9 mm in diameter) was filled with a mixture of powders consisting of hexagonal BN (0.100g), fv ^ Alg (0.010g) and Mo (0.007g) under a slab (3mm thick) of quality "883-Carboloy" -5 sintered carbide. The powders had been cold pressed in pill form and heated in hydrogen at 800 ° C for 1 hour before being introduced into the Mo cylinder. At the same time, the composition was subjected to a pressure of 55 kb and a temperature of 1500 ° C for 70 minutes. A composite product was obtained in which a strong, hard mass adhered to the carbide.

10 The composite product polished very well. The hard mass consists of fine CBN crystals in a metal matrix.

EXAMPLE VIII

A containment member consisting of a Mo sleeve (0.025 mm thick 15 x 6.4 mm diameter) together with a Mo slice (0.05 mm thick) was filled with a Ni slice (0.034g), an Al slice (0.004g) bordering the nickel disk, a slice (1.3mm thick) of quality “883 Carboloy” sintered carbide and a mixture of hexagonal BN (0.025g) and CBN crystals (1-10µ, 0.025g ) placed as a mass between 20 the sintered carbide disk and the two metal discs, the composition was simultaneously subjected to a pressure of 55 kb and a temperature of 1550 ° C for 60 minutes, a composite product consisting of a hard bonded solid was obtained The hard mass consists of CBN crystals of any column shape that are retained in a metal 25. The wear test groove had a depth of 0.030 mm.

Reference is now made to the composite tool inserts shown in FIG. 3, 5 and 6, in the preparation of these non-circular blanks, a modified design of the salt liner 21 and plugs 22, 22 'is required. Thus, the structure fitting in the heating tube 20 may be formed as a series of cylindrical blocks in stacked cooperative arrangement to provide molds which can be filled with a pre-formed sintered carbide body 52 (or with the powder components thereof), a mass 53 of hexagonal BN (or hexagonal BN and CBN fingods) or hexagonal BN as well as the carbide powder mixture and the alloy system. By way of example, the salt block 21a in FIG. 7 is provided with a recess 54 corresponding to the shape of the desired tool insert, taking into account the thickness of the protective metal shield 56. The recess 54 is lined with metal 56 as shown and the masses 52 and 53 are of suitable size. placed herein. The catalyst system for the mass 53 can be supplied as a powdery mixture of aluminum and the alloying component thereof (selected from the group consisting of Co, Ni and Mn) interrupted by the hexagonal BN or as slices (not shown) by a outer surface of the mass 53. The low salt block 21b is provided with recesses to open space for the cover plate 57 which completes the protective metal enclosure for the powder and preferably a sintered carbide SC reserve block to reduce puncturing of the protective metal layer 57. A number of such cooperatively pairs of salt blocks such as 21a, 21b may be used with said content.

In the composite tool insert assembly 60 shown in FIG. 3, both surfaces 61 and 62 of the cemented carbide 63 and the CBN compact mass 64 are inclined (Fig. 4) 15 to facilitate alignment of the CBN cutting edges of the CBN compact blank 64 relative to the workpiece.

In designing the thin layers 71, 81 of the consolidated CBN in the tool insert structures 72, 82 shown in FIG. 5 and 6, the layer of CBN on the sintered carbide bodies, respectively, 73, 83 20 is limited to a maximum thickness of approx. 1.5 mm and a minimum thickness of approx. 0.025 mm, although the possibility exists of making such layers in thicknesses up to approx. 2.0 mm. The intention of deliberately making these layers 71, 81 very thin is that a) produce the CBN layers 71, 81 as chip break surfaces and b) facilitate the sharpening of the tool inserts 72, 82. Ideally, the relationship between the properties of the CBN layer and the cemented carbide such that the edge of the CBN layer will wear away slightly more slowly than the cemented carbide. When this is the case, a small portion of the CBN layer will continue to protrude from the cemented carbide body and provide a cutting edge and the amount of CBN used will correspond to the tool life.

After completing the high-temperature high-pressure treatment, the temperature is first reduced and then the pressure. In providing the tool insert masses, the protective shield metal remains bonded to their external surfaces. The exposure of the desired surfaces to the composite tool insert is achieved by simply abrasive the protective shield.

Special properties can be imparted to the CBN layer by introducing tungsten into the system. This can be done deliberately in the form of 12 UU15 tungsten metal or as tungsten carbide addition to the hexagonal BN content.

It is to be understood that composite products made by the practice of the present invention will usually be associated with a larger body, e.g. a tool shank or cutter on drill bit for advancing against the material to be treated.