International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Cobalt substitution in PCD cutting tool materials

Piotr Klimczyk1, Lucyna Jaworska1, Magdalena Szutkowska1,

Sławomir Cygan1, Maciej Sitarz2

1Institute of Advanced Manufacturing Technology, Poland

2AGH University of Science and Technology, Faculty of Materials Science and

Ceramics, Poland

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Reliable material for cutting inserts

high: • hardness,

• wear resistance,

• flexural strength,

• fracture toughness,

• thermal stability,

• thermal shock resistance,

• thermal conductivity,

• chemical stability,

low: • coefficient of thermal expansion,

• coefficient of friction.

Introduction material properties

http://www.tungaloy.co.jp

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Introduction diamond, a metastable allotrope of carbon

Diamond has the highest hardness and

thermal conductivity of any bulk material

The oxidation process occurs during heat

treatment of diamond in oxygen at

elevated temperatures

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Polycrystalline diamond PCD is a two phase product in which the diamond crystals

are sintered together in the presence of metal catalyst phase

Introduction PCD materials

Cobalt belongs to the iron group of

materials, which are known to be

good solvents/catalysts for diamond

synthesis and also for the binder

phase during the diamond powder

sintering process.

Unfortunately, cobalt belongs

also to the group of critical raw

materials.

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Introduction PCD materials

Sintered polycrystalline diamond

compacts (PCD) are widely used for:

• cutting tools

• wire drawing dies

• and rock drill bits

cutting brazing finishing

sintered compact

final product

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

The aim diamond based materials with high thermal resistance

and without CRM

Typical PCD cutting tool

material

Innovative PCD

composite

WC (~90%) + Co (~10%)

substrate layer

PCD +

Co (12 - 18%)

working layer

no substrate layer necessary

AMBITION: down to 0% WC, 0% Co)CRM (WC, Co)

substitution

Cobalt promotes graphitisation of diamond and decreases thermal stability

of sintered PCD parts (e.g. cutting tools)

One of the possibilities to increase the thermal resistance of PCD materials

is to reduce the cobalt bonding phase content

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Starting powders

• diamond (Element Six, Micron+MDA, 3-6 µm,)

• titanium diboride (American Elements, <100 nm )

• cobalt (ABCR, 0.5-1.5 µm)

Preparation of material for sintering

• mixing: Planetary mill PULVERISETTE 6,

WC grinding balls φ 5 mm, acetone, 200 rpm / 2h,

• drying,

• compaction: manual hydraulic press, ~200 MPa,

discs φ 15 x 5mm

Experimental details samples preparation

diamond + 10% TiB2 diamond + 5% TiB2 + 2% Co

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

High pressure hydraulic press equipped with Bridgman’s type toroidal anvils

pressure up to ~8 GPa, temperature up to ~2400 °C,

duration of typical sintering process ~1 min

Experimental details HPHT sintering

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Sintering batch

assemble

1 – ceramic gasket (outside part)

2 – ceramic gasket (inside part)

3 – ceramic disc

4 – molybdenum disc

5 – sample

6 – graphite disc

7 – graphite tube

8 – thermocouple (only for T-calibration)

Experimental details HPHT sintering

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Pressure distribution in the sample during

plastic deformation of gasket in Bridgman's

anvils system

Experimental details HPHT sintering

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

0 10 20 30 40 50 60 70 800

1

2

3

4

5 P (Power of heating)

T [s]

P [

kW

]

0

1

2

3

4

5

R (Resistance)

R

Sintering process takes only one minute !!!

Experimental details HPHT sintering

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Sample in the gasket before sintering

Sample in the

gasket after sintering

Sintered

compact

(raw

sample)

Sintered

compacts

after grinding

process

Experimental details HPHT sintering

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Results microstructure

Diamond – TiB2 – Co composite: SEM image and X-ray maps of C, Ti and W

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Results microstructure

Diamond – Co (commercial): SEM image and X-ray maps of C, Co and W

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Results physical and mechanical properties

Composition

wt.%

Density

g/cm3

Hardness

GPa

Young’s

modulus

GPa

diamond + 10% TiB2 3.38 ±0.01 45.4 ±2.4 552 ±14

diamond + 5% TiB2 + 2% Co 4.04 ±0.01 66.6 ±2.9 834 ±23

diamond + 10 Co + 2 WC

(commercial) 4.14 ±0.01 78.6 ±13 976 ±34

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Investigations tribological tests

Ball-On-Disc: coefficient of friction

Fn - applied normal force (load)

Ff - measured friction force

• ball material: Al2O3

• ball diameter: 3.175 mm

• applied load: 4 N

• sliding speed: 0.1 m/s

• radius of the sliding circle: 4 mm

• sliding distance: 200 m

• number of cycles: ~ 8 000

n

f

F

Fμ

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Investigations tribological tests

Friction coefficient of diamond – TiB2 composite during sliding against Al2O3 ball

at 25, 200, 400, 600, 700 and 800 °C

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Investigations tribological tests

Friction coefficient of diamond – TiB2 – Co composite during sliding against Al2O3 ball

at 25, 200, 400, 600, 700 and 800 °C

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Investigations tribological tests

Friction coefficient of diamond – Co commercial material during sliding against Al2O3

ball at 25, 200, 400, 600 and 700 °C

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Investigations hardness

Hardness of diamond composites as function of heat treatment temperature (air atmosphere)

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Investigations XRD

XRD pattern of diamond - TiB2 composite after HPHT sintering

and after HT tribotests

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Conclusions

• Diamond with 10 wt.% of TiB2 and diamond with 5% TiB2 and 2% Co

composites were sintered using HPHT apparatus under the pressure of

8GPa at the temperature of 2000°C. The composites were compared with

PCD commercial material

• The composites are homogeneous – their ingredients are uniformly

distributed in the volume of material

• The friction coefficient of all materials is the lowest (0.1 – 0.3) at lower

temperatures and rise up to about 0.7 – 0.8 at highest temperatures

• RT mechanical properties of diamond composites are lower

in comparison with PCD commercial material

• Diamond composite with addition 5% TiB2 and 2% Co is the most

resistant to the hardness changes at elevated temperatures. This material

maintains the high hardness value up to 800°C

International Days in Critical Raw Materials 25-26th June 2015, Burgos, Spain

Development of a sintering center and know-how

exchange for non equilibrium sintering methods

of advanced ceramic composite materials” – SINTERCER

REGPOT-2012-2013-1 EU FP7 Research Potential

SINTERCER - project no. 316232

duration: 01.06.2013 - 31.11.2016

The research activities carried out by

Institute of Advanced Manufacturing

Technology scientists are supported by the

European Commission under the FP7

Specific Programme 'Capacities'