Composite body, especially for a cutting tool

Details Composite body, especially for a cutting tool Composite body, especially for a cutting tool

1999-05-26

2001-05-08

Turner, Archene (Department: 1775)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Physical dimension specified

C051S307000, C051S309000, C075S238000, C075S239000, C075S242000, C075S244000, C428S469000, C428S698000

Reexamination Certificate

active

06228484

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a composite body, and more particularly, to a composite body which comprises a hard material phase, for example, a cermet or hard metal, in a binder metal phase for use in or as a cutting tool, for example, as a so-called cutting insert for a milling cutter, a turning machine (lathe) or the like.
The invention relates in particular to cermet and hard metal composites which are formed by sintering in a microwave field.
BACKGROUND OF THE INVENTION
The formation of wear resistant composites which are hard enough to function as cutting tools or which can be coated with wear resistant materials so as to function as cutting tools is known. Reference may be had, for example, to Japanese Patent Document 4-187739 published Jul. 6, 1992 and described in Patent Abstracts of Japan C-997, Oct. 21, 1992, Vol. 16, No. 509, DE 43 40 652 A1, DE 38 06 602 C2, DE 196 01 234 A1. The principle of microwave sintering as used for such composites is described in WO 96/33830.
OBJECTS OF THE INVENTION
It is the principal object of the present invention to provide an improved composite body, especially for use as a cutting tool, e.g. as a cutting insert for a milling cutter, whereby drawbacks of earlier composite material are avoided.
Another object of this invention is to provide a composite body of the class mentioned previously which has improved properties, inter alia as far as the field strength of the microwave field during sintering is concerned.
Yet another object of this invention is to provide a composite body with an improved surface modification.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a composite body can be composed essentially of a microwave-sintered composition of a cermet composed of 0 to 30 mass-percent of a binder metal phase and the balance a carbonitride phase or
a hard metal composed of 70 to 100% of a hard material phase and the balance of a binder metal phase; and
a layer on a surface of the composition and bonded to the composition, of a thickness of 0.01 to 1 mm and having a density gradually decreasing from 100% of theoretical density at an outer face of the layer to about 60% of theoretical density inwardly of the outer face.
The thickness of the layer is preferably 0.5 to 1 mm.
This composite body which can be used especially as a cutter for high speed milling can thus have a hard dense surface with a porous core and as a result can be 40% lighter than the usual cutting insert for such a milling cutter. As a consequence, the centrifugal force generated when the cutter is rotated can be minimized and hence the strain on the cutter can be reduced in machining applications. The body also has the advantage that it can be removed or partly ground away and then infiltrated by a further material as, for example, silver if the body is to be used as an electrical contact material. When the body is employed as a wear protecting structure it has the advantage of reduced thermal conductivity and thus can be used to protect structures against overheating.
Alternatively, the composite body can be composed essentially of
a microwave-sintered composition of
a cermet composed of 0 to 30 mass-percent of a binder metal phase and the balance a carbonitride phase or
a hard metal composed of 70 to 100% of a hard material phase and the balance of a binder metal phase; and
a layer on a surface of the composition and bonded to the composition, of a thickness up to 1 mm and having compacts distributed locally therein of diameters of 30 to 50 &mgr;m.
In this case, the layer or coating on the composite compression, with a thickness up to 1 mm, has local dense regions of compacts with diameters of 30 &mgr;m to 50 &mgr;m and hence locally harder regions at the surface. This system has the advantage also of a reduction in weight because of the higher porosity in the less dense regions and the body can be utilized with advantage as a cutter or as a cutting insert for a milling cutter in high speed milling, as an electrical contact component when impregnated with silver, for example, and as a wear protecting body.
In still another aspect of the invention, the composite body is composed essentially of a microwaresintered composition of
a cermet composed of 0 to 30 mass-percent of a binder metal phase and the balance a carbonitride phase or
a hard metal composed of 70 to 100% of a hard material phase and the balance of a binder metal phase; and
a layer on a surface of the composition and bonded to the composition, of a thickness of 1 to 10 &mgr;m, of a substantially pure metal capable of increasing field strength during microwave sintering.
This thickness can be 1 to 3 &mgr;m and the layer can be composed of a metal of the hard material phase, for example, tungsten. With a pure metal from the hard material phase or a number of pure metals from this phase, and especially tungsten, the body has a high degree of wear resistance and can be used effectively for the purposes described.
In a fourth alternative, the composite body can comprise:
a microwave-sintered composition of
a cermet composed of 0 to 30 mass-percent of a binder metal phase and the balance a carbonitride phase or
a hard metal composed of 70 to 100% of a hard material phase and the balance of a binder metal phase; and
a layer in which a binder metal or one of the binder metal phases is removed from a surface of the composition in a thickness or to a depth up to half a mean grain size of a carbonitride or hard material phase (WC) so that within the thickness or depth only a hard material skeleton is formed to enhance a field strength during microwave sintering.
This thickness, in particular, can be up to half the mean grain size of tungsten carbide in the composition.
The cermet can have a carbonitride phase of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and/or W and a binder metal phase of Co and/or Ni. The hard metal phase can be an oxycarbide, oxynitride, oxycarbonitride or boride of one of these elements. Preferably the hard metal composition of the invention comprises hexagonal WC as a first phase and a cubic carbide of a mixed crystal of W, Ti, Ta and/or Nb as a second phase with a binder metal phase of Co, Ni, Fe or mixtures thereof. The hard metal can be especially composed of hexagonal mixed carbides of WC with MoC and/or cubic mixed carbides of the elements Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and/or W and a binder metal phase of Co and/or Ni.
The binder metal phase can have up to 10 mass % of one of the metals Mo, W, Ti, Mn and/or Al (with respect to the total mass of the binder metal phase).
Preferably the binder metal phase is composed of an Ni/Al alloy with an Ni/Al weight ratio of 90:10 to 70:3. The binder metal phase can, in addition, contain up to 1 mass % boron (calculated based upon the total mass of the binder metal phase).
The binder metal phase can also be composed of Ni
3
Al, TiSi
3
, Ti
2
Si
3
, Ti
3
Al, Ti
5
Si
3
, TiAl, Ni
2
TiAl, TiSi
2
, NiSi, MoSi
2
, or mixtures thereof. In addition, the binder metal phase can contain 0 to 16 mass % cobalt, nickel, iron and/or rare earth metals.
Alternatively, the binder metal phase can be composed of nickel and chromium with additions of molybdenum, maganese, aluminum, silicon and copper in amounts of 0.01 to 5 mass %.
According to a further feature of the invention, the composite body can be provided with one or more surface layers which can be applied by plasma vapor deposition (PVD), chemical vapor deposition (CVD) or plasma assisted chemical vapor deposition (PCVD), preferably in a microwave field. The composition basically can be that of WO 96/33830 with, however, the surface modifications of the invention so that the advantages, features and uses of the compositions described in that document can apply here as well.
When cutter or tool inserts of the composite body of the invention are produced from tungsten carbide with cobalt as a binder, the pulverulent cobalt can be mixed in an amount of six weight % with 1.5 weight % of wax as a plastifier and the balance WC to form a green body. The green body is placed in an i

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