Text

theses

The focus of this thesis is the effect of diffuse boundary layers on overall material failure in a tungsten heavy alloy (WHA) and D2 tool steel composite. D2 tool steel powder was sintered and joined to macroscopic WHA material using field assisted sintering, where high DC fields are introduced during the consolidation process. Diffuse boundary layers were formed during the field assisted sintering of the metal in metal matrix. To investigate the failure mechanisms, bulk and localized material properties of the metal in metal matrix composites were determined, including impact energy and hardness and findings suggest the diffusion zone is not uniformly thick. The diffusion zone is approximately 40-50 µm thick. Mechanical properties are generally bilaterally affected 30-40 µm deep into the WHA compared to wrought, but can also be affected up to 10 µm into the D2 steel, while the impact toughness of the composite is close to that of wrought D2 tool steel. Material specimens were processed using equipment located at US Army RDECOM ARDEC. The resulting microstructures were examined using optical and scanning electron microscopy. Mechanical properties and failure properties were measured using equipment located at Rutgers University and US Army RDECOM ARDEC. The mechanical properties were evaluated at room temperature using custom impact testing and nanoindentation. Failure modes were examined with respect to metal boundary separation, crack initiation, and propagation due to strain, at, in, or near the diffusion affected zone and onset of fracture was found to occur at the interface as well as in the bulk WHA. These methods and data were used in the determination of constitutive model parameters. A validation of model parameters was completed with an explicit finite element model of the composite configurations. Initial assessments of damage were modeled using Johnson-Cook material and damage models. The models were refined and results represent fracture location, deformation, and failure modes.

ETD_8655

Ph.D.

Includes bibliographical references

by Ryan Hooke

doi:10.7282/T31J9DZV

ETD doctoral

The author owns the copyright to this work.