Accession Number : AD0475132


Title :   THE NUCLEATION AND GROWTH OF S' PRECIPITATES IN AN ALUMINUM - 2.5% COPPER - 1.2% MAGNESIUM ALLOY.


Descriptive Note : Technical rept.,


Corporate Author : ROYAL AIRCRAFT ESTABLISHMENT FARNBOROUGH (UNITED KINGDOM)


Personal Author(s) : Wilson, R N


Report Date : Mar 1965


Pagination or Media Count : 20


Abstract : The nucleation and growth of S' precipitates in an aluminium-2.5% copper-1.2% magnesium alloy aged at 190 C were examined by transmission electron microscopy. The S' precipitates were shown to be heterogeneously nucleated at dislocations, and to grow as laths on (210) planes in a 001 direction. The shape of the laths is consistent with the degree of mismatch of the matrix and precipitate planes at the precipitate-matrix interfaces. Precipitate sheets are formed at dislocations by the growth of the laths on (210) planes with a common 001 growth direction; the growth planes conform to the strain energy requirement that the misfit vector of the precipitate should lie approximately parallel to the Burgers vector of the dislocation, and are those expected from consideration of the effect of the line tension of the dislocation. The possibility of refining the precipitate distribution is discussed, and an increase in the density of sites for heterogeneous nucleation (e.g. by prestrain prior to ageing) or a modification of the interfacial energy (e.g. by addition of silicon) are both shown to result in refinement of the S' precipitate distribution. (Author)


Descriptors :   *NUCLEATION , *ALUMINUM ALLOYS , ELECTRON MICROSCOPY , CRYSTAL GROWTH , CRYSTAL DEFECTS , COPPER ALLOYS , MAGNESIUM ALLOYS , METAL CRYSTALS , SOLID SOLUTIONS , UNITED KINGDOM


Subject Categories : Crystallography
      Thermodynamics


Distribution Statement : APPROVED FOR PUBLIC RELEASE