Additions of boron in modified titanium alloys and Ti-B composites result in the in situ formation during high temperature processing of TiB reinforcement phases that improve the mechanical properties and wear resistance of unreinforced titanium alloys, while still utilizing the high strength-to-weight ratio and excellent corrosion resistance of titanium. Several boron-modified titanium alloys and Ti-B composites in a Ti-6Al-4V matrix have been investigated to determine the effect of processing parameters on the TiB reinforcement phases and resultant microstructures and mechanical properties. Using optical microscopy, scanning electron microscopy, conventional characterization techniques, and newly developed methodologies for three-dimensional visualization, the microstructures of these Ti-B materials have been studied. Observations included a similar anisotropic whisker morphology with roughly hexagonal cross-sections among all TiB phases; alignment of all TiB phases with extrusion, with the extent of alignment affected by thermomechanical processing parameters; brittle fracture behavior of TiB whiskers, with fracture down the length of whiskers not aligned in the tensile direction and across the width of whiskers aligned in the tensile direction; and discoveries of the anisotropic morphologies of the coarse primary TiB phase and the sub-micron precipitated TiB phase. It has been observed that extruded boron-modified alloys with compositions in the hypoeutectic regime of the quaternary system of titanium, alloying elements aluminum and vanadium, and boron, containing a unimodal size distribution of eutectic TiB whiskers, significantly improve the strength and stiffness compared to unreinforced Ti-6Al-4V alloy while also demonstrating tensile elongation to failure within the fracture-critical limits required for aerospace structural applications. Materials design methodologies have been developed using Ti-B materials, and they show promise for predicting the effects of processing parameters and the resultant microstructures and mechanical properties for boron-modified titanium alloys and Ti-B composites optimized for a variety of commercial and industrial applications.

The central goal of this research is to quantitatively characterize the relationships between processing, microstructure, and mechanical properties of important high-pressure die-cast (HPDC) Mg-alloys. For this purpose, a new digital image processing technique for automatic detection and segmentation of gas and shrinkage pores in the cast microstructure is developed and it is applied to quantitatively characterize the effects of HPDC process parameters on the size distribution and spatial arrangement of porosity. To get better insights into detailed geometry and distribution of porosity and other microstructural features, an efficient and unbiased montage based serial sectioning technique is applied for reconstruction of three-dimensional microstructures. The quantitative microstructural data have been correlated to the HPDC process parameters and the mechanical properties. The analysis has led to hypothesis of formation of new type of shrinkage porosity called, gas induced shrinkage porosity that has been substantiated via simple heat transfer simulations. The presence of inverse surface macrosegregation has been also shown for the first time in the HPDC Mg-alloys. An image analysis based technique has been proposed for simulations of realistic virtual microstructures that have realistic complex pore morphologies. These virtual microstructures can be implemented in the object oriented finite elements framework to model the variability in the fracture sensitive mechanical properties of the HPDC alloys.

A novel and efficient methodology is developed for computer simulations of realistic two-dimensional (2D) and three-dimensional (3D) microstructures. The simulations incorporate realistic 2D and 3D complex morphologies/shapes, spatial patterns, anisotropy, volume fractions, and size distributions of the microstructural features statistically similar to those in the corresponding real microstructures. The methodology permits simulations of sufficiently large 2D as well as 3D microstructural windows that incorporate short-range (on the order of particle/feature size) as well as long-range (hundred times the particle/feature size) microstructural heterogeneities and spatial patterns at high resolution. The utility of the technique has been successfully demonstrated through its application to the 2D microstructures of the constituent particles in wrought Al-alloys, the 3D microstructure of discontinuously reinforced Al-alloy (DRA) composites containing SiC particles that have complex 3D shapes/morphologies and spatial clustering, and 3D microstructure of boron modified Ti-6Al-4V composites containing fine TiB whiskers and coarse primary TiB particles. The simulation parameters are correlated with the materials processing parameters (such as composition, particle size ratio, extrusion ratio, extrusion temperature, etc.), which enables the simulations of rational virtual 3D microstructures for the parametric studies on microstructure-properties relationships. The simulated microstructures have been implemented in the 3D finite-elements (FE)-based framework for simulations of micro-mechanical response and stress-strain curves. Finally, a new unbiased and assumption free dual-scale virtual cycloids probe for estimating surface area of 3D objects constructed by 2D serial section images is also presented.