Improved diamond tools for rock drilling, metal cutting and wear part applications

Abstract: The present invention relates to buttons, inserts and bodies for rock drilling, rock cutting, metal cutting and wear part applications. The buttons, inserts and bodies comprise cemented carbide provided with bodies and/or layers of CVD- or PVD-fabricated diamond and then HP/HT treated in the diamond stable area. All the bodies of cemented carbide should have a uniform structure or a multi-structure containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase.

Description: FIELD OF THE INVENTION The present invention concerns the fields of rock drilling, metal cutting and wear part applications. More particularly the invention relates to bit buttons for percussive and rotary crushing rock drilling, bit inserts for rock cutting, inserts for metal cutting such as turning, milling and drilling and bodies for various wear part applications. The buttons, inserts and bodies comprise cemented carbide provided with layers of diamond. BACKGROUND OF THE INVENTION There are three main groups of rock drilling methods: percussive, rotary crushing and cutting rock drilling. In percussive and rotary crushing rock drilling the inserts generally have a rounded shape, often of a cylinder with a rounded top surface generally referred to as a button. In rotary cutting rock drilling the inserts are provided with an edge acting as a cutter. The inserts for metal cutting are provided with a sharp edge acting as a cutter. The bodies for various types of wear part applications have different non-cutting configurations. There already exists a number of such high pressure-high temperature sintered buttons, inserts and bodies of cemented carbide provided with polycrystalline diamond bodies or layers. The technique when producing such polycrystalline diamond tools using high pressure-high temperature (HP/HT) where diamond is the stable phase has been described in a number of patents, e.g.: US Patent No 2,941,248: "High temperature high pressure apparatus". US Patent No 3,141,746: "Diamond compact abrasive". High pressure bonded body having more than 50 vol% diamond and a metal binder: Co, Ni, Ti, Cr, Mn, Ta etc. These patents disclose the use of a pressure and a temperature where diamond is the stable phase. In some later patents: e.g. US Patent Nos 4,764,434 and 4,766,040 high Pressure-high temperature sintered polycrystalline diamond tools are described. In the first patent the diamond layer is bonded to a support body having a complex, non-plane geometry by means of a thin layer of a refractory material applied by PVD or CVD technique. In the second patent temperature resistant abrasive polycrystalline diamond bodies are described having different additions of binder metals at different distances from the working surface. A recent development in this field is the use of one or more continuous layers of polycrystalline diamond on the top surface of the cemented carbide button. US Patent No 4,811,801 discloses rock bit buttons including such a polycrystalline diamond surface on lop of the cemented carbide buttons. Another development is disclosed in US Patent No 4,592,433 including a cutting blank for use on a drill bit comprising a substrate of a hard material having a cutting surface with strips of polycrystalline diamond dispersed in grooves, arranged in various patterns. US Patent No 4,784,023 discloses a cutting element comprising a stud and a composite bonded thereto. The composite comprises a substrate formed of cemented carbide and a diamond layer bonded to a substrate. The interface between the diamond layer and the substrate is defined by alternating ridges of diamond and cemented carbide which are mutually interlocked. The top surface of the diamond body is continuous and covering the whole insert. The sides of the diamond body are not in direct contact with any cemented carbide. US Patent 4,819,516 discloses a cutting element with a V-shaped diamond cutting face. The cutting element is formed from a single circular cutting blank by cutting the blank into segments, joining two identical ones of the segments and truncating the joined segments. Also in this case the surface of the diamond body is continuous and the sides are not in direct contact with any cemented carbide. European Patent Application No 0312281 discloses a tool insert comprising a body of cemented carbide with a layer of polycrystalline diamond and between the layer and the cemented carbide a number of recesses filled with abrasive compact material extending into the supporting body of cemented carbide. US Patent No 4,871,377 discloses a composite compact including a table of diamond particles with a strong, chemically inert binder matrix and a thin metal layer bonded directly to the table in a HP/HT press. Another development in this field is the use of cemented carbide bodies having different structures in different distances from the surface, such as disclosed in US Patent No 4,743,515 and No 4,843,039 where bodies of cemented carbide containing eta-phase are surrounded by a surface zone of cemented carbide free of eta-phase and having a low content of cobalt in the surface zone and a higher content of cobalt closer to the eta-phase zone. US Patent 4,820.482 discloses rock bit buttons of cemented carbide having a content of binder phase in the surface that is lower and in the center higher than the nominal content. In the center there is a zone having a uniform content of binder phase. The tungsten carbide grain size is uniform throughout the body. US-A-4 931 068 discloses a method for consolidating finely divided diamond particles to produce a fully dense article. The particles are heated to an elevated temperature for compacting to form the article. The article is then held at said temperature for rearrangement and reduction of the dislocations in the article. EP-A-389 800 discloses a method for producing tool blanks, at which an assembly having a mass of diamond or CBN particles and a mass of cemented carbide is subjected to a high pressure/high temperature process resulting in diamond or CBN compacts. EP-A-384 011 discloses a diamond-coated sintered body in which layers of diamond have been deposited by CVD- or PVD-technique on a cemented carbide body. OBJECT OF THE INVENTION The object of the invention is to provide diamond tools for rock drilling, metal cutting and wear part applications having buttons, inserts or bodies of cemented carbide provided with diamond layers with high and uniform compression of the diamond by sintering the diamond and the cemented carbide together at high pressure and high temperature in the diamond stable area. The diamond layers are fabricated by CVD- or PVD-technique before the HP/HT treatment. It is a further object of the invention to make it possible to maximize the strength of the diamond to resist cracking, chipping and wear. SUMMARY OF THE INVENTION The cemented carbide buttons, inserts and bodies according to the present invention are provided with one or more layers of diamond and then HP/HT treated. The layers of diamond are prefabricated by CVD-or PVD-technique directly on to the cemented carbide. BRIEF DESCRIPTION OF THE DRAWINGS 1 = cemented carbide button or insert 2 = diamond coating directly deposited by CVD- or PVD-technique 3 = prefabricated diamond body made by CVD- or PVD-technique 4 = cemented carbide : Co poor zone 5 = cemented carbide : Co rich zone 6 = cemented carbide : eta-phase containing core 7 = brazing metal or alloy FIG.1 shows a cemented carbide insert having a layer of directly deposited CVD-diamond (prior art). FIG.2 shows a cemented carbide insert having the same type of layer of diamond as in FIG.1 but with the cemented carbide containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase. FIG.3 shows a cemented carbide insert similar to FIG.1 but with a layer of brazing alloy between the CVD-diamond and the cemented carbide (prior art). FIG.4 shows a cemented carbide insert similar to FIG.3 but with the cemented carbide containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase. FIG.5 shows an insert similar to FIG.1 but where the insert has been HP/HT treated according to the invention). FIG. 6 shows a cemented carbide insert similar to FIG.2 but where the insert has been HP/HT treated (according to the invention). FIG.7 shows an insert provided with a number of separately fabricated bodies of CVD-diamond that have been placed into prefabricated holes in the cemented carbide and brazed. FIG.8 shows a cemented carbide insert similar to FIG.7 but with the cemented carbide containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase. FIG.9 shows an insert similar to FIG.7 but without any brazing. Instead the insert has been HP/HT treated. FIG.10 shows a cemented carbide insert similar to FIG.9 but with the cemented carbide containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase . FIG.11 shows a cemented carbide button provided with a number of separately fabricated bodies of CVD-diamond that has been placed into prefabricated holes in the cemented carbide and brazed. FIG.12 shows a cemented carbide button similar to FIG.11 but with the cemented carbide containing surrounded by a surface zone of cemented carbide free of eta-phase. FIG.13 shows a cemented carbide button provided with a number of separately fabricated bodies of CVD-diamond that have been placed into prefabricated holes in the cemented carbide and then HP/HT treated. FIG.14 shows a cemented carbide button similar to FIG.13 but with the cemented carbide containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase. FIG.15 shows a cemented carbide button provided with a top layer of directly deposited CVD-diamond (prior art). FIG.16 shows a cemented carbide button similar to FIG.15 but with the cemented carbide containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase. FIG.17 shows a cemented carbide button similar to FIG.15 but where the button has been HP/HT treated (according to the invention). FIG.18 shows a cemented carbide button similar to FIG.16 but where the button has been HP/HT treated (according to the invention). DETAILED DESCRIPTION OF THE INVENTION. According to the present invention there are provided buttons inserts and bodies for rock drilling, metal cutting and wear part applications comprising a body of cemented carbide with conventional uniform structure or having a multi-structure according to US Patent No 4,743,515. The cemented carbide body is provided with one or more layers of diamond that are fabricated by CVD- or PVD-technique and then attached to the cemented carbide body by the HP/HT technique. The HP/HT treatment gives a favourable stress distribution, i.e. a high and uniform compression of the diamond caused by the difference in thermal expansion between the cemented carbide and the diamond. Furthermore the HP/HT treatment gives a strong binding between the cemented carbide and the diamond and a healing of small defects like cracks in the CVD/PVD diamond as well as a transformation of graphite residues into the diamond. A number of different combinations may also be used between various bodies and layers of CVD/PVD-made diamond and between these and conventional types of HP/HT-sintered diamond, e.g. untreated CVD/PVD-layer on top of HP/HT treated CVD/PVD-layer. HP/HT treated CVD/PVD-layer on a substrate that has been provided with a thin layer of TiN or other material that can prevent the migration of binder metal like Co. HP/HT treated CVD/PVD-layer on top of a body or layer of conventional HP/HT- sintered diamond. HP/HT treated CVD/PVD-layer between bodies or layers of conventional HP/HT-sintered diamond. The buttons, inserts and bodies above can be adapted to different applications by changing the material properties and geometries of the cemented carbide and the diamond, especially hardness, elasticity and thermal expansion, giving different wear resistance and strength. The thickness of the layers of diamond shall be 50 micrometer - 2 mm, preferably 50 micrometer - 1 mm. The cemented carbide grade shall be chosen with respect to the application, i.e. rock drilling, rock cutting, metal cutting or wear part applications. It is important to chose a grade which has a suitable wear resistance compared to that of the diamond body or layer. The binder phase content shall be 3-35 weight % and the grain size of the cemented carbide at least 1 micrometer, preferably 2-6 micrometer. The cemented carbide shall have a uniform structure or a multi-structure according to US Patent 4,743,515 having a core containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase. The size of this core shall be 10-95%, preferably 30-65% of the total amount of cemented carbide in the button or insert. The core should contain at least 2% by volume, preferably at least 10% by volume of eta-phase but at most 60% by volume, preferably at the most 35% by volume. In the zone free of eta-phase the content of binder phase, i.e. in general the content of cobalt, shall in the surface be 0,1-0,9, preferably 0,2-0,7 of the nominal content of binder phase and the binder phase content shall increase in the direction towards the core up to a maximum of at least 1,2 preferably 1,4-2,5 of the nominal content of binder phase. For metal cutting applications the zone free of eta-phase shall be below 1 mm, preferably below 300 micrometer thick. The width of the zone poor of binder phase shall be 5-100 micrometer. For other applications the width of the zone poor of binder phase shall be 0,2-0,8, preferably 0,3-0,7 of the width of the zone free of eta-phase, but at least 0,4 mm and preferably at least 0,8 mm in width. The cemented carbide buttons, inserts and bodies are manufactured by powder metallurgical methods according to US Patent No 4,743,515. After sintering of the cemented carbide the bodies or layers of diamond are put on the surface of the cemented carbide body and HP/HT treated, normally in the diamond stable area, i.e. at high pressure, more than 3,5 GPa, preferably at 6-7 GPa and at a temperature of more than 1100 °C, preferably 1700 °C for 1-30 minutes, preferably about 3 minutes. In some cases the treatment can be done at lower pressures and temperatures such as more than 0,02 GPa and more than 500 °C. After the HP/HT treatment the buttons, inserts and bodies are blasted and ground to final shape and dimension. The invention has been described with reference to conventional cemented carbide. It is obvious, especially for metal cutting, that the cemented carbide may contain in addition so called gamma-phase. The invention also applies to so called cermets, i.e. titanium carbonitride based alloys and ceramic materials such as white ceramics, black ceramics and sialons. Hammer impact tests of inserts of the type according to FIG.1 with a substrate of cemented carbide and a top layer of directly deposited CVD-fabricated diamond revealed a strong tendency of chipping off after a small number of blows The same happened when a brazing alloy was used between the substrate and the CVD-diamond according to FIG.3. After using a HP/HT treatment according to FIG.5 the directly deposited CVD-diamond was surprisingly found to resist more blows and if the cemented carbide at the same time had a multi-structure according to US Patent No 4,743,515 the layer of CVD-diamond appeared to be still much stronger (FIG.6). A similar improvement was achieved for buttons according to FIG.15,17 and 18. The explanation of this effect, the increase of the resistance against chipping,might might be a favourable stress pattern caused by the difference between the thermal expansion of the diamond layer and the cemented carbide body, giving the layer a high and uniform compressive prestress. Another contributing effect might be the improvement of the binding between the cemented carbide and the CVD-diamond caused by the HP/HT treatment. Still another effect is the healing of small defects, e.g. cracks, in the CVD/PVD diamond body and the transformation of graphite residues into diamond. EXAMPLE 1 A hammer impact test was made using a modified Charpy pendulum and cemented carbide inserts according to FIG.1,3,5 and 6 having layers of directly deposited CVD-diamond. The diamond layer had a thickness of 0,7 mm. The total height of the inserts was 3,5 mm and the diameter 13,3 mm. The hammer was released from a certain height and the chipping was observed after each blow. The number of blows before chipping was taken as the measure of the shock resistance. RESULTS Number of blows before chipping Insert with a layer of CVD-diamond (FIG.1): 1 Insert with a layer of CVD-diamond and a layer of brazing (FIG.3): 1 Insert with a layer of CVD-diamond that has been HP/HT treated according to the invention (FIG.5) : 5 Insert with a layer of CVD-diamond and an eta-phase core and a HP/HT treatment according to the invention (FIG.6): 7 EXAMPLE 2 Example 1 was repeated but with cemented carbide buttons according to FIG.15,17 and 18 having layers of directly deposited CVD-diamond and with the hammer released from another height. RESULTS Number of blows before chipping Button with a layer of CVD-diamond (FIG.15): 1 Button with a layer of CVD-diamond that has been HP/HT treated according to the invention (FIG.17) : 4 Button with a layer of CVD-diamond and an eta-Phase core and a HP/HT treatment according to the invention (FIG.18): 6 EXAMPLE 3 Cemented carbide cutting tool inserts were coated with a 700 micrometer diamond layer using a high rate CVD method, e.g. DC arc jet. The geometry of the inserts was chosen to give a tool geometry of TPUN 160308 (slightly oversized) after deposition. The inserts were then subjected to a HP/HT treatment according to the invention. The final step was a grinding/lapping treatment to ensure a smooth surface finish of the diamond layer and that the insert was within the tolerances for the TPUN 160308 geometry. Machining tests were performed in 390 alloy (Al-18%Si) to compare the performance of the inserts according to the invention with 1/ inserts manufactured as above excluding the HP/HT treatment (prior art) 2/ inserts manufactured from a 700 micrometer free-standing diamond film that was brazed to the cemented carbide insert and ground to final geometry (prior art). The cutting conditions were as follows: longitudinal turning with coolant, cutting speed 700 m/min, feed rate 0,2 mm/rev and depth of cut 1,0 mm. In all cases tool life was determined by a maximum flank wear of 0,3 mm. The tool life results were as follows: Tool according to invention 750 min Prior art according to 1/ 1 min Prior art according to 2/ 400 min The short tool life in the case of prior art according to 1/ is due to immediate flaking of the coating.

Claims: Method of producing bodies of cemented carbide having a grain size of at least 1 micrometer and containing 3-35 weight-% binder phase for rock drilling, rock cutting, metal cutting and wear part applications, said bodies being provided with diamond layers, characterized in that the diamond layers are directly deposited to said bodies by CVD- or PVD-technique to a thickness of 50 micrometer - 2 mm and then HP/HT (high pressure/high temperature) treated in the diamond stable area in order to increase the adhesion. Method according to claim 1, characterized in that said bodies comprise cemented carbide with a multi-structure having an eta-phase containing core surrounded by a surface zone of cemented carbide free of eta-phase.

Inventors: DENNIS MAHLON D, FISCHER UDO, HILLERT LARS, WALDENSTROEM MATS, DENNIS, MAHLON D., FISCHER, UDO, HILLERT, LARS, WALDENSTROEM, MATS, Waldenström, Mats
Applicants: DIAMANT BOART STRATABIT SA, SANDVIK AB, DIAMANT BOART STRATABIT S.A., SANDVIK AKTIEBOLAG
Application year: 1991
Main classification: C23C16
IPC codes: C23C14, B22F7, C23C16, E21B10, B23P15