Tensile strength of Ni/Cu/(001)Ni triple layer films
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I.
INTRODUCTION
THE possibility of a metallic composite material with a very high strength and ductility was proposed by Koehler. The proposed material has a laminate structure of multiple layer films composed of two kinds of evaporated materials with such a thickness that Frank-Read sources cannot operate in the inside. Investigations for combinations of polycrystal films, such as Ni and Cu, 2'3 A1 and Cu, 4 Fe and Cu, 3 and A1 and A1203 amorphous films 5 showed various degrees of strengthening, and the strengthening with a reduction in film thickness was explained from Koehler's theoretical predictions. It is known that evaporated multiple films contain many dislocations in the individual layer as well as on the interface. However, there are only a few reports 6'7 on the contributions of these dislocations to strengthening of layer films. The present work aims to study the influence of these dislocations on the mechanical properties of multiple layer films composed of Ni and Cu single crystals, which is one of the preferable combinations suggested by Koehler. Tensile tests for Ni and Cu single crystal films and Ni/Cu/ (001)Ni triple layer films are carried out, and the influence of interfacial dislocations on the strength of multiple layer films is discussed. II.
EXPERIMENTAL PROCEDURES
The tensile specimens of Ni and Cu single crystal films and Ni-Cu-Ni triple layer films were made by evaporating Ni and Cu having the purity of 99.99 pct on (001)NaC1 substrates in the vacuum of less than 1.5 x 10-6 Pa. 8 NaC1 substrates were cleaved in air and the cleavage steps on (001) surface were removed by polishing with a solution of water and alcohol. Ni or Cu single crystal film was evaporated on (001)NaC1 at the substrate temperature of 350 ~ For the preparation of Ni-Cu-Ni triple layer film, Ni film was first deposited on (001)NaC1 at 350 ~ subsequently KUMAYASU YOSHII, Assistant Professor, MASATAKA UMENO, Associate Professor, and HIDEAKI KAWABE, Professor, are all with the Department of Precision Engineering, Faculty of Engineering, Osaka University, 2-1 Yamada-Oka, Suita, Osaka, Japan. HIROSHI TAKAGI, formerly Graduate Student, Faculty of Engineering, Osaka University, is now with Wafer Process Engineering, Mitsubishi Electric Corporation, Kita-Itami Works, 4-1, Mizuhara, Itami, Hyogo, Japan. Manuscript submitted September 21, 1983. METALLURGICALTRANSACTIONSA
Cu film on the initial Ni film at 150 ~ and lastly Ni film on the Cu film at 150 ~ All evaporations were carried out without breaking the vacuum at the evaporation rate of 2.0 nm per second for Ni, and 1.0 nm per second for Cu. Tensile tests were made for specimen films having the gauge length of 10 mm and the width of 2 mm with the specially designed tensile machine, the details of which have been described elsewhere. 9 Transmission and scanning electron microscopes (TEM and SEM) used in the present study were HU-3000 operating at 2 MeV and JSM-25SIII at 25 kV.
III.
MICROSTRUCTURES OF THE SPECIMENS
The epitaxial growth, the continuity, and the microstruc
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