The mechanisms that control the ductility or embrittlement in iron-manganese, platinum-rhodium-tungsten, iridium, and nickel aluminide by the presence of small amounts of impurities will be studied. These alloys represent a range of crystal structures and will allow one to test the generality of the observed effects. Hall-Petch experiments on materials doped with either ductilizing or embrittling impurities will be done to determine the effect of impurity on the ability of grain boundaries to impede the transmission of slip. Measurement of the relative impurity segregation behavior to surfaces and grain boundaries will be made. In situ deformation in TEM will provide a detailed understanding of the mechanisms involved in slip transmission.
