Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
1999-08-10
2001-07-17
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S307000, C051S293000, C051S295000, C419S011000, C419S018000, C419S014000, C428S551000, C075S237000, C075S238000, C075S240000, C075S241000, C075S242000, C075S243000
Reexamination Certificate
active
06261329
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a diamond sintered body having high strength and high wear resistance, and particularly, to a highly strong and highly abrasion-resisting diamond sintered body having high wear resistance, chipping resistance, shock resistance and thermal conductivity, and a tool including the sintered body.
BACKGROUND ART
Diamond is the hardest material present on earth. Particularly, a diamond sintered body hardly suffers from chips caused by the cleavage, a shortcoming of monocrystalline diamond, and therefore is often used as a material for a cutting tool for a nonferrous material such as an aluminum-silicon alloy. Japanese Patent Publication Nos. 39-20483 and 52-12126 for example disclose sintered bodies formed by sintering diamond particles using a ferrous metallic binder such as cobalt.
Among these diamond sintered bodies, those having granules with a diamond particle size of less than 5 &mgr;m or those having extra fine granules with a particle size of at most 1 m are known as highly chipping-resisting materials. Japanese Patent Publication No. 39-20483 for example discloses a diamond sintered body including fine diamond particles and ferrous metal powder which allows diamond to be dissolved and re-precipitated, and Japanese Patent Publication No. 58-32224 for example discloses a diamond sintered body including sintered diamond particles having a particle size of at most 1 &mgr;m, a carbide, a nitride and a boride of a metal belonging to group 4a, 5a or 6a in the periodic table, a solid solution or mixture thereof and a ferrous alloy.
When these fine diamond particles and a ferrous metal such as cobalt or tungsten carbide-cobalt are used as starting materials for sintering, diamond particles could often grow abnormally unless the temperature and pressure conditions are strictly controlled, because such diamond particles are extremely active. Therefore, the size of the diamond particles partly becomes extremely large, which makes it difficult to provide a diamond sintered body having a particle size of at most 1 &mgr;m and a homogeneous microstructure with high yields.
In order to solve this problem, there is known a method of controlling the growth of particles by providing hard particles such as tungsten carbide, cubic boron nitride and silicon carbide at diamond grain boundaries. Japanese Patent Publication No. 61-58432 for example discloses a diamond sintered body formed by adding tungsten carbide as hard particles.
This method however controls abnormal growth of diamond particles by providing hard particles having low compatibility with diamond particles between the diamond particles, thereby physically and chemically preventing direct bonding between the diamond particles, and therefore the formation of skeletons by sintering between the diamond particles is insufficient. As a result, the chipping resistance, shock resistance and thermal conductivity, i.e., essential characteristics of diamond are disadvantageously lowered.
Meanwhile, among various diamond sintered bodies, coarse grained ones having a particle size from at least 5 &mgr;m to at most 100 &mgr;m are generally known as having high wear resistance. Such coarse grained diamond particles are, however, not easily sintered, and therefore a known method forms a carbide on the surface of diamond particles in order to make sintering easier. Japanese Patent Laying-Open No. 63-134565 for example discloses a method of producing a carbide on the surface of diamond particles, thereby enhancing the binding force of a sintering aid metal to individual diamond particles to ease sintering. Many products of diamond sintered body using sintering aid including a tungsten carbide in order to ease sintering are manufactured.
When a carbide is thus generated on the surface of diamond particles, however, the wear resistance, chipping resistance, shock resistance and thermal conductivity are lower than diamond sintered bodies including only diamond particles and a ferrous metal. If a tungsten carbide is added to a sintering aid, the content of the sintering aid increases, which is more likely to deteriorate the wear resistance of the diamond sintered body.
In recent years, harder materials difficult to cut have increased the need for machining tools with a diamond sintered body for cutting these harder materials. As a result, it is required that the sintered body has a wear resistance, a chipping resistance, a shock resistance and a thermal conductivity higher than conventional sintered bodies for making cutting tools.
The present invention is directed to a solution to the above-described problems, and it is an object of the present invention to provide a diamond sintered body having a required wear resistance, chipping resistance, shock resistance and thermal conductivity higher than conventional diamond sintered bodies.
SUMMARY OF THE INVENTION
The inventors have found that the strength such as the chipping and shock resistance, the wear resistance and the thermal conductivity of a diamond sintered body can be improved by strengthening direct bonds between the diamond particles and the chipping. Conventionally hard particles have been used by sintered bodies using granular diamond powder. Such hard particles have a low compatibility with diamond particles in order to restrain the growth of the diamond particles. Methods of restraining grain growth without using such hard particles were considered by the inventors.
As a result, it was found that diamond dissolved in a ferrous metal as a sintering aid at the time of sintering, and as the diamond sintered body cooled down after the sintering, the diamond in the ferrous metal was re-precipitated, which caused abnormal growth of diamond particles. It was then found that in order to prevent this phenomenon, metallic tungsten should be added to the ferrous metal as the sintering aid, which reduced the amount of diamond dissolved in the ferrous metal, which could reduce re-precipitation and prevent diamond particles from growing abnormally. By this method, the use of conventional hard particles is not necessary, diamond particles are more easily bonded with one another, so that a strong skeleton is formed. Furthermore, since the hard particles are not necessary, the content of diamond in the resultant diamond sintered body increases.
In a sintered body using coarse-grained diamond powder, metal tungsten added in a sintering aid makes it easier to sinter the diamond particles. Therefore, the addition of tungsten carbide as conventionally practiced is not necessary, which improves the wear resistance of the diamond sintered body.
It was also found that the wear resistance of the sintered body increased as the content of diamond particles in the diamond sintered body increased.
It was also found that the size of defects in the sintered body was closely related with strength characteristics such as the chipping resistance and shock resistance of the sintered body. The defects herein are diamond particles having an extremely large size in the sintered body, a pool of a sintering aid such as a solvent metal, a fault in the diamond sintered body and the like. The strength of the sintered body increases as defects in the diamond sintered body are reduced.
A high strength and abrasion resistant diamond sintered body according to the present invention is based on the above knowledge and includes sintered diamond particles, a sintering aid and an inevitable impurity as the remainder. The content of the sintered diamond particles is at least 80 vol. % and less than 99 vol. %. The diamond particles have a particle size in the range from at least 0.1 &mgr;m to at most 70 &mgr;m. Sintered diamond particles next to each other are directly bonded. The sintering aid includes at least one kind selected from the group consisting of iron, cobalt and nickel, and metallic tungsten. Herein, the substance represented by the word “tungsten” may be metallic tungsten or a tungsten compound such as tungsten carbide. The content of tungsten in the sintered body is in t
Kanada Yasuyuki
Kukino Satoru
Nakai Tetsuo
Ogata Yasunobu
Shiraishi Junichi
Fasse W. F.
Fasse W. G.
Marcheschi Michael
Sumitomo Electric Industries Ltd.
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