Mechanical Behavior and Flow Mechanisms in Refractory Metal Composites
Final rept. 1 Mar 90-30 Sep 93
WRIGHT STATE UNIV DAYTON OH DEPT OF MECHANICAL AND MATERIALS ENGINEERING
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This report clearly demonstrates that the mechanical behavior of a refractory metal based composite, such as Nb-10 ao Si alloy, can be improved considerably by tailoring the microstructure through thermomechanical processing TMP. This desired microstructure consists of a fine grain silicide matrix reinforced with polygrain Nb particles which are elongated, oriented and aligned in a direction transverse to crack propagation. The powder processing route can achieve a fine grain structure which would exhibit high strength. But, significant improvements in fracture toughness would probably not be possible because factors such as the elongation, alignment, and orientation of the ductile reinforcement phase are critical and provide additional energy absorption mechanisms such as pull-out, interface sliding, and crack bridging. The directional solidification DS process can produce a composite with reinforcing phase particles of specific size, spacing, and orientation. However, in the DS material, both the matrix and the ductile particles have single grain structures, which are prone to cleavage. Therefore, TMP by hot extrusion of a DS material will result in a composite with optimum properties.
- Laminates and Composite Materials