|Title of Invention||
CUTTING INSERT FOR METAL CUTTING OPERATION AND THE PROCESS FOR THE MANUFACTURE OF THIS CUTTING INSERT
|Abstract||Disclosed herein is a cutting insert cutting insert for machining operations consisting essentially of a cermet or ceramic substrate body with a multilayer coating having an outer cover layer consisting of a single-phase or multiphase layer of Hf or Zr carbides, nitrides or carbonitrides applied by means of CVD providing inner compressive strains, and at least one underlying layer such that any underlying layer is applied also by CVD and has exclusively inner tensile strains, at least one underlying layer consisting of a material selected from the group which consists of TiN, TiC and Ti(C,N) or mixtures thereof, the strain relationship of said layers being such that of said layers only said outer cover layer has internal compressive strain and all of the others of said layers have internal tensile strain.|
This invention concerns a cutting insert for metal cutting operation, consisting of a hardmetal substrate body, a cermet substrate body or a ceramic substrate body with a multilayered coating.
Substrate bodies with hard material coating, if needed, also with multilayered coating, are already known from the state-of-the-art technology, in general, the hard materials coating is supposed to serve the purpose, to achieve a wear resistant surface layer, whi ch is combi ned wi th tough substrate bodi es, whi ch are subjected to mechanically high stresses. As per the state—of— the—art—technology, two processes are generally used, namely so— cal 1 ed chemi cal vapour deposi ti on (CVD) process CH- physi cal vapour deposition (PVD) process for coating the substrate bodies. Usually the protective layers are made of, for example, TiC, TiN and/or aluminium oxide. Multilayered coatings with the order (sequence) of the layers TiN, Ti ‹C,N› Ti ‹C,N›, TiN on a substrate body, with freely selected CsN - mixing ratio have also been already recommended.
From DE 195 3O 517 Al, metallic carbonitride—hardmaterial layers on a substrate body are also known, in which the metal of the metallic carbonitride layer contains two or more elements of the group Ti, Zr, Hf, V, Nb, Ta, Cr, Ho and W- The layer is deposited by using the CVD process, especially in form of a quaternary layer made of (Ti, Zr) ‹C,N)-
For an indexable insert, as a special example of application,
a coating made of an approximately 1 jam thick TiN-layer, a second
B urn thick ‹Ti,Zr) ‹C,N› layer and a last Al O - layer with a
2 3 thickness between 1 urn and 5 urn was deposited on a hardmetal
The above mentioned PVD coatings, which can be produced from
o approximately 4OO C onwards, are used in most cases for
temperature sensitive substrate bodies, especially in the coating
of high speed steels, which should not be subjected to high
temperatures during the deposition.
Besides, from the publications WO 92/O5296 or US 5 143 488, which are having similar contents, one can observe, that the TiN -coati ngs deposi ted by CVD—processes have tensi1e stresses, whereas the Ti N—coat i ngs deposi ted by PVD—process have compressive stresses, which do not lead to cracks as in the case of tensile stresses. In order to improve the resistance to fracture, it has therefore been recommended in these publications, to combine one or more CVD—layer or CVD-layers with one or more layers deposited by PVD—process respectively. Nitrides of titanium, hafnium and/or zirconium are recommended as material for the inner layer deposited by using the CVD—process and nitrides and carbonitrides of the above mentioned metals for layers deposited by using the PVD-process. As regards process
technology, there exists the disadvantage, that two relatively expensive and different depositions ‹CVD, PVD) need to be carried out one after the other with different equipments- Moreover, it has been observed, that the raultilayered coating consisting of inner layers deposited by using CVD-process and at least one external layer deposited with the PVD-process, in case of larger thickness of the coating, has the tendency to chip off.
Hence it is the task of the present invention to develop a cutti ng i nsert, whi ch does not have the above mentioned di sadvantages. The cutti ng i nsert should have upto 1arger coating thickness relatively high fracture toughness (bending strength). One should be able to execute the process needed for its production cost effectively and by using the minimum possible equipments.
This task has been solved by a cutting insert as per this invention and which is described in the patent claim 1.
The multilayered coating on a hard metal substrate body, cermet substrate body or ceramic substrate body has an external layer (cover coating), which is made of a single-phase or multi-phase layer of carbides, nitrides or carbonitride on zirconium base of hafnium base and which has internal compressive stresses. The layer or layers located underneath (below) have, without any exception, tensile stresses, whereby at least one or the only
layer underneath it is made of titanium nitride, titanium carbide and/or titanium carbonitride. All layers are deposited by using the CVD—process, whereby it is also passible to have design versions, in which the cover coating can be made of many single layers having the same or different material composition- As per the present invention it is important, that the cover coating in each case contains zirconium or hafnium bonded with carbide, nitride or carbonitride and is combined with a layer below it, which is made of titanium carbide, titanium nitride and/or titanium carbonitride.
Preferably the compressive stresses ^r& lying between — 5OO MPa to — 25OO rtpa CAs per defi ni ti on, compressi ve stresses ar& designated with negative values as against the tensile stresses for which positive values are specified).
Especi al1y as si ngle—phase cover coati ng, one can select a
carbide, nitride or carbonitride of zirconium or hafnium.
However as an alternative to this, there are also single—phase
cover coatings made of a carbide, nitride or carbonitride of the
H = Zr or Hf and H = Ti, Hf, Nb
case, one speaks about so-called
A two—phase exteral layer, which is generally preferred, consists
of a carbide, nitride or carbonitride of zirconium or hafnium and
ZrO . ZrO can be present either in monoclinic modification, 2 2
tetragonal modi f i cati on and/or cubi cal nodi f i cation.
Particularly the external layer can have a composition in the
form M ‹C N ›, whereby M = Zr or Hf and O-3 ‹_ x £ 7. In
e x i—x e
case the cover coating is a single—phase one, then it is
distinguished from a two-phase coating thereby, that it has a
uniform structure and lattice constant, which particularly
i ncludes tertiary and quaternary carbi de, ni tride or
carbonitride, in which zirconium or hafnium alone or totally must
at least be present in SO atom X. The concerned metal atoms are
then distributed statistically on a lower lattice, whereas their
metalloids, carbons and nitrogen are distibuted unarranged on the
other lower lattice.
In a two phase layer, which is particularly made of a carbide,
ni tr i de or carboni tride of z i rconi um or hafniurn and has
additionally ZrO , there exists two, side by side phases, which
2 are entirely different with respect to the crystal structure and
lattice. The second phase ZrO is present preferably with a
2 relative proportion between 15 and 6O mass %.
Accordi ng to a further development of thi s i nventi on,
additionally one of the lower layers, between the cover coating
and at least one of the layers close to the substrate body, can
be made of Al O -
Generally preferred thickness of the cover coating lies between 2 jam and maximum 10 jam, whereby preferably the total thickness of the inner layers, which are under tensile stress and the external layers, which are under compressive stress, lies between 5jjm and 25 31m, particularly between lO^µm and 2Ojaro.
Preferred is a first TiN—layer with a thickness of upto 2 JIIB deposited on the substrate body and one or more TiCN—layers of upto 5 31m thickness, on which a single—phase or two—phase cover coating of upto 5^µm thickness has been deposited.
For the production of the cutting insert of the type mentioned
above, the deposition is carried out an uninterrupted CVD—process
at temperatures between 9OO C and llOO C and by changing the
respective gas compositions.
The compressive stress of an external layer made of a single-phase multimetal—carboni tri de can be parti cular1y enhanced thereby, that after the CVD—deposition, a heat treatment follows at a temperature higher than the substrate body temperature
during the last deposition. The concerned temperatures lie
o between 950 C and the eutectic temperature of the material of the
5ub5tate body. The heat treatment lasts for IS minutes, so that
a segregation into a titanium rich and a zirconium rich phase
The present invent!cm is further explained in detail with the help of examples of application.
After the compl et i on of the CVD—process, the coat i ng i s preferably subjected to an additional, surface smoothening mechanical process, such as polishing with emery-brush or dry or wet shot blasting with fine shot blasting medium, preferably glass beads or corundum.
In CVD—tests, various coating which are compiled in Table 1 have
been deposited on indexable inserts made of a hard metal. On
these coatings, the stresses in the layer bordering the surface
have been measured by using a measuring method with X—rays (so—
2 called Sin — method). For the purpose of comparison, the
measured values of TiN—layers and TiC—layers (refer example 1 and
2) which were produced by using PVD—process are also given in
Table 1. It has been observed, that the layers deposited using
PVD—proces5 have high residual compress!ve stresses, which are
already known from the state—of—the—art technology, while the
TiN-layers, TiC and Ti (C,N› layers according to the examples 3
to 5 have varyingly large tensile stresses, which are likewise
known from the state—of—the—art technology. As against this, in
examples 6 to 8, depositions according to this invent!cm are
given, namely, in each case, an inner layer made of Ti (C,N) and
an cover coating made of Zr (C N ) (example 6) , a two-
O.49 O.5l phase layer made of Zr (C N )/Zr D (example 7) and a cover
O.5 O.5 2 coating made of Hf (C N ).
Properties of hard material layers, in which tensile stresses are i ndicated Mi th positi ve si gn and compressi ve stresses with negative sign:
In order to establish the improved toughness of the hard metal
bodi es, which are coated accordi ng to thi s i nventi on, test
samples as per the standard DIN ISO 3327 have been produced out
of a hard metal alloy (83.5 mass X WC, 11 mass %‹Ti, Ta, Nb)C,
5.5 mass % Co). The test samples having the dimension L x H x B
= 20 x 5.25 x 6.5 mm were used to determine the bending strength.
A part of the test samples were coated with a layer made of Ti
‹C N ) with help of the known CVD— process at a temperature O.5 O.5
o of 1010 C . In another CVD—process, a further 1ot of test
samples were provided with a two—layered coating made of B^µro Ti
‹C N ) and 3^um Zr (C N )- After the determination of
O.5 O.5 O.5 0-5
the layer thickness, in each case 11 test samples, for the
purpose of statistic were subjected to load till fracture. The
test results are presented in a Weibull-statistic in Figure 1 of
the accompanying drawi ngs. The f1exural strength 1 of the
2 uncoated test sample is 2O95 + I5O N/mm . With an approximately
8j_im thick coating made of Ti CC N ) the flexural strength 2
2 of the test sample is reduced to 1332 +. 34 N/mm . This effect
has been described many times in the technical literature, for
example, in the US 5 143 488. Thicker the layer, that much
larger is this effect.
Likewise in Figure 1, the flexure strength 3 of a coating, which
according to this invention is made of 831m Ti CC N ) and 3
0.5 O.5 jam Zr (C N ) is shown- In this case the mean value of the 0.5 O.5
2 flexural strength 2O2l J: 194 N/mm is only marginally less than
that of the uncoated test samples. This indicates, that the
fracture—toughness of the composite body coated according to this
invention is practically maintained fully.
Further, indexable inserts of the type CNttßl2O4l2 - 5 were produced out of a hard metal al1oy havi ng the chemi cal composition 83.5 mass X liC, 11 mass X (Ti , Ta, Nb›C, 5.5 massX Co and coated by means of a CVD—process with the layers (5) and ‹6›
in the order (sequence) of the layer specified in Table 1.
Machining tests were carried out with these cutting inserts. The
toughness behavior was investigated in a pin—turning test
according to Brechbuehl. Hereby it concerns a transverse
machining (facing) of four round rods of 4O mm diameter which are
clamped parallel to the axis of rotation and which are made of
2 steel C45N ‹57O N/fiun ). The cutting corner makes four cuts per
revolution into the material. Each time after three runs, the
feed *f' is systematically increased. Further parameters of the
cut are cutting speed V = 25O m/mm and depth of the cut a = 2
mm. During this test, fracture toughness of the composite body
made of hard metal and the coating on it were subjected to
special stresses. The results of these tests are compiled in
The number of runs during the fracture toughness test according to Brechbuhl.
The indexable insert with the coating ‹5› according to the state-of-the-art technology failed due to fracture of the cutting edge at a feed of f = O.4 mm/ revolution after 16 runs. The indexable insert with the coating ‹6› according to this invention has achieved 34 runs during the facing operation.
1. Cutting insert for machining purpose, made of an hard metal substrate body, cermet substrate body or ceramic substrate body with a multilayered coating on it, whose external layer (cover coating) consists of a single—phase or two—phase layer made of carbides, nitrides or carbonitrides of the Zr—base of Hf—base, which has been deposited by using the CVD—process and which has internal compressive stresses and whose lower layer (layers), which is/are likewise deposited by means of CVD—process, has/have exclusively tensile stresses, whereby at least one or the only layer which is underneath is made to TiN, TiC and/or Ti ‹C,N).
2. Cutting insert as claimed in claim 1, characterised in that
the external layer is single—phase and made of a carbide, nitride
or carbonitride of the form CM , M ) (C N ) where M = Zr or
1 2 x 1-x 1
Hf and M « Ti, Hf, Nb and O£x_‹ 1.
3. Cutting insert as claimed in claim 1, characterised in that
the external layer is two-phase and is made to a carbide, nitride
or carbonitride of Zr or Hf and ZrO .
4. Cutting insert as claimed in any one of claims 1 to 3,
characterised in that a layer lying between the cover coating and
at least one of the layer close to the substrate body is made of
Al O . 2 3
5. Cutting insert as claimed in any one of the claims 1, 2 or 4,
characterised in that the external layer has a composition M (C
e x N ) with M = Zr or Hf and 0.3 ‹_ x £ 7. 1-x e
6. Cutting insert as claimed in claim 3 or 4, characterised in
that additionally as second phase, the external layer contains
ZrO with a relative proportion between IS and 6O mass X.
7. Cutting insert as claimed in any one of the claims 1 to 6, characterised in that the external layer (cover coating) has a thickness of minimum 2 um and maximum lOµm.
8. Cutting insert as claimed in any one of the claims 1 to 7, characterised in that the total thickness of the inner layer (layers), which is Care) under tensile stress and the external layer (layers), which is (are) under compressive stress, lies between 5 µm and 25µm, preferably between 10 µm and 2Oµm•
9. Cutting insert as claimed in any one of the claims 1 to 7, characterised in that the order (sequence) of the layer deposited on the substrate body is TiN with a thickness of upto 2_µm, TiCN with a thickness of upto 5 31m and the single—phase or two—phase cover coating with a thickness of upto 5_µm.
10. Process for the manufacturing of a cutting insert as claimed
in any one of the claims 1 to 9, characterised in that the
deposition is carried out by means of an uninterrupted CVD~
process at temperatures between 9OO C and llOO C with respective
change in the compositions of the gas.
11. Process few the manufacturing of a cutting insert with an
external layer made of a single—phase multimetal-carbonitride
characterised in that after the deposition of the external layer,
this layer is subjected to a heat treatment at least for 15
minute at a temperature which is higher thant he last CVD-
deposition temperature and below the eutectic temperature of the
substrate body, whereby a spinodal segregation takes place.
12. Process as claimed in claim 11, characterised in that the
o heat treatment is carried out at temperatures between 1000 C and
o I2OO C, preferably in a protective gas atmosphere.
13. Process as claimed in any one of the claims lO to 12
characteri sed i n that the coati ng (cover coati ng› after
completion of the CVD-deposition process is additionally
subjected to a surface smoothening mechanical process using an
emery brush or by means of dry or wet shot blasting with fine
shot blasting medium, preferably with glass beads or corundum.
|Indian Patent Application Number||2311/MAS/1997|
|PG Journal Number||07/2008|
|Date of Filing||16-Oct-1997|
|Name of Patentee||WIDIA GMBH|
|Applicant Address||MUNCHENR STRASSE 90, D-4300, ESSEN 1,|
|PCT International Classification Number||B23B 27/16|
|PCT International Application Number||N/A|
|PCT International Filing date|