A sintered material includes a first phase and a second phase, wherein the first phase is composed of cubic boron nitride particles, and the following relational expressions are satisfied when more than or equal to two cubic boron nitride particles adjacent to and in direct contact with each other among the cubic boron nitride particles are defined as a contact body, Di represents a length of an entire perimeter of the contact body, n represents the number of contact locations at which the cubic boron nitride particles are in direct contact with each other, d.sub.k represents a length of each of the contact locations, and d.sub.k (where k=1 to n) represents a total length of the contact locations: Dii=Di+(2d.sub.k (where k=1 to n)); and [(DiiDi)/Dii]10050.

A sintered material includes a first phase and a second phase, wherein the first phase is composed of cubic boron nitride particles, and the following relational expressions are satisfied when more than or equal to two cubic boron nitride particles adjacent to and in direct contact with each other among the cubic boron nitride particles are defined as a contact body, Di represents a length of an entire perimeter of the contact body, n represents the number of contact locations at which the cubic boron nitride particles are in direct contact with each other, d.sub.k represents a length of each of the contact locations, and d.sub.k (where k=1 to n) represents a total length of the contact locations: Dii=Di+(2d.sub.k (where k=1 to n)); and [(DiiDi)/Dii]10050.

It is an object to provide a cubic boron nitride polycrystalline material excellent in toughness. A cubic boron nitride polycrystalline material containing fine cubic boron nitride which is granular, has a maximum grain size not greater than 100 nm, and has an average grain size not greater than 70 nm and at least one of plate-shaped cubic boron nitride in a form of a plate having an average major radius not smaller than 50 nm and not greater than 10000 nm and coarse cubic boron nitride which is granular, has a minimum grain size exceeding 100 nm, and has an average grain size not greater than 1000 nm is provided.

The present diamond single crystal is a diamond single crystal containing nitrogen atoms, in which a concentration of the nitrogen atoms changes periodically along a crystal orientation of the diamond single crystal, and an arithmetic average value A.sub.ave, a maximum value A.sub.max, and a minimum value A.sub.min of the distance of one period along the crystal orientation satisfy the relationship expressed by the following equation (I):
(A.sub.max)/1.25(A.sub.ave)(A.sub.min)/0.75(I).

The present diamond single crystal is a diamond single crystal containing nitrogen atoms, in which a concentration of the nitrogen atoms changes periodically along a crystal orientation of the diamond single crystal, and an arithmetic average value A.sub.ave, a maximum value A.sub.max, and a minimum value A.sub.min of the distance of one period along the crystal orientation satisfy the relationship expressed by the following equation (I):
(A.sub.max)/1.25(A.sub.ave)(A.sub.min)/0.75(I).

In a surface-coated cutting tool, an A layer made of an (Al.sub.1-xTi.sub.x)N layer (0.35x0.6 by an atom ratio) and a B layer made of a (Al.sub.1-y-zTi.sub.ySi.sub.z)N layer (0.35y0.6 and 0.01z0.1 by an atom ratio) are layered on a surface of a tool body in which at least a cutting edge is made of a cBN sintered body. A layer thickness ratio of the A layer and the B layer (t.sub.B/t.sub.A) is 2 to 5, an X-ray diffraction intensity ratio I(200)/I(111) as the entire hard coating layer is more than 3 and 12 or less, a full width at half maximum of a peak of I(200) is 0.3 to 1.0, the I.sub.A(200)/I.sub.A(111) of the A layer is 2 to 10, and a full width at half maximum of the peak of the I.sub.A(200) is 0.3 to 1.0.

In a surface-coated cutting tool, an A layer made of an (Al.sub.1-xTi.sub.x)N layer (0.35x0.6 by an atom ratio) and a B layer made of a (Al.sub.1-y-zTi.sub.ySi.sub.z)N layer (0.35y0.6 and 0.01z0.1 by an atom ratio) are layered on a surface of a tool body in which at least a cutting edge is made of a cBN sintered body. A layer thickness ratio of the A layer and the B layer (t.sub.B/t.sub.A) is 2 to 5, an X-ray diffraction intensity ratio I(200)/I(111) as the entire hard coating layer is more than 3 and 12 or less, a full width at half maximum of a peak of I(200) is 0.3 to 1.0, the I.sub.A(200)/I.sub.A(111) of the A layer is 2 to 10, and a full width at half maximum of the peak of the I.sub.A(200) is 0.3 to 1.0.

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 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 method of forming a supporting substrate for a cutting element comprises forming a precursor composition comprising discrete WC particles, a binding agent, and discrete particles comprising Co, Al, and one or more of C and W. The precursor composition is subjected to a consolidation process to form a consolidated structure including WC particles dispersed in a homogenized binder comprising Co, Al, W, and C. A method of forming a cutting element, a cutting element, a related structure, and an earth-boring tool are also described.