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Polycrystalline Cubic Boron Nitride (PCBN)

Polycrystalline cubic boron nitride (PCBN) composites are produced by sintering micron cBN (cubic boron nitride) powders with various ceramic binders yielding hard and thermally stable tool materials. Most PCBN materials have a cemented carbide substrate. CBN is the second hardest material known, after diamond, but has high thermal and chemical resistance. PCBN composites provide extreme resistance to deformation and wear at high temperatures.

About two thirds of all PCBN tools are used for the machining of hardened steels. Other applications are the machining of hard, grey and high-strength cast iron, and cold and hot-work tool steels. The machining of nickel and cobalt-based superalloys is a growing application for PCBN.

DBC50 SEM
PCBN Microstructure
Dark phase is cBN (50%)
Light phase is binder (TiC)
AMB90 SEM
PCBN Microstructure
Dark phase is cBN (90%)
Light phase is binder (ceramics)

Comparison of tool & workpiece hardness


Nb C H a r dn e ss V i c k e r s (Gpa) 50 40 30 20 10 T i C cB N P C BN A l 2 O 3 WC H a r d e n ed steels Ca s t irons W r ou g h t & cast aluminium alloys 70 80 60 P C D

How PCBN works

The effectiveness of PCBN in machining hardened steels is due PCBN’s high hot hardness and chemical stability at elevated temperatures. Self-induced heat generated in the cutting zone reduces the hardness of the material in contact with the cutting tool.

PropertyAl2O3+TiCN (30% Vol)Tungsten Carbide K10PCBN
Vickers Hardness (GPa)191725-40
Fracture Toughness (MPam0.5)3.610.54.0-7.2
Thermal Conductivity (W/m/°K)3210034-100
workpiece hardness

General indicator of applications by cBN content


cB N - Con t e n t ( %) 40 90 10 0 50 0 10 0 20 0 0 Ca st I r on s S in t e r ed I r on s S u p e r a l l o ys H a r d - f a c i n g s F in i s h H a r d T u r n i ng & M ill in g C u t t i ng S p e e d ( m / m i n ) C u t t i ng S p e e d ( m / m i n ) T u r n i ng c a se- ha r den e d s t ee l s M i l li n g t oo l st e e l s R ea m i n g R ou g h & f i n i s h tu r n i ng G G 2 5 M i l li n g G G 2 5 R ough t u r n i ng ha r dened s t ee l s F i n i s h t u r n i n g S upe r a l l o ys F i n i s h t u r n i n g C GI, N C I, A DI T u r n i ng Hi - C r i r o n s F i n i s h m i l li n g c a se- ha r den e d s t ee l s T u r n i n g ba l l - bea r i n g & t h r u - ha r den e d s t ee l s I n t e r r up t ed t u r n i n g S i n t e r ed i r on s

Standard disc specifications

PCBN with substrate
Outer disc diameter: 75mm
Useable disc diameter: 70mm
PCBN layer thickness: 0.7-1.0mm
Overall thicknesses: 1.6, 2.38, 3.18 and 4.76mm
(+/- 0.05mm)

Grades:

cBN (%)
45
50
65
85
90
90

Grain size (µm)
<1
1.5
3
2
4
3

Binder
TiCN
TiC
TiN
AlWCoB
Novel
TiCN-Al

Solid PCBN, conductive
Outer disc diameter: 94mm
Useable disc diameter: 95% 90mm
Overall thicknesses: 1.0, 1.6, 2.38, 3.18 and 4.76
(+/- 0.05mm)
Grades:

cBN (%)
45
50
50

Grain size (µm)
<1
1.5
4

Binder
TiCN
TiC
TiC/TiN

Solid PCBN, non-conductive
Outer disc diameter: 101mm
Useable disc diameter: 95% 97mm
Overall thicknesses: 3.18, 4.76 and 6.35
(+/- 0.13mm)
Grades:

cBN (%)
65
70
90
90

Grain size (µm)
<4
<1
3-10
3-60

Binder
TiC/TiN
TiCN
AlN+AlBx
AlN+AlBx


Tool geometry suggestions


Hardened steel - rough turning
(Left: standard turning; Right: profiling)

20-40µm edge hone 20° x 0.2mm 20° x 0.2mm 20-40µm edge hone -6° 5-7°

Hardened steel - finish turning
(Left to Right: standard turning, thin wall & small internal diameters)

10-20µm edge hone 10-20µm edge hone 10-20µm edge hone 20° x 0.1mm 20° x 0.1mm -6° 5-7° 5-7°

Grey cast iron - through the skin

20-40µm edge hone 20° x 0.2mm -6° 20° x 0.2mm 20-40µm edge hone 5-7°

Grey cast iron - finish machining

10-20µm edge hone 10-20µm edge hone 10-20µm edge hone -6° 5-7° 5-7° 5-7°

Tool manufacture

Suggested edge preparation for hard turning:

Chamfer
standard 20° x 0.2mm
heavy roughing 20° x 0.2-0.4mm

Hone
standard 10-20µm
roughing 20-40µm

10-20µm edge hone 10-20µm edge hone 20° x 0.1mm 20° x 0.1mm -6° 5-7°

(Left: standard turning; Right: thin wall)


Tool and cutter grinder Potential crack initiators Peripheral grinding
PCBN nose radius

Nose radius

PCBN chamfer

Chamfer


PCBN processing

Tool production, using PCBN, involves several techniques depending upon:
• the tool material and
• the tool application.
The processes involved in tool fabrication are:

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