Abstract A mixture containing less than 50 wt. percent of graphite-like boron nitride treated by a shock wave and highly defective wurtzite-like boron nitride obtained by a shock-wave method is compressed and heated at pressure and temperature values corresponding to the region of the phase diagram for boron nitride defined by the graphite-like boron nitride compact modifications of boron nitride equilibrium line and the cubic boron nitride wurtzite-like boron nitride equilibrium line, whereby the resulting crystals of boron nitride exhibit a structure of wurtzite-like boron nitride or of both wurtzite-like and cubic boron nitride. The resulting material exhibits higher plasticity as compared with polycrystalline cubic boron nitride, while tools made of this compact polycrystalline material have a longer service life under impact loads in machining hardened steel and chilled iron.
A METHOD OF PRODUCING POLYCRYSTALLINE BORON NITRIDE COMPRISING THE STEPS OF: PREPARING A MIXTURE CONTAINING HIGHLY DEFECTIVE BORON NITRIDE HAVING A WURTZITE STRUCTURE OBTAINED BY A SHOCK-WAVE METHOD AND LESS THAN 50 WT, PERCENT BORON NITRIDE OF A GRAPHITE STRUCTURE SUBJECTED TO A SHOCK-WAVE TREATMENT; COMPRESSING AND HEATING THE MIXTURE AT TEMPERATURE AND PRESSURE VALUES CORRESPONDING TO THE REGION OG THE PHASE DIAGRAM FOR BOROM NITRIDE DEFINED BY BORON NITRIDE OF A GRAPHITE STRUCTURE COMPACT MODIFICATIONS OF BORON NITRIDE EQUILIBRIUM LINE AND THE CUBIC BORON NITRIDE- BORON NITRIDE A WURTZITE STRUCTURE EQUILLBRIUM LINE.
Claim 2
Independent Claim
93 words
A METHOD OF PRODUCING POLYCRYSTALLINE BORON NITRIDE COMPRISING THE STEPS OF: PREPARING A MIXTURE CONTAINING HIGHLY DEFECTIVE BORON NITRIDE HAVING A WURTZITE STRUCTURE OBTAINED BY A SHOCK-WAVE METHOD AND LESS THAN 50 WT, PERCENT BORON NITRIDE OF A GRAPHITE STRUCTURE SUBJECTED TO A SHOCK-WAVE TREATMENT; COMPRESSING AND HEATING THE MIXTURE AT TEMPERATURE AND PRESSURE VALUES CORRESPONDING TO THE REGION OG THE PHASE DIAGRAM FOR BOROM NITRIDE DEFINED BY BORON NITRIDE OF A GRAPHITE STRUCTURE COMPACT MODIFICATIONS OF BORON NITRIDE EQUILIBRIUM LINE AND THE CUBIC BORON NITRIDE- BORON NITRIDE A WURTZITE STRUCTURE EQUILLBRIUM LINE.
Claim 3
Dependent Claim
27 words
The method as claimed in claim 1, wherein the mixture is subjected to a pressure between 50 and 300 kbars and a temperature between 20.degree.C and 3,000.degree.C.
Claim 4
Dependent Claim
38 words
The method as claimed in claim 1, further comprising the step of shielding said mixture, during the compression and heating, from directly contacting a pressure transmitting medium so as to produce polycrystalline boron nitride having the wurtzite structure.