Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
1999-12-03
2001-07-24
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C501S096100
Reexamination Certificate
active
06265337
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high strength sintered body using a high pressure form boron nitride incorporated therein.
2. Description of the Related Art
cBN is the hardest material next to diamond. cBN-based sintered bodies are used in various cutting tools, abrasion-resistant parts etc.
This kind of sintered body can hardly exhibit a high hardness and a high strength at the same time. Techniques for satisfying the two requirements at the same time are described in, e.g., JP-B-62-25630 (The term “JP-B” as used herein means an “examined Japanese patent application”), JP-B-62-25631 and JP-A-5-186272 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”).
However, the foregoing various techniques are not necessarily sufficient with respect to the simultaneous accomplishment of the two requirements. In particular, these techniques leave something to be desired in strength under severe cutting conditions as in interrupted cutting of hard to cut materials.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a sintered body which exhibits a high hardness and a high strength at the same time and thus has an assured long life.
A sintered body contains a high pressure form boron nitride in the range of 20 to 70% by volume, a first binding material surrounding the high pressure form boron nitride with a thickness in the range of 5 nm to 300 nm and a second binding material of the balance. The first binding material is composed of at least one of nitride and boride of Ti and Al. The second binding material is composed of at least one selected from the group consisting of nitride, carbide, carbonitride, boride and oxide of Al and transition metals belonging to the group 4a, 5a and 6a in the periodic table and mutual solid solution thereof. Supposing that X is the amount of Al contained per unit volume in the first binding material and Y is the amount of Al contained per unit volume in the second binding material, the ratio X/Y is not less than 1.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described as follows in detail.
A sintered body according to the present invention contains 20 to 70% by volume of a high pressure form boron nitride, a first binding material surrounding the high pressure form boron nitride with a thickness of 5 nm to 300 nm and the balance of a second binding material. The first binding material is composed of at least one of nitride and boride of Ti and Al. The second binding material is composed of at least one selected from the group consisting of nitride, carbide, carbonitride, boride and oxide of Al and transition metals belonging to the group 4a, 5a and 6a in the periodic table and mutual solid solution thereof. Supposing that X is the amount of Al contained per unit volume in the first binding material and Y is the amount of Al contained per unit volume in the second binding material, the ratio X/Y is not less than 1.
Examples of the high pressure form boron nitride employable herein include cubic boron nitride (cBN) and wurtzite boron nitride (wBN).
The nitride of Ti and Al to be contained in the first binding material are preferably in the form of cubic structure.
In a region containing at least 100 high pressure form boron nitride particles, the proportion of the number of the high pressure form boron nitride particles in contact with other high pressure form boron nitride particles is preferably from not less than 0.1% to less than 20.0%.
Further, when the sintered body according to the present invention is subjected to the following dissolution treatment, the residual high pressure form boron nitride particles are present in the form of single particle in a proportion of at least 90% thereof.
Specimen: Rectangular parallelepiped sintered body having a side of 3 mm to 7 mm and a thickness of from not less than 0.3 mm to not more than 0.5 mm
Solution: Fluoronitric acid comprising 40 ml of diluted nitric acid obtained by diluting nitric acid having a concentration of 60.0% to 65.0% by weight twice and 10 ml of hydrofluoric acid having a concentration of 45.0% to 50.0% by weight in admixture-
Temperature: From 120° C. to 150° C.
Time: From 3 hours to 5 hours
Such a sintered body has heretofore been hardly produced. In the present invention, the foregoing sintered body is obtained by a process including coating high pressure form boron nitride particles with a nitride or boride of Ti and Al by PVD process (physical vapor deposition), mixing the coated particles to a binding material made of a nitride, carbide or boride of Al or a transition metal belonging to the group 4a, 5a or 6a in the periodic table, and then sintering the material at an ultrahigh pressure and temperature. The sintering pressure and temperature may be from 3 to 5 Gpa and from 1,000 to 1,500° C., respectively. As the means for coating the first binding material there may be used a chemical vaporization process (CVD process) besides PVD process.
In order to enhance the strength of the sintered body, it is effective to enhance the strength of bond between the high pressure form boron nitride and the binding material. If a nitride or boride of Ti and Al is present as a first material around the high pressure form boron nitride particles, the interface with the high pressure form boron nitride exhibits an enhanced reactivity that increases the bond strength and hence the strength of the sintered body. In particular, an Al compound has a high reactivity. It is preferred that the first binding material have a higher Al concentration than the second binding material. If the Al concentration of the second binding material is higher than that of the first binding material, the resulting sintered body exhibits a deteriorated abrasion resistance.
Further, if the first binding material is made of cubic TiAlN, it exhibits a higher hardness and strength than that made of a hexagonal nitride of Ti and Al. Further, cubic boron nitride (cBN) is preferable as the high pressure form boron nitride. It's average particle diameter is preferably in the range of 0.1 to 10 &mgr;m.
The reason why the main conditions are predetermined as mentioned above will be described hereinafter.
<Content of High Pressure Form Boron Nitride>
If the content of high pressure form boron nitride falls below 20% by volume, the resulting sintered body of high pressure form boron nitride doesn't exhibit its inherent properties. On the contrary, if the content of high pressure form boron nitride exceeds 70% by volume, the amount of the binding material is decreased, causing a drop of strength.
<Thickness of First Binding Material>
If the thickness of the first binding material falls below 5 nm, the desired effect cannot be exerted. On the contrary, if the thickness of the first binding material exceeds 300 nm, the content of Al in the sintered body is increased, causing a rise in abrasion resistance.
<Contact Ratio of High Pressure Form Boron Nitride>
If the contact ratio of high pressure form boron nitride exceeds 20%, the resulting contact points become defects causing a drop of strength.
<State of High Pressure Form Boron Nitride Particles Which Have been Acid-Treated>
If the ratio of single particles falls below 90%, it means that many high pressure form boron nitride particles come in contact with each other to generate many defects causing a drop of strength.
REFERENCES:
patent: 5466642 (1995-11-01), Tajima et al.
patent: 5948716 (1999-09-01), Kume et al.
patent: 6001757 (1999-12-01), fukaya et al.
patent: 6001758 (1999-12-01), Fukaya et al.
patent: 6008153 (1999-12-01), Kukino et al.
patent: 6140262 (2000-10-01), Collier et al.
patent: 0 879 806 A1 (1998-11-01), None
patent: 2 320 725 (1998-07-01), None
Fukaya Tomohiro
Kukino Satoru
Nakai Tetsuo
Shiraishi Junichi
Group Karl
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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