High-hardness sintered article and method for manufacture thereof

A method for the manufacture of a high-hardness sintered article, of substantially hardness, which method comprises preparing a mixture of

• (A) 65 to 95% by volume of a high-pressure phase boron nitride consisting of a cubic phase boron nitride alone or a cubic phase boron nitride containing 5 to 30% by volume, based on the total amount of boron nitride, of a wurtzite type boron nitride having a continuous grain size distribution ranging from a maximum grain size of 10 to 50 .mu.m to a minimum grain size of less than 1 .mu.m, said grain size distribution further characterized that when all of the particles of grain sizes exceeding 1 .mu.m are classified in stepped units of 5 .mu.m , at least one particle of a grain size belonging to a given class is present in a total of 100 particles and the number of particles of a grain size not exceeding 1 .mu.m accounting for not less than 10% of the number of particles of grain sizes not smaller than 1 .mu.m, said high-pressure phase boron nitride particles being bound to form a continuous matrix with
• (B) 4 to 34% by volume of an additive selected from the group consisting of
• (a) at least one member selected from the group consisting of carbide, nitride, and carbonitride of titanium and
• (b) a mixture of at least one member selected from the group consisting of carbide, nitride, and carbonitride of titanium with at least one member selected from the group consisting of carbide, nitride, and carbonitride of tantalum;
• and
• (C) the balance to make up 100% by volume of aluminum, and then sintering said mixture under conditions of at least 1,200.degree. C. and 20,000 atmospheres, thereby forming a continuous matrix made up of mutually bound high-pressure phase boron nitride particles.