History review on cubic boron nitride, intended for edge cutting tool (part 4)

Abstract

The paper presents historical materials on edge cutting tools design, based on cubic boron nitride, and describes modern state of local cutting superhard materials production. Parameters of hexagonal boron nitride conversion into cubic form are considered, and it is shown that gas-phase transport reactions with hydrogen play the main role. The author note likeness between processes of graphite gas-phase synthesis and hexagonal boron nitride, and also obtaining diamond and cubic boron nitride; though diamond synthesis has been performed both from methane and indirectly from graphite. It is shown that there is a similar scheme for the cubic boron nitride. In spite of the fact that today we have only indirect process of cubic structure synthesis from hexagonal modification in a high-pressure device, it does mot mean that it is impossible to obtain diamond-like boron nitride directly from gaseous compositions of boron and nitrogen. The paper presents positive investigation results on the cubic boron nitride synthesis in conditions excluding any pressure on initial burden of hexagonal boron nitride and catalyst metal. Estimated conditions of gas-phase synthesis of the cubic boron nitride from boron and nitrogen compound at normal pressure are proposed and description of the device for the process realization is presented. Conditions of microwave heating that are similar to ones for diamond synthesis from methane should be created to obtain gas-phase synthesis of the cubic boron nitride without high pressures; i.e. it is necessary to increase supplied specific power and find experimentally optimum concentration of initial gaseous substances, containing boron and nitrogen, to obtain the cubic boron nitride.