NO151691B - TOOL COMPONENTS, SPECIFICALLY FOR CUTTING, DRILLING AND CUTTING TOOLS, AND PROCEDURES IN MANUFACTURING THEREOF - Google Patents

Description

The invention relates to machine tool components, in particular

for cutting, drilling and forming tools, and more specifically machine tool components comprising compacted articles of abrasive particles of diamond or cubic boron nitride.

It has been shown that a compacted diamond object produced

as described in US patent document no. 3745623 and in US patent

document no. 3609818, has limited application due to the fact that it breaks down thermally at a temperature above approx. 700°C. It has also been shown that a compacted object of cubic boron nitride (KBN) produced as described in US patent document no. 3767371 and in US patent document no. 3743489 has limited application. It also breaks down thermally at a temperature above approx. 700°C. This precludes the use of such compacted objects for applications where it is required that (1) the compacted object be bonded to a substrate by means of a brazing material with a melting point close to or above the com-

compacted object's thermal decomposition point or (2) that the compacted object is to be cast into a wear-resistant base material with a high melting point, as commonly used in a surface-hardened drill bit for rock.

The invention thus relates to a tool component, in particular

for cutting, drilling and shaping tools, with abrasive par-

ticles of diamond or cubic boron nitride, a metallic sintering aid and empty pores, and the tool component is special-

characterized by the fact that the abrasive particles are self-bound and make up 70-95% by volume of the tool component, that 0.05-3% by volume of the tool component consists of the metallic sintering aid

agent that serves to bind the self-bound particles together,

and that the empty pores delimited by the self-bound particles are distributed in the tool component with an interconnected structure, the pores making up 5-30% by volume of the tool component.

The invention also relates to a method of manufacture

of a tool component according to the invention, where

a) a mass of diamond particles or of particles consisting of cubic boron nitride, and also a mass of metallic

sintering aid for the particle mass in question is introduced into a reaction vessel,

b) the reaction vessel with its contents is simultaneously exposed to temperatures in the range of 1200-2000°C and pressure above 40

kilobar,

c) the heat supply to the reaction vessel is shut off and the pressure is reduced, and d) the grinding body formed in process steps a) to c) and which consists of the particles directly bonded to each other and the

metallic sintering aid that has seeped between the particles is removed from the reaction vessel, and the method is characterized by the fact that the metallic sintering aid that has been introduced into the body is removed from it until a proportion of 0.05-3 volume remains in the body % of the body.

The invention will be described in more detail with reference to the drawing which is a photomicrograph of part of a ground surface of a compacted object of diamond and produced according to the invention.

Although a compacted object of diamond is shown in Fig. 1, this is equally illustrative of other embodiments of the invention where the abrasive particles are made up of cubic boron nitride.

The compacted object comprises diamond particles 11 which make up 70-95% by volume of the compacted object (particle is used herein to denote a separate crystallite or a fragment thereof). Interfaces 13 are representative of the self-bonding or diamond-diamond bonding between neighboring particles 11. The same diamond crystals 11 that can be seen in the ground surface of the compacted object shown in the drawing are bonded in the third dimension to the neighboring diamond crystals (not visible). A metallic phase of the sintering aid material (not shown in the drawing) is substantially uniformly infiltrated throughout the compacted object and is believed to be encapsulated in closed areas formed by adjacent diamond particles. This phase makes up 0.05-3% by volume of the compacted object. A network of interconnected,

empty pores 15 are dispersed throughout the compacted re-

state and is delimited by the diamond particles 11 and the metallic phase (not shown). The pores 15 make up 5-30% by volume of the compacted object.

According to one embodiment, the compacted object consists exclusively of the self-bound particles. According to another embodiment, the compacted object is bonded to a substrate (not shown), preferably of cobalt cement-tungsten carbide.

An acceptable particle size range for the diamond particles 11 is 1-1000 pm. For cubic boron nitride, the acceptable size range is 1-300 pm.

"Simultaneous" as used in step (b) of the present method is intended to mean that the high pressure/high temperature (HP/HT) conditions exist or occur at the same time, but does not imply that it is necessary that the times for the beginning or the end of The HP and HT conditions must coincide (although occasionally they can).

"Sintering aid" or "material" as used herein

is intended to denote materials which are a catalyst for diamond as further explained below, and/or which promote the sintering of cubic boron nitride as further explained below. The mechanism (catalytic or otherwise) underlying the sintering aid materials' promotion of the self-bonding of cubic boron nitride is not known.

Preferred embodiments of steps (a) - (d) of the above method in the manufacture of a tool component of diamond particles are more fully described in US Patent Documents No. 3745623 and in US Patent Document No. 3609818.

Briefly summarized, as described in these patents, compacted objects of diamond are produced by processing under high pressure and high temperature, where hot, compressed diamond particles are infiltrated with a catalytic material by axial or radial flow of the material through the diamond particles. During the flow, catalyzed sintering of the diamond particles occurs, and this leads to a strong diamond-diamond bond.

As described in US patent documents no. 2947609 and no. 2947610 is

the catalytic material selected from the group (1) a catalytic metal in an elemental state from the group consisting of the metals Cr, Mn and To from group VIII of the periodic table, (2) a mixture of alloyable metals of the catalytic metal or metals and the or the non-catalytic metals, (3) an alloy of at least two of these catalytic metals, and (4) an alloy of the catalytic metal or metals and the non-catalytic metal or metals. Cobalt in elemental form or as an alloy is preferred. This material forms a metallic phase in the abrasive article which has been produced at high pressure and high temperature, as indicated in the above step (d).

Preferred embodiments of steps (a) - (d) of the above-described method of manufacturing a tool component of cubic boron nitride particles are more fully described in US Patent No. 3767371. As described in and in connection with Example 1 herein patent, compacted objects of cubic boron nitride are produced by an HP/HT process, where particles of cubic boron nitride are infiltrated with a molten sintering aid material (metallic cobalt) by axial flow of the material through the cubic boron nitride particles. During the flow through, sintering of the cubic boron nitride particles occurs, and this leads to an extensive binding of cubic boron nitride particles to each other. Other materials that can be used as sintering aids for cubic boron nitride are described in US patent document no. 3743489, column 3, line 6 - line 20, and are alloys of aluminum and an alloying metal from the group of nickel, cobalt, manganese, iron, vanadium and chromium. Cobalt and cobalt alloys are preferred. The sintering aid material forms the metallic phase described in step (d) above.

In the execution of an embodiment of steps (a) - (d) according to US patent documents no. 3745623,. no. 3767371 and no. 3743489, a composite compacted object is produced by in situ bonding of a layer of abrasive particles (diamond or cubic boron nitride)

to a cemented carbide substrate. The material for making the carbide substrate (either from a carbide casting powder or from a preformed article) is the preferred source of the sintering aid material. Reference can be made here to US patent no. 3745623, column 5, line 58 - column 6, line 8, and to column 8, line 57

-column 9, line 9, for example details regarding the substrate.

Another embodiment of the invention concerns the formation of

a compacted object consisting essentially of self-bonded abrasive particles. In this embodiment, steps (a) - (d) are carried out in the same way as described above, but with the difference that the material for forming the carbide substrate for the layer of abrasive particles, either as a carbide casting powder or in a preformed state, is preferably looped. When this is done, the sintering aid material is separately added, e.g. as described in US patent no. 3609818. A substrate of cemented carbide or other material can of course be brazed to the compacted object after the metallic phase has been removed,

for obtaining a tool blank or insert.

According to the invention, it has been shown that the metallic phase can be removed from the compacted object by treatment with an acid, by extraction with liquid zinc, by electrolytic depletion or by similar processes, so that a compacted object of essentially 100 % abrasive particles in self-bonded state. The compacted object thus essentially contains no residual metal phase which would be able to catalyze a reverse conversion of the bonds between the abrasive particles and/or an expansion and thereby break the bonds between the particles, these being the two mechanisms which, according to the theory, have led to the known compacted objects have been thermally degraded at high temperature. It has been shown that the compacted object produced according to the invention can withstand temperatures of up to 1200-1300°C without any significant thermal degradation.

Example 1

A series of disk-shaped compacted diamond objects were prepared by 1) a 1.4 mm layer of finely divided diamond particles with a nominal size of less than 8 pm and 3.2 mm thick x 8.8 mm diameter cemented tungsten carbide (13 wt% Co, 87 wt % WC) was placed in a 0.05 mm container assembly of zirconium, 2) a number of these assemblies were stacked in a high-pressure, high-temperature apparatus according to Fig. 1 for the container in US patent document no. 3745623, 3) the pressure was increased to approx. 65 kilobars and at a temperature of approx. 1400°C for 15 minutes, 4) the temperature was first slowly lowered and then pressed, and 5) the samples were removed from the high-pressure-high-temperature apparatus and ground to obtain compacted objects with 0.5 mm thick diamond bonded to the cobalt-cemented tungsten carbide layer with a thickness of 2.7 mm. The carbide layer for each compacted object was removed by surface grinding.

As indicated in Table I, half of the samples were leached with hot, concentrated acid solutions to remove the metal phase and any other soluble materials that did not consist of diamond. Two different methods were used to remove the infiltrating material. For a first group, designated as samples A-I and A-4, only hot (concentrated nitric acid-fluoric acid in a ratio of 1:1) was used to treat samples A-3 and A-4. On another group, designated as samples B-l —B-4, the alternating nitric acid-flux-acid mixture and a hot mixture of concentrated hydrochloric acid-nitric acid (aqua regia) in the ratio 3:1 were used to treat samples B-3 and B-4. It was found that the rate of removal increased greatly by to use the latter acid solution. Samples A-3 and A-4 were treated with acid for a time between 8 and 12 days. Samples B-3 and B-4 were treated for between 3 and 6 days. For

with both methods, the dimensions of the samples did not change during treatment, and no flaking of the diamond could be observed. One

any weight loss can therefore be attributed to the removal of the infiltrating metal phase because diamond is not dissolved by the acids.

The amount of the infiltrating metal phase in such compacted objects was calculated to be approx. 80.1% by volume, or 19.8% by weight, based on specific gravity measurements of the compacted object, before leaching due to the diamond and metal starting materials for the production of the compacted object. After leaching, approx. 0.5 volume* or 2% by weight of the infiltrating material back. The removal of up to 90% by weight (sample B-4) of the infiltrating material further suggests that the localization of the majority of the metallic phase is in a continuous network of pores. An examination using scanning electron microscopy (SEM) of a fractured surface of a leached sample shows that the network of pores runs through the entire diamond layer. The holes are found to be distributed throughout the layer, and most holes have a diameter of less than 1 pm. This suggests that the acid penetrated the overall diamond layer and removed the metallic phase essentially uniformly throughout this layer. The transverse breaking stress (TBS) and Young's modulus of elasticity (E) were also measured for the diamond layers, as indicated in Table I. The stress measurement was carried out using a load apparatus with a beam supported at three points. The apparatus comprises two steel rollers which are arranged on a support, and with a third steel roller centered above and with its axis parallel to the axis of the other two rollers. The samples were centered over the lower rollers and loaded until failure. The strain of the samples was measured in parallel with the tensile stress using resistance strain gauges attached to a resistance indicator. The samples A-I to A-4 were prepared for the stress measurement and surface treated with a diamond disc (diamond particles with a size of 177-250 pm). Samples B-1 to B-4 were prepared for stress measurement by being surface treated with a lapping machine using a 15 µm diamond abrasive to obtain a more crack-free surface than the surface obtained by grinding for samples A-I to A-4. It is assumed that the better polished surfaces for the samples that were "surface treated with finely divided diamond" give higher stress values due to the achieved more perfect surface conditions, i.e. fewer stress concentrating defects. This is believed to explain the lower TBS that was measured for the leached samples (A-3, ;A-4, B-3 and B-4). ;Unlike the TBS test results, the E measurements (Table I) are not affected by the porosity because E is a measure of a material's internal strength and stiffness and not for micro-cracking. The average change in E was only about 12% lower when the infiltrating metal phase was removed from the samples. This difference should be corrected for the porosity of the leached samples because ;E = Young's modulus ;M = moment ;C = distance to the outer fiber ;I = moment of inertia of the area, ;and M-C does not change, but I has been reduced due to the fact that the effective area has been reduced in proportion to the porosity. If therefore spherical voids and an arbitrary distribution assumed, E <=><Y>~~fl-x)' X = Porosity fraction, °9; the value for E would be greater than the measured one. The average value of 79 x lo 3 kg/mm 2 for E for samples B-3 and B-4 (leached) is corrected to 85 x IO<3> kg/mm<2> or approx. 5% lower than the average value of 90 x 10 3 kg/mm 2 for E for samples B-1 and B-2. The removal of the infiltrating metal phase therefore has only a very small effect on E and shows that the strength of the diamond layer is almost entirely due to the diamond-diamond bond. The E-value of 90 x 10 3 kg/mm 2 is approx. 10% lower than the average value of 100 x 10 3 kg/mm 2 which can be calculated from elasticity constants for single crystals of diamond. ;Example 2 ;A compacted article was prepared in the same manner as described in Example 1 for samples A-I to A-4, but with the exception that a 1:1 mixture of 149-177 pm and 105-125 pm diamond particles was used instead of the particles at 8 p.m. Before the leaching, it was calculated that the compacted object contained 89.1% by weight diamond (96.5% by volume) and 11.9% by weight metal phase (4.5% by volume). After leaching, there was a reduction of 11.5% of the total weight of the compacted object or approx. 0.15% by weight of the metallic phase (0.06% by volume) was back in the compacted article. Example 3 Four compacted diamond objects were prepared as described in Example 1. The carbide was ground away from each compacted object. For two of these, the infiltrating metal phase was removed by leaching with hot acids consisting of ;1HF:1HN03 and 3HC1:1HNC>3. All compacted objects were then epoxy mounted onto a 0.89 cm round tungsten carbide substrate. This composite object was mounted in a tool holder in a lathe, and investigations to determine the resistance to wear during turning were then carried out. The workpiece was a rubber block filled with quartz sand and sold under the trademark "Ebonite Black Diamond". The test conditions were as follows: surface speed' 107-168 surface meters/min (for a heat treatment group the maximum speed was 24 surface meters/min), depth of cut 0.76 mm, cross feed 0.13 mm/rev and test time 60 minutes. After the experiment, the samples were heat-treated in a tube furnace in a flowing, dry argon atmosphere. The treatment temperatures were 700-1300°C with exposure at intervals of 100°C. The exposure time was 10 minutes at each temperature. After each treatment, the samples were examined to determine degradation under a scanning electron microscope (SEM) and then mounted for abrasion examination, with the exception of after the treatments at 1000°C, 1100°C and 1300°C. Both top and bottom edges were used as cutting edges before they were ground again. The abrasion test results are given in Table II. ;The samples remained essentially the same during the examination. There was a tendency for reduced abrasion resistance from the untreated samples and for the first heat treatment at 700°C. The non-leached samples, samples 3 and 4, did not change until a catastrophic thermal failure occurred between 800 and 900°C. The heat treatment proved to be independent of the abrasion resistance until the diamond phase could no longer contain the enclosed metal phase and cracking occurred. This behavior also suggests that two separate phases are present, i.e. the bonded diamond phase which performs the cutting during the test, and the metal phase which is a remnant from the sintering process. The leached samples, i.e. samples 1 and 2, resisted the heat treatment very well, even up to 1200°C. The tendency at 1200°C appears to be a slight degradation of the sample, and this may suggest the initiation of a thermal back-conversion at the surface. ;;The results in table II represent the time per wear unit for the compacted object in 2.54 cm x 100. Tool wear was determined by measuring the width of the "face" on the compacted object caused by contact with the workpiece. The results are of significance only for comparing the relative behavior of the leached and non-leached samples. The leached samples have on average a higher test result than the non-leached samples. This may be due to thermal degradation of the non-leached compacted object during the cutting tests carried out with the samples. The same degradation mechanism can thus work during the abrasion tests as during the heat treatments. If this is the case, when the tool tip is heated to a high temperature when in contact with the workpiece, the cobalt phase will expand more strongly than the diamond phase and crack the tip edge in the first few particle layers. The damaged tip is thereby weakened and gives a worse result. However, the leached samples are thermally stable against a higher working temperature and are not thermally damaged when they are in contact with the workpiece. SEM analysis showed that the non-leached samples had a number of different properties compared to the leached samples. The metallic phase began to extrude from the surface at a temperature between 700 and 800°C, as observed under a magnification of 2000X. As the temperature was increased to 900°C, the samples cracked radially from the rounded cutting edge towards the center of the sample. The leached samples did not show this behaviour, but remained relatively unchanged up to a temperature of 1300°C. The diamond layers are clean at 1200°C, but at 1300°C the samples in photographs taken at 20x magnification looked rounded and fluffy, and photographs taken at 1000X magnification showed an etched surface. with a number of exposed crystals. This is presumably a thermal degradation of the surface, but may also be the result of minor oxygen contamination in the tube furnace's argon atmosphere. Example 4 Two compacted diameter objects (samples IV-1 and IV-2) were produced as described in example 1, but with the change that the carbide substrates were not ground off. An epoxy resin ("Epon 826" resin with nodic methyl anhydride and benzyldimethylamine curing agent) was cast around sample IV-1 and cured. The surface of the diamond layer was exposed by removing all plastic on the surface of the layer with sand. Sample IV-1 was then placed in boiling 3 HC1:1 HNO2 ; for 37.15 hours. After the acid had been removed, the plate was removed from the carbide layer and visually inspected. Signs of a weak reaction between the acid and the unexposed surfaces were observed. However, the surface of the carbide layer did not appear to be significantly damaged by the acid. The diamond layer* surface was then examined under a SEM (with a magnification of up to 2000X). The surface of the diamond layer had a similar appearance to the appearance of the diamond layer of the leached samples of Example 1. Sample IV-1 was then examined by energy dispersive X-ray analysis to compare the intensities of the constituents of the metallic phase with those of a compacted object of the same type, but which had not been leached. The results of the SEM analysis and X-ray analysis suggested that the acid penetrated the diamond layer and acted to remove a significant part of the metallic phase.

Samples IV-1 and IV-2 were then subjected to an abrasion-rotation test which was performed in the same manner as described in Example 3. The abrasion test results (calculated as in Example 3) were 120-150 for sample IV-1 (leached) and 100-120 for sample IV-2 (not leached). These test results showing the superiority of the leached compacted article agree with the results obtained according to Example 3, and they thus substantiate that when the metallic phase is removed in the area of the cutting edge, the results obtained with the compacted diamond article are improved.

Claims (10)

1. Tool component, especially for cutting, drilling and shaping tools, with abrasive particles of diamond or cubic boron nitride, a metallic sintering aid and empty pores, characterized in that the abrasive particles are self-bonded and make up 70-95% by volume of the tool component, that 0.05-3% by volume of the tool component consists of the metallic sintering aid which serves to bind the self-bonded particles together, and that the empty pores delimited by the self-bonded particles are distributed in the tool component with an interconnected structure, the pores makes up 5-30% by volume of the tool component. 2. Tool component according to claim 1, characterized in that the abrasive particles consist of diamond particles and that the metallic sintering aid consists of (1) a catalyst metal from group VIII in the periodic table, chromium, manganese and tantalum or a mixture of these or of (2) an alloy of at least two of the aforementioned catalyst metals. 3. Tool component according to claim 1 or 2, characterized in that the diamond particles have a particle size within the range 1-1000 µm. 4. Tool component according to claim 1, characterized in that the particles consist of cubic boron nitride and that the metallic phase, which is essentially uniformly distributed in the tool component, consists of cobalt, a cobalt alloy or an alloy of aluminum with nickel, manganese, iron, vanadium or chromium as the alloying metal. 5. Tool component according to claims 4 and 4, characterized in that the particles consist of cubic boron nitride with a particle size of 1-300 µm. 6. Tool component according to claims 1-5, characterized in that the self-bonded particles are bonded to a substrate of cemented carbide. 7. Method for the production of a tool component according to claims 1-6, where 1 a) a mass of diamond particles or of particles consisting of cubic boron nitride, and also a mass of metallic sintering aid for the relevant particle mass is introduced into a reaction vessel, b) the reaction vessel with its contents is simultaneously exposed to temperatures within the range of 1200-2000°C and pressure above 40 kilobars, c) the heat supply to the reaction vessel is shut off and the pressure is reduced, and d) the grinding body formed in process steps a) to c) and which consists of the directly to particles bound to each other and the metallic sintering aid that has seeped between the particles are removed from the reaction vessel, characterized in that the metallic sintering aid which has been introduced into the body is removed from it until there remains in the body a proportion which constitutes 0.05-3% by volume of the body. 8. Method according to claim 7, characterized in that the metal is removed from the body by immersing the body in an acid, preferably aqua regia, nitric acid, hydrochloric acid or hydrofluoric acid. 9. Method according to claim 7, characterized by the metal being removed from the body by extraction with liquid zinc. 10. Method according to claim 7, characterized by the metal being released from the body by means of electrolysis.