Experimental Analysis on Matrix of Impregnated Diamond Bit
Yin-long Ma 1, You-hong Sun 1 ,2, Xian-zheng Zhang 1, Ke Gao 1, Xiao-yang Li 1, Shou-sheng Li3
1
College of Construction Engineering，Ji Lin University，Chang Chun 130026，PR China
2
State Key Lab Superhard Mat, Changchun 130012, PR China
3
Yellow River Engineering Consulting Co., Ltd., He Nan 471002, PR China
(mayilo@126.com)
Abstract - Six matrix formulas are introduced in this
paper, and the moulds are designed to manufacture eighteen
matrix samples through the method of hot pressing sintering
， and then Rockwell hardness and bending strength of the
samples are tested. Based on the analysis of test results, the
optimal matrix formula of impregnated diamond bit is
recommended. And tungsten carbide (WC) as a kind of
framework ingredients which has high melting
temperature can improve Rockwell hardness and wear
resistance of matrix. According to the result of experiment,
the average value of hardness and bending strength are
bigger and bigger as WC volume fraction is higher and
higher.
Rockwell hardness and wear resistance of matrix will be
reduced, and if too low, the framework ingredients will
not be bonded solidly, which can easily cause diamond
bits broken [8] [9].
According to the above analysis and practical
experiences, six formulas of matrix are designed, and then
they are tested after sintered, at last the optimal formula is
recommended when different stratum are drilled. And
both ingredients and volume fraction of each formula are
shown as table Ⅰ.
TABLE I
Matrix formulas of bit
Formula
Keywords - impregnated diamond bit, matrix formula,
hot pressing sintering method, and performance test
I. INTRODUCTION
In recent years, as the national economy and the
urbanization are developing quickly, the government has
made good efforts to prospect the resources of minerals
and oil. As a kind of tools to prospect the resources, the
diamond bits have excellent advantages of impact
resistance and wear resistance to drill rocks and have been
widely used in drilling field [1-4]. During the process of
drilling, in order to improve the efficiency, the matrix
performances including the Rockwell hardness and
bending strength must fit with drillability of stratum [3, 5].
And the performances are greatly related to the matrix
formula and sintering method. So the selections of matrix
formula and sintering method are very important to
manufacture good quality of diamond bits [6][7].
II. MATERIALS AND METHODS
A Experimental design
(1) Design of matrix formulas
The performances of matrix of diamond bit mainly
depend on the formula of matrix, which includes
ingredients and volume fraction. The ingredients are
mainly divided into two kinds: one is framework
ingredients, which is used as hard spots; and another is
binder metal of low melting point, which is used to bond
framework ingredients and diamond. The volume fraction
of binder metal must be moderate, and if the volume
fraction is too high, the thick metal layer will be generated
among the framework ingredients and the diamond,
Ⅰ
Ⅱ
Ⅲ
Ⅳ
Ⅴ
Ⅵ
WC
45
40
40
40
45
50
Ingredient and volume fraction/%
YG6
Ni
Mn
Co
0
7
5
3
20
5
5
0
15
7
5
3
15
5
5
0
15
5
5
0
15
5
5
0
ZQSn663
40
30
30
35
30
25
(2) Mould design
Fig.1 the image of Mould
Graphite is selected as the material of moulds, as it
has high temperature resistance and enough strength. In
addition, it also does not contaminate the matrix. In order
to reduce error, three samples are manufactured for every
formula. And it is well known that the densification of
matrix has an important effect on performances of matrix.
So these samples need to be compressed to improve the
densification. And the compression is stopped when the
samples are compressed to a certain position in the
process of sintering. The mould is made up of three parts:
cover mould, top column and bottom column. Firstly the
bottom columns are put into the cover mould, and then
ingredients which have already mixed well are put into
the cover mould, and at last the top columns are put into
the cover mould. Then the top column are compressed
into the cover mould, the process of compression is
stopped [10-15]. The mould is showed as Fig.1.
The dimension of mould is as follows: the thickness of
cover mould is 25mm;
the bottom columns
are 5mm; the top
columns are 15mm,
and cross-section of
three parts is same, as
showed in Fig. 2.
Fig.2 cross-section of sample
(3) Design of sintering
The important function of matrix is to connect
diamond and steel body, which has an important effect on
the lifespan of bits. So all ingredients must be mixed well
in order to improve impact resistance and wear resistance
of matrix. The recommended time of mixing is 24 hours
at least [16].
Based on the same parameters, eighteen samples of
six formulas are sintered. And then these samples are
taken out from the mould. And after cleaned, they are
polished to expose a fresh surface by grinding wheel. In
the end, the samples are tested on Rockwell hardness
tester. Four random points are tested on the fresh surface,
and the average values are calculated.
(2) Bending strength test
The bending strength of matrix is a very important
performance for diamond bit. If the value is too low , the
bit is broken easily. After Rockwell hardness is tested,
bending strength of the samples is tested. The test results
are shown as table 3.
Bending strength tester
Pressure sensor
Fig.4 bending strength tester
Fig.3 sintering furnace
After the mixed ingredients are put into the mould,
the samples are ready to be sintered. Compare to the
normal method of manufacturing impregnated diamond
bit, the hot pressing sintering method is convenient and
selected to sinter samples. Temperature is a main factor to
affect the alloying extent of matrix, and the pressure is
mainly to control the matrix densification. At the same
time, the rate of heat increasing shouldn’t too high.
Because the heating rate is too quick, gas generating in
the mould can’t be discharged completely. This can
disturb the ingredients, even to bring the ingredients out
of the mould. The recommended heating rate is
250~350°C/ min. Heat preservation is necessary to reduce
temperature difference of matrix, and it also gives enough
time to complete alloying process. This is helpful to
improve the strength of cementing diamond.
Sintering parameters are selected as follows: the
temperature of sintering is 960 ℃ ; the pressure is
150kgf/cm2; the time of heat preservation is 5 minutes.
Sintering furnace is showed in Fig. 3.
B Performance test
The standard bending strength tester is used to test
bending strength of these samples. In addition, in order to
reduce error, a pressure sensor is used to show the broken
stress. The bending strength is got through following
calculation equation (1):
3PL

2bh 2
(1)
Where is, P—broken stress, N; L—distance between
two fulcrums, L＝24mm; b—width of the sample, mm；
h—height of the sample, mm.
According to the dimension of mould, the b and h
can be calculated, that is, b=5mm and h=8mm, the
bending strength can be calculated after the broken stress
is tested.
TABLE II
Test data of Rockwell hardness
Formula
Ⅰ
Ⅱ
Ⅲ
Ⅳ
(1) Rockwell hardness test
Ⅴ
NO.
1-1
1-2
1-3
2-1
2-2
2-3
3-1
3-2
3-3
4-1
4-2
4-3
5-1
5-2
5-3
1
28.2
28.0
32.2
31.8
28.3
31.9
38.3
39.5
39.1
34.4
38.0
37.3
42.7
44.7
42.2
Rockwell hardness value
2
3
4
average
28.1
31.2
29.7
29.3
28.5
28.1
27.7
28.1
31.1
29.5
30.4
30.8
32.1
30.9
30.7
31.4
28.8
30.8
30.1
29.5
30.4
29.9
32.2
30.9
39.1
39.5
37.8
38.7
36.1
37.0
35.4
36.9
39.7
38.9
40.7
39.6
35.7
33.9
35.1
34.8
36.1
36.5
37.8
37.1
38.1
36.5
34.9
36.7
46.0
44.4
48.1
45.3
46.2
42.6
48.4
45.5
43.1
45.2
43.9
43.6
average
value
29.4
30.6
38.4
36.2
44.8
Ⅵ
6-1
6-2
6-3
44.9
49.4
48.2
46.3
48.5
48.7
48.4
48.0
50.1
47.5
48.9
49.3
46.8
48.7
49.1
48.2
III. RESULTS
The test results of Rockwell hardness are shown as
tableⅡ. For further analysis, the fitting curve is drawn as
fig.5. The test results of bending strength are shown as
table Ⅲ.
TABLE III
Test data of bending strength
Formula
Ⅰ
Ⅱ
Ⅲ
Ⅳ
Ⅴ
Ⅵ
Bending strength value (MPa)
NO.1
NO.2
NO.3
sample
sample
sample
436
388
397
538
439
439
583
724
610
516
604
584
938
781
816
831
789
906
average
value
407
472
639
568
845
842
In order to contrast difference values of bending
strength, the fitting curve is drawn as Fig.6.
Rockwell hardness value
Fig.5.fitting curve of Rockwell hardness
Bending strength value (MPa)
(1) According to the fitting curves, the average value
of hardness and bending strength are bigger and bigger as
WC volume fraction is higher and higher. So WC as a
kind of framework ingredients which has high melting
temperature can improve Rockwell hardness and wear
resistance of matrix.
(2) Compare formula Ⅰ with formula Ⅱ, although
WC fraction of formula Ⅰ is higher than formula Ⅱ, but
formula Ⅱ does not include YG6, and YG6 is made up of
94%WC and 6%Co, so in fact total WC fraction of
formula Ⅱ is higher than formula Ⅰ . The Rockwell
hardness value of formula Ⅱ increases by 4% than
formulaⅠ, and bending strength value by 16%. Formula
Ⅱ should be selected when the stratum is hard and lowabrasive, because if the Rockwell hardness is low,
diamond is exposed easily, and the drilling efficiency
would be improved.
(3) Compare formula Ⅲ with formula Ⅳ , WC
fractions of both is same, and binder metal fractions are
adjusted only. The Rockwell hardness value of formula Ⅲ
increases by 6.1% than formula Ⅳ, and bending strength
value increases by 12.5%. So the formula Ⅲ including Co
can improve alloying extend of matrix. Formula Ⅲ is
recommended when the hardness and abrasiveness of
stratum are moderate.
(4) Compare formula Ⅴ with formula Ⅵ, WC
fraction of formula Ⅵ is higher than that of formula Ⅴ,
and bender metal fraction of formula Ⅵ is lower than that
of formula Ⅴ correspondingly. According to the test data,
Rockwell hardness value of formula Ⅵimproves by 7.6%
than that of formulaⅤ, and bending strength values of
both formulas are almost same. So formula Ⅵ should be
selected when the stratum is soft and high-abrasive in
order to improve the life of bit.
(5) The sintering process and sintering parameters
are important to the sample manufacturing. Especially the
sintering temperature and time of heat preservation
greatly affect the performances of matrix. In this
experiment, the matrix is heated to 960℃, and the time of
heat preservation is 5minutes, and these samples are
natural cooled in the sand. And this gives enough time to
complete alloying process. In addition, it is helpful to
form the excellent metallographic structure.
V. CONCLUSION
Fig.6.fitting curve of bending strength
IV. DISCUSSION
The six formulas are based on practical experiences,
and the test results are different, because the volume
fraction of framework ingredients and binder metal are
adjusted. Based on the test data, the conclusions are listed
as follows:
(1) From the experiment, WC as the framework
material can obviously increase the hardness, bending
strength, and structure strength and wear resistance of the
matrix .And with the increasing of Co content, alloying
degree and toughness of the matrix can be greatly
improved.
(2) As the experiment results are shown, number Ⅱ
formula is suitable to application in the rock of hardness
and weak-abrasiveness. Number Ⅲ formula is suitable to
application in the rock of medium hardness and medium
— abrasiveness. Number Ⅳ formula is suitable to
application in the rock of softness and strong—
abrasiveness.
(3) The experiment is performed as followed: in the
sintering process the ultimate temperature need to be
heated to 960 ℃, and keep this temperature for 5 minutes,
then put the heated matrix into perlite powder for natural
cooling that would be benefit to form good
metallographic organization of the matrix.
(4) The research of matrix formula is a complex
project, and is not summarized by three formulas.
Combining with the production practice and the practical
application, this thesis is only to test the several
representative formulas, and still need further research.
ACKNOWLEDGMENT
The work was supported by the special program of
the ministry of land and resources public welfare industry
research（SinoProbe-09-05）; National 863 plan project
(Grant No. 2009 AA06Z201); National Natural Science
Youth Foundation of China (Grant No. 51004052)
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