IE85780B1 - Controlling ultra hard material quality - Google Patents

Abstract

ABSTRACT A method is provided for controlling the consistency of the quality of ultra hard materials formed over tungsten carbide substrates formed from different batches of tungsten carbide powder by controlling the tungsten carbide particle size distribution in each batch. (FIGURE 1)

Description

BACKGROUND OF THE INVENTION Tungsten carbide substrates are formed by sintering tungsten carbide powder mixed with cobalt at sufficient Tungsten carbide substrate manufacturers are Magnetic temperature. concerned with obtaining the requisite hardness, Saturation and Coercivity from the substrates they make.

However, the quality of an ultra hard material such as polycrystalline diamond (“PCD”) or polycrystalline cubic boron nitride (“PCBN”) formed on such tungsten carbide substrates varies from substrate to substrate. As such, a method for forming an ultra hard material having consistent quality, as for example, consistent strength and consistent minimum interface deformities, i.e. deformities at the _ interface between the ultra hard material and the substrate, such as cobalt eruptions, is desired. “Cobalt eruptions” are non-homogeneous dendritic tungsten carbide growths.

SUMMARY OF THE INVENTION A method for controlling the consistency of the quality of ultra hard materials formed over tungsten carbide substrates is provided. In an exemplary embodiment, the consistency is controlled by controlling the particle size distribution of the tungsten carbide particles forming the substrate. This is accomplished by forming the ultra hard material over substrates which have a predetermined tungsten carbide particle size distribution.

In another exemplary embodiment, a method for controlling the infiltration kinetics into the ultra hard material during sintering is provided, this method for controlling comprising selecting tungsten carbide substrates over which to form the ultra hard material which substrates have a predetermined particle size. In an exemplary embodiment, by controlling the tungsten carbide particle size distribution, a constant cobalt contribution is achieved in the substrate which is able to infiltrate the ultra hard material during sintering. In one exemplary embodiment, the present invention allows the strength of PCD layers formed over multiple carbide substrates to have a deviation of less than il6% from layer to layer. In another exemplary “ embodiment, the consistency of the PCD strength is kept to a standard deviation of not greater than i7%. In yet a further exemplary embodiment, the consistency of the PCD strength is kept to a standard deviation of not greater than i5%.

In another exemplary embodiment a method is provided for controlling the quality of ultra hard material layers formed over a plurality of substrates formed from different batches of tungsten carbide powder. The method includes selecting a first batch of tungsten carbide substrate powder material having a predefined particle size distribution, and selecting a second batch of tungsten carbide substrate powder material having a predefined particle size distribution, such that deviation between the particle size distribution of the first batch and the particle size distribution of the second batch is’no greater than about 30%. The method further includes forming a first substrate from the first batch of powder substrate material, forming a second substrate from the second batch of powder substrate material, placing a first ultra hard material over the first substrate, high pressure and high temperature sintering the first ultra hard material powder with the first substrate forming a first ultra hard. material layer over the first substrate, placing a second ultra hard material over the second substrate, and high pressure and high temperature sintering the second ultra hard material powder with the second substrate forming a second ultra hard material layer over the second substrate, wherein a standard deviation of the strength of the two ultra hard material layers is not greater than 14%.

In another exemplary embodiment, the strength of the first ultra hard material layer does not differ from the strength of the second ultra hard material layer by more than %. In a further exemplary embodiment, the strength of the first ultra hard material layer does not differ from the strength of the second ultra hard material layer by more'than %. In another exemplary embodiment, the hardness'of the first substrate does not differ from the hardness of the second substrate by more than 2%. In yet a further exemplary embodiment, the hardness of the first substrate does not differ from the hardness of the second substrate by more than 1%, preferably by more than 0.5%. In yet a further exemplary embodiment, the magnetic saturation of the first substrate does not differ from the magnetic saturation of the second substrate by more than 15.4%, In yet another exemplary embodiment, the coercivity of the first substrate does not differ from the coercivity of the second substrate by more than about 43%.

In another exemplary embodiment, the two substrates have a hardness within 2% of each other, preferably within 1% of each other, a magnetic saturation within 15% of each other, and a coercivity within 43% of each other. In yet another exemplary embodiment, each substrate has a carbide particle mean size in the range of 3pm to 6pm. In yet a further exemplary embodiment, each substrate has a carbide particle mean size of about 3pm and a maximum particle size of about 18pm. In another exemplary embodiment, each substrate has a carbide particle mean size of about 4.5pm to about 5.5um. In one exemplary embodiment, each substrate has a carbide particle mean size of about 3pm. In yet other exemplary embodiments the deviation between the ' two particle size distributions is not greater than about 20%, not greater than about 10%, and not greater than about 5%, respectively. ’ n In another exemplary embodiment, each batch has 10% of its particles by volume having a size less than a first particle size, has 50% of its particles by volume having a size less than a second particle size, and has 90% of its particles by volume having a size less than a third particle size. wherein the deviation between the first particle sizes of the two batches is not greater than 5%, wherein the deviation between the second particles sizes of the two batches is not greater than 20% and wherein the deviation between the third particle sizes of the two batches is not greater than 30%.

In another exemplary embodiment, the method further includes selecting a third batch of tungsten carbide substrate powder material having a predefined particle size distribution, wherein the deviation between the particle size distribution of the first batch, the particle size distribution of the second batch, and the particle size distribution of the third batch is no greater than about 30%.

The method also includes forming a third substrate from the third batch of powder substrate material, placing a third ultra hard material over the third substrate, sintering‘the third ultra hard material with the third substrate forming a third ultra hard material laver over the third substrate, wherein a standard deviation of the strength of the three ultra hard material layers is not greater than 14%. In a further exemplary embodiment, the strength of each ultra hard material layer is within 10% of the strength of each of the .other ultra hard material layers. In another exemplary embodiment the strength of each ultra hard material layer is within 5% of the strength of each of the other ultra hard material layers. In yet other exemplary embodiments the deviation between the three particle size distributions is not greater than about 20%, not greater than about 10%, and not greater than about 5%, respectively. In a further exemplary embodiment, each batch has 10% of its particles by volume having a size less than a first particle size, has 50% of its particles by volume having a size less than a second particle size, and has 90% of its particles by volume having a size less than a third particle size, wherein the deviation between the first particle sizes of the three batches is not greater than 5%, wherein the deviation between the second particles sizes of the three batches is not greater than 20% and wherein the deviation between the third particle sizes of the three batches is not greater than 30%.

In an alternate exemplary embodiment, a method is provided for controlling the quality of ultra hard material layers formed over a plurality of substrates, each substrate formed from a different batch of tungsten carbide powder and cobalt. The method includes forming a first ultra hard material over a first substrate formed from a first batch of tungsten carbide powder, wherein cobalt from the first substrate infiltrates the first ultra hard material via infiltration kinetics during the forming of the first ultra hard material layer. The method also includes forming a second ultra hard material over a second substrate formed from a second batch of tungsten carbide powder, wherein cobalt from the second substrate infiltrates the second ultra hard material via infiltration kinetics during the forming of the second ultra hard material layer.‘ The method further includes controlling the infiltration kinetics of the cobalt from the first substrate to the first ultra hard material layer, and controlling the infiltration kinetics of the cobalt from the second substrate to the second ultra hard material layer. Controlling the infiltration kinetics of the cobalt from the first substrate to the first ultra hard material layer comprises selecting the first batch of tungsten carbide substrate powder material to have a predefined particle size distribution. Controlling the infiltration kinetics of the cobalt from the second substrate to the second ultra hard material layer comprises selecting the second batch of tungsten carbide substrate powder material to have a predefined particle size distribution.

The deviation between the particle size distribution of the first batch and the particle size distribution of the second batch is no greater than about 30%.

In another exemplary embodiment, controlling the infiltration kinetics of the cobalt in the first substrate includes controlling a first mean free path of the cobalt from the first substrate to the first ultra hard material layer and controlling the infiltration kinetics of the cobalt in the second substrate includes controlling a second mean free path of the cobalt from the second substrate to the In a further exemplary second ultra hard material layer. embodiment, controlling the first mean path includes selecting the first batch of tungsten carbide substrate powder material to have a predefined particle size distribution, and controlling the second mean path includes selecting the second batch of tungsten carbide substrate powder material to have a predefined particle size distribution, such that the deviation between the particle size distribution of the first batch and the particle size distribution of the second batch is no greater than about %. In yet further exemplary embodiments, the deviation between the two particle size distributions is not greater than about 20%, than about 10% and than about 5%, respectively.

In another exemplary embodiment, a method for controlling the quality of ultra hard material layers formed over a plurality of substrates formed from different batches of tungsten carbide powder is provided. The method includes selecting a first batch of tungsten carbide powder material having a particle size distribution, selecting a second batch of tungsten carbide substrate powder material having a particle size distribution, wherein the deviation between the particle size distribution of the first batch and the particle size distribution of the second batch is no greater than about 30%. The method also requires forming a first substrate from .% ?f7 the first batch of material, forming a second substrate from the second batch of material, placing a first ultra hard layer material powder over the first substrate, sintering the first ultra hard material with a first substrate forming a first ultra hard material layer over the first substrate, placing a second ultra hard material over the second substrate, and sintering the second ultra hard material with a second substrate forming a second ultra hard material layer over the second substrate. In an exemplary embodiment, the first batch has particle sizes in the range of 2 pm to 11.5 pm and a median particle size in the range of 4.5 pm to 5.5 pm. another exemplary embodiment the second batch has particle sizes in the range of 2 pm to 11.5 pm and a median particle In yet a further size in the range of 4.5 pm to 5.5 pm. exemplary embodiment, each batch has 10% of its particles by volume having a size less than a first particle size, has 50% of its particles by volume having a size less than a second particle size, and has 90% of its particles by volume having a size less than a third particle size, wherein the deviation between the first particle sizes of the two batches is not greater than 5%, wherein the deviation between the second particles sizes of the two batches is not greater than 20% and wherein the deviation between the third particle sizes of the two batches is not greater than 30%.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic depiction of a particle size distribution of a tungsten carbide substrate.

FIGS. 2 and 3 are tables of specifications and data for various tungsten carbide substrates and PCD layers formed over such substrates, respectively. .30.

. The container and its DETAILED DESCRIPTION OF THE INVENTION Applicants have discovered that consistent better quality ultra hard material as for example polycrystalline diamond ("PCB") or polycrystalline cubic boron nitride ('PCBN") by controlling the tungsten carbide particle size distribution in tungsten carbide substrates over which they can make more the ultra hard material is formed.

Ultra hard neterial is formed by sintering ultra hard material particles over a tungsten carbide substrate at high pressure and high temperature where the ultra hard material is thermodynamically stable. These temperatures and. pressures are typically in the range of 130o°c to 15oo°c and S to 7 Gpa, respectively. In one exemplary embodiment, to form an ultra hard material, a tungsten carbide substrate is placed in a refractory metal container such as a niobium container. Ultra hard material particles such as diamond or CBN are then placed over the substrate in the container. The container is covered wi-th a cover made from the same material as the container. contents are then exposed to the temperatures and pressures where the ultra hard material is thermodynamically stable. The high temperature and pressure causes the ultra hard material particles with binder to convert to a polycrystalline ultra hard material.

Tungsten carbide substrates are formed by cementing together tungsten carbide particles in a cobalt binder matrix.

During ultra hard material sintering. the cobalt in the substrate is "squeezed" from: the tungsten. carbide substrate and infiltrates the ultra hard. material, e.g., diamond or cubic boron nitride. Applicants have discovered that the consistency in the cobalt infiltration kinetics determines the quality of the ultra hard material quality of the consistency of_ the sintering, and thus, the resulting -35. polycrystalline ultra hard material. Infiltration kinetics are the kinetics that affect the infiltration of the cobalt from the tungsten carbide substrate to the‘ ultra hard material layer. Infiltration kinetics are evaluated based on the amount of cobalt infiltrating the ultra hard material over a given time. By controlling the cobalt infiltration kinetics, i.e., by controlling the amount of cobalt that infiltrates the ultra hard material over a given time, applicants can control the amount of cobalt infiltrating the ultra hard material layer during a given time and a given temperature. and thus, control the quality and thus, the consistency of the quality of the ultra hard material. Applicants have also discovered that they can control the infiltration kinetics of the cobalt by controlling the mean free path of the cobalt from the substrate into the ultra hard material by controlling the tungsten carbide particle size distribution in the carbide substrate. In other words by controlling the tungsten carbide particle size distribution, the sweep of cobalt into the ultra hard material layer can be better controlled.

Thus, once a desired tungsten carbide particle size distribution is determined for optizmnn cobalt infiltration kinetics, the consistency of the quality of the ultra hard material formed over tungsten carbide substrates formed from different batches of tungsten carbide powder can be maintained by maintaining a consistent particle size distribution from batch to batch of tungsten carbide powder. In other words, by using batches of tungsten carbide powder having a consistent desired particle size distribution, the quality of ultra hard material layers formed over substrates formed from these batches will also be consistently better.

In general, tungsten carbide particle distribution in a tungsten carbide substrate follows a general curve as for example shown in FIG. 1. For a substrate material having the particle size distribution disclosed in FIG. 1. it may be said that the substrate has a mean particle size of Y with a majority of the particle distribution being between X and z (i.e., the points of the curve where the curve turns toward the horizontal). In an exemplary embodiment, X is the 10% particles by volume point, Y is the 50% particles by volume point, and Z is the 90% particles by volume point. In other words, X is the point where 10% of the particles by volume have a particle size less than a particular value, Y is the point where 50% of the particles by volume have a particle size less than another value (the mean particle size), and 2'. is the point where 90% of the particles by volume have a particle size less than yet another value. In other exemplary embodiments. such 10%, 50% and 90% points may be at points on Z points. In yet the distribution curve other than the X, Y, particle size further alternate exemplary embodiments, distribution may be specified by specific amounts of particles having specific particle sizes or particle size ranges.

By tailoring the tungsten carbide particle size distribution, applicants believe that a consistent sweep or cobalt into the ultra hard material, i.e., a consistent amount of cobalt infiltrating the ultra hard material, can be achieved. Consequently, a consistent better quality of polycrystalline ultra hard material will be formed over such substrates. Thus, by selecting substrates with a specified tungsten carbide ’PaJ~’ti.C1eV size distribution, a‘ consistent sweep of cobalt from the substrate to the ultra hard material layer is achieved from substrate to substrate. Consequently, by using the same particle size distribution from substrate to substrate, or by using a similar particle size distribution from substrate to substrate such that the maximum deviation of particle size distribution between substrates is within a predetermined range, the resulting ultra hard sintered on such substrates will be of consistent better In other words, by using batches of tungsten ‘carbide the same or similar) particle material quality. powder having consistent (i.e., size distributions, the quality of ultra hard aterial formed over such substrates will be consistently better.

Applicants believe that a consistent better quality of ultra hard material may be formed by keeping the deviation, i.e., the variation, of the particle size distribution from tungsten carbide powder batch to batch to no greater than 30%.

Better consistent quality is believed to be obtained by reducing the deviation of the“ particle size distribution from batch to batch. For example, no deviation will produce a more consistent quality ultra hard material than a 5% deviation, which will produce a more consistent quality of ultra hard material than a 10% deviation, which will produce a more consistent quality of ultra hard material than a 20% deviation which will produce a more consistent quality of ultra hard material than a 30% deviation. "Deviation" as used in relation to the particle distribution herein refers to the deviation in the mean particle size and the deviation in the majority particle distribution when such factors are used to define the particle size distribution, or the deviation in the amount of particles having specific particle sizes or particle size ranges or the deviation in the particle sizes or particle size ranges "when such factors are used to define the particle size distribution. For example, in the case where the particle size distribution islprovided by looking at the 10%, 50%, and 90% particle levels, a given deviation would mean a given deviation in the 10% level, the 50% level, and the 90% level. Alternatively, one deviation may be given for the 10% level, another may be given for the 50% level and another may be given for the 90% level.

Applicants believe that during sintering of the tungsten carbide substrates, the carbon balance, the mixing of the cobalt and the cleanness of the sintering furnace used to sinter the tungsten carbide powder into a solid substrate should be controlled so as to achieve the desired cobalt infiltration kinetics. The carbon balance needs to be controlled during sintering of the substrate so that the carbon in the tungsten carbide powder remains stochiometric during sintering with the cobalt. Mixing of the cobalt with the tungsten carbide powder also needs to be controlled.

Such mixing is typically performed with a mill. Overmixing with the mill will cause the particles in the tungsten carbide powder to significantly breakdown to smaller particles thereby significantly changing the particle size distribution of the powder.

A sintering furnace that is not cleaned of carbon may affect the carbon balance. Thus, it is important that during sintering of the tungsten carbide substrates, the carbon balance, the mixing of the cobalt and the cleanness of the sintering furnace should be properly controlled. Once the tungsten carbide particle size distribution and the aforementioned-factors are controlled, the quality of the ultra hard material may be further controlled or fine tuned by controlling the particle size distribution of the ultra hard material particles forming the ultra hard material, thus, further controlling the mean free path of the cobalt from the substrate into the ultra hard material.

Polycrystalline ultra hard material formed using the inventive method will produce consistent strength and hardness, as well as a decrease in the interface deformities that are typically formed on the. interface between the polycrystalline ultra hard material and the substrate, such as cobalt eruptions.

FIGS. 2 and 3 are tables of data -of three current tungsten carbide substrate grades designated as carbide substrates A, B and C, respectively and of PCD layers formed over these three tungsten carbide substrates. The PCD grade, interface geometry, PCD layer geometry and sintering conditions were kept constant for each PCD layer formed over each of the three carbide substrates. The data in FIGS. 2 and 3 was obtained from over 1000 specimens having tungsten carbide substrates formed from different batches of tungsten carbide powder. Hardness, Magnetic Saturation. Coercivity and Strength data presented in FIGS. 2 and 3 have been normalized to the data in relation- to substrate A. Consequently, Hardness, Magnetic Saturation. Coercivity and Strength data in relation to substrate A has a value of 100.

Substrate A had a tungsten carbide mean particle (grain) size of 6pm and a maximum particle (grain) size of 36pm.

Carbide substrates B and C each had a tungsten carbide nwan particle size of 3pm and a maximum particle size of 24pm and 18pm, respectively. As can be seen from FIG. 3, all layers of PCD formed over the three tungsten carbide substrates had about the same density. However, as the particle size distribution changed, the strength of the PCD layers and the cobalt eruptions at the interface of the substrate and the PCD layer also changed. As can also be seen from FIG. 3. when the distribution of particle size was in a smaller range, e.g., up to about 18pm (substrate C) versus up to about 36pm (substrate A), the cobalt eruptions at the interface virtually disappeared. Furthermore, as can. be seen in FIG. 3, the standard deviation of PCD strength based on data collected from nmltiple PCD layers formed over each of carbide substrates A, B and C, was reduced from about i16% for PCD layers formed over substrates A to about i7% for Pcb layers formed over substrates B. to-15% for PCD layers formed over substrates C. In other words, the strength of each of the PCD layers formed over substrates C was within :5% of the strength of each other PCD layer formed over substrates C. Thus, PCD strength were formed over layers with more consistent substrates C.

Applicants also believe that the polycrystalline ultra hard material can be controlling the amount of cobalt content in the ultra hard material layer. Furthermore. applicants believe that by using a carbide particle size distribution having a smaller range in the substrate, the quality and the consistency in quality of the PCD formed will be improved without necessarily having to decrease the mean particle size. For example, applicants believe that the quality and consistency in quality of PCD formed over substrates having a mean carbide particle size of 6pm but a maximum particle size of 18pm, will be.better than quality of the improved by that of PCD formed over substrate A.

Applicants have also been able to get a consistent Vquality of ultra hard material formed over substrates which were formed from two different batches of tungsten carbide powder. The first batch had 10% of its particles by volume having a particle size of 2.4pm or less, 50% of its particles by vo1ume(i.e., having a mean particle size), having a particle size of 4.7pm or less, and 90% of its particles by volume having a particle size of 8.8um or less. The second batch had 10% of its particles by volume having a particle size of 2.3pm or less, 50% of its particles by volume having a particle size of 5.4um or less, and 90% of its particles by volume having a particle size of l1.2um or less. Applicants also believe they can get a high quality ultra hard material layer by forming it over a tungsten carbide substrate having a tungsten particle size range between 2 pm. and 11.5 pm with a medium particle size in the range of 4.5 pm to 5.5.pm.

Applicants further believe that they can get a high quality ultra hard material layer over tungsten carbide substrates formed from different batches of tungsten carbide powders where the deviation in the particle size distribution is not greater than 5% at that 10% level, not greater than 20% in the % level and not greater than 30% in the 90% level. believe that the deviation in Moreover, Applicants tungsten carbide magnetic saturation and hardness for substrates formed front different batches of the same grade tungsten carbide powders, according to the principles of the present invention, as well as the deviation in the strength of ultra hard material layer formed over such substrates will be much lower than that depicted in FIGS. 2 and 3. Similarly the cobalt eruptions formed at the interface of PCD layers formed over such substrates will be negligible and at times non— existent. In fact it is expected that the deviation in the ultra hard material strength will be less than tS%.

Although the present invention. has been described and illustrated to respect to nmltiple embodiments thereof, it is to be understood that it is not to be so limited, since changes and modifications may be made therein which are within the full intended scope of this invention as ‘hereinafter claimed.

Claims (35)

1. A method for controlling the quality of ultra hard material layers formed over a plurality of substrates formed from different batches of tungsten carbide powder, the method comprising: selecting a first batch of tungsten carbide substrate ipowder material having a predefined particle size distribution: selecting a second batch of tungsten carbide substrate powder material having a predefined particle size distribution, wherein the deviation between the particle size distribution of the first batch and the particle size distribution of the second batch is no.greater than about 30%; forming a first substrate from the first batch of powder substrate material; forming a second substrate from the second batch of powder substrate material; placing a first ultra hard material over the first substrate; high pressure and high temperature sintering the first ultra hard material with the first substrate forming a first ultra hard material layer over the first substrate; placing a second ultra hard material over the second substrate; and high pressure and high temperature sintering the second ultra hard material with the second substrate forming a second ultra hard material layer over the second substrate, wherein a standard deviation of the strength of the two ultra hard material layers is not greater than 14%.

2. A method as claimed in Claim 1, wherein the deviation between the two particle size distributions is not greater than about 20%.

3. A method as claimed in Claim 2, wherein the deviation between the two particle size distributions is not greater than about 10%.

4. A method as claimed in Claim 3, wherein the deviation between the two particle size distributions is not greater than about 5%.

5. A method as claim in Claim 1, wherein each batch has 10% of its particles by volume having a size less than a first particle size, has 50% of its particles by volume having a size less than a second particle size, and has 90% of its particles by volume having a size less than a third particle size, wherein the deviation between the first particle sizes of the two batches is not greater than 5%, wherein the deviation between the second particles sizes of the two batches is not greater than 20% and wherein the deviation between the third particle sizes of the two batches is not greater than 30%.

6. A method as claimed in any preceding claim, wherein the strength of the first ultra hard material layer does not differ from the strength of the second ultra hard material layer by more than 10%

7. A method as claimed in Claim 6, wherein the strength of the first ultra hard material layer does not differ from the strength of the second ultra hard material layer by more than

8. A method as claimed in any preceding claim, wherein the hardness of the first substrate does not differ from the hardness of the second substrate by more than 2%.

9. A method as claimed in Claim 8, wherein the hardness of the first substrate does not differ from the hardness of the second substrate by more than 1%.

10. A method-as claimed in any preceding claim, wherein the magnetic saturation of the first substrate does not differ -from the magnetic saturation of the second substrate by more than 15.4%.

11. A method as claimed in any preceding claim, wherein the coercivity of the first substrate does not differ from the coercivity of the second substrate by more than about 43%.

12. A method as claimed in any preceding claim, wherein the two substrates have a hardness within 1% of each other, a magnetic saturation within 15% of each other, and a coercivity within 43% of each other.

13. substrate has a carbide particle mean size in the range of A method as claimed in any preceding claim, wherein each about 3pm to 6pm.

14. A method as claimed in Claim 13, wherein each substrate has a carbide particle mean size of about 3pm and a maximum particle size of about laum. 19s 10 I5 30

15. A method as c1aimed_in Claim 13, wherein each substrate has a carbide particle mean-size of about 4.5um to about 5.5pm.

16. A method as claimed in Claim 1, further comprising: selecting a third batch of tungsten carbide substrate powder material having a predefined particle size distribution, wherein the deviation between the particle size distribution of the first batch, the particle size distribution of the second batch, and the particle size g distribution of the third batch is no greater than about 30%; forming a third substrate from the third batch of powder substrate material; _ placing a third ultra hard material over the third substrate; high pressure and high temperature sintering the third ultra hard material with the third substrate forming a third ultra hard material layer over the third substrate, wherein a standard deviation of the strength of the three ultra hard material layers is not greater than 14%.

17. A method as claimed in Claim 16, wherein the strength of each ultra hard material layer is within 10% of the strength of each or the other ultra hard material layers.

18. A.method as claimed in Claim 17, wherein the strength of each ultra hard material layer is within 5% of the strength of each of the other ultra hard material layers.

19. A method as claimed in any one of Claims 16 to 18, wherein the deviation between the three particle size distributions is not greater than about 20%. 30

20. A method as claimed in Claim 19, wherein the deviation between the three particle size distributions is not greater than about 10%.

21. A.method as claimed in Claim 20, wherein the deviation between the two particle size distributions is not greater than about 5%.

22. A method as claimed in Claims 16 to 18, wherein each batch has 10% of its particles by volume having a size less than a first particle size, has 50% of its particles by volume having a size less than a second particle size, and has 90% of its particles by volume having a size less than a third particle size, wherein the deviation between the first particle sizes of the three batches is not greater than 5%, wherein the deviation between the second particle sizes of the three batches is not greater than 20% and wherein the deviation between the third particle sizes of the three batches is not greater than 30%.

23. A method for controlling the quality of ultra hard I material layers formed over a plurality of substrates formed from different batches of tungsten carbide powder and cobalt, the method comprising: forming a first ultra hard material over a first substrate formed from a first batch of tungsten carbide powder, wherein cobalt from the first substrate infiltrates said first ultra hard material via infiltration kinetics during said forming of said first ultra hard material layer; forming a second ultra hard material over a second substrate formed from a second batch of tungsten carbide powder, wherein cobalt from the second substrate infiltrates 30 said second ultra hard material via infiltration kinetics during said forming of said second ultra hard material layer; controlling the infiltration kinetics of the cobalt from the first substrate to the first ultra hard material layer : and controlling the infiltration kinetics of the cobalt from the second substrate to the second ultra hard material layer; wherein controlling the infiltration kinetics of the cobalt from the first substrate to the first ultra hard material layer comprises selecting the first batch of tungsten carbide substrate powder material to have a predefined particle size distribution; wherein controlling the infiltration kinetics of the cobalt from the second substrate to the second ultra hard material layer comprises selecting the second batch of tungsten carbide substrate powder material to have a predefined particle size distribution; and wherein the deviation between the particle size distribution of the first batch and the particle size distribution of the second batch is no greater than about 30%.

24. A method as claimed in Claim 23, wherein controlling the infiltration kinetics of the cobalt in the first substrate comprises controlling a first mean free path of the cobalt from the first substrate to the first ultra hard material layer and wherein controlling the infiltration kinetics of the cobalt in the second substrate comprises controlling a second mean free path of the cobalt from the second substrate to the second ultra hard material layer.

25. A method as claimed in Claim 24, wherein controlling the first mean path comprises selecting the first batch of tungsten carbide substrate powder material to have the 30 predefined particle size distribution, and wherein controlling the second mean path comprises selecting the second batch of tungsten carbide substrate powder material to have the predefined particle size distribution.

26. A method as claimed in any one of Claims 23 to 25, wherein the deviation between the two particle size distributions is not greater than about 20%.

27. A method as claimed in Claim 26, wherein the deviation between the two particle size distributions is not greater than about 10%.

28. A method as claimed in Claim 27, wherein the deviation between the two particle size distributions is not greater than about 5%.

29. A method as claimed in any one of Claims 23 to 25, wherein each batch has 10% of its particles by volume having a size less than a first particle size, has 50% of its particles by volume having a size less than a second particle size, and has 90% of its particles by volume having a size less than a third particle size, wherein the deviation the first particle sizes of the two batches is not than 5%, wherein the deviation between the second particle sizes of between greater the two batches is not greater than 20% and wherein the deviation between the third particle sizes of the two batches is not greater than 30%.

30. material layers formed over a plurality of substrates formed A method for controlling the quality of ultra hard I5 30 from different batches of tungsten carbide powder, the method comprising: selecting a first batch of tungsten carbide powder material having a particle size distribution; selecting a second batch of tungsten carbide substrate powder material having a particle size distribution, wherein the deviation between the particle size distribution of the first batch and the particle size distribution of the second batch is no greater than about 30%: forming a first substrate from the first batch of material: ' forming a second substrate from the second batch of material; placing a first ultra hard material powder over the first substrate: high pressure and high temperature sintering the first ultra hard material with a first substrate forming a first ultra hard material layer over the first substrate: placing a second ultra hard material over the second substrate; and high pressure and high temperature sintering the second ultra hard material with a second substrate forming a second ultra hard material layer over the second substrate.

31. A method as claimed in Claim 30, wherein the first batch has particle sizes in the range of 2pm to 11.5um and a median particle size in the range of 4.5um to 5.53m.

32. A method as claimed in Claim 31, wherein the second batch has particle sizes in the range of 2pm to l1.5pm and a median particle size in the range of 4.5um to 5.5um.

33. '33. A method as claimed in any one of Claims 30 to 32, wherein each batch has 10% of its particles by volume having a size less than a first particle size, has 50% of its particles by volume having a size less than a second particle size, and has 90% of its particles by volume having a size less than a third particle size, wherein the deviation between the first particle sizes of the two batches is not greater than 5%, wherein the deviation between the second particle sizes of the two batches is not greater than 20% and wherein the deviation between the third particle sizes of the two batches is not greater than 30%.

34. A method for controlling the quality of ultra hard material layers formed over a plurality of substrates formed from different batches of tungsten carbide powder substantially as hereinbefore described with reference to the accompanying figures.

35. A method for controlling the quality of ultra hard material layers formed over a plurality of substrates formed from different batches of tungsten carbide powder and cobalt substantially as hereinbefore described with reference to the accompanying figures. MACLACHLAN & DONALDSON Applicants’ Agents 47 Menion Square INJBLDWZ 25