ELASTIC PROPERTY DEPENDENCE ON LAYER PERIODICITY IN CU NI SUPERLATTICES/

Cu/Ni superlattices are prepared by magnetron sputter deposition and s tructurally characterized with X-ray diffraction measurement. A 1.2-4. 5 nm range of layer pair spacings is produced in a series of 1-2-mu m- thick films which have a [111] textured growth. Uniaxial tensile testi ng is used to produce load-displacement curves from free-standing Cu/N i films and calibration standards of Cu and Ni films. Direct measureme nt of the yield and ultimate stresses as well as Young's modulus is pe rformed for the Cu/Ni films. The measured Young's modulus shows a bimo dal variation with layer pair spacing. A maximum increase of 50% in Yo ung's modulus, above the rule-of-mixtures value, is measured for a 2-n m-thick layer pair sample. The yield stress behavior follows the modul us trend with layer pair spacing, whereas the ultimate stress inversel y follows the trend, that is, the stiff est samples are the most britt le. Isothermal annealing of the 2-nm-thick Cu/Ni sample progressively homogenizes the layered structure and diminishes the modulus enhanceme nt to the rule-of-mixtures value.