SE514667C2 - Diamond coated cemented carbide body especially a tool insert - Google Patents

Abstract

Body of cemented carbide or cermet coated with a diamond layer has a surface zone of depth 2-10 micron, preferably about 8 micron, at the interface with the diamond coating where the average binder content is at least 20% preferably about 50% lower than the nominal content. The coercive force of the body is at least 10%, preferably at least 20%, and especially about 30% higher than that for a reference body of the same WC phase grain size and binder content subjected to standard sintering and has a saturation magnetisation at most 95%, preferably at most 85%, and especially at most 70% of that of the reference body. Method comprises post-sintering an eta-phase containing cemented carbide body at 1400-1510 deg C, preferably about 1450 deg C, in an H2-containing carburising atmosphere prior to diamond coating, so as to convert eta-phase in the surface zone to carbides and binder phase.

Description

A similarly brittle core which proves to be insufficient for toughness demanding cutting applications. A more radical way of preparing a cemented carbide body for diamond coating is to use a very low binder phase content as described in WO 95/15258, but again the toughness of such a body is insufficient in some applications.

It is well accepted in the technology for diamond coating of cemented carbide that it is not possible to achieve a well-adherent coating without removing the bonding phase, typically Co, from a surface zone of the body.

It is therefore surprising to find that a well-adhering diamond layer deposited on a cemented carbide insert, by using a cemented carbide containing binder phase, can typically be obtained Co, in a surface zone near the diamond coating. This is achieved by a slight reduction in the binder phase concentration of the surface in combination with a carburizing treatment.

Fig. 1 shows in 120X the microstructure of a cemented carbide according to the invention.

Fig. 2 shows the concentration of the elements Co, W and C as a function of the distance from the surface of the body in a diamond-coated body according to the invention.

In Figs. 1 and 2 A: concentration in relative value B: distance from the surface DE: Co depleted zone According to the present invention, the cemented carbide according to the invention contains binder phase with a concentration close to the nominal in the whole body with the exception of a surface zone where there is a depletion of binding phase, see Figs. 1 and 2.

More particularly, according to the present invention, there is now a cemented carbide insert coated with at least one diamond layer.

The cemented carbide consists of WC and Co with a content of 3-8, preferably 4-7% by weight. The zone closest to the intermediate phase of the cemented carbide insert in contact with the diamond layer is depleted in the binder phase to a depth of at least 2 μm and a maximum of 10 μm.

The binder phase content in this zone is on average 50% lower than the nominal binder phase content. The binder phase content increases in this zone to the nominal concentration without maximum. The core 10 15 20 25 30 3 514 667 of the insert may contain an eta-phase containing zone at a distance from the surface of the insert of at least 0.5 mm, but preferably at least 1 mm.

An insert according to the invention shows a coercive force at least 30% higher than an insert prepared according to standard sintering, ie using a similarly produced powder mixture with a carbon content above the limit for eta phase formation and sintering at 1400-115 ° C in a carbon-free atmosphere.

The specific saturation magnetization of an insert according to the invention is at most 70% of the specific saturation magnetization of an insert produced according to standard sintering.

According to a method of preparing the above-described insert comprising a treatment after sintering of a sintered insert containing eta phase where the post-sintering step adds carbon to the insert to transform eta phase to carbide and binder phase. The carbon can be supplied from the sintering atmosphere or from supporting devices of the inserts, for example graphite plates, zirconia sprayed graphite plates or carbonated paper. The post-sintering is carried out at a temperature above 140 ° C.

Example 1 A WC-6% Co cemented carbide insert containing eta-phase uniformly distributed in the insert, (140 ° C, Ar atmosphere), and then post-treated in a H then to final shape pussy plates for an hour. After this post-sintering, the saturation magnetization was 80% of the value of an insert of the same geometric shape produced from WC-6% Co without eta phase according to standard sintering. The coercive force of the insert according to the invention was 1.3 times that of the reference insert. Both types of inserts were then coated with diamond using standard parameters in a microwave plasma reactor to a diamond coating 10 μm thick. The insert according to the invention showed a well-adhering diamond coating, while for the reference insert the diamond coating showed spontaneous flaking.

Example 2 Six WC-6% Co carbide inserts containing eta phase uniformly distributed in the bodies, first sintered according to a standard procedure (1410 ° C, Ar atmosphere), then post-treated in a H 2 sintering at 1450 ° C on graphite then to final form and plates for one hour. The grain size of the bodies after post-sintering was 2-6 μm. The inserts were then coated with diamond in a reactor based high current DC discharge to a coating thickness of 6-8 μm. An additional set of inserts using an eta phase containing material prepared by standard sintering was subjected to a post-sintering for 1 h at 134 ° C in a CH 4 -H 2 atmosphere to obtain a co-depleted surface zone of 100 μm and an inner eta phase core was present from a distance of 0.3 mm from the surface of the body. The inserts were coated with diamond according to the same procedure as the inserts described above.

Both types of inserts were subjected to a turning test by an end user. The sample comprised turning in an Al-8% Si alloy using the following cutting data: v = 1800 m / min f = 0.8 mm a = 1-3 mm dry working The set of pre-treated inserts according to the invention "lasted" 100-150 components in the sample until a insufficient surface finish was achieved on the machined components. The cause of the accident was found to be uniform wear. The reference inserts "lasted" no longer than a maximum of 50 components and in a larger part of the inserts there were large nose fractures. Example 3 Six WC-6% Co cemented carbide inserts containing eta phase uniformly distributed in the bodies were first sintered according to a standard procedure (1410 ° C, Ar atmosphere), and after was then treated in a vacuum sintering at 140 ° C and then ground to final form carbonated paper on graphite plates for one hour.The grain size of the bodies after post-sintering was 1-3 μm for one fraction and 5-10 μm for a second fraction. was then coated with diamond in a high current DC arc reactor to a coating thickness of 10-12 μm.

Another set of inserts was manufactured using a WC-2% Co composition by standard sintering.

The inserts were subjected to a post-sintering treatment for 1 h at 115 ° C in vacuo whereby the surface was co-depleted. The inserts were coated with diamond according to the same procedure as for the inserts described above.

Both types of inserts were subjected to a turning toughness test in SSl3l2 steel using the following cutting data: v = 110 m / min f = 0.1 mm a = 1.5 mm dry working The diamond-coated set of inserts pretreated according to the invention "lasted" 3 minutes in the test with only minor edge damage . For the reference inserts, large fractures were detected after only 0.2 min.

Claims (2)

l0 l5 20 514 667 6 EE: Carbide cutting tool inserts coated with at least one diamond layer, characterized in that before the diamond coating an eta-phase containing carbide body consisting of tungsten carbide and cobalt with a content of 3-8, of 2-6 μm was treated by means of a sintering treatment at a minimum preferably 4 ~ 7% by weight and an average grain size of 1400 ° C and a maximum of 1510 ° C by a carburizing sintering containing H2 whereby the eta phase in a surface zone of the body is converted to carbide and binder phase so that in the surface zone an area of maximum 10 μm width and minimum 2 μm width in the body closest to the diamond coating the average content of binder phase is 50% lower than the nominal binder phase content and that the coercive force of the body is 30% higher than that of a reference body of the same WC grain size and binder phase content as the insert sintered, sintered according to a standard procedure and a specific saturation magnetization of not more than 70% of that of the reference body. Cutting according to claim 1, characterized in that the body has a stage core at a distance of at least 0.5 mm, preferably 1 mm from the surface of the body.