Numerical study of deformation behavior in intermetallic and refractory metal composites.

Abstract

The deformation behavior of refractory metal matrix composites reinforced with intermetallic compounds and intermetallic compounds matrix composites reinforced with refractory metals was studied by using the finite element method. As model systems, an intermetallic compound MoSi$\sb2$ and a refractory metal Mo were selected. For the Mo matrix composites reinforced with intermetallic platelets, the effects of platelet reinforcements distributions and a thickness change in the reinforcements were investigated with two extreme models--aligned reinforcement composite (AC) and staggered reinforcement composite (SC), by using the three dimensional elastic-plastic formulations. The change in the spatial arrangement of the reinforcements gives rise to significant changes in the strengthening aspects of the X, Y and Z direction, as in SC, compared with AC. For the microlaminate composites, the composite strengthening was investigated in the finite element method with two interface models--line interface and interface-layer zone model, and with different thickness-to-width ratios, in two- and three-dimensional formulations. The strengthening in these composites as a function of layer thickness was simulated with the interface layer zone model. The study of composite with loading normal to the layer was extended from the analyses of ceramic/metal bonded systems and butt joints, and in this loading, three hardening stages were characterized. For the ductile-phase toughened intermetallic laminate composites, the stress-strain response was studied as a function of reinforcement volume fraction, and by considering perfectly bonded, partially and fully debonded interfaces. Results show that moderate to weak bond of interface gives the maximum toughness increase in a MoSi$\sb2$ matrix composite reinforced with a Mo phase. For the medium strength interface, the major contribution to the toughness is obtained from both the plastic deformation of ductile phase and extensive debonding at the interface. The material with a high strain hardening exponent and a high yield strength is a good choice for the reinforced ductile materials on the toughness point of view. The results show that the toughness increase depends upon the coupled effects of debonding and constrained plastic flow.