Floating-zone crystal growth of WC

Abstract

Single crystals of tungsten carbide were grown by the floating-zone technique by adding boron in the molten zone. It is confirmed that WC decomposes into cubic WC_1−x and carbon at an elevated temperature and cannot coexist with the liquid which consists of only tungsten and carbon. It was theoretically expected that addition of boron would stabilize the WC structure so that the WC phase could coexist with the liquid. This was proved by the float zoning through the WC rod which contained boron. The WC phase was deposited from the molten zone which consists of tungsten, carbon and boron. The growth of single crystals of WC was carried out under pressurized helium gas atmosphere of 1 M Pa. The molten zone, whose temperature was about 2900°C, was inductively heated and driven downwards. The compositions of the molten zone and the feed rod were [W]/[C]/[B] = 1/0.65/0.06 and 1/1.08/0.007 (atomic ratio), respectively. Single crystals with dimensions 9 mm diameter and 5 mm long can be cut out from the zone-passed rod. The boron content in the crystal could be lowered to the order of 100 p.p.m.