Advances in coating technology for metal cutting tools

Advancesin coating technologyfor metal cutting tools Coatings have a major influence on the performance of cutting tools. Staffan Siiderberg, Mats Sjiistrand and Bjiirn Ljungberg of Sandvik Coromant, Sweden, highlight some of the advanced coating technologies that are part of today’s modern tool material grades. They also overview the history of coating technology, with a focus on developments at Sandvik, and look forward to see what new developments we may see in the next five to ten years.

T

he introduction

of coated

metal cutting

tools

has been one of the main success stories in the

industrial application of modern coating technology over the last three decades. The first coated cemented

carbide

introduced

indexable

inserts for turning

in 1969 and had an immediate

brittleness of Al,O,

ceramics posed both then and now a

strong limitation to a more general use for metal cutting. A period of intensive research on the CVD of A1,O3 resulted in the first TiC/Al,O,

were

impact on

the metal cutting industry. The first grade from Sandvik - GC 125 - had a XC

coated carbide grade in

1975 - GC 015. This grade consisted of a thin Al,O, coating on top of an inner TX coating. One reason for the inclusion of an inner TiCI coating was the problem of achieving

sufficient adhesion directly on the cemented

coating only a few microns thick deposited by thermal

carbide. However, this combination

CVD,

(or carbonitride)

but the coating had a strong effect on both the

of an inner carbide

coating and an outer Al,O,

coating has

chemical and abrasive wear resistance of the inserts. This

become almost an industry standard since then due to the

boost

fact that the two coatings complement

in wear resistance

gave room for a significant

increase in cutting speed and thereby improved produc-

each other in

limiting wear at the cutting edge.

tivity at the machine shop floor. The cutting speeds used with the new coated inserts

Early limitations

were soon lifted to a level where again chemical wear of the Tic coating became a limiting factor. An obvious

The first generations of coated metal cutting inserts had several limitations that restricted a more general

candidate coating material to enhance

application

chemical

wear was Al,O,,

stability. Al,O, tool material

the resistance to

known for its high chemical

was already used at that time as a cutting

in the form of a bulk ceramic.

However,

in metal cutting.

tion temperature

in diffusion of chemical

the

Firstly, the high deposi“C) during CVD

of the coating edge, especially if sig-

1969

First coated grade (TIC)

GC 125

nificant

1975

First Al,O, coated grade

GC 015

the

1980

First thick A&O, coated grade

GC 415

grades this problem was partly overcome

1982

First PVD coated tool

Delta drill

1983

First Al,O, coating with improved adhesion

GC 415

1990

First PVD coated insert grade

GC 1020

1994

First 100% a-AJO,

GC 4015

1994

The first grade with MTCVD inner coating

coated grade

results

elements from the carbide sub-

strate to the coating during growth. The main effect is an embrittlement

amounts of the brittle eta-phase

substratecoating

interface.

edge to give a tougher micro-geometry carbide substrates with chemical

is formed near

In the

first

coated

by honing the

and by selecting

compositions

less sen-

sitive to diffusion loss during coating (mainly high carbon content). A second limitation

was the ability to grow thicker

GC 3020

coatings

to further enhance

problem with thicker coatings is that adhesion generally drops drastically with increasing thickness. For Al,O,

the wear resistance.

One

1994

First PACVD diamond coated grade

GC 1810

1995

First TiCN PVD coated grade

GC 1025

1995

First PVD coated cermet

GC 1525

thickness

1997

First A&O, coated steel milling grade

GC 4030

chemistry

growth at the cutting edge. The latter problem was to a

1998

First TiAlN PVD coated grade

GC 2145

2000

Ultraspeed steel tnrning grade

GC 4015

Figure I: The history of coating Coromant perspective.

24

(950-1050

MPR

April 2001

development

for metal cutting

from the Sandvik

there was also a major problem with uneven

coating

for thicker coatings due to the fact that the of the CVD

process results in more rapid

large extent overcome in 1980 when Sandvik Coromant introduced its first grade - GC 415 - where the Al,O, process was enhanced by using a patented dopant process. This dopant also enhanced growth rate, and grades with

0026.0657/01/$

-see

front

matter 0 2001Elsevier

Science Ltd. All rights reserved.

significantly

higher

Al,O,

thickness

(up to 8-10

urn)

could now be produced.

Introducing

, 994

1

PVD

The problem

with insufficient

major

in the development

topics

nologies for metal cutting proprietary, innovations been

made

strong

over

driving

deposited

the

In particular,

to find

temperatures

that

in order

to allow tools

normally

batches

with even coating

over the whole have

about

in PVD was to find a process material

a commercial

Coromant

thickness

for each

application

was TiN

19-30 .

given and

material

Figure

tools

2:

This was a characteristic

of the first

PVD coated

grades - they were often developed

lem solvers

for operations

with

TiAlN

very special

and TiB, were introduced.

for PVD

is still in applications

demands.

required

(threading,

parting,

etc.) and in applications cutting

sharp

grooving,

In solid carbide

PVD is the standard

In spite of the above-mentioned

and optimization

in addition,

it is still the only coating

depositing reduce

high-quality

the decarburizing

have been developed ture to be reduced diffusion

of a coating coatings.

effects

of CVD,

processes

of PVD,

the

to

Edge depression

l

Edge impression

force for

important

for TEN

step

coatings

at

called

is today commonly

l

Edge line flaking

l

Thermal

l

Plastic deformation

and/or

Figure 3: Wear and failure

of the

advanced

today’s modern

coating

used in

are a considerable

and failure

and coating

adhesion.

technology

from

presented

a unique,

Coromant

patented

wear resistance

Some of the highlights

a Sandvik

in coating

perspective

are

in Figure 1. where coating

interaction

of metal cut-

material and

mized for different

tests tion

cutting

tool materials

user productivity

has had a dramatic

impact

(Figure 2). We will now highlight

www.metal-powder.net

of

on endsome

of metal

must

of

ahead

of important cutting

be taken and/or

wear

tools

into

(Figure

account

a grade

trolled

actual

-

the basic wear, in that

laboratory

application

wear mechanisms

plastic

deformation,

application tests.

area

In addition,

defining

the

by Figure 4. a new tool

area is to isolate - such

as flank

toughness

and

by carefully

con-

special

functional

are designed that simulate the complex of several wear and failure mechanisms cutting

when

for a specific

of the main parameters

grade for a given

crater

flaking

areas. The development

are part

properties of the end product are illustrated At Sandvik, our approach in developing

ting tools is an industry standard with a multitude of grades (combinations of layer stacks and substrates) optiapplication

that

3). It can be readily seen that it is a complex process where several wear and failure mechanisms interact.

and study

Today, we have a situation

cutting.

grades, before looking

number

mechanisms

Some

with

in 1994 and com-

in an unrivalled

in metal

Wear and failure of cutting tools There

application.

coating

flaking

technologies

tool material

a geometry

inner

fatigue

flaking

induced

mechanisms

developing

resulting

thermal

mechanical

This

coating,

and/or

or bulk fracture

grade GC 3020, that was introduced MTCVD

wear

(attrition)

fatigue

combination with traditional CVD processes for A&O, and other coatings. One example is the cast iron milling bined

productivity.

to future developments.

tempera-

800 and 950 “C, commonly

Al,O,

on end-user

Coating Removal(stochastic)

order

In

temperatures

This type of process

l

Top slice fracture

of

of a process

MTCVD.

(diffusion)

l

capable

was the introduction between

Chemical

Mechanical

new processes

One

wear

l

Edge chipping

layer stack but,

the driving

at the interface.

wear

Adhesive

l

(end-mills

that allow the deposition

as well as limiting

development

on a tough

process

Al,O,

Abrasive

l

l

majority of carbide inserts are still coated by CVD. As will be discussed later, the CVD process allows significant engineering

.

Wear by Fracture(stochastic)

technology.

success

l

are

edges

tools

coating

The effect of tool material

use

end-milling,

with high demands

edge (drilling).

and drills)

The main

where

1&oz6oo

Wear/Failure by Plastic Deformation (logarithmic)

as prob-

During the1990s, PVD had a major impact in coating of metal cutting tools and new coating materials such as TiCN,

.

ContinuousWear (linear)

- the

delta drill - in 1982. The first grade - GC 1020 - for inserts was introduced in 1990 and was especially developed for threading.

19.70

to

and Sandvik

its first TiN-coated

.

19-50

in large

on each insert

The first PVD coating

introduced

IO

500 “C. The

such that it could be deposited batch.

In in

be

temperature coating

1969

was a

could

edges to be coated without any embrittleThe solution was PVD where deposition

challenge

coating

highly have

with sharper ment effect.

can be kept

1980 Thick p#“-‘__

tech-

there

coatings

1

1989 Functka grad&**

is still one of the

of new coating

although many, often in process technology

years.

force

at lower

adhesion

2000 New CornKey generation

interacin an

operation.

MPR April

2001

25

Cutting tool insert

Grade (wearkougness)

Geometry (cutting forces/chip

-

flow)

Substrate

I Powder

-

Pressing

-

Sintering

Coating

- Feed range

I

- D.0.C range -Strength

I PVD

With gradient Without gradient

I CVD

-TIN

-TIC

- TiCN _TiAIN

-TiCN -TIN

Grinding

-

Figure4: Factors affecting

the final properties

- Grinding/ honing

of a cutting

wear

adhesive

wear

l

Reduced

abrasive

l

Reduced

adhesive

l

wear wear

Reduced

thermal

load on substrate

low Adhesion to Work Material

- Workpiece finish - Size control L Surface finish

A'2o3

abrasive

Reduced

low Thermal Diffusivity

- Cutting forces

-Cutting forces - Workpiece finish l wiper - Size control

Reduced

l

Chemical Inertness

I

I

l

l

Reduced

abrasive

wear

l

Reduced

adhesive

wear

CoatingAdhesion and Residual Stress

tool.

Figure5: Key properties wear on the clearance Consequently,

for coatings

in metal cutting.

face is more abrasive in nature.

the Al,O,

coating

is rapidly worn away

on the flank and the inner coating constitutes

the main

protection. 25

ZrO,

Although

this paper deals with the coating of cutting

tools, it is important to realize that the design of a modern coated carbide grade also involves the optimization of

26 months

1.2 x10-5

%O,

pm wear

1.2 x10-z

the underlying substrate. With improved coating proper-

HfC

1.0

ties as well as increasing coating thickness, the main pur-

ZrN

1.6

pose of the substrate is to support the coating and to

TIC

2.9

provide crack

TiN (afler B M

mechanical

5.9

Kramer

arrest to prevent

failure,

if and when

or thermal cracks penetrate the coating, For

turning inserts, most modem grades include a gradient sintered cemented carbide in which the surface zone is

1980)

enriched

with the metallic

binder to provide a tough

The most important coating properties to reduce wear and failure of metal cutting tools are listed in Figure 5.

near-surface zone. Figure 6 shows one example of a gradi-

From the earlier discussion on the development

of coat-

width of the gradient zone is decreased near the edge line

of resistance to

to enhance the plastic deformation resistance of the cut-

chemical wear is clear. In 1980 BM Kramer made a series of predictions on the chemical wear resistance of various

of a modem coated tool. These are the building blocks

ings for metal cutting, the significance

ent sintered carbide where it can also be seen that the

ting edge. In summary, Figure 7 illustrates the basic design

materials (Table 1). The vast difference between Al,O, and the cubic carbides and nitrides explains the importance of Al,O,

Consequences

in metal cutting.

for coating design

With this background,

the basis for the design of a coat-

ing layer stack for a modern metal cutting tool can readily be understood. The inner coating is normally based on a TiC/TiCN/TiN multilayer structure, which has the function

to provide a strong bonding

and give the insert good resistance This is followed by an Al,O, mal insulation

to the substrate to abrasive wear.

coating that provides ther-

as well as protection

from chemical

and

adhesive wear. The outermost layer is often a TiN layer which has the main function

of wear detection,

that is,

to allow the operator to distinguish between a used and a new cutting

edge corner.

In addition,

this layer of

course adds to the total wear resistance of the insert. The TiCN and Al,O, sub-layers have complementary effects. At the rake face where the cutting temperature is the highest, chemical wear dominates while the flank

26

MPR

April

2001

Figure 6: Functional gradient sintered reinforcement of the cutting edge.

carbide

showing

www.metal-powder.net

Al,O, coating that is the most critical for the resulting structure and some of the process

steps used to control

properties

Al,O,

are highly proprietary.

sign of the industrial

importance

coating

that

technology

modelling

of Al,O,

the

of the K-Al,O,

coating

It is surely a theoretical

structure

one of the first industrial

became

case studies for the

1998 Nobel-Prize

rewarded

density-functional

theory

highly

advanced

(DFT).

Typical for the latest generation of Al,O, coated grades is that not only is the crystal structure

controlled

ture, namely, Figure 7: Design

of a modern

that most modem

coated

cemented

and

of the

microstructure

cutting

Al,O,

insert.

sition are

we will look at

in more detail to provide

importance

engineering

of process in

coating

control

can be controlled

grow to form a (012) texture. a highly

columnar

growth

For instance,

coating

flexibility

to various mechanical

excellent

protection

depo-

to let the coating

This particular which

direction

a-Al*O,

growth yields

gives the coating

high

loads while maintaining

to chemical

and adhesive

wear and

of metal

in A&O, coatings

is a material that can be found in nature in difforms. Corundum and emery are both based on and commonly

used as abrasives.

ruby are examples

of modifications

used as gem stones

and where

the result

of small amounts

and C$+).

Al,O,

dehydration

the attractive

of metallic

crystal

structures,

stable

of Al,O,

The most common K-A~~O~. This

are

appears

j

L

Boehmite Y-AIO(OH)

’ ’

(Ti3’

by coating.

apart from a-Al,O,

is frequently appears

on cubic carbides

found

I 100

/

/

I

300

500

I

I

700

900

I 1100

C

resulted

topography

impaired

is

Figure 8: Transformation hydroxides in air.

series

of aluminium

hydroxides

and aluminium

such as

3 ‘9

of coated cutof a mixture

in an uneven coating

oxide

to pre-

and nitrides

was often composed

a- and K-A~~O~, which that severely

a -~~~~--

after CVD

to be linked

Tic, TiCN and TiN. In the first generations ting tools, the coating

complex

CY. ._ I

is illustrated in Figure 8 several of the unstable

can be obtained

structure

The

is the

B-AlpO, .___~_.._____

I--

of

in sever-

a-Al,O,

form.

modification

and its formation

ferred nucleation

colours

impurities

of which

transformation series for Al,O, and is included here because

deposition

are

by dehydration

is that Al,O,

thermodynamically

modifications

and

that

such as gibbsite, bayerite, boehmite interesting observation from such

experiments

al different

Sapphire

of Al,O,

can also be obtained

aluminium hydrates and diaspore. The

only

of the coating.

tools.

Developments Al,O, ferent

two sections,

technologies

an understanding

carbide

carbide grades for cutting

based on. In the following the various coating

cemented

but also the crystal tex-

the crystallic

of

te

coating

performance.

In the last ten years, much progress has been made towards the control of the Al,O, crystal structure and texture, and the modem metal cutting tool material grades have a carefully designed Al,O, layer that has been optimized

for its particular

coating

optimized

application.

for adhsion

much more homogeneous &K-Al,O, cation

coated

topography

grades. Although

is thermodynamically

not a problem during cutting is the desired modification. shown

that

than a-Al,O,

A 100%

has a

than the old mixed the K-Al,O,

unstable,

this

modifi-

is generally Temperature

and in many applications it For example, it has been

K-AI~O~ has a lower

thermal

(Figure 9). It is the nucleation

www.metal-powder.net

a-Al,O,

and wear resistance

conductivity step of the

Figure g: Thermal

conductivity

of alumina

(K)

(after Cahill et al.,/.

Appl. Phys., 83

(lpp~), p. 5783).

MPR Atxil2001

27

Multilayer

PVD coatings

(“superlattices”)

l

Multilayer

CVD coatings

TiCN/Ti,ZrN

l

Nanocrystalline

l

superhard

l

TiAlCrYN

l

Lubricious

l

PVD or PACVD alumina

process.

etc.

coating

A characteristic

strongly adhesion

TiAlSiN

PVD coatings

mechanical

loads.

on flaking

resistance.

The reason top coatings

l

Nanocrystalline

l

CBN coatings

for reduced

smearing

technologies

proposed

regard

Compared

for metal cutting.

coating,

403

improvement

to a traditional

(012)

a-Al,O,

in coating

adhesion,

a/K-

mixed

shows

become

by flaking

in TiC/TiCN/TiN/TiAIN

this

to alternative performance

coatings

layer

such

as sputtering

grades

these

processes

coated

tools.

Earlier

CVD

coated

to CVD

a renewed

has

coatings

interest

limited

coating

in alternative

Sandvik

- GC

most recent all include pared

4020,

stainless Al,O,

GC

4030,

GC

steel milling

layers. This

inserts

were

coated

used in cast iron milling sion were less severe. A modern layers,

CVD

including

diffusion

barrier

enhance

adhesion

is normally

inner

coating

a substrate and

TiCN

to the Al,O,. deposited

the

consists

com-

25% of all

could

the demands

bonding

a surface

change

less than

and Al,O,

where

- and

grade CC 2040 that

is a drastic

to only ten years ago when

milling

4040

from

only

be

of adhe-

of several

sub-

layer, a substrate

adhesion

material lead

coating

due In

droplets coating

no coating

arc-evaporation,

in the coating

ion-plating.

These

to be pulled

as proposed

the

by

type

(Rapid-Coating-System) Typical inserts l

‘superlattice’ coatings consist of several hundred layers of at least two different materials.

solution

of the

surface

than

can cause exhibit

the

Since pros and

it remains to be stand up in the

is some

by Balzers

can

metallic

materials.

and arc-evaporation

Maybe

MTCVD

particles

sputtering

future.

an

leads to a rougher

of

which of

for metal cutting applications, how these two processes will

process

suffi-

parts

cons seen

to

to ensure re-sputtering

formation

both

layer

layer

that

effect,

off in smearing

both

problems

on critical

protruding

The main coating

modification

technologies,

some fundamental

to a hollow-cathode

tem-

However,

but this in turn causes

to virtually

tools.

the high

and arc-deposition. have

recent

tools has spurred

cient

grades

has

with

The

to enhance

of PVD coated

ple of this

milling

such

flexibility

materials.

limit the coating performance. In sputtering, a high bias is required

is the new steel

properties

but this difference

with TiC/TiCN/TiN only have now been replaced with more modern coatings that include Al,O,. One examtrend

coatings

with time.

process

regards

in TiAlN

for Al,O,

as opposed

tempera-

In addition,

oration

interest

and an outer

coating

when inherent

less pronounced

perature

as an inner

lower

were compared

In this area, CVD and PVD technologies have developed in parallel. For CVD coating, TiC/TiCN/TiN are used both

over

of ‘pure’ TiN and TiCN

that

CVD coatings

However,

tests.

Developments

effect

For TiN and TiCN the Balzers thermionic arc evapis the benchmark technology. process

a dramatic

as measured

has a strong

to micro-toughness.

are crack-free

as wear resistance loads.

coating various

and have a residual stress that is beneficial in some applications. Earlier PVD processes often came out worse than comparable

thermal

TiCN

is the advantages

the coatings

Figure IO: New coating

Columnar

to the deposition

tures give with

coatings

is that it gives a

that PVD has more and more taken

with regards coatings

diamond

of this process

columnar structure that enhances and increases its ability to withstand

with

form their

reactor. applications

for

in metal cutting

are:

of hybrid latest

RCS

PVD-coated

Finishing

l

Parting-off

l

Grooving

l l

Threading Turning/milling

l

Turning

l

End milling

stainless

heat resistant

l

Short hole drilling

l

Solid carbide

steel

superalloys

drills

Solid carbide endmills. In many of these applications, l

proved

to give an advantage

higher

resistance

28

MPR April

2001

coating.

of TiAlN

coatings

can be controlled

optimized

by the formation

is that

has of its

temperature

the residual

stress state and

of multilayer

structures.

One particular multilayer

high

loads. In addition,

TiNmAIN Figure II: TiN/NbN

to

TiAlN because

aspect

the coating

of PVD technology thickness

is strongly

www.metal-powder.net

dependent

on the loading

cally a line-of-sight thickness

control

properties,

of the reactor

deposition.

to produce

house with a well-defined batch

An alternative assisted)

a clear

the deposition

competitive

is PACVD

(plasmain con-

500 and 600 “C PACVD coated

have been on the market for about

ten years but it has so far had limited with

0.6

in-

temperature

CVD is reduced to between aid of plasma activitation.

Problems

(4

route and full con-

gives

to PVD technology

inserts with TiN/XCN

tools,

in optimizing

PVD coatings

processing

build-up

CVD where

ventional with the

cutting

is one of the key factors

and the ability

trol of the advantage.

since it is basi-

For metal

PACVD

include

commercial the

impact.

incorporation

2

0.5

.k 2

0.4

5 y

0.3

S “,

0.2

$ z 4

0.1 0

of

600

1600

3000

4200

Milled

impurity elements from the precursor gases (mainly chlorine); otherwise the coating microstructure resembles that

length

5400

6600

(mm)

of PVD.

A look into the future In spite of coated

cutting

tools having

more than 30 years of industrial

a background

application,

there

coating

materials

and coating

of cutting

tools

PACVD

while

reactor

materials

Experience

tool

Some

and

companies,

tool coating

that have been proposed

nologies

of PVD

cutting

and universities.

are listed in Figure

The work on

development

involve

manufacturers,

well as institutes

used new

done by the manufacturers

the

technologies

coating

techniques.

CVD is mainly

suppliers

as

of new coating

in the past few years

10.

has shown

that it takes time for new tech-

to gain a foothold

from the first proposal

on the market.

of a new coating

ing process to its first successful

Milled

in the future.

Here

in coatings:

material

commercial

tice’) coatings peratures

we concentrate the deposition

is

on just two current (‘superlat-

of alumina

at low tem-

Figure 12: Performance of various TIN and TiCN-based of (a) carbon steel, (b) stainless steel.

multilayer

as compared

to the

reference.

In stainless

steel milling,

the PVD multilay-

er coating

also

early PVD

coatings

were

to enhance

proposed

late

than

the CVD

of TiN type

than

CVD

in the

the hardness

stant

may have

them

This

creates

a coating

hardness

increase

TiN/VN

multilayers

of more

been

for

TiN/TaN

and

hardness

values

what

the resulting

tests on a carbon

coatings and stainless

in

wear

www.metal-powder.net

strain,

and a

more

hardness such

like.

resistance

coating

two different Sumitomo

in

structure

proposed

layer wavelength Multilayers

In face milling

Valenite a

coatings

and

the

steel,

the

wear

was no better lower

Although in a PVD

has been taken fura TiN/AlN

Theoretically

this

mulshould

effect since TiN and AIN have

structures

(fee and hcp).

that it is possible is kept short

However,

to stabilize

a cubic

AlN as long as the multi(see pp. 16-18

for more

by CVD have also been proposed

by Widia

using multilayers

the information

TiCN

cutting.

(fee) of the hexagonal

details).

in the face milling

case due to

and significantly

which has introduced

crystal

of

for

in metal

commercially.

11

12), a significant

TiCN

TiCN/Al,O,/TiN.

of multilayer

Figure

is shown

reference

layer

a future

as an example

moderate.

(Figure

increases

multilayer

PVD

were achieved with inserts coated the results indicate that multilayer

ther by Sumitomo, tilayer

In carbon

not give the superlattice

has later

as TiN/CrN,

the

coating look

for

insert.

TiCN

The concept

nm.

to TiN or VN only.

although

been

a thick5-15

100% was reported

systems,

multilayer

than

lattice

increased

other

have

a TiN/NbN

improvement

than

TiN/NbN,

shows

high

as compared

to achieve

with

not more

with

The possibility verified

alternatively

layers

CVD

layer, in the latter

TiN/NbN

triple

these results pilot reactor,

and to deposit

of the

of the

coatings. The original idea was to use two coatings with the same crystal structure and similar lattice conness of the individual

outperformed triple

fracture

resistance

1980s as a method

coatings

TiN/NbN

TiCN/Al,O,/TiN

or PVD.

Superlattices Superlattice

(mm)

or coat-

application

of multilayer

and the deposition

by PACVD

length

The time span

often ten years or more. It is therefore very difficult to predict which of these new coatings will come out as winners trends

(h)

is still

intensive research activity to improve the currently coating materials and processes as well as to develop conventional

of

of TiCN/(Ti,Zr)N,

according

to

from the company.

MPR April

2001

29

Currently,

several

PVD

reactors

even

announced

cial process y and Al metal

y and a

Amorphous

y

haps

Al,O,

The

tion of insulating es has been

Crystalline

been

produced

temperatures inherent

coatings

solved

plies.

between

that currently creates great community is the ability to

at lower

or PVD.

by plasma

coating by both “C.

y-Al,O,

or amorphous

Table

2 shows

the

chemistry

lower

the

suphave

at temperatures temperatures

crys-

may be formed.

of temperature Al,O,

process-

DC power

coatings

influence on

deposi-

of a-AIZO,

techniques At

“C) by

with

activated

consisting

talline phase

(500-800

problem

by the use of pulsed

700-800

and

crystallinity

gas

plant

also function

equipment

have

in metal

shown

cutting

that

to give

y-Al,O,

can

an advantage

compared to PVD TiN. Although the data are limited, this may offer a possibility to lower deposition temperatures

below

the

never

had

to have

have

impact,

PACVD and

have

a commer-

we should

on the market

a real been

first

of

and some

Al,O,

in the mid-1990s those

discontinued.

grades

Keeping

POWDER

shop floor.

Contact: Staffan Siiderberg Director, R&D Materials and Processes Sandvik Coromant Lerkrogsvagen 1g Stockholm, SE-126 80, Sweden. Tel: +46-8726-6698; Fax: +46-8726-6760. E-mail: [email protected] URL: www.sandvik.com This paper is modified, with permission, from a presentation given at the ‘Advanced Coatings and Surface Systems for Cutting Tools & Wear Parts’ meeting, held in Atlanta, 13-15 November 2000, organized by Gorham Advanced Materials (www.goradv.com).

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30

MPR

April

2001

E-mail: [email protected] Website: www.parksidetool.co.uk

No 606. Go to www.metal-powder.net

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PACVD, and similar relationships have been presented for PVD. Tentative tests with samples coated in pilot

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will soon

that

manufacturers

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