Microstructure and Strengthening Mechanisms of Highly Textured Cu/Ni Multilayers
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In this thesis, I planned to fabricate Cu/Ni metallic multilayers with equal layer thicknesses on different substrates by using magnetic sputtering technique. My objective was to characterize the texture, structure and hardness, in order to study strengthening mechanisms and nanotwins in the Cu/Ni multilayers. Sputtered, highly textured (111) and (100) Cu/Ni multilayers with individual layer thickness, h, vary from 1 to 200 nm. At greater h, X-ray diffraction (XRD) patterns of Cu and Ni (100 or 111) peaks are clearly separated indicating that the interface between Cu and Ni is semi-coherent. When h decreases to 5 nm or less, XRD spectra show significant peak distortions due to coherency stress. High resolution microscopy studies confirm the coexistence of nanotwins and coherent layer interfaces in highly (111) textured Cu/Ni mutilayers. Nanoscale twins can be formed in Cu at all h and in Ni at smaller h. Multilayer hardnesses increase with decreasing h, approach maxima at h of 2.5-5 nm, and show softening thereafter. A detail comparison between (111) and (100) textured Cu/Ni is made in both microstructure and strengthening. In this thesis, the possible mechanisms to form high density growth twins in Ni are discussed. Furthermore, the influences of both coherent layer interfaces and twin interfaces on strengthening mechanisms are discussed.