Conversaziones and Receptions, 1964

THE conversazione held on 9 July to mark the quater-centenary of the birth of Galileo is described on page 119. The usual conversaziones were held on 7 May and 22 October at which the following exhibits were shown. The strength and fracture of metals was the subject of three exhibits. It is known that the strength of metals is far below its theoretical limit due to the presence of dislocations in the crystal structure. All strengthening processes introduce barriers to dislocation movement but many of these reduce ductility and make metals brittle. The British Iron and Steel Research Association demonstrated how modern physical metallurgical research is indicating new ways in which steel can be strengthened without impairment of ductility or toughness. Miss J. M. Silcock of the Central Electricity Research Laboratories and Mr W. J. Tunstall of the Cavendish Laboratory arranged an exhibit showing stacking fault precipitation in austenitic stainless steels. Electron microscopy has shown that stacking faults appear and grow during the precipitation of carbides in certain austenitic steels. Systematic observations coupled with new calculations have established the nature of the associated partial dislocations and have led to the conclusion that the faults are extrinsic. The Chemistry, Physics and Metallurgy Department of the Royal Aircraft Establishment arranged an exhibit on the fracture of metals. Various forms of fracture were exhibited and research observations and tentative conclusions of the causes of fracture were made known.