Accession Number : AD0667238

Title :   ON THE INTERACTION BETWEEN POINT DEFECTS AND INCLUSIONS IN CRYSTALS.

Descriptive Note : Technical rept.,

Corporate Author : HARVARD UNIV CAMBRIDGE MASS DIV OF ENGINEERING AND APPLIED PHYSICS

Personal Author(s) : Ashby,M. F.

Report Date : JAN 1968

Pagination or Media Count : 29

Abstract : When a crystal containing incoherent inclusions is quenched, the vacancy concentration in it can approach its new equilibrium value if vacancies enter the inclusion - matrix interface. The loss of vacancies lowers the free energy of the matrix, but it generates misfit at the inclusion which is associated with an increasing elastic strain-energy. Equilibrium is temporarily re-established when a vacancy leaving the matrix and entering the interface lowers the chemical free energy of the matrix and increases the strain energy by equal amounts. This equilibrium is temporary only, since, given time, the vacancies ultimately drain to the free surface, the vacancy concentration falls to its true equilibrium value, and the elastic strain disappears again. This report calculates the magnitude of the elastic strains which form at inclusions due to this effect. They can be large: much larger than those due to difference in coefficient of thermal expansion. If the strains are large enough, prismatic punching will occur at the inclusions to relieve them. Inclusions thus provide a mechanism for condensing vacancies into prismatic loops without the usual nucleation step. The actual number of vacancies which can be accepted by an inclusion is large, in spite of the strains which form; this means that a volume fraction of, say, 1% of inclusions can act an an efficient sink for vacancies.

Descriptors :   (*CRYSTAL DEFECTS, INTERACTIONS), (*METALS, CRYSTAL DEFECTS), FREE ENERGY, ELASTIC PROPERTIES, STRESSES, STRAIN(MECHANICS), INTERFACES, QUENCHING, DIFFUSION

Subject Categories : Metallurgy and Metallography
      Crystallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE