Deformation and failure mechanisms in titanium-aluminum-vanadium/titanium carbide particulate and layered composites

Composite materials are attractive for high performance applications due to their high specific strengths. The compressive deformation behavior of Ti-6Al-4V (Ti64) and Ti64/TiC particulate and layered composites was studied for ballistic applications at strain rates from 0.1 s−1 to 1000 s−1 and strengthening and failure mechanisms were identified.; The behavior of Ti64 with the equiaxed and Widmanstatten microstructures was characterized in order to interpret data from the composite materials. The interstitial content was determined to influence yield stress more than grain size. True stress - true strain behavior at 0.1 s−1 was influenced by damage accumulation while at 1.0 s−1 and 10 s−1 behavior was more influenced by thermal softening occurring in regions of intense inhomogeneous deformation. The aspect ratio of the laths in the Widmanstatten microstructure facilitated softening and failure compared to the equiaxed microstructure due to the available shear and crack paths. Failure occurred by fracture along adiabatic shear bands at 10 s−1.; The yield strength of the particulate composites increased significantly with the addition of only 1%TiC. TEM results showed a carbon deficiency in the TiC. Carbon in solution was the most potent strengthening mechanism. Load transfer and an increased dislocation density contributed to a much lesser degree. Grain size and subgrain size refinement were not considered to be important strengthening mechanisms. Samples tested at high strain rates failed along adiabatic shear bands at smaller strains than those to which the monolithic material was tested.; Two symmetric three-layered composites consisting of Ti64 and Ti64/10%TiC were fabricated and tested. Grain growth occurred across the layer-interface, eliminating the interface. Both layered structures had higher strengths than the Ti64 and more damage resistance than Ti64/10TiC. Large cracks were deflected away from the interface. A simple finite element model accounted for the engineering stress-strain behavior and the macroscopic specimen shape-change.