THE MICROSTRAIN REGION IN HIGH-PURITY REFRACTORY METALS.
Abstract
Modifications to a conventional electron beam floating zone unit are described. The filament is hidden from the specimen and this results in increased stability of operation, longer filament life, and excellent uniformity of crystal diameter (0.130 in plus or minus 0.001 in). Molybdenum single crystals grown from vacuum arc-cast and hot swaged stock contain inclusions, and the crystals exhibit a high grown-in dislocation density about 6 x 10 to the 7th power/sq cm; 90% of these dislocations are associated with and are attributable to the inclusions. Variations in zoning speed, number of zone passes, and annealing treatments at 1700C in vacuum or in argon have no appreciable effect on the number of inclusions. The inclusions are effectively removed from zoned crystals by annealing in hydrogen at about 2000C; this is accompanied by a decrease in dislocation density to about 1,000,000/sq cm. Hydrogen annealing of the as-received material followed by zone melting gives inclusion-free crystals, and a dislocation density about 4,500,000/sq cm; a further hydrogen anneal after zone melting reduces the density to about 200,000/sq cm. Preliminary dislocation velocity experiments are described. The basic relations in mechanical hysteresis were reexamined. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- May 31, 1966
- Accession Number
- AD0634128
Entities
People
- A. Lawley
- H. L. Prekel
- J. D. Meakin
Organizations
- Franklin Institute