Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-06-21
2001-05-22
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S702000, C428S469000, C428S472000, C428S472200, C428S408000, C427S419200, C427S419700, C427S249100, C427S249170, C427S249190, C427S255110, C427S255190
Reexamination Certificate
active
06235416
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a composite body which is comprised of a substrate body with a monolayer or multilayer coating.
The invention relates further to a process for producing a layer on a substrate body of a hard metal, cermet or a ceramic.
BACKGROUND OF THE INVENTION
The first coatings, according to the state of the art, which allowed an improved wear prevention against free surface wear to be obtained, were comprised of titanium carbide with a thickness up to 8 &mgr;m. Further, double or multiple coatings of titanium carbide and titanium nitride, especially with titanium nitride as an outermost layer, are known in the art for reduced cratering when the product is used as a cutting insert in machining. For further improvement of such cutting inserts, multilayer coatings of the layer sequence TiC, Ti(C,N), TiN, have been proposed. It has been found that the natural brittleness of ceramics, like Al
2
O
3
can be minimized when Al
2
O
3
is applied in a thin layer form and thus, TiCTi(C,N) and an outer layer of Al
2
O
3
have been provided as multiple coatings. While the patent literature, for example EP 0 299 282 B1 describes in special cases the use of carbides, nitrides and/or carbonitrides of the elements titanium, zirconium, hafnium, vanadium, niobium and/or tantalum, these have been described only as useful in an example with titanium compounds as coating materials, in part in combination with aluminum oxide. The same is true with the description of ZrO
2
in the combination with or as a replacement for oxide coatings. DE 36 20 901 A1 or EP 0 250 865 A1 which has the same content, describes for the first time a cutting tool whose cutting edge is coated with titanium carbide, titanium carbonitride and/or titanium nitride and whose outermost cover layer is composed of a thin zirconium nitride layer. The zirconium nitride, which has poorer wear characteristics than the aforementioned titanium compounds should hinder the oxidation of the base layer underlying this coating by atmospheric oxygen, whereby the good wear characteristics of the titanium carbide, titanium carbonitride and/or titanium nitride coatings can be fully maintained.
By contrast, in U.S. Pat. No. 3,854,991 (or CH A 585273) a coating of a sintered hard metal product is described in which the coating is comprised of HfCN and/or ZrCN and has an X-ray diffraction lattice constant which in the case of HfCN and a mixture of HfCN and ZrCN lies between 4.5570 and 4.630 angstrom and in the case of ZrCN lies between 4.6 and 4.62 angstrom. In the case of ZrCN the CN ratio is clearly less than 1. For the production of these hafnium or zirconium carbonitrides, a hafnium halogenide and/or a zirconium halogenide can be fed over a substrate together with hydrogen, nitrogen and a hydrocarbon at a temperature of 1000 to 1300° C.
U.S. Pat. No. 4,714,660 describes a cutting insert of a CVD-coated substrate body in which the first CVD layer is comprised of at least two phases deposited simultaneously together, of which the first is composed of a member of the group of carbides, carbonitrides, nitrides, oxycarbides, oxycarbonitrides, suicides or borides of titanium, zirconium, hafnium, vanadium, niobium or tantalum, or a carbidesilicide or boride of chromium, molybdenum or tungsten, or a silicon or boron carbide and a second of these phases is selected from the group of oxides or oxynitrides of aluminum, titanium, zirconium, hafnium, magnesium, silicon and calcium or very stabilized zirconium oxide.
Of the deposited mentioned phases, at least one of the phases is composed of fibers, spikes or column-shaped particles with an elongated axial orientation extending in a direction which is perpendicular to the substrate/coating surface of the composite.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a composite body of the type described at the outset which has a high microhardness, good wear characteristics, especially in chip removal machining operations like turning or milling, or hard abrasively loaded wear hardness.
SUMMARY OF THE INVENTION
This object is achieved with the composite body which, according to the invention, is characterized in that at least one layer has two or three phases which are comprised of cubic ZrCN and monoclinic and/or tetragonal ZrO
2
.
In the CVD deposition of TiCN, when oxygen is contained in the gas atmosphere, it is incorporated in the (single phasic) lattice whereby Ti(C,O,N) deposits result. The presence of oxygen in the gas phase results in the deposition of two adjoining phases in the coating, namely, ZrCN and ZrO
2
when certain boundary conditions are maintained. This can be expected from the chemical similarity of zirconium and titanium, which both are from the same group of the periodic system, along with good adherence of the resulting coating on the substrate body or on another layer or as an intermediate layer. The new coating has been found even with composite bodies which are formed as cutting inserts, to give rise to significant improvements in the useful life of the insert in the milling of steel. The useful life, e.g. as a steel milling insert, can be increased by about 30%. Further this coating is suitable in a significant manner for the efficiency improvement of deformation shaping tools which are subject to friction wear.
Thickness of the layer according to the invention should be between 2 and 10 &mgr;m, preferably at least 3 &mgr;m. Based on the different characteristics of the ZrCN on the one hand and the ZrO
2
on the other, known in the art, which can be advantageously used, it is another basic thought of the invention established in the layer a gradient of the relative ZrO
2
/ZrCN proportions. Depending upon the desired boundary zone, for example, the ZrO
2
content in the layer can decrease outwardly. For example for the machining of castings, a higher ZrCN content is advantageous whereas in the use of a ZrCN/ZrO
2
layer as an outer layer or a single layer for cutting inserts which are to be used for machining castings, the ZrO
2
relative content toward the exterior can be decreased preferably to zero. Conversely the adhesion of ZrO
2
to substrate bodies as well as to other layers is in part better than that of ZrCN so that the ZrO
2
component can increase inwardly, preferably to the boundary with the substrate body, growing, for example up to 100%. The gradient adjustment can be carried out during the CVD coating by adjusting the CO
2
content as a function of time.
Apart from the aforedescribed boundary zones, it is preferred, especially with a two phase coating that there be a homogeneous distribution of the relative mass proportions of ZrO
2
between 5 and 75 mass %, preferably between 5 and 60% and most preferably between 20 and 40%. The ZrO
2
proportion which is selected in the layer can be chosen in consideration of the purpose for which the composite body is to be used and set accordingly. Furthermore, the ratio of monoclinic to tetragonal ZrO
2
can be varied via the coating geometry. Preferably this ratio is in the range of (3 to 4):(7 to 6). Thus at a coating temperature of about 950°, it is possible to obtain ⅔ of the ZrO
2
component as tetragonal ZrO
2
in addition to the Zr(C,N) phase. At higher temperatures the tetragonal ZrO
2
proportion grows and can reach 100% at a coating temperature of about 1100° C. The ZrCN phase is present in cubic form.
The substrate body, upon which one or more layers can be coated, of which one can be the coating of the invention, can be composed of hard metal, cermet or a ceramic. The coating can be a multilayer coating and apart from the layer of ZrCN/ZrO
2
can comprise at least one layer of a carbide, nitride and/or carbonitride of an element from group IVa or Group Va or group VIa of the periodic system, and optionally also a coating of Al
2
O
3
and/or ZrO
2
, whereby dioxide layers can form the outermost layer and also a layer underlying the ZrCN/ZrO
2
layer when that is outermost. Finally a diamond-like layer can be used as the outer layer. In a preferred
Konig Udo
Sottke Volkmar
Westphal Hartmut
Boss Wendy
Dubno Herbert
Jones Deborah
Widia GmbH
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