ARCHIVES OF METALLURGY AND MATERIALS

Volume 55 2010 Issue 4

DOI: 10.2478/v10172-010-0009-1

A. ROMAŃSKI∗

FACTORS AFFECTING DIAMOND RETENTION IN POWDER METALLURGY DIAMOND TOOLS

CZYNNIKI DECYDUJĄCE O WŁASNOŚCIACH RETENCYJNYCH OSNOWY W NARZĘDZIOWYCH SPIEKACH

METALICZNO-DIAMENTOWYCH

This paper describes the effects of principle factors which have an influence on potential diamond retention capabilities in

powder metallurgy diamond tools. Investigations were carried out using a 3-D computer model of diamond particle embedded

in a metallic matrix. The proposed model assumed that the material was fully densified by the hot pressing technique and then

cooled down to room temperature. The energies of plastic and elastic deformation of the matrix around the diamond grit as

well as recoverable strain energy accumulated in the grit on cooling were calculated. The effects of Young’s modulus and yield

strength of the matrix as well as friction between diamond and matrix on these energies were analysed. The obtained results

have shown that a matrix characterised by high yield strength ensures better diamond retention capacity whereas high Young’s

modulus of the matrix and its chemical affinity to carbon, which increases friction at the diamond-matrix interface seem to

have lower importance.

Keywords: PM Diamond Tools, Diamond Retention, Computer Modeling, Mechanical Properties

W pracy przedstawiono analizę wpływu podstawowych czynników mających wpływ na własności retencyjne materiału

osnowy w narzędziowych spiekach metaliczno-diamentowych. Badania wykonano z zastosowaniem modeli 3-D cząstki dia-

mentu osadzonej w osnowie. W zaproponowanym modelu założono, że materiał został zagęszczony do gęstości teoretycznej w

wyniku prasowania na gorąco i następnie ochłodzony do temperatury otoczenia. Dla temperatury otoczenia obliczano całkowitą

energię odkształcenia oraz energię odkształcenia plastycznego materiału osnowy wokół diamentu oraz energię odkształcenia

sprężystego cząstki diamentu. Analizie poddano wpływ modułu Younga i granicy plastyczności osnowy oraz współczynnika

tarcia pomiędzy cząstką diamentu i osnową na te energie.

W wyniku analizy otrzymanych rezultatów badań modelowych stwierdzono, że materiał osnowy odznaczający się większą

granicą plastyczności zapewnia wyższe własności retencyjne osnowy. Natomiast większy moduł Younga oraz zwiększenie

współczynnika tarcia, np. poprzez zastosowanie osnowy odznaczającej się powinowactwem chemicznym do węgla mają z

punktu widzenia retencji diamentu mniejsze znaczenie.

1. Introduction

Powder metallurgy diamond tools are widely used

for machining natural stones and other difficult to cut

materials, such reinforced concrete or asphalt. In order

to maintain the highest productivity of the tool at the

lowest cost, the tool composition has to be properly ad-

justed to the workpiece properties and operating con-

ditions. A well engineered matrix must hold the dia-

monds firmly and wear at a rate fast enough to discard

degraded diamond grits in order to keep the tool sharp

and ensure its long service. The wear resistance of the

metallic matrix can be easily changed by adding soft

or hard components to the powder mixture [1]. More

difficult task is to control the hold on the diamond grits,

which is affected by the matrix mechanical properties,

mismatch between the thermal expansion coefficients of

the matrix and diamond, and phenomena taking place

at the diamond-metal interface. Most often the bond-

ing between diamond crystals and matrix relies on me-

chanical locking. During cooling to room temperature,

due to the mismatch between thermal expansion coeffi-

cients, diamond grits are tightened by the surrounding

matrix wherein complex stress and strain fields occur.

When coated diamond is used additional chemical bond-

ing may occur which increases friction/adhesion at the

diamond-matrix interface [2-5].

Computer aided modelling (CAM) seems to be a

perfect technique to study phenomena affecting diamond

∗FACULTY OF METALS ENGINEERING AND INDUSTRIAL COMPUTERSCIENCE, AGH UNIVERSITY OF SCIENCE AND TECHNOLOGY, 30-059 KRAKOW, 30 MICKIEWICZA STR., POLAND

Diamond tool and metallurgy, Study notes of Metallurgy

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A. ROMAŃSKI∗

FACTORS AFFECTING DIAMOND RETENTION IN POWDER METALLURGY DIAMOND TOOLS

CZYNNIKI DECYDUJĄCE O WŁASNOŚCIACH RETENCYJNYCH OSNOWY W NARZĘDZIOWYCH SPIEKACH

METALICZNO-DIAMENTOWYCH

1. Introduction

Powder metallurgy diamond tools are widely used

for machining natural stones and other difficult to cut

materials, such reinforced concrete or asphalt. In order

to maintain the highest productivity of the tool at the

lowest cost, the tool composition has to be properly ad-

justed to the workpiece properties and operating con-

ditions. A well engineered matrix must hold the dia-

monds firmly and wear at a rate fast enough to discard

degraded diamond grits in order to keep the tool sharp

and ensure its long service. The wear resistance of the

metallic matrix can be easily changed by adding soft

or hard components to the powder mixture [1]. More

difficult task is to control the hold on the diamond grits,

which is affected by the matrix mechanical properties,

mismatch between the thermal expansion coefficients of

the matrix and diamond, and phenomena taking place

at the diamond-metal interface. Most often the bond-

ing between diamond crystals and matrix relies on me-

chanical locking. During cooling to room temperature,

due to the mismatch between thermal expansion coeffi-

cients, diamond grits are tightened by the surrounding

matrix wherein complex stress and strain fields occur.

When coated diamond is used additional chemical bond-

ing may occur which increases friction/adhesion at the

diamond-matrix interface [2-5].

Computer aided modelling (CAM) seems to be a

perfect technique to study phenomena affecting diamond

retention in the matrix, which has been utilised to evalu-

ate residual stresses and local plastic deformation zones

in diamond impregnated metal matrix composites [6-11].

Basing on the finite element modelling results it has been

suggested that diamond retention depends on the energy

of elastic and plastic deformation of the matrix around

the diamond crystal. None of the above cited studies,

however, did not scrutinized the effects of matrix char-

acteristics, such as Young’s modulus, yield strength, etc,

on its retention properties. Therefore the main objective

of the present research was to investigate the combined

effects of mechanical properties of the matrix and fric-

tion between matrix and diamond on retention of the

embedded grits. To this end the Abaqus software was

used to create a 3-D model.

2. Experimental procedure and results

The simulations were performed on an elastic-plastic

model, where the linear tetrahedral type C3D4 elements

and linear hexahedral type C3D8R elements were used

to generate the mesh in the matrix and diamond, respec-

tively.

The mesh configuration is presented in Fig. 1,

whereas mechanical and thermal properties of the

analysed matrices are summarised in Table 1.

TABLE 1

1.6· 10 −^5

(0-1200◦C)

3. Discussion and concluding remarks

As seen in Figs 2 and 3 the local stress is proportion-

al to the yield strength of the matrix, whereas the size

of plastically deformed zone shows the inverse trend.

From Tables 2-4 it is evident that ALLIE markedly

increases with the yield strength and Young’s modulus

while the effect of friction can be neglected. The ef-

fect of yield strength on ALLIE is more pronounced for

lower diamond protrusion and the opposite situation is

seen for Young’s modulus. Interestingly, the effect of the

coefficient of friction increases by a factor of ∼2.5 as the

height of diamond protrusion rises from 25 to 100μm.

Contrary to ALLIE, ALLPD is mainly affected by

Young’s modulus, and its dependence on yield strength

is markedly weaker.

It is noteworthy that RSE strongly depends on the

yield strength of the matrix whereas the other two factors