Boron nitride system including an hBN starting material with a catalyst and a sintered cNB body having a high heat conductivity based on the catalyst

A boron nitride system produced from a starting material including a hexagonal, non-pyrolytic boron nitride having diffused therein, as an additive, a member selected from the group consisting of an alkaline earth metal boron nitride (Me'.sub.3 B.sub.2 N.sub.4) and an alkali boron nitride (Me.sub.3 BN.sub.2) in an amount within the range of 0.6 mol % to 1.3 mol % of said hexagonal, nonpyrolytic boron nitride, and wherein after conversion of said hexagonal, non-pyrolytic boron nitride by sintering, said system comprises a sintered body comprising cubic boron nitride within the range of 99.9% by weight up to 99.3% by weight of said sintered body and a metal remainder in the form of said metal of said additive, said metal remainder being present in said sintered cubic boron nitride body within the range of 0.1% by weight when said additive is 0.6 mol %, and 0.7% by weight when said additive is 1.3 mol %, except for minute quantities of naturally occurring impurities, said cubic boron nitride sintered body having a thermal conductivity of at least 4 W/cm..degree.C. due to the presence of said metal remainder, said system further comprising on a surface of said cubic boron nitride sintered body, a coating having a thickness of 1 .mu.m or less made of at least one transition metal selected from the group consisting of groups IVa, Va, and VIa of the periodic table and alloys thereof, and an interface between said sintered body of cubic boron nitride and said coating, said interface including a member selected from the group consisting of boride, nitride and boron nitride formed by a reaction between said transition metal of said coating with said cubic boron nitride, said reaction forming a reaction bond between said sintered body of cubic boron nitride and said coating for an improved adherence between the cubic boron nitride body and said coating.