Accession Number : AD0663248

Title :   PREPARATION AND CHARACTERIZATION OF HIGH QUALITY SINGLE CRYSTAL REFRACTORY METAL CARBIDES.

Descriptive Note : Technical rept. Apr 66-Apr 67,

Corporate Author : WESTINGHOUSE ELECTRIC CORP PITTSBURGH PA ASTRONUCLEAR LAB

Personal Author(s) : Tobin,J. M. ; Fleischer,L. R.

Report Date : OCT 1967

Pagination or Media Count : 77

Abstract : A process for growing single crystals of ZrC was developed. The crystals are grown by direct reaction of the elements at very high temperatures. Process yields of crystals measuring 0.28 inch diameter and over 0.5 inch long are high. Eighty percent of the starting rods will produce a crystal. The resulting crystals are characteristically free of microscopic pores and inclusions. After prolonged heating, the crystals are found to be homogeneous (49.4 atomic percent carbon) and free of strain. The lattice parameters vary among crystals between 4.6996 to 4.6999 Angstrom units. The crystals are randomly oriented with respect to their axes. They are readily cleaved on the (100) plane of the crystals. Absence of strain is indicated by the flatness of the cleavage plane faces. Sub-grain boundaries are observed infrequently. Each step in the multiple-step time and temperature program used to produce the crystals was analyzed to yield an understanding of the crystal growth mechanism. The crystals grow by a solid state recrystallization mechanism which is initiated by plastic strain. The feasibility of the use of the technique to grow crystals of HfC, TaC, NbC and VC was demonstrated. Crystals of HfC were grown, but the crystals are small and the yield is low. Development continues. Polycrystalline TaC, Ta2C and W2C was produced in rod diameters from 0.25 to 0.5 inches. The two sub-carbides were produced as single-phased carbide. But the structures are severely cracked. Development of the direct reaction process applied to solid transition metals continues. (Author)

Descriptors :   (*REFRACTORY MATERIALS, CRYSTAL GROWTH), (*CARBIDES, *CRYSTAL GROWTH), (*ZIRCONIUM COMPOUNDS, SINGLE CRYSTALS), HAFNIUM COMPOUNDS, TANTALUM COMPOUNDS, NIOBIUM COMPOUNDS, VANADIUM COMPOUNDS, TUNGSTEN COMPOUNDS, HEATERS, CRYSTALLIZATION, MELTING, X RAY DIFFRACTION, CHEMICAL ANALYSIS, ETCHED CRYSTALS, FRACTURE(MECHANICS)

Subject Categories : Ceramics, Refractories and Glass
      Crystallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE