Accession Number : ADA332726

Title :   Influence of Electric Currents and Fields on the Kinetics and Microstructure of Phase Transformations in Metals and Ceramics

Descriptive Note : Final rept. 1 Sep 94-31 Aug 97

Corporate Author : NORTH CAROLINA STATE UNIV AT RALEIGH DEPT OF MATERIALS SCIENCE AND ENGINEERING

Personal Author(s) : Conrad, Hans

PDF Url : ADA332726

Report Date : 15 OCT 1997

Pagination or Media Count : 30

Abstract : Electropulsing: The decrease in the flow stress of FCC metals produced by individual high density electropulses was mainly due to an increase in the pre-exponential in the Arrhenius rate equation for plastic flow. An order of magnitude decrease in the colony size of eutectic Pb-Sn castings was produced by electropulsing, the effect being in accord with an increased nucleation rate. Electropulsing caused the precipitation of nanometer alpha-Fe particles from the matrix of amorphous Fe-Si-B alloys at temperatures well below the normal crystallization temperature. Electric Field: An external electric field of 1 kV/cm applied during the superplastic deformation of 7475 Al alloy enhanced the formation of whiskers having elongations greater than 1000%. The application of an electric field of -1 kV/cm during the deformation of polycrystalline NaCl at 0.28 - 0.75 TM gave the following: (a) reduced the flow stress, (b) raised the brittle-to-ductile transition temperature and (c) increased the elongation. The effect of the field at T < 0.65 TM was in accord with an enhancement of cross slip; that at T = 0.75 TM with a retardation of grain growth. The combined action of a non-contacting, orthogonal electric field of ^ 1 kV/cm and a current density of ^ 1 A/(cm2) during the superplastic deformation of 3Y-TZP at 1500 deg C produced the following effects: (a) reduced the flow stress, (b) increased the elongation and (c) a retarded grain growth and cavitation. A decrease in flow stress and increase in elongation also occurred in fine-grained Al2O3 at 1500 deg C and MgO at 1600 deg C for a contacting, axial electric field. Magnetopulsing: The fatigue life of a low-carbon steel was prolonged by exposing the specimen to magnetic pulses after cycling to approximately half of its normal fatigue life.

Descriptors :   *METALS, *PHASE TRANSFORMATIONS, *ELECTRIC FIELDS, *CERAMIC MATERIALS, *ELECTRIC CURRENT, PLASTIC DEFORMATION, STRESSES, MAGNETIC FIELDS, FATIGUE LIFE, CRYSTALLIZATION, FRACTURE(MECHANICS), DUCTILE BRITTLE TRANSITION, TRANSITION TEMPERATURE, DUCTILITY, GRAIN GROWTH, CAVITATION, ARRHENIUS EQUATION.

Subject Categories : Ceramics, Refractories and Glass
      Properties of Metals and Alloys
      Electricity and Magnetism
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE