HOT-PRESS SINTERING KINETICS OF METAL POWDERS

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 1962

OSTI ID:4745663

Carlson, R G

Lead alloy spheres were hot-pressed at four temperatares of 300, 330, 550, and 400 deg F, at a constant pressure of 1185 psi; identically, four compressive pressures were applied at 665, 1165, 1665, and 2500 psi, while the temperature was held constant at 400 deg F. In the second pant, hotpressings were made on four types of Nb particles: Nb spheres (30/35 mesh); fine mesh Nb powder (-200 mesh),; a slightly coarser mesh Nb powder (-200 +350 mesh); and prealloyed 50% tungsten-50% Nb powder (-200 +350 mesh). The powders were pressed in the temperature range between 2750 to 3825 deg F at pressures up to 4000 psi. Because of the need for the higher temperatures, experiments were made to determine the necessary conditions for a controlled environment under pressure. From the proximity experiments, tantalum sheet was found to be an excellent carbon barrier during the compaction of the Nb particles. Also in the experiments it was determined that there is no significant difference in the densification rates between the static and the fluctuating (hydraulic press) methods of pressure application. Two activation energies, as determined by the rates of sintering were observed to exist in the hot-pressing process. The one at higher temperatures, was of the order of the activation energy for seif diffusion, and, hence, is believed to be controlled by a diffusion process. The activation energy at lower temperature was observed to be distinctly different. It is hypothesized that the lower temperature activation energy can be attributed to a glide mechanism of material flow, and its magnitude is determined by the type of dislocation interaction. It appears that the yield strength of the material has a significant effect on the rates of densification in hot-pressing. Equations developed in the studies are listed. (Dissertation Abst., 23: No. 5, Nov. 1982)

• Research Organization: Originating Research Org. not identified
• NSA Number: NSA-17-008770
• OSTI ID: 4745663
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

DEFECTS
DENSITY
DIFFUSION
DISLOCATIONS
ENVIRONMENT
EQUATIONS
GRAIN SIZE
HEATING
HIGH TEMPERATURE
LEAD ALLOYS
LOW TEMPERATURE
MEASURED VALUES
METALS, CERAMICS, AND OTHER MATERIALS
NIOBIUM
NIOBIUM ALLOYS
POWDER METALLURGY
PRESSURE
REACTION KINETICS
SINTERING
TENSILE PROPERTIES
THERMODYNAMICS
TUNGSTEN ALLOYS