Conventional sintering processes convert a portion of cBN to hBN which is softer than cBN which negatively affects functional properties of an alumina composite. The invention is directed to method for making an alumina-cubic boron nitride (Al.sub.2O.sub.3-cBN) composite that contains substantially no hexagonal boron nitride (hBN) by non-conventional spark plasma sintering of cBN with nano-sized alumina particles. The invention is also directed to Al.sub.2O.sub.3-cBN/Ni composites, which contain substantially no hBN, and which exhibit superior physical and mechanical properties compared to alumina composites containing higher amounts of hBN.

A drilling tip according to the disclosure has a tip body which is provided with a tip portion tapered toward a tip side of the tip body; and a hard layer which is formed on a surface of the tip portion of the tip body, an outermost layer of the hard layer is a cBN sintered material having 70 to 95 vol % of cBN grains, and when a cross-sectional structure of the outermost layer is observed, a binder phase having a width of 1 nm or greater and 30 nm or less and containing Al, B, and N, and in which a ratio of an O content to an Al content is 0.1 or less exists between neighboring cBN grains.

The present application is a new improvement in the fine-grained cubic Boron Nitride sintered compact which may be employed to manufacture a cutting tool. The compact contains at least 80 vol % cBN and is sintered under HPHT conditions. The invention has lower levels of unreacted cobalt in the final sintered material than conventions materials. The invention has proved beneficial in the machining of ferrous metal alloys such as sintered metal alloys.

The present application is a new improvement in the fine-grained cubic boron nitride sintered compact which may be employed to manufacture a cutting tool. The compact contains at least 80 vol % cBN with a metallic binder system and is sintered under HPHT conditions. The improvement incorporates alloys of aluminum in the metallic binder system. The invention has proved beneficial in the machining of cast iron.

A cBN sintered body contains cBN particles whose proportion is 85-97% by volume, and a binding phase whose proportion is 3-15% by volume. The cBN sintered body contains Al whose ratio to the entirety of the cBN sintered body is 0.1-5% by mass, and Co whose mass ratio to the Al is 3 to 40, and includes Al.sub.3B.sub.6Co.sub.20.

A cBN sintered material cutting tool is provided. The cBN cutting tool includes a cutting tool body, which is a sintered material including cBN grains and a binder phase, wherein the sintered material comprises: the cubic boron nitride grains in a range of 40 volume % or more and less than 60 volume %; and Al in a range from a lower limit of 2 mass % to an upper limit Y, satisfying a relationship, Y=0.1X+10, Y and X being an Al content in mass % and a content of the cubic boron nitride grains in volume %, respectively, the binder phase comprises: at least a Ti compound; Al.sub.2O.sub.3; and inevitable impurities, the Al.sub.2O.sub.3 includes fine Al.sub.2O.sub.3 grains with a diameter of 10 nm to 100 nm dispersedly formed in the binder phase, and there are 30 or more of the fine Al.sub.2O.sub.3 grains generated in an area of 1 m1 m in a cross section of the binder phase.

A cutting tool according to an aspect of the present disclosure includes a shank, a joint, and a cutting portion attached through the joint to the shank. The cutting portion includes a core and a surface portion. The surface portion is disposed around a central axis of the cutting portion to cover an outer circumferential surface of the core. The surface portion includes a cutting edge. The cutting edge is disposed on an outer circumferential surface of the surface portion and formed in a helical shape about the central axis. The surface portion is a composite sintered material including a hard phase formed of a plurality of diamond particles and a plurality of cubic boron nitride particles, and a binder phase forming the remainder.

A rotary cutting blade material has an attaching structure forming portion that is to serve as an attaching portion to the shank, a cutting structure forming portion that is to serve as a cutting blade, and a joint portion. The cutting structure forming portion has a core portion and a surface portion provided on the attaching structure forming portion with the joint portion being interposed, and the surface portion covers at least a part of a surface of the core portion. The attaching structure forming portion includes a hard material including a hard component and one or two or more types of iron group elements, and the hard material has a Young's modulus of not more than 350 GPa. The core portion includes a cemented carbide material, and the surface portion includes PCD or CBN.

A cBN sintered body contains cBN particles whose proportion is 85-97% by volume, and a binding phase whose proportion is 3-15% by volume. The cBN sintered body contains Al whose ratio to the entirety of the cBN sintered body is 0.1-5% by mass, and Co whose mass ratio to the Al is 3 to 40, and includes Al.sub.3B.sub.6Co.sub.20.

An object is to prolong the life of a cubic boron nitride cutting tool used for cutting a heat-resistant alloy. A cubic boron nitride cutting tool includes an edge tip made of a sintered cubic boron nitride compact including cubic boron nitride particles; and a base metal that holds the edge tip at a corner portion of the base metal, wherein a cutting edge formed on the edge tip of the tool has a positive rake angle.