MECHANICAL PROPERTIES OF COMPOSITION MODULATED COPPER-PALLADIUM FOILS

An investigation was made of the mechanical properties of composition modulated Cu-Pd foils using a bulge test. Composition modulated foils were made by alternately evaporating copper and palladium on a heated mica substrate. Transmission Laue patterns showed that foils had grown in two orientations, both of which were closed-packaged directions alined on the mica substrate. The boundaries of the two orientations were double positioning boundaries. The structure of the specimen was determined by X-ray diffraction. Wavelengths of the composition modulation of specimens were 1.5 to 3.2 nm.;The relationship between stress and strain in the elastic region was measured using this method to determine the initial deflection of the bulge. Composition modulated Cu-Pd foils had a linear relationship between stress and strain, contrary to the non-linearity which was observed by Yang, Tsakalakos and Hilliard.;Their non-linear stress-strain curves were reproduced by a simulation that omitted the initial deflection of the bulge. The initial deflections were assumed to be 0 to 60 um. It is therefore possible that their reported non-linearity of the stress-strain curves might come from the misanalysis of the data and, that in fact composition modulated Cu-Pd foils have a linear relationship between stress and strain in the elastic region.;A different foil mounting method for the bulge test was also used. The foil was mounted on the washer without releasing the foil from the substrate. Thus the residual stress between the foil and the substrate remained in the foil. The residual stress was about 0.2 GPa for pure copper and palladium foils. While the yield stresses of the pure foils were about 0.4 GPa, those of homogeneous Cu-Pd foils produced by co-deposition were 0.8 GPa. It is believed that this effect was due to solid solution hardening. This is in agreement with the results of hardness measurements on bulk Cu-Pd alloys.;First, the elastic properties of the foils were investigated. Foils were mounted after releasing the foils from the mica substrate. Thus the residual stress between the foil and the substrate was released and the mounted foil had no tensions but was wrinkled. An analysis is therefore given for the determination of the initial deflection of the bulge for a wrinkled foil. It is shown that the initial deflection can be determined from a plot of the cube root of pressure vs. the measured bulge-height. This analysis was confirmed by the measurement of the bulge-height using Newton's rings.;Composition modulated Co-Ni foils were also made. X-ray analysis showed that these foils had both f.c.c. and h.c.p. structures.