Nanoscale brass/steel multilayer composites produced by cold rolling
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SATYAM S. SAHAY, Research Associate, KAKKAVERI S. RAVICHANDRAN, Assistant Professor, and J. GERALD BYRNE, Professor and Chairman, are with the Department of Metallurgical Engineering, the University of Utah, Salt Lake City, UT 84112. Manuscript submitted February 8, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
Fig. 1---(a) and (b) Optical micrographs of the as-bonded multilayer composite.
in a Cambridge Stereoscan scanning electron microscope (SEM) and a Cameca SX50 electron microprobe. Brass and steel layer thicknesses were measured from optical and SEM micrographs. Microstructures of the as-bonded specimen shown in Figures l(a) and (b) indicate that the uniformity in spacing and the discreteness of layers were maintained during bonding. The penetration of the brass layer into the steel layer along the grain boundaries can be seen (Figure l(b)). This penetration led to the formation of rough interface and provided interfacial locking, assisting to maintain interfacial strength during subsequent rolling operations. The presence of discrete particles in the steel layer can also be seen. Microstructures of multilayers, rolled to various layer thicknesses, are shown in Figures 2(a) through (c). The preservation of separate layers and the laminate structure were evident in all the rolled specimens. The presence of particles in the steel layer, and the localized deformation of layers around these particles, may be seen in Figure 2(c). The particles were more prevalent in specimens with smaller interlayer thickness. Electron probe microanalysis was carried out to determine the composition of the particles in the rolled specimens. The analyses indicated that the particles are rich in Fe, Cu, and Mn. The average composition of these particles was 95.90 wt pct Fe, 1.52 wt pet Cu, and 2.53 wt pct Mn. The presence of Cu indicates the diffusion of Cu from brass to steel layers. The average level of Mn in the as-received VOLUME 27A, AUGUST 1996--2383
mined due to their smaller layer thicknesses as compared to the probe size. The deformation behavior of the brass and steel layers in the multilayer composite was studied by following the layer thicknesses as a function of nominal reduction during rolling. The nominal percentage reductions were calculated from the bilayer thicknesses of the rolled specimens and the original bilayer thickness (50/xm). These data are given in Table I along with the thicknesses of brass and steel layers. Table I indicates that with an increase in percentage reduction, the reduction in the thickness of the steel layer is higher as compared to that of the brass layer. This inhomogeneous deformation may be explained on the basis of their relative flow stress levels. The flow stress of CDA 260 brass I61 is higher than that of 1010 steelt71 at reductions exceeding 30 pct cold work. The difference in flow stresses further increases with an increasing amount of cold work. Therefore, under the series arrangement of layers, steel is expected to preferentially reduce compared to brass, leading to a decr
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