THE PHASES WITH THE BORON COORDINATION NUMBER 8 IN THE SYSTEM COBALT-VANADIUMBORON (DIE PHASEN MIT DER BORKOORDINATIONSZAHL 8 IM SYSTEM KOBALT-VANADIUM-BOR

The cobalt-rich alloys in the system cobalt-vanadiumboron exhibit two borides with the same coordination number around the boron atom, namely the solid solution of vanadium in Co2B and a ternary phase with the Cr23C6 structure. In the cobalt-rich corner of the ternary system a liquidus projection and an isothermal section at 800C were worked out. The solubility of vanadium in Co2B at 800C is 8 at.-%. The substitution of vanadium in Co2B is accompanied by an increase in the tetragonal lattice parameters a and c but a decrease in the axial ratio c/a. The correlation between the average number of outer electrons and the axial ratio for this structure is discussed by means of several examples. At 800C the congruently melting ternary phase extends from Co21V2B6 to Co20V3B6 and its boron content remains practically stoichiometric. Its lattice constant also increases with increasing vanadium content and, for alloys quenched from 800C, lies between 10.47 sub 6 and 10.49 sub 7. (Author) Pub. in Zeitschrift fur Metallkunde v56 (S8) p508-11 (West Germany) 1965 (Special ed.). (Copies available only to DDC users). Text in German, summary in English.