Accession Number : ADA182871

Title :   Mechanistic Understanding of Powder Compaction in Metals.

Descriptive Note : Final rept. 1 Apr 84-30 Nov 86,

Corporate Author : CORNELL UNIV ITHACA NY DEPT OF MATERIALS SCIENCE AND ENGINEERING

Personal Author(s) : Raj,Rishi

PDF Url : ADA182871

Report Date : 25 Jun 1987

Pagination or Media Count : 45

Abstract : Powder compacts of nickel aluminide were compressed under uniaxial load above 1373 K, in a way such that the material was free to move in the lateral direction. Lateral and axial displacements were measured by means of three LVDTs. The data so obtained gave a full description of the applied stress state and the strain state as a function of time during the flow and densification process. That allowed us to obtain simultaneous measurements of the time dependent, and density dependent and shear and densification behavior of the powder compact. The shear rate was non-linear in stress suggesting a dislocation flow mechanism. A model for densification by power law creep was applied to the data. It greatly overestimated the measured densification rates. Interestingly it was found that it is difficult to densify the powder to a density of greater than about 0.80 (relative) by means of uniaxial compression. Further experiments were done where the powder was hot-pressed in a constraint cavity. In this case large hydrostatic pressures could be applied to the specimen and near theoretical densities were obtained, presumably because the hydrostatic pressure promoted the diffusional transport mechanism of densification.

Descriptors :   *ALUMINIDES, *NICKEL, *COMPACTING, *POWDER METALS, RECRYSTALLIZATION, MICROSTRUCTURE, CERAMIC FIBERS, METAL MATRIX COMPOSITES, POWDER METALLURGY, TITANIUM ALLOYS, SINTERING, INTERMETALLIC COMPOUNDS, FORGING, AXES, COMPRESSION, CREEP, DENSITY, DISLOCATIONS, FLOW, HYDROSTATIC PRESSURE, MEASUREMENT, POWDERS, POWER, RATES, SHEAR PROPERTIES, STRESSES, SYNCHRONISM, TRANSPORT

Subject Categories : Properties of Metals and Alloys
      Fabrication Metallurgy

Distribution Statement : APPROVED FOR PUBLIC RELEASE