Chemical reactions in the manufacture of diamond drill bits

ISSN 0967�0912, Steel in Translation, 2013, Vol. 43, No. 5, pp. 239–244. © Allerton Press, Inc., 2013.Original Russian Text © A.I. Laptev, N.N. Stepareva, N.I. Polushin, M.N. Sorokin, 2013, published in “Izvestiya VUZ. Chernaya Metallurgiya,” 2013, No. 3, pp. 27–33.

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Diamond drill bits are most often produced by sin�tering under pressure in graphite molds. On holding atdifferent temperatures, the components of the binderreact with one another, with plasticizer residues, andwith the diamond powder. In this process, the binderacquires the required strength and hardness. Besidesthe mechanical properties of the binder, tool perfor�mance will also be affected by the change in propertiesof the diamond powder on sintering [1, 2]. The use ofEMB 20/40 natural diamonds in sintering in nickel�based matrices leads to losses of diamond andcobalt—up to 1.61 and 4.59%, respectively [1]. De Beersdata are summarized in [2]. Synthetic SDA100 40/50diamonds were used to produce tools on the basis ofthree types of binders by sintering in a controlledatmosphere, with subsequent hot pressing at78.8 MPa. The losses of diamond by graphitization,oxidation, and solution in the matrix were determined.After sintering at 1000°C, the loss of diamond incobalt�based binder was 8%. Sintering above 900°Calso significantly impairs the mechanical properties ofSDA100 diamonds. Therefore, it is important to studythe reactions on sintering to as to optimize the manu�facturing conditions for drill bits.

In the present work, we study the chemical reac�tions between binder components in the manufactureof diamond drill bits. We consider three types of binderthat are commonly used for this purpose: Diacob�1400cobalt (extrafine) binder (99.9% cobalt); V�21iron�based binder (74% Fe, 15% Co, 9% Cu, 1% Sn,1% P); and B�13 binder based on copper and nickel(42% Cu, 34% Ni, 12% Fe, 0.5% Co, 0.5% W, 6.5% Sn,and 4% Cr). Samples without diamond and with theaddition of ground SDB 1085 40/50 diamond powderand AM 14/10 micropowder are produced by sinteringunder pressure in graphite molds in Fritsch equipment(Germany). The reactivity of the powder is increased

by 3�min treatment in a planetary mill. Micropowder isintroduced so as to increase the diamond–binder con�tact surface. In one cycle, 24 samples (5 × 7 × 24 mm)are sintered. The cobalt�binder samples are sinteredfor 3 min. For V�21 and B�13 binders, the sinteringtime is varied, while the temperature is 860 and 880°C,respectively. The phase and chemical composition isstudied by X�ray phase and X�ray microspectral anal�ysis and by means of a JSM�6700F scanning electronmicroscope with a JED�2300F energy–dispersionspectrometric attachment (JEOL, Japan).

Table 1 presents the X�ray phase data for the cobaltbinder. We see that CoO phase appears in theCo binder ground in a planetary mill. This is evidentlyassociated with the adsorption of oxygen on grindingCo binder.

On adding AM diamond powder to the initialCo binder and sintering at 1000°C for 3 min, the α�Cophase completely disappears. The lattice parameter Aof β�Co increases from 3.540 to 3.550 Å. Increase inthe lattice parameter is typical of the formation of acobalt solid solution and corresponds to the com�pound Co197C3 (3.551 Å). The lattice parameter of thediamond is 3.5667 Å, which corresponds to the stan�dard value (3.567 Å).

Chips are prepared from the samples for electron�microscope study. In Fig. 1a, we show a zone withrelief corresponding to a diamond grain on the side ofthe chip. In Fig. 1b, we show the composition of thiszone, which indicates chemical inhomogeneity. (Thisimage is taken in reflected electrons.) In Figs. 1c and 1d,we show the carbon and cobalt distributions, respec�tively, over a particular line. In Fig. 2, we plot the Cand Co distributions: SE shows the surface relief alongthe line; BSE shows the boundary between zones withdifferent chemical composition (the phase boundary).A crack between the crystal and the binder is clearly

Chemical Reactions in the Manufacture of Diamond Drill BitsA. I. Laptev, N. N. Stepareva, N. I. Polushin, and M. N. Sorokin

Moscow Institute of Steel and AlloysReceived January 17, 2013

Abstract—The reactions of three types of binders based on cobalt, iron (V�21), and copper and nickel (B�13)in the production of diamond tools by hot pressing are considered. Pressure intensifies the reactions of thebasic components of cobalt and B�13 binders with diamond. Active solution of diamond in cobalt is observed.In B�13 binder, the diamond reacts with the solid solution based on α�Fe to form iron carbides Fe3C. At dia�mond–binder contact, active chemical reaction leads to embrittlement of the binder and the appearance ofcracks in chip manufacture. Adding AM 14/10 diamond powder to V�21 binder and sintering at 860°C for9 min does not change the parameters of the iron�based solid solution. In other words, the binder–diamondreaction is considerably slower, and no embrittlement of the diamond–binder contact zone is observed.

DOI: 10.3103/S0967091213050094

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LAPTEV et al.

visible in Fig. 2. This is confirmed by the drop in inten�sity on the line in the SE plot, followed by sharp rise inintensity at the edge of the crystal.

Table 2 presents the X�ray phase data for V�21binder. The phase composition of the initial andground powder in the planetary mill consists of copper,a solid solution based on copper, and iron intermetal�lide (Fe17Co3). Grinding has practically no effect onthe diameter of the coherent�scattering regions for thecopper�based phases; for Fe17Co3, the diameter ofthese regions is reduced by more than half: from 65 to32 nm.

Table 2 presents quantitative data for binder sin�tered at 860°C for 9 min. The pure copper has com�pletely disappeared. We only observe solid solutionsbased on the copper lattice (with parameter 3.687 Å)and the iron lattice (with parameter 2.869 Å). There ispractically no change in the dimensions of the coher�ent�scattering regions on sintering.

For V�21 binder ground in a planetary mill and sin�tered at 860°C for 9 min, the changes observed are typ�ical of the sintering of V�21 diabase without additionalgrinding. The lattice parameter of the solid solutions isunchanged. The diameter of the coherent�scattering

Table 1. Phase composition of cobalt samples

SamplePhase composition

phase content, %*

Initial cobaltCo�β (A1, fcc, T > 400 ~ C) 39

Co�α (A3, hcp, T < 400 ~ C) 61

Cobalt after sintering (1000°C, 35 MPa, 3 min)Co�β (A1, fcc, T > 400 ~ C) 33

Co�α (A3, hcp, T < 400 ~ C) 67

Cobalt after additional grinding (3 min) and sintering(1000°C, 35 MPa, 3 min)

Co�β (A1, fcc, T > 400 ~ C) 14

Co�α (A3, hcp, T < 400 ~ C) 85.5

CoO (type NaCl) 0.5

Cobalt + AM 14/10 powder after sintering (1000°C, 35 MPa, 3 min)Co�β (A1, fcc, T > 400 ~ C) 77

C (A4, diamond) 23

* Calculated with an error of ±10–15%.

(a) (b)

(c) (d)

Fig. 1. Chip of Co binder with SDB 1085 40/50 diamonds (×100): (a) SE, 255; (b) BSE, 255; (c) CKa, 6; (d) CoKa, 6.


CHEMICAL REACTIONS IN THE MANUFACTURE OF DIAMOND DRILL BITS 241

regions remains the same, within the limits of compu�tational error.

After adding AM diamond powder to the initialV�21 binder and subsequent sintering at 860°C for9 min, the lattice parameters of the solid solutions aresomewhat reduced: from 3.687 to 3.662 Å in the caseof copper; and from 2.869 to 2.866 Å in the case ofiron. If the V�21 binder is ground in a planetary millbefore adding AM diamond powder and sintering at860°C for 9 min, the lattice parameter of the iron solidsolution remains unchanged. The lattice parameter ofthe copper solid solution declines from 3.687 to 3.658 Å.

Chips of the samples are observed on an electronmicroscope. In Fig. 3a, we show the surface relief. InFig. 3b, we show the chemical composition of thesame zone, indicating chemical inhomogeneity. InFigs. 3c–3f, we present the distribution of elements inthe zone. Analysis indicates that all the elementsexcept carbon are distributed relatively uniformly inthe matrix. That is confirmed by Fig. 4, which showsthe distribution of C, Fe, Co, Cu, Sn, and P over a line.The SE and BSE plots in Fig. 4 are clearly in agree�ment with the distributions.

Table 3 presents X�ray phase data for B�13 binderafter grinding in a planetary mill and sintering at880°C for 9 min. We conclude that this binder containsthe following phases: nickel, α�Fe, and a copper solidsolution. At the background level, we see reflexes ofvery low intensity, regarded as corresponding to thesuperstructure. They may be associated with thephases Ni(tetr), Cu17Sn3, and CrB2.

In sintering B�13 binder samples at 880°C for9 min, the solid solution based on α�Fe (solid solution I)is more uniform in composition than the Cu solidsolution (solid solution II). The binder samples consist

255 µm

SE, 6905030

BSE, 2084643

CKa, 170

CoKa, 140

Fig. 2. Distribution of elements in cobalt–diamondboundary zone (×200).

(a) (b) (c) (d)

(e) (f) (g) (h)

Fig. 3. Chip of V�21 binder with SDB 1085 40/50 diamonds (×50): (a) SE, 255; (b) BSE, 255; (c) CKa, 4; (d) CuKa, 7; (e) FeKa, 13;(f) CoKb, 3; (g) SnLa, 1.5; (h) PKa, 5.

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Table 2. Phase composition of V�21 samples

Sample Phase composition

phase content, %

Initial V�21 powder

Cu (A = 3.614 ± 0.001 Å) 2

Cu (A = 3.668 ± 0.001 Å) 17

Fe17Co3 (A = 2.865 ± 0.001 Å) 81

V�21 powder after additional grinding (3 min)

Cu (A = 3.618 ± 0.001 Å) 5

Cu (A = 3.665 ± 0.001 Å) 17

Fe17Co3 78

V�21 powder after sintering (860°C, 35 MPa, 9 min)

Cu (A = 3.687 ± 0.001 Å) 16

Fe�α (A2, bcc, T < 900 ~ C) A = 2.869 ± 0.00002 Å 84

V�21 powder after additional grinding (3 min) and sintering (860°C, 35 MPa, 9 min)

Fe�α ( A2, bcc, T < 900 ~ C) A = 2.87 ± 0.00002 Å 81

Cu (A = 3.6871 ± 0.0001 Å) 19

V�21 + AM 14/10 powder after sintering (860°C, 35 MPa, 9 min)

Fe�α (A2, bcc, T < 900 ~ C) A = 2.8656 ± 0.00003 Å 45

Cu (A = 3.662 ± 0.0003 Å) 13

C (A4, diamond) 42

V�21 after additional grinding (3 min) + AM 14/10 powder after sintering (1000°C, 35 MPa, 3 min)

Fe�α (A2, bcc, T < 900 ~ C) A = 2.8664 ± 0.00003 Å 51

Cu (A = 3.6576 ± 0.0003 Å) 14

C (A4, diamond) 35

Table 3. Phase composition of B�13 samples

SamplePhase composition

phase content, %

Initial B�13 powder

Fe�α (A2, bcc, T < 900 ~ C) A = 2.866 ± 0.004 Å 24

Ni (A = 3.523 ± 0.002 Å) 32

Cu (A = 3.679 ± 0.001 Å) 56

B�13 powder after additional grinding (3 min)

Fe�α (A2, bcc, T < 900 ~ C) A = 2.8663 ± 0.004 Å 25

Ni (A = 3.5234 ± 0.002 Å) 31

Cu (A = 3.7017 ± 0.001 Å) 49

B�13 powder after sintering (880°C, 35 MPa, 9 min)

Ni (A = 3.5746 ± 0.004 Å) 15

Fe�α (A2, bcc, T < 900 ~ C) A = 2.8683 ± 0.0003 Å 20

Cu (A = 3.6358 ± 0.0002 Å) 65

B�13 powder after additional grinding (3 min) and sintering (880°C, 35 MPa, 9 min)

Fe−α (A2, bcc, T < 900 ~ C) A = 2.871 ± 0.00008 Å 23

Cu (A = 3.6378 ± 0.0003 Å) 77

B�13 powder + AM powder after sintering (880°C, 35 MPa, 9 min)

Fe�α (A2, bcc, T < 900 ~ C) A = 2.8749 ± 0.0003 Å 9

Cu (A = 3.6413 ± 0.0003 Å) 59

C (A4, diamond) 26

Fe3C (type L'''3) 6

B�13 powder after additional grinding (3 min) + AM 14/10 powder after sintering (1000°C, 35 MPa, 3 min)

Fe�α (A2, bcc, T < 900 ~ C) A = 2.8709 ± 0.0002 Å 18

Cu (A = 3.6341 ± 0.0002 Å) 43

C (A4, diamond) 32

Fe3C (type L'''3) 7


CHEMICAL REACTIONS IN THE MANUFACTURE OF DIAMOND DRILL BITS 243

of a mixture of solid solutions with the same compo�nents but different proportions. A residual nickelphase in the disperse state is also seen. On sinteringB�13 binder after preliminary grinding in a planetarymill, solid solution II is homogenized, and its propor�tion increases with respect to solid solution I. Thenickel phase enters solid solution II. The coherent�scattering regions for solid solution I shrink from 12 to23 nm.

Chips of the samples are observed on an electronmicroscope. In Fig. 5a, we show the surface relief withdiamond grains. In Fig. 5b, we show the chemicalcomposition of the same zone, indicating chemicalinhomogeneity. (This image is taken in reflected elec�

919 µm

SE, 4574203

BSE, 4987697

CKa, 3006

PKa, 168

SnLa1, 106

FeKa, 799

CoKb, 53

CuKa, 364

Fig. 4. Distribution of elements in V�21–diamond bound�ary zone (×50).

(a) (b)

(c) (d)

(e) (f)

(g) (h)

Fig. 5. Chip of B�13 binder with SDB 1085 40/50 dia�monds (×50): (a) SE, 255; (b) BSE, 255; (c) CKa, 7;(d) FeKa, 10; (e) NiKa, 8; (f) CuKb, 3; (g) SnLa, 1.5;(h) CrKa, 7.

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trons.) In Figs. 5c–5h, we present the distribution ofelements in the zone. Some of the diamonds on thechip have a coating whose composition corresponds tothat of the binder, according to spectral analysis.Hence, in B�13 binder, in contrast to Co and V�21binders, the diamonds are attached not only mechan�ically but also by adhesion.

In Fig. 6, we show the SE and BSE plots and thedistribution of C, Fe, Ni, Cu, Sn, and Cr over a line.

For the carbon distribution, the intensity of thelines is considerably greater in the zone with anuncoated diamond crystal than in the binder region,where the intensity is practically zero. At the crystal,we also see low�intensity curves corresponding to cop�per and tin. The intensity of the Fe, Ni, Cr lines isgreatest in the binder region and practically zero at thediamond crystal. In studying the distribution of C, Fe,Ni, Cu, Sn, and Cr over a line passing through thebinder and two crystals, one of which has a bindercoating, we find complete agreement with Fig. 6. Thatalso demonstrates that the crystal is covered withbinder. In other words, the binder is in tight contactwith the diamond and is chemically active with respectto the diamond. Note also that cracks are observed atthe diamond–binder contact, which indicates insuffi�cient plasticity of the binder in that zone.

CONCLUSIONS

In studying the reactions of Co, V�21, and B�13binders with diamond on sintering under pressure, wefind that the pressure intensifies the reactions of thebasic components of cobalt and B�13 binders with dia�mond. Active solution of diamond in cobalt isobserved. In B�13 binder, the diamond reacts with thesolid solution based on α�Fe to form iron carbidesFe3C. At diamond–binder contact, active chemicalreaction leads to embrittlement of the binder and theappearance of cracks in chip manufacture. AddingAM 14/10 diamond powder to V�21 binder and sinter�ing at 860°C for 9 min does not change the parametersof the iron�based solid solution. In other words, thebinder–diamond reaction is considerably slower, andno embrittlement of the diamond–binder contactzone is observed.

REFERENCES

1. Young, B., Ind. Diamond Rev., 1966, vol. 26, no. 312,pp. 483–488.

2. Bullen, O.J., Ind. Diamond Rev., 1975, no. 10, pp. 363–365.

Translated by B. Gilbert

929 µm

SE, 8863272

BSE, 3413484

CKa, 284

CrKa, 663

SnLa1, 265

FeKa, 910

CuKb, 67

NiKa, 522

Fig. 6. Distribution of elements in B�13–diamond boundary zone (×50).

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Chemical reactions in the manufacture of diamond drill bits