U.S. patent application number 09/782226 was filed with the patent office on 2001-12-06 for pvd a12o3 coated cutting tool.
Invention is credited to Alfredsson, Viveka, Fietzke, Fred, Goedicke, Klaus, Hilding, Tomas, Ljungberg, Bjorn, Schiller, Siegfried, Sjostrand, Mats, Zywitzki, Olaf.
Application Number | 20010049011 09/782226 |
Document ID | / |
Family ID | 20408890 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010049011 |
Kind Code |
A1 |
Schiller, Siegfried ; et
al. |
December 6, 2001 |
PVD A12O3 coated cutting tool
Abstract
The present invention describes a coated cutting tool for metal
machining. The coating is composed of one or more layers of
refractory compounds of which at least one layer consists of
fine-grained, crystalline .gamma.-phase alumina, Al.sub.2O.sub.3,
with a grainsize less than 0.1 .mu.m. The Al.sub.2O.sub.3 layer is
deposited with a bipolar pulsed DMS technique (Dual Magnetron
Sputtering) at substrate temperatures in the range 450.degree. C.
to 700.degree. C., preferably 550.degree. C. to 650.degree. C.,
depending on the particular material of the tool body to be coated.
Identification of the .gamma.-phase alumina is made by X-ray
diffraction. Reflexes from the (400) and (440) planes occurring at
at the 2.theta.-angles 45.8 and 66.8, degrees when using
Cu.sub.K.alpha. radiation identify the .gamma.-phase
Al.sub.2O.sub.3. The alumina layer is also very strongly textured
in the [440]-direction. In contrast to prior art, the
Al.sub.2O.sub.3 layer is virtually free of cracks and halogen
impurities and, furthermore, the Al.sub.2O.sub.3 layer gives the
cutting edge of the tool an extremely smoth surface finish which
compared to prior art .alpha.-Al.sub.2O.sub.3 coated tools, results
in an improved surface finish also of the workpiece being machined,
and when coated cemented carbide cutting tools according to the
invention are used in the machining of steel or cast iron, several
important improvements compared to prior art have been observed
which will be demonstrated in the forthcoming examples.
Inventors: |
Schiller, Siegfried;
(Dresden, DE) ; Goedicke, Klaus; (Dresden, DE)
; Fietzke, Fred; (Dresden, DE) ; Zywitzki,
Olaf; (Freiberg, DE) ; Sjostrand, Mats;
(Kista, SE) ; Ljungberg, Bjorn; (Enskede, SE)
; Hilding, Tomas; (Mariefred, SE) ; Alfredsson,
Viveka; (Lund, SE) |
Correspondence
Address: |
Ronald L. Grudziecki
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
20408890 |
Appl. No.: |
09/782226 |
Filed: |
February 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09782226 |
Feb 14, 2001 |
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09187006 |
Nov 6, 1998 |
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6210726 |
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Current U.S.
Class: |
428/216 ;
510/307 |
Current CPC
Class: |
Y10T 428/25 20150115;
Y10T 428/252 20150115; Y10T 428/24975 20150115; C23C 14/081
20130101; Y10T 407/27 20150115; C23C 14/352 20130101; Y10T 428/265
20150115 |
Class at
Publication: |
428/216 ;
510/307 |
International
Class: |
B32B 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 1997 |
SE |
9704066-1 |
Claims
1. Cutting tool comprising a body of sintered cemented carbide or
cermet, ceramic or high speed steel substrate and on which at least
on the functioning parts of the surface of the body, a 0.5 to 20
.mu.m, preferably 1 to 15 .mu.m, thick, adherent, hard and wear
resistant coating is applied, and said coating is characterized in
comprising a structure of one or more refractory compounds layer,
of which at least one layer with a thickness of 0.5 to 15 .mu.m,
preferably 1-10 .mu.m, essentially consists of very fine-grained,
crystalline .gamma.-Al.sub.2O.sub.3 phase, said very fine-grained
crystalline .gamma.-Al.sub.2O.sub.3 layer exhibiting significant
X-ray diffraction reflexes from at least one of the (440) and (400)
crystal planes, having a hardness of at least 20 GPa, a compressive
stress of at least 1 GPa and being free from any halogen
impurities.
2. Cutting tool according to claim 1 characterized in that the
Al.sub.2O.sub.3 layer has a preferred growth orientation in the
[440]-direction with a texture coefficient .gtoreq.1.5 defined as
below: 2 TC ( hk1 ) = I ( hkl ) I O ( hkl ) { 1 n I ( hkl ) I O (
hkl ) } - 1 where I(hkl)=measured intensity of the (hkl) reflection
I.sub.o(hkl)=standard intensity from the ASTM standard powder
pattern diffraction data n=number of reflections used in the
calculation (hkl) reflections used are: (111), (311), (222), (400)
and (440)
3. Cutting tool according to any of the previous claims
characterized in that the fine-grained crystalline
.gamma.-Al.sub.2O.sub.3 layer contains portions (detectable by XRD
technique) of additional alumina phases from the .gamma.-series of
the Al.sub.2O.sub.3 polymorphs.
4. Cutting tool according to claim 3 characterized in that the
additional alumina phase is the .theta.-phase.
5. Cutting tool according to any of the previous claims
characterized in having at least one layer of thickness 0.1-10
.mu.m, preferably 0.5-5 .mu.m, comprising of metal nitrides and/or
carbides with the metal elements selected from Ti, Nb, Hf, V, Ta,
Mo, Zr, Cr, W and Al.
6. Cutting tool according to claim 5 characterized in that said
layer consists of TiC, TiCN, TiN or TiAlN.
7. Cutting tool according to any of the previous claims
characterized in that the outer layer is Al.sub.2O.sub.3.
8. Cutting tool according to any of the claims 1-6 characterized in
that the outer layer is TiN.
9. A process for producing a coated cutting tool, wherein at least
one refractory layer consisting of fine-grained, crystalline
.gamma.-Al.sub.2O.sub.3 as per claim 1, is deposited by magnetron
sputtering onto the moving substrate in a vacuum, characterized in
that the Al.sub.2O.sub.3 layer is deposited by pulsed magnetron
sputtering in an argon-containing gas, that the pulse frequency is
set for 10 to 100 kHz, preferably 50 kHz, that deposition occurs
with a rate of at least 1 nm/s with reference to a stationarily
arranged substrate, that the magnetron target power density in time
average is set for at least 10W/cm.sup.2 and that the substrate
temperature is set in the range 450 to 700.degree. C., preferably
in the range 550 to 650.degree. C., depending on the material of
the tool body being coated.
10. A process according to claim 9, characterized in that the
Al.sub.2O.sub.3 layer is deposited by the sputtering of two
magnetrons with Al targets that are alternatively switched as a
cathode and as a anode of a magnetron sputtering apparatus.
11. A process according to at least one of the claims 9 and 10
characterized in that additional, non-Al.sub.2O.sub.3 layers are
also deposited by a PVD process (Physical Vapor Depostion),
particularly by pulsed magnetron sputtering.
12. A process according to claim 11, characterized in that all
layers, Al.sub.2O.sub.3 and non-Al.sub.2O.sub.3 layer(s), are
deposited in the same coating apparatus without vacuum
interuption.
13. A process of at least one of the claims 9 and 10, characterized
in that additional, non-Al.sub.2O.sub.3 layers are applied by a CVD
process (Chemical Vapor Deposition).
Description
[0001] The present invention describes a cutting tool for metal
machining, having a body of cemented carbide, cermet, ceramics or
high speed steel and on the surface of said body, a hard and wear
resistant refractory coating is deposited. The coating is
adherently bonded to the body and covering all functional parts of
the tool. The coating is composed of one or more layers of
refractory compounds of which at least one layer consists of
fine-crystalline alumina, Al.sub.2O.sub.3, deposited by Physical
Vapour Deposition PVD) and the non-Al.sub.2O.sub.3 layer(s), if any
at all, consists of metal nitrides and/or carbides with the metal
elements chosen from Ti, Nb, Hf, V, Ta, Mo, Zr, Cr, W and Al.
[0002] It is well known that for e.g. cemented carbide cutting
tools used in metal machining, the wear resistance of the tool edge
considerably can be increased by applying thin, hard surface layers
of metal oxides, carbides or nitrides with the metal either
selected from the transition metals from the groups IV, V and VI of
the Periodic Table or from silicon, boron and aluminium. The
coating thickness usually varies between 1 and 15 .mu.m and the
most widespread techniques for depositing such coatings are PVD and
CVD (Chemical Vapor Deposition). It is also known that further
improvements of the performance of a cutting tool can be achieved
by applying a pure ceramic layer such as Al.sub.2O.sub.3 on top of
layers of metal carbides and nitrides (U.S. Pat. No. 5,674,564;
U.S. Pat. No. 5,487,625).
[0003] Cemented carbide cutting tools coated with alumina layers
have been commercially available for over two decades. The CVD
technique usually employed involves the deposition of material from
a reactive gas atmosphere on a substrate surface held at elevated
temperatures. Al.sub.2O.sub.3, crystallizes into several different
phases such as .alpha.(alfa), .kappa.(kappa) and .chi.(chi) called
the ".alpha.-series" with hcp (hexagonal close packing) stacking of
the oxygen atoms, and into .gamma.(gamma), .theta.(theta),
.eta.(eta) and .delta.(delta) called the ".gamma.-series" with fcc
(face centered cubic) stacking of the oxygen atoms. The most often
occurring Al.sub.2O.sub.3-phases in CVD coatings deposited on
cemented carbides at conventional CVD temperatures,
1000.degree.-1050.degree. C., are the stable alpha and the
metastable kappa phases, however, occasionally the metastable theta
phase has also been observed.
[0004] The CVD Al.sub.2O.sub.3 coatings of the .alpha.-, .kappa.-
and/or .theta.-phase are fully crystalline with a grain size in the
range 0.5-5 .mu.m and having well-facetted grain structures.
[0005] The inherently high deposition temperature of about
1000.degree. C. renders the total stress in CVD Al.sub.2O.sub.3
coatings on cemented carbide substrates to be tensile, hence the
total stress is dominated by thermal stresses caused by the
difference in thermal expansion coefficients between the substrate
and the coating and less by intrinsic stresses which have there
origin from the deposition process itself and are of compressive
nature. The tensile stresses may exceed the rupture limit of
Al.sub.2O.sub.3 and cause the coating to crack extensively and thus
degrade the performance of the cutting edge in e.g. wet machining
where the corrosive chemicals in the coolant fluid may exploit the
cracks in the coating as diffusion paths.
[0006] Generally CVD-coated tools perform very well when machining
various steels and cast irons under dry or wet cutting conditions.
However, there exists a number of cutting operations or machining
conditions when PVD-coated tools are more suitable e.g. in
drilling, parting and threading and other operations where sharp
cutting edges are required. Such cutting operations are often
referred to as the PVD coated tool application area.
[0007] Plasma assisted CVD technique, PACVD, makes it possible to
deposit coatings at lower substrate temperatures as compared to
thermal CVD temperatures and thus avoid the dominance of the
thermal stresses. Thin Al.sub.2O.sub.3 PACVD films, free of cracks,
have been deposited on cemented carbides at substrate temperatures
450.degree.-700.degree. C. (DE 41 10 005; DE 41 10 006; DE 42 09
975). The PACVD process for depositing Al.sub.2O.sub.3 includes the
reaction between an Al-halogenide, e.g. AlCl.sub.3, and an oxygen
donor, e.g. CO.sub.2, and because of the incompleteness of this
chemical reaction, chlorine is to a large extent trapped in the
Al.sub.2O.sub.3 coating and its content could be as large as 3.5%.
Furthermore, these PACVD Al.sub.2O.sub.3 coatings are generally
composed of, besides the crystalline alfa- and/or
gamma-Al.sub.2O.sub.3 phase, a substantial amount of amorphous
alumina which in combination with the high content of halogen
impurities, degrades both the chemical and mechanical properties of
said coating, hence making the coating material non-optimized as a
tool material.
[0008] The field of the present invention relates particularly to
the art of PVD Al.sub.2O.sub.3 coated carbide cutting tools or
tools of similar hard materials such as cermets, ceramics and high
speed steel.
[0009] There exist several PVD techniques capable of producing
refractory thin films on cutting tools and the most established
methods are ion plating, DC- and RF magnetron sputtering, arc
discharge evaporation, BAD (Ion Beam Assisted Deposition) and
Activated Reactive Evaporation (ARE). Each method has its own
merits and the intrinsic properties of the produced coatings such
as microstructure/grain size, hardness, state of stress, intrinsic
cohesion and adhesion to the underlying substrate may vary
depending on the particular PVD method chosen. Early attempts to
PVD deposit Al.sub.2O.sub.3 at typical PVD temperatures,
400.degree.-500.degree. C., resulted in amorphous alumina layers
which did not offer any notable improvement in wear resistance when
applied on cutting tools. PVD deposition by HF diod- or magnetron
sputtering resulted in crystalline .alpha.-Al.sub.2O.sub.3 only
when the substrate temperature was kept as high as 1000.degree. C.
(Thornton and Chin, Ceramic Bulletin, 56 (1977) 504). Likewise,
applying the ARE method for depositing Al.sub.2O.sub.3, only
resulted in fully dense and hard Al.sub.2O.sub.3 coatings at
substrate temperatures around 1000.degree. C. (Bunshah and Schramm,
Thin Solid Films, 40 (1977) 211).
[0010] With the invention of the bipolar pulsed DMS technique (Dual
Magnetron Sputtering) which is disclosed in DD 252 205 and DE 195
18 779, a wide range of opportunities opened up for the deposition
of insulating layers such as Al.sub.2O.sub.3 and, furthermore, the
method has made it possible to deposit crystalline Al.sub.2O.sub.3
layers at substrate temperatures in the range 500.degree. to
800.degree. C. In the bipolar dual magnetron system, the two
magnetrons alternately act as an anode and a cathode and, hence,
preserve a metallic anode over long process times. At high enough
frequencies, possible electron charging on the insulating layers
will be suppressed and the otherwise troublesome phenomenon of
arcing will be limited. Hence, according to DE 195 18 779, the DMS
sputtering technique is capable of depositing and producing
high-quality, well-adherent, crystalline .alpha.-Al.sub.2O.sub.3
thin films at substrate temperatures less than 800.degree. C. The
".alpha.-Al.sub.2O.sub.3 layers", with a typical size of the
.alpha.-grains varying between 0.2-2 .mu.m, may partially also
contain the gamma(.gamma.) phase from the ".gamma.-series" of the
Al.sub.2O.sub.3 polymorphs. The size of the .gamma.-grains in the
coating is much smaller than the size of the .alpha.-grains. The
.gamma.-Al.sub.2O.sub.3 grainsize typically varies between 0.05 to
0.1 .mu.m. In the Al.sub.2O.sub.3 layers where both modifications
of .gamma.- and .alpha.-phase were found, the
.gamma.-Al.sub.2O.sub.3 phase showed a preferred growth orientation
with a (440)-texture. When compared to prior art plasma assisted
deposition techniques such as PACVD as described in DE 49 09 975,
the novel, pulsed DMS sputtering deposition method has the
decisive, important advantage that no impurities such as halogen
atoms, e.g. chlorine, are incorporated in the Al.sub.2O.sub.3
coating.
[0011] According to the present invention there is provided a
cutting tool for metal machining such as turning (threading and
parting), milling and drilling comprising a body of a hard alloy of
cemented carbide, cermet, ceramics or high speed steel onto which a
hard and wear resistant refractory coating is deposited by the DMS
PVD method at substrate temperatures of 450.degree. to 700.degree.
C., preferably 550.degree. to 650.degree. C., depending on the
particular material of the tool body, and that said wear resistant
coating is composed of one or more layers of refractory compounds
of which at least one layer, preferably the outermost layer,
consists of Al.sub.2O.sub.3 and that the innermost layer(s), if any
at all, between the tool body and the Al.sub.2O.sub.3 layer, is
composed of metal nitrides and/or carbides with the metal elements
selected from Ti, Nb, Hf, V, Ta, Mo, Zr, Cr, W and Al. In contrast
to the state of the art, the Al.sub.2O.sub.3 layers consist of
high-quality, dense, fine-grained crystalline
.gamma.-Al.sub.2O.sub.3 with a grainsize less than 0.1 .mu.m.
Furthermore, the .gamma.-Al.sub.2O.sub.3 layers are virtually free
of cracks and halogen impurities. The latter property is
illustrated in FIG. 1 which is an EDS-analysis of an
Al.sub.2O.sub.3 layer deposited by PACVD (with Al.sub.2O.sub.3 as a
precurser) containing Cl-impurities and in FIG. 2 which is an
EDS-analysis of a .gamma.-Al.sub.2O.sub.3 layer according to the
invention. In the latter Al.sub.2O.sub.3 layer no detectable
impurities are present.
[0012] The .gamma.-Al.sub.2O.sub.3 layers according to the
invention further give the cutting edges of the tool an extremely
smooth surface finish which, compared to prior art
.alpha.-Al.sub.2O.sub.3 coated tools, results in an improved
surface finish also of the workpiece being machined. The very
smooth surface finish can be attributed to the very fine
crystallinity of the coating. The ".gamma.-Al.sub.2O.sub.3" layers
may also partially contain other phases from the ".gamma.-series"
like .theta., .delta. and .eta.. Identification of the .gamma.-
and/or .theta.-phases in the Al.sub.2O.sub.3 layers according to
the invention can preferably be made by X-ray diffraction. Reflexes
from the (400) and (440) planes of the .gamma.-Al.sub.2O.sub.3
layers occurring at the 2.theta.-angles 45.80 and 66.80 when using
Cu.sub.K.alpha. radiation, unequivocally identifies the
.gamma.-phase (FIG. 3). Weaker reflexes from the (222), (200) and
(311) planes of the .gamma.-phase can occasionally be identified.
When the .theta.-phase is present in the Al.sub.2O.sub.3 layers
according to the invention, said phase is identified by the
reflexes from the (200, 20-2) planes (FIG. 4).
[0013] A second identification method for the Al.sub.2O.sub.3
phases is based on electron diffraction in a Transmission Electron
Microscope (TEM). A diffraction pattern from an Al.sub.2O.sub.3
layer deposited at a substrate temperature of 650.degree. C. is
shown in FIG. 5. The pattern shows rings from a polycrystalline
phase with grains considerably smaller than the diameter of the
electron beam and, furthermore, the intensity of the rings and the
distances between the rings again unequivocally identifies the
.gamma.-phase of Al.sub.2O.sub.3.
[0014] The fine-grained, crystalline .gamma.-Al.sub.2O.sub.3
according to the invention is strongly textured in the
[440]-direction. A Texture Coefficient, TC, can be defined as: 1 TC
( hk1 ) = I ( hkl ) I O ( hkl ) { 1 n I ( hkl ) I O ( hkl ) } -
1
[0015] where
[0016] I(hkl)=measured intensity of the (hkl) reflection
[0017] I.sub.o(hkl)=standard intensity from the ASTM standard
powder pattern diffraction data
[0018] n=number of reflections used in the calculation (hkl)
reflections used are: (111), (311), (222), (400) and (440) and
whenever the TC(hkl)>1, there is a texture in the
[hkl]-direction. The larger the value of TC(hkl), the more
prenounced is the texture.
[0019] According to the present invention, the TC for the set of
(440) crystal planes is greater than 1.5.
[0020] When the very fine-grained .gamma.-Al.sub.2O.sub.3 coated
cemented carbide cutting tools according to the invention are used
in the machining of steel or cast iron, several important
improvements compared to prior art have been observed which will be
demonstrated in the forthcoming examples. Surprisingly, the PVD
.gamma.-Al.sub.2O.sub.3 without containing any portion of the
coarser and thermodynamically stable .alpha.-Al.sub.2O.sub.3 phase,
shows in certain metal machining operations, a wear resistance
which is equal to the wear resistance found in coarser CVD
.alpha.-Al.sub.2O.sub.3 coatings deposited at temperatures around
1000.degree. C. Furthermore, the fine-grained PVD
.gamma.-Al.sub.2O.sub.3 coatings show a wear resistance
considerably better than prior art PVD coatings. These observations
open up the possibility to considerably improve the cutting
performance and prolong the tool lives of coated PVD tools. The low
deposition temperature will also make it possible to deposit PVD
.gamma.-Al.sub.2O.sub.3 coatings on high speed steel tools.
[0021] A further improvement in cutting performance can be
anticipated if the edges of the .gamma.-Al.sub.2O.sub.3 coated
cutting tools according to the invention are treated by a gentle
wet-blasting process or by edge brushing with brushes based on e.g.
SiC as disclosed in the Swedish patent application 9402543-4.
[0022] The total coating thickness according to the present
invention varies between 0.5 and 20 .mu.m, preferably between 1 and
15 .mu.m with the thickness of the non-Al.sub.2O.sub.3 layer(s)
varying between 0.1 and 10 .mu.m, preferably between 0.5 and 5
.mu.m. The fine-grained .gamma.-Al.sub.2O.sub.3 coating can also be
deposited directly onto the cutting tool substrate of cemented
carbide, cermet, ceramics or high speed steel and the thickness of
said .gamma.-Al.sub.2O.sub.3 varies then between 0.5 and 15 .mu.m
preferably between 1 and 10 .mu.m. Likewise can further coatings of
metal nitrides and/or carbides with the metal elements selected
from Ti, Nb, Hf, V, Ta, Mo, Zr, Cr, W and Al be deposited on top of
of the Al.sub.2O.sub.3 layer.
[0023] The .gamma.-Al.sub.2O.sub.3 layer according to the invention
is deposited by a bipolar dual magnetron sputtering technique at
substrate temperatures of 450.degree.-700.degree. C., preferably
550.degree.-650.degree. C., using aluminium targets, a gas mixture
of Ar and O.sub.2 and a process pressure in the range 1-5 .mu.bar.
The substrate may be floating or pulsed biased, the exact
conditions depending to a certain extent on the design of the
equipment being used.
[0024] It is within the purview of the skilled artisan to determine
whether the requisite grainsize and phase compositions have been
obtained and to modify the deposition conditions in accordance with
the present specification, if desired, to affect the nanostructure
of the Al.sub.2O.sub.3 layer within the frame of the invention.
[0025] The layer(s) described in the present invention, comprising
metal nitrides and/or carbides and/or carbonitrides and with the
metal elements selected from Ti, Nb, Hf, V, Ta, Mo, Zr, Cr, W and
Al can be deposited by PVD-technique, CVD- and/or MTCVD-technique
(Medium Temperature Chemical Vapor Deposition).
[0026] The superiority of the fine-grained .gamma.-Al.sub.2O.sub.3
PVD layers according to the present invention, compared to prior
art PVD coatings is demonstrated in Examples 1, 2 and 5. Examples
3, 4 and 6 demonstrate the suprisingly good wear resistance
properties of the fine-grained .gamma.-Al.sub.2O.sub.3 layers
compared to traditionally CVD-deposited single phase
.kappa.-Al.sub.2O.sub.3 and single phase .alpha.-Al.sub.2O.sub.3
layers.
EXAMPLE 1
[0027] A) Commercially available cemented carbide threading inserts
of style R166.OG-16MM01-150 having a composition of 10 w %/ Co and
balance WC, coated with an approximately 2 .mu.m TiN layer by an
ion plating technique.
[0028] B) TiN coated tools from A) were coated with a 1 .mu.m
fine-grained .gamma.-Al.sub.2O.sub.3 layer in a separate experiment
with the pulsed magnetron sputtering technique. The deposition
temperature was 650.degree. C. and the process pressure was 1
.mu.bar.
[0029] C) Cemented carbide threading inserts of style
R166.OG-16MM01-150 having a composition of 10 w % Co and balance
WC, coated with an approximately 3 .mu.m TiN layer by an ion
plating technique.
[0030] Coated tool inserts from B) and C) were then tested in a
threading operation at a customers site in the production of engine
oil plugs of cast iron (SS0125; 180-240 HB). The thread of the plug
being produced was of size M36.times.1.5.
1 Cutting data: Speed: 154 m/min 5 passages per thread
[0031] The results below is expressed as the number of machined
plugs per cutting edge.
2 C) prior art 300 plugs Large crater wear, cutting edge is worn
out B) invention >500 plugs No detectable wear on the cutting
edge. The edge can produce more plugs
[0032] From the above results it is obvious that the alumina coated
insert according to the invention is superior with respect to
cutting performance.
EXAMPLE 2
[0033] D) Commercial PVD-TiN coated cemented carbide drilling
inserts of style LCMX 040308-53 with a coating thickness of
approximately 3 .mu.m having a cemented carbide composition of 10 w
% Co and balance WC.
[0034] E) TiN coated tools from D), coated with a 1 .mu.m
fine-grained .gamma.-Al.sub.2O.sub.3 layer in a separate experiment
with the pulsed magnetron sputtering technique. The deposition
temperature was 650.degree. C. and the process pressure was 1
.mu.bar.
[0035] The alumina coating from E) appeared transparent and very
smooth. SEM studies of a fracture cross section of the alumina
coating showed a very fine-grained structure. A XRD-investigation
identified the alumina phase as pure .gamma.-Al.sub.2O.sub.3.
[0036] Coated tool inserts from D) and E) were then tested in a
drilling operation in a workpiece material of a low alloyed,
non-hardened steel (SS 2541).
3 Cutting data: Speed: 150 m/min Feed: 0.12 mm/rev Hole diameter:
25 mm Hole depth: 46 mm Coolant being used
[0037] Both flank and crater wear were developed on the cutting
edges. The extent of the flank wear determined the life time of the
cutting tool. The results below express the number of holes being
drilled per cutting edge.
4 D) prior art 150 holes Flank wear 0.15 mm 200 holes Flank wear
0.22 mm, cutting edge is damaged E) invention 150 holes Flank wear
0.07 mm 200 holes Flank wear 0.09 mm / 250 holes Flank wear 0.10
mm, cutting edge is slightly damaged
[0038] From the above results it is obvious that the alumina coated
inserts according to the invention are able to drill more holes
than the prior art inserts.
EXAMPLE 3
[0039] F) Cemented carbide inserts of style CNMA 120412-KR having a
composition of 6 w % Co and balance WC, coated with a first layer
of 8 .mu.m TiCN and thereafter with a top layer of 4.7 .mu.m
.alpha.-Al.sub.2O.sub.3. Both the TiCN and the Al.sub.2O.sub.3
layer were deposited by conventional CVD-technique. The
Al.sub.2O.sub.3 layer had an average grain size of 1.2 .mu.m.
[0040] G) Cemented carbide inserts of the same style and
composition as in F), first coated with an approximately 3.6 .mu.m
TiCN layer by conventional CVD-technique and thereafter coated with
a 2.3 .mu.m fine-grained .gamma.-Al.sub.2O.sub.3 layer in a
separate experiment with the pulsed magnetron sputtering technique.
The deposition temperature was 650.degree. C. and the process
pressure was 1 .mu.bar.
[0041] Coated inserts from F) and G) were then tested in a
continuous turning operation in a ball bearing steel (Ovako 825).
The crater wear of the cutting edges was measured.
5 Cutting data: Speed: 210 m/min Feed: 0.25 mm/rev Depth of cut:
2.0 mm Coolant being used
[0042] The cutting operation was periodically interupted in order
to measure the crater wear of the cutting edges. The crater wear
was measured in an optical microscope. The machining time until the
Al.sub.2O.sub.3 layer was worn through, was registered (i.e. when
the inner TiCN coating just becoming visible). In order to define a
figure of merit for the intrinsic wear resistance of the
Al.sub.2O.sub.3 layers, the thickness (.mu.m) of the
Al.sub.2O.sub.3 layer was divided by the above defined machining
time (min). The results below express the wear rate figure of
merit.
6 F) prior art .alpha.-Al.sub.2O.sub.3 layers 0.5 .mu./min C)
invention 0.5 .mu.m/min
[0043] From the above results it is obvious that the wear
resistance of the fine-grained .gamma.-Al.sub.2O.sub.3 layer
suprisingly is as good as the wear resistance of the
coarser-grained .alpha.-Al.sub.2O.sub.3 layer deposited by CVD
technique.
EXAMPLE 4
[0044] H) Cemented carbide inserts of style CNMA 120412-KR having a
composition of 6 w % Co and balance WC, coated with a first layer
of 6 .mu.m TiCN and thereafter with a top layer of 1.1 .mu.m
.kappa.-Al.sub.2O.sub.3. Both the TiCN and the Al.sub.2O.sub.3
layer were deposited by conventional CVD technique. The
Al.sub.2O.sub.3 layer had an average grain size of 1 .mu.m.
[0045] I) Cemented carbide inserts of the same style and
composition as in H), coated with an approximately 2.5 .mu.m TiN
layer by an ion plating technique.
[0046] J) TiN coated tools from I), coated with a 1.2 .mu.m
fine-grained .gamma.-Al.sub.2O.sub.3 layer in a separate experiment
with the pulsed magnetron sputtering technique. The deposition
temperature was 600.degree. C. and the process pressure was 1
.mu.bar.
[0047] K) TiN coated tools from I), coated with a 1.7 .mu.m
fine-grained .gamma.-Al.sub.2O.sub.3 layer in a separate experiment
with the pulsed magnetron sputtering technique. The deposition
temperature was 730.degree. C. and the process pressure was 1
.mu.bar.
[0048] Coated inserts from H), J) and K), were then tested in a
continuous turning operation in a ball bearing steel (Ovako 825).
The crater wear of the cutting edges was measured.
7 Speed: 250 m/min Feed: 0.25 mm/rev Depth of cut: 2.0 mm Coolant
being used
[0049] The cutting operation was periodically interupted in order
to measure the crater wear of the cutting edges. The crater wear
was measured in an optical microscope. The machining time until the
Al.sub.2O.sub.3 layer was worn through, was registered (i.e. when
the inner TiN or TiCN coating just becoming visible). In order to
define a figure of merit for the intrinsic wear resistance of the
Al.sub.2O.sub.3 layers, the thickness (.mu.m) of the
Al.sub.2O.sub.3 layer was divided by the above defined machining
time (min). The results below express the wear rate figure of
merit.
8 H) prior art .kappa.-Al.sub.2O.sub.3 layers 0.44 .mu.m/min J)
invention TiN + .gamma.-Al.sub.2O.sub.3 0.40 .mu.m/min K) invention
TiN + .gamma.-Al.sub.2O.sub.3 0.46 .mu.m/min
[0050] From the above results it is obvious that the wear
resistance of the fine-grained .gamma.-Al.sub.2O.sub.3 layer
suprisingly is as good as the wear resistance of the
coarser-grained .kappa.-Al.sub.2O.sub.3 layer deposited by CVD
technique.
EXAMPLE 5
[0051] Coated cutting inserts from I), J) and K) in Example 4 were
tested under the same cutting conditions and cutting data as in
Example 4. The machining time until a predetermined crater wear had
developed on the rake face of the inserts was registered. The
results below express said machining time until the predetermined
crater wear.
9 I) prior art TiN 4 min J) invention TiN + .gamma.-Al.sub.2O.sub.3
9 min K) invention TiN + .gamma.-Al.sub.2O.sub.3 9.7 min
[0052] From the above results it is obvious that a top coating of
the fine-grained .gamma.-Al.sub.2O.sub.3 layer on PVD TiN
considerably improves the crater wear resistance of the cutting
tool.
EXAMPLE 6
[0053] L) Cemented carbide inserts of style CNMA 120412-KR having a
composition of 6 w % Co and balance WC, coated with a first layer
of 6 .mu.m TiCN and thereafter with a top layer of 4.8 .mu.m
.alpha.-Al.sub.2O.sub.3. Both the TiCN and the Al.sub.2O.sub.3
layer were deposited by conventional CVD-technique. The
Al.sub.2O.sub.3 layer had an average grain size of 1 .mu.m.
[0054] M) Cemented carbide inserts of the same style and
composition as in L), first coated with an approximately 5 .mu.m
TiAlN layer and thereafter, without vacuum interruption, coated
with a 4.4 .mu.m fine-grained .gamma.-Al.sub.2O.sub.3 layer, both
layers deposited with the pulsed magnetron sputtering technique.
The deposition temperature was 600.degree. C. and the process
pressure was 1 .mu.bar.
[0055] Coated inserts from L) and M) were then tested in a
continuous turning operation in a low alloyed, non-hardened steel
(SS2541). The crater wear of the cutting edges was measured.
10 Speed: 250 m/min Feed: 0.25 mm/rev Depth of cut: 2.0 mm Coolant
being used
[0056] The cutting operation was periodically interupted in order
to measure the crater wear of the cutting edges. The crater wear
was measured in an optical microscope. The machining time until the
Al.sub.2O.sub.3 layer was worn through, was registered (i.e. when
the inner TiCN or TIAlN coating just becoming visible). In order to
define a f igure of merit for the intrinsic wear resistance of the
Al.sub.2O.sub.3 layers, the thickness (.mu.m) of the
Al.sub.2O.sub.3 layer was divided by the above defined machining
time (min). The results below express the wear rate figure of
merit.
11 L) prior art .alpha.-Al.sub.2O.sub.3 layers 0.69 .mu.m/min M)
invention 0.73 .mu.m/min
[0057] From the above results it is obvious that the wear
resistance of the fine-grained .gamma.-Al.sub.2O.sub.3 layer
suprisingly is as good as the wear resistance of the
coarser-grained .alpha.-Al.sub.2O.sub.3 layer deposited by CVD
technique.
* * * * *