U.S. patent application number 12/310681 was filed with the patent office on 2011-08-04 for coated twist drill.
Invention is credited to Thomas Heil, Peter Mueller, Thomas Schneider.
Application Number | 20110188956 12/310681 |
Document ID | / |
Family ID | 38698372 |
Filed Date | 2011-08-04 |
United States Patent
Application |
20110188956 |
Kind Code |
A1 |
Mueller; Peter ; et
al. |
August 4, 2011 |
Coated twist drill
Abstract
The present invention concerns a twist drill comprising a shank
and a cutting portion which is defined by the axial length of the
chip flutes and which is at least partially coated. To provide a
twist drill having the aforementioned features and a process for
the production thereof, which on the one hand have very good
properties in terms of service life and chip formation or chip
transport, but which on the other hand are also highly suited for
reconditioning including coating, in accordance with the invention
it is proposed that the cutting portion has substantially over its
useable length a first coating, wherein there is provided a second
coating which is different from the first coating only in the
region of the tip of the drill and which extends over an axial
length which corresponds at a maximum to twice the nominal diameter
of the drill.
Inventors: |
Mueller; Peter; (Ortenberg,
DE) ; Schneider; Thomas; (St. Ingbert, DE) ;
Heil; Thomas; (Bruchkoebel, DE) |
Family ID: |
38698372 |
Appl. No.: |
12/310681 |
Filed: |
August 24, 2007 |
PCT Filed: |
August 24, 2007 |
PCT NO: |
PCT/EP2007/058806 |
371 Date: |
November 19, 2009 |
Current U.S.
Class: |
408/230 ;
29/527.4 |
Current CPC
Class: |
Y10T 408/78 20150115;
Y10T 408/9097 20150115; B23B 2224/24 20130101; B23P 15/32 20130101;
C23C 28/044 20130101; C23C 30/005 20130101; B23B 2224/32 20130101;
C23C 28/42 20130101; B23B 2224/36 20130101; Y10T 29/49986 20150115;
B23B 2224/28 20130101; B23B 2228/10 20130101; B23B 51/02 20130101;
Y10T 407/27 20150115 |
Class at
Publication: |
408/230 ;
29/527.4 |
International
Class: |
B23B 51/02 20060101
B23B051/02; B23P 15/32 20060101 B23P015/32 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2006 |
DE |
10 2006 042 226.0 |
Claims
1. A twist drill comprising a shank and a cutting portion which is
defined by the axial length of the chip flutes and which is at
least partially coated, wherein the cutting portion has
substantially over its useable length a first coating, wherein in
addition a second is applied only in a region at the tip of the
drill, which extends over an axial length which corresponds at a
maximum to twice the nominal diameter of the drill.
2. A twist drill as set forth in claim 1 wherein the cutting
portion is of an axial length which is at least four times the
nominal diameter.
3. A twist drill as set forth in claim 2 wherein the axial length
of the cutting portion is at least six times the nominal
diameter.
4. A twist drill as set forth in claim 1 wherein the second coating
is restricted to a region of the tip of the drill, which is between
0.3 times and 1.5 times, preferably between 0.3 times and 1.2
times, the nominal diameter.
5. A twist drill as set forth in claim 1 wherein the first layer is
applied over the entire useable length of the cutting portion with
the exception of the end clearance surfaces, wherein the end
clearance surfaces are provided only with the second coating.
6. A twist drill as set forth in claim 1 wherein at least the
cutting part of the drill and preferably the entire drill comprise
solid hard metal.
7. A twist drill as set forth in claim 1 wherein the two layers
differ at least by their color.
8. A twist drill as set forth in claim 1 wherein at least the color
of the first layer differs from the base color of the drill.
9. A twist drill as set forth in claim 1 wherein the first layer is
smoothed in the chip flutes at least outside the region of the
second layer.
10. A twist drill as set forth in claim 9 wherein in addition the
peripheral surfaces of the drill lands and/or the round lands of
the cutting part are also smoothed.
11. A process for the production of a twist drill comprising the
following steps: a) providing a drill blank comprising a shank and
a cutting portion having possibly pre-shaped chip flutes as well as
a drill tip to be provided with main cutting edges, b) grinding the
chip flutes, the round lands and the peripheral surfaces adjoining
the round lands, c) completely coating at least the chip flutes of
the round lands and the peripheral surfaces forming the periphery
of the drill lands with a first layer, d) grinding the drill tip
including removing any first layer also applied to the end
clearance surfaces, and e) coating the drill tip with a second
layer different from the first layer, wherein the second layer,
measured from the tip of the drill, extends axially over a region
which at a maximum corresponds to twice the nominal diameter of the
drill, wherein the sequence of steps c) and d) is reversible.
12. A process as set forth in claim 11 wherein the end clearance
surfaces of the drill prior to step are not coated with the first
layer and then only with the second layer.
13. A process as set forth in claim 11 wherein the first layer is
smoothed at least in the region of the chip flutes outside the tip
portion provided with the second layer.
14. A process as set forth in claim 13 wherein the first layer is
additionally smoothed in the region of the round lands and the
relieved peripheral surfaces.
15. A process as set forth in claim 11 wherein the first and second
layers comprise the same material.
Description
[0001] The present invention concerns a twist drill having a shank
and a cutting portion which is defined by the axial extent of
flutes and which is at least partially coated.
[0002] The invention also concerns a process for the production of
a corresponding twist drill.
[0003] Coated twist drills have long been known. In that respect
the coating can serve very different purposes. In general the
attempt is made to increase the resistance to wear of the drill, in
particular in the region of the drill tip, by a corresponding
coating. If moreover the drill geometry or the specific uses mean
that the round lands or guide lands or the peripheral surfaces of
the drill are also stressed they can also be protected from
premature wear by a complete coating on the cutting portion. Other
coatings which are generally restricted to the region of the tip of
a drill, beside increasing the resistance to wear, are also
intended in particular to influence the chip shape and to produce a
chip which either breaks quickly or which rolls up very tightly and
which can be transported by the chip flutes extending in a spiral
configuration, more easily than long, less heavily curved chips.
Chip transport is important in particular in relation to drills
whose cutting portions are relatively great in comparison with the
diameter (nominal diameter of the cutting portion), being for
example more than six times the nominal diameter.
[0004] Frequently however it can happen that chip transport is even
worsened in relation to an uncoated drill, by virtue of the coating
on the chip flutes, which it will be appreciated is at least
partially dependent on whether the layer does or does not involve a
surface treatment, for example by grinding, polishing or smoothing.
Depending on the respective machining condition or machinability
and wear characteristics of the flute surface however a coating on
the flutes can additionally improve chip transport. It will be
appreciated that the drills involved here are metal drills, that is
to say drills which are provided for working on metallic
workpieces, in which respect however different metallic materials
may also exhibit very different chip cutting characteristics.
[0005] In that respect the main focus of the coatings was in the
past clearly on improving the wear characteristics and the
production of chips which are easy to transport. Both essentially
relate to the region of the tip of the drill, in particular the
region of the main cutting edges and the chip flute portions
directly adjoining same, that is to say the rake surface.
Nonetheless drills in accordance with the state of the art were
hitherto coated predominantly along the entire cutting portion
because limiting a coating to the tip region is more complicated
and expensive in conventional coating installations, than a
complete coating.
[0006] In the meantime, numerous different coatings have been
developed to optimize the wear and chip formation characteristics,
the best-known and most wide-spread coating being titanium nitrite
(TiN). Numerous further layers have been developed on the basis of
that layer, the further layers additionally containing for example
carbon or aluminum such as for example (AlTi)N, (TiAl)N or Ti(CN).
In part titanium has also been replaced by chromium (as for example
in the case of (CrAl)N), and coatings based on tungsten carbide
(WC/C) have also been developed.
[0007] Some of those coatings are only possible with a high level
of complication and expenditure and while observing complex process
parameters. Because of the complexity of highly developed coating
processes and because of the special composition of high-efficiency
coatings, a coating of that kind is only possible at all in very
few specialized areas of operation. On the other hand however there
is a need for corresponding drills which are worn in the region of
their main cutting edges to be re-ground, in which case the coating
in the region of the drill tip also has to be renewed again.
Renewing a corresponding high-efficiency coating is however
uneconomical for individual drills or for relatively small numbers
of items, as typically occur for re-grinding in an industrial
operation using corresponding drills. In contrast, simple coatings
as have already been known for a prolonged period of time are
relatively easily available without involving major effort.
[0008] Irrespective of the aforementioned problems, there is a
further problem which specifically concerns such drills which are
coated at their periphery, that is to say in particular along the
round lands or guide lands and the outside surfaces of the drill
flute lands. That problem is described by the technical term
"pitting" or "pitting formation" and involves the wear-resistant
layer chipping off the guide lands, more specifically typically in
a region which is spaced from the drill tip or from the cutting
corner defined by the transition from the main cutting edge to the
secondary cutting edge. In the case of pitting formation, often it
is not only the applied layer but also a part of the subjacent base
material of the guide land or round land of the drill, that is
fixedly connected to the applied layer, that chips off. Upon a
first use of the drill that does not yet have a detrimental effect
because the main cutting edge and the chip rake surface are not
affected by the pitting since, as already mentioned, that chipping
off of the layer at the guide lands occurs only at a certain
distance from the cutting corner or from the main cutting edge. It
will be noted however that those chipped-off regions become a
problem when re-grinding the drill, more specifically when the worn
tip of the drill is removed to such a degree that the main cutting
edge is displaced further back in the direction of the shank and
then the freshly produced cutting corner (at the transition from
the main cutting edge to the secondary cutting edge) can very
readily come into the region affected by the pitting. That means
that the cutting corner is undefined and the drill can only be
limitedly used, it wears more rapidly and must be shortened until
by chance a position which is not affected by the pitting is
reached at both sides on the oppositely disposed round lands. It
will be appreciated that this also reduces the useful working life
of the drill.
[0009] It has been found that of all things more recent types of
very hard and brittle layers which are particularly suitable in
particular for affording wear protection at the main cutting edges
and the chip rake surfaces have a very severe tendency to such
pitting formation.
[0010] In comparison with that state of the art the object of the
present invention is to provide a twist drill having the features
set forth in the opening part of this specification and a process
for the production thereof, which on the one hand ensure very good
properties in regard to service life and chip formation and chip
transport, but which on the other hand are also highly suited for
re-working, including subsequent coating on the other hand.
[0011] In regard to the twist drill itself that object is attained
in that the cutting portion has a first coating substantially over
the entire useable length of the cutting portion, wherein there is
provided a second coating that is different from the first coating
only at the tip of the drill and there includes a region which
measured from the drill tip corresponds at a maximum to twice the
nominal diameter of the drill.
[0012] That makes it possible to satisfy the in part mutually
contradictory requirements on the one hand for a very durable layer
which however does not adversely affect chip transport and on the
other hand for particular resistance to wear but also
re-workability of the drill tip. By way of example in first
manufacture of the drill the cutting portion can be provided
substantially over its entire length with a high-performance layer
which is possibly not yet optimum in terms of resistance to wear
but in return is also not exposed to the danger of pitting or
spalling of the layers. Preferably such a high-performance layer
should afford a lower level of friction in relation to the chips.
An additional, particularly hard and wear-resistant layer can then
possibly be applied to that layer, wherein the additional layer is
however restricted to the tip of the drill and for that reason
alone is not or is only immaterially affected by pitting and also
does not adversely influence chip transport, by virtue of its short
length. Pitting is avoided not only by virtue of the fact that the
second layer extends only over a relatively short distance beyond
the cutting edge, but also by virtue of the fact that in the
proximity of the cutting edges the second layer is applied to the
first layer and not directly to the base material of the drill,
wherein, even if the second layer chips off the first layer in that
region, at any event the first layer itself is not affected by that
chipping.
[0013] When working and re-grinding worn drills the drill tip is
effectively shortened by a certain amount and removed to such a
degree that all severely worn regions which are concentrated in
particular around the main cutting edges disappear. The second
layer is typically of its greatest thickness at the end of the
drill and/or around the main cutting edges and then becomes
progressively thinner towards the shank end until it is reduced to
zero at the latest approximately at twice the diameter, measured
from the drill tip. Accordingly, the thicker regions of the second
layer are simultaneously removed with the removal of the drill tip
so that the subsequent re-coating of the new tip with the second
layer is effected on residues which are possibly still present of
the second layer and the adjoining regions which are possibly not
yet affected by the original second layer so that the result is a
coated drill tip which is completely identical to the original
drill tip.
[0014] In that respect it is desirable if the second layer is so
selected that it can be restored without involving major
complication and effort and without a complex process control.
[0015] In the drill reconditioning operation the first layer which
extends from the tip to the shank end of the cutting portion
remains substantially preserved as the drill is shortened or
removed essentially only at the particularly severely wearing tip
with the main cutting edges so that the positive properties of the
first layer in respect of chip transport, the avoidance of surface
pickup phenomena and protection for the guide lands is also
retained.
[0016] Preferably the present invention is applied to twist drills
whose cutting portion is of an axial length of at least four times
the diameter. In the case of shorter drills chip formation and chip
transport play a lesser part so that it is possible substantially
to concentrate on protection from wear, for which purpose it is
generally possible to manage with a single layer although for
particular situations of use the double layer according to the
invention may nonetheless be appropriate in relation to short
drills.
[0017] A particularly preferred twist drill according to the
invention is one in which the cutting portion is at least six times
its diameter. In that case the cutting portion is defined by the
axial length of the chip flutes or that useable part which can be
moved downwardly into a drilled hole without blocking chip
discharge.
[0018] In the preferred embodiment the second layer is limited in
respect of its axial extent to between 0.3 and 1.5 times, in
particular to between 0.3 and 1.2 times, the nominal diameter,
measured in each case from the tip of the drill. It is possible to
completely dispense with the first coating on the free clearance
surfaces of the main cutting edges at the end of the drill,
especially as when re-conditioning a worn drill that tip region is
in any case completely ground away so that in the re-grinding
operation and subsequent re-coating procedure with the second layer
it is in any case only the second layer that is applied to the
clearance surfaces at the end.
[0019] A particularly preferred twist drill according to the
invention is one in which at least the cutting portion but
preferably the entire drill including the shank is produced from
solid hard metal. Although solid hard metal drills which typically
comprise a tungsten carbide-cobalt compound are in themselves
already relatively wear-resistant, it is however nonetheless also
possible by coatings in relation to solid hard metal drills, to
still considerably improve the properties both in regard to
resistance to wear and also in regard to chip formation and chip
transport.
[0020] The first layer can have an advantageous effect in
particular but not only in relation to solid hard metal drills, in
regard to a whole series of properties. On the one hand many of the
metallic elements which constitute the materials to be machined can
diffuse into the WC--Co compound, which is also substantially
metallic, of a solid hard metal drill. Conversely elements can also
diffuse out of the solid hard metal, and that respectively
manifests itself in corresponding detrimental ageing effects. In
addition particularly in the proximity of the cutting edges, when
machining many metallic materials, there is a severe tendency for
the chips to build up by a welding effect.
[0021] Many modern coatings in contrast involve a more or less
ceramic character, that is to say they are not metallic, they act
as a diffusion barrier layer for metals and they are also not
subject to the risk of welding build-up of the chips. In addition
ceramic layers of that kind have thermally insulating properties
and finally they also contribute to a further wear resistance as
they are generally even harder than the base material of the drill,
even if the drill in turn comprises solid hard metal.
[0022] Many of those properties such as for example thermal
insulation and resistance to chip welding build-up are particularly
important in the proximity of the cutting edge, but other
properties are also significant for chip transport and load-bearing
capability and breaking strength of the drill and are therefore
important for the entire cutting part of the drill. With the two
coatings according to the invention, it is possible to optimally
fulfill and combine the different demands on the coatings in the
proximity of the cutting edge and in regions which are further
back.
[0023] In addition however it is not out of the question for the
first and second coatings to comprise an identical material, in
which respect however it will be noted that they may certainly
still differ in respect of layer thickness, variation in the layer
thickness in dependence on the axial position and the surface
nature, that is to say smooth or not smooth. In that respect
consideration is to be given in particular to the fact that, in a
grinding or smoothing operation, in principle the cutting edges are
also detrimentally affected so that it may be appropriate for the
second layer in the proximity of the main cutting edges to be
applied only after smoothing or grinding of the first layer and
after grinding of the drill tip.
[0024] A particularly preferred configuration of the present
invention is one in which the applied first and second layers are
of different colors. In that way it is possible to clearly see how
far the second layer extends over the tip of the drill, how far
which layer is worn, and what type of drill is confronting the
person handling it, as drills with different coatings can certainly
be adapted to special, different machining operations or
materials.
[0025] In addition it is desirable if the color of the first
complete layer also differs from the color of the base material.
That also makes it easier to recognize any flaws or any wear
phenomena on the first layer.
[0026] A particularly preferred embodiment of the invention is one
in which the first layer is smoothed at least in the region of the
chip flutes and in those chip flutes at least outside the region of
the tip, which is covered by the second layer. The coating applied
to the round lands and the adjoining, relieved peripheral surfaces
of the drill flute lands can also be selectively smoothed. In that
respect in particular the drill tip can be left untouched in order
not to cause wear of the main cutting edges from the outset due to
the smoothing operation. Alternatively however the tip grind and
the coating operation with the second layer can be effected only
after the step of smoothing the cutting part provided with the
first layer and in particular the chip flutes.
[0027] A process according to the invention for the production of
corresponding twist drills has the features:
[0028] a) providing a generally cylindrical drill blank comprising
a shank and a cutting portion having possibly pre-shaped chip
flutes as well as a drill tip to be provided with main cutting
edges,
[0029] b) producing the chip flutes, the round lands and the
relieving the adjoining the round lands, at the final dimension,
apart from coatings which are still to be applied,
[0030] c) completely coating at least the chip flutes of the round
lands and the peripheral surfaces forming the periphery of the
drill lands with a first layer,
[0031] d) grinding the drill tip including removing any first layer
also applied to the end clearance surfaces, and
[0032] e) coating the drill tip with a second layer, wherein the
second layer, measured from the tip of the drill, extends axially
over a region which at a maximum corresponds to twice the nominal
diameter of the drill.
[0033] In that respect the sequence of the steps (c) and (d) could
also be reversed although the above-specified sequence is
preferred.
[0034] In regard to that sequence of the process steps, a procedure
as is also implemented when reconditioning the drill tip is
effectively already used upon fresh production of the drill.
Accordingly a reconditioned drill practically completely
corresponds in all its properties to a new drill, apart from the
fact that it has become slightly shorter due to the re-grinding
operation.
[0035] Furthermore a preferred process is one in which the first
layer is smoothed at least in the chip flutes and in that respect
at least outside the region affected by the second layer. In
addition it may be advantageous if the guide lands and peripheral
surfaces of the drill lands are also smoothed after application of
the first layer. That smoothing operation is intended to reduce
friction with the drilled hole walls and/or chips produced by the
drill tip and in particular to promote chip transport. As already
mentioned it will be noted however that smoothing can be limited to
a region at a spacing from the main cutting edges, or the smoothing
operation can be effected between foregoing steps (c) and (d).
[0036] Further advantages, features and possible uses of the
present invention will be clearly apparent from the description
hereinafter of a preferred embodiment and the accompanying
drawings.
[0037] FIG. 1 shows a side view of a twist drill according to the
invention,
[0038] FIG. 2 shows a section through the drill of FIG. 1 along
line II-II in FIG. 1,
[0039] FIG. 3 shows a view along the axis 12 onto the end or tip 3
of the drill, and
[0040] FIG. 4 shows an enlarged side view of the tip and the
adjoining region of the drill.
[0041] FIG. 1 shows a drill which is generally identified by
reference 100 and which has a shank 10 and a cutting portion 1. The
cutting portion 1 is characterized by chip flutes 2 extending from
the drill tip 3 to close to the shank 10. The chip flutes extend in
a spiral at a certain helical angle or twist angle around the axis
12 of the drill, wherein the twist angle of the chip flutes 2, or
more precisely the twist angle of the secondary cutting edges which
are formed at the transition of the chip flutes 2 to the guide
lands 6, must be selected to be sufficiently large relative to the
axis 12 in order to provide for effective chip transport from the
tip 3 of the drill to the shank and out of the chip flutes.
Typically that so-called "twist angle" is in the range of between
20.degree. and 40.degree. relative to the axis 12.
[0042] As can be seen in detail by reference to FIGS. 1 through 4
the drill in accordance with the embodiment illustrated here has at
its tip two slightly convexly curved cutting edges 5 and the
transverse cutting edge bridging over the two main cutting edges 5
is substantially reduced in terms of a cutting edge. The main
cutting edges 5 are adjoined at the end of the drill by a clearance
surface comprising a first bevel-like portion 4a and a portion 4b
which is angled in relation thereto and at a larger fall angle.
Coolant bores 11 can be seen at the end as shown in FIG. 3 of the
drill (and also in FIGS. 2 and 4). The diameter of the drill is
defined by two oppositely disposed cutting corners 13 formed by the
transition between the main cutting edges 5 and the secondary
cutting edges 8 which extend along the periphery of the cutting
portion in a helical configuration around the drill. Adjoining the
secondary cutting edges 8 are so-called "guide lands" or also
"round lands" which are effectively clearance surfaces lying on a
cylindrical surface, of the secondary cutting edges 8, and which
contribute to stabilizing and guiding the drill in a bore hole. The
peripheral surfaces 9 of the drill, adjoining the guide lands 6
(see FIGS. 2 through 4) are undercut in relation to the round lands
6 or reduced to a smaller diameter to reduce the friction of the
drill in the bore hole.
[0043] FIG. 2 shows the drill in section along line II-II in FIG.
1, and it is also possible to see here the coolant bores 11 as well
as the flutes 2 and the bottom 2a of the flutes 2, the bottom being
provided with the first layer.
[0044] The entire cutting portion 1, that is to say the portion
from the drill tip 3 to the end of the flutes 2, is coated with a
first layer comprising a wear-resistant material which promotes
chip transport. Only a front end portion 7 at the tip 3 of the
drill, in addition to the first coating, has a second layer which
is applied to the first layer and which comprises a particularly
wear-resistant material. In that respect the end clearance surfaces
4a, b can be left untouched by the first layer so that they are
only coated with the second layer. The axial length of the portion
7 is preferably in the range of between 0.3 and 1.2 times the
diameter and in the illustrated embodiment approximately
corresponds to the diameter.
[0045] The first coating is smoothed above the region 7 of the
second coating at least within the chip flutes. That can be
effected for example by wet or dry blasting, by brushing or by
magnet-abrasive removal.
[0046] When regrinding a corresponding drill tip essentially the
material on the rake surfaces 4a, b is removed, in which case
possibly also the cutting tip at the center of the drill or the
transition thereof to the chip flutes has to be reground. That
means that a considerable part of the region 7 provided with the
second layer is also reduced. After the main cutting edge including
the cutting corners, that is to say the transitions to the
secondary cutting edges formed at the round lands 6, are in the
finished ground condition, coating is again effected over a
corresponding fresh region 7, exclusively with the material of the
second layer, in which case the first layer in any case is
retained. In that way re-coating has to be effected only with the
material of the second layer. Any residue of the second layer which
has still remained of the previous region 7 at the tip of the drill
does not have a troublesome effect in that respect, especially as
the thickness of the second layer preferably continuously decreases
from the drill tip in the direction of the shank.
[0047] Preferably the first and second layers comprise a different
material so that the demands on their properties, which in
principle are somewhat different, can also be suitably optimized.
In addition however aspects regarding the capability of producing
the coatings also play a part. If desired the two coatings can also
comprise the same material.
[0048] The following coatings have proven to be particularly
desirable, in which respect the left-hand half of the Table
specifies preferred first layers and the right-hand half specifies
the preferred second layers, which in principle can be combined
together as desired:
TABLE-US-00001 1st layer: 2nd layer: Coating After- Coating After-
Composition* Color process treatment Composition* Color process
treatment TiN gold ionitron -- (TiAl)N gray-blue arc -- TiN gold
ionitron -- (AlCr)N copper- arc -- reddish Ti(CN) gray- ionitron --
(AlCr)N copper- arc -- blue reddish Ti(CN) reddish ionitron --
(TiAl)N gray-blue arc -- Ti(CN) + TiN gold ionitron -- (TiAl)N
gray-blue arc -- Ti(CN) + TiN gold ionitron -- (AlCr)N copper- arc
-- reddish (TiAl)N gray- sputtering -- (AlCr)N copper- arc -- blue
reddish (AlTi)N gray- sputtering -- (AlCr)N copper- arc -- blue
reddish (TiAl)N gray- sputtering smoothed (AlCr)N copper- arc --
blue reddish (AlTi)N gray- sputtering smoothed (AlCr)N copper- arc
-- blue reddish (TiAl)N gray- arc smoothed (AlCr)N copper- arc --
blue reddish (AlTi)N gray- arc smoothed (AlCr)N copper- arc -- blue
reddish (AlTi)N cover arc smoothed (TiAl)N gray-blue arc -- layer
reddish (TiAl)N cover arc smoothed (TiAl)N gray-blue arc -- layer
reddish (AlTi)N cover arc smoothed (AlCr)N copper- arc -- layer
reddish bright gold (AlTi)N cover arc smoothed (TiAl)N gray-blue
arc -- layer bright gold (AlCr)N copper- arc smoothed (TiAl)N
gray-blue arc -- reddish *essential component: also multi-layers
with intermediate layers of a different composition or different
structure
* * * * *