Accession Number : AD0820384

Title :   DEFECT STRUCTURE OF SINGLE-CRYSTAL TITANIUM DIBORIDE.

Descriptive Note : Technical rept. Oct 63-Jun 67,

Corporate Author : AIR FORCE MATERIALS LAB WRIGHT-PATTERSON AFB OH

Personal Author(s) : Vahldiek, F. W. ; Mersol, S. A. ; Lynch, C. T.

Report Date : JUL 1967

Pagination or Media Count : 83

Abstract : Single crystals of TiB2, grown by a modified Verneuil process, were found to have a platelet-like Widmanstatten precipitate on all planes of the boules. Electron diffraction, electron microprobe, and chemical analyses showed this precipitate to be off-stoichiometric TiB(2, 03), with hexagonal TiB2 symmetry. The effects of annealing on the substructure were investigated up to 2350 C. Below 2100 C, essentially no substructural changes were noted. From 2100 to 2350 C an increasing spheroidization and dispersion of the platelets within the matrix was noted with increasing annealing temperatures, resulting in increasing formation of etch pits and in a concomitant hardening effect. Dislocation etch pits and rosettes were produced in these crystals by impacting them with steel and WC balls at 850 C in air and argon atmospheres. Stacking faults were frequently observed by electron transmission, with their direction being parallel to the c- or the a-axes. Room temperature slip was produced in these crystals independently by microhardness and by high pressure methods. Electrical resistivity measurements on single-crystal TiB2 did not reveal anisotropy. Anisotropy in elastic and shear moduli was determined to follow the lattice parameter ratio c/a = 1.066. The Debye temperature values calculated from mean sound velocities ranged from 952 to 964 K. A metallic bonding mechanism is indicated for TiB2.

Descriptors :   *BORIDES), (*TITANIUM COMPOUNDS, (*SINGLE CRYSTALS, CRYSTAL DEFECTS), CRYSTAL GROWTH, ELECTRICAL RESISTANCE, MODULUS OF ELASTICITY, BONDING, ELECTRON MICROSCOPY.

Subject Categories : Crystallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE