Characterization of the Texture of Heavily Deformed Metal-Metal Composites with Acoustic Microscopy
Review of Progress in Quantitative Nondestructive Evaluation
Composite materials are playing an increasingly important role as structural components. Familiar motivations for their use include the ability to achieve high ratios of strength to weight, tailored elastic stiffnesses, damage tolerance, etc. A new class of these materials which has recently received considerable attention for structural applications is the heavily deformed metal-metal compositesl,2. Through extensive deformation processing of two ductile components, e.g. Nb dendrites in a Cu
... dendrites in a Cu matrix, a fine, highly aligned, reinforced structure is produced. These heavily deformed metal-metal composites have been found to exhibit large mechanical strength in combination with high thermal and electrical conductivities at elevated temperatures3,4. In attempting to understand the mechanisms leading to these superior properties, an experimental determination of the microstructure developed during the deformation processing was undertaken. One aspect is the texture, or preferred grain orientation, developed during the deformation. The preparation of these materials utilizes a casting procedure to produce, for the case of a Cu-Nb composite, an array of Nb dendrites in a copper matrix. Subsequent extrusion or rolling breaks up the dendrites and aligns them into long, ribbon-like filaments or platelets for the case of rod or plate material respectively. Figure l illustrates a typical microstructure for the case of Cu-Nb plate material. For the large reductions in area which produce the most interesting properties, the dimensions and separations of the Nb reinforcements are less than a micron. The crystallographic texture of the filaments and matrix are believed to jointly play a strong role in determining the mechanical properties by determining those directions along which easy dislocation motion can occur.