The laminated system processed using FusionTM technology is reported to contain a compositional gradient between the different layers. The interface region exhibits various precipitation characteristic during the subsequent heat treatment. The precipitation behavior at the interface region and core layer of a laminated AA3xxx-AA6xxx alloy system is investigated and discussed. The precipitation hardening capacity at the interface region is shown to scale with the existing compositional gradient. TEM observations reveal the precipitates at the interface region with a larger size and a lower number density than those at the core layer. A yield strength model developed for bulk AA6xxx series is employed to predict precipitate hardening behavior of the laminated sheet, and the modeling result shows an agreement with the measured values using a mass correction. The annealing behavior of the laminated system is investigated in a wide temperature range and at various deformation levels. The size and aspect ratio of the recrystallized grains are found to be determined by the interaction between recrystallization and precipitation, and by dissolution/coarsening of pre-existing precipitates. Under the condition of a low annealing temperature and a high deformation level, recrystallization initiates first at the interface region and then progresses into the core layer along the compositional gradient. The preferential onset of recrystallization at the interface is attributed to a higher driving pressure and a lower Zener drag pressure due to a low volume fraction of precipitates. Nucleation from large particles and grain boundaries is found to be operative nucleation mechanism in this system.

Independent control of the surface and bulk properties is advantageous for many applications such as adhesives, release coatings, and antimicrobial films. Traditional methods for achieving independent control typically require multiple processing steps such as wet-on-wet or wet-on-dry coating methods. Independent control over the surface properties can achieved in a single step utilizing the temporal and spatial control inherent to photopolymerization. Specifically, a co-photopolymerization of monomers with different reactivities in the presence of a light gradient is capable of producing a polymer film with a surface chemistry that differs from the bulk chemistry. The light gradient, produced via the concentration of photoinitiator in the formulation, results in a reaction gradient through the film with the higher rates of reaction occurring in the high light intensity regions of the film. The preferentially reacting monomer adds at a greater rate in the high light intensity regions resulting in non-uniform consumption yielding a concentration gradient. Consequently, diffusion of the preferentially reacting monomer from the bulk to the surface of the film and a counter-diffusion of the other monomer from the surface to the bulk of the film occurs from the non-uniform monomer consumption thus producing a film with a concentration gradient through the depth of the film with the preferentially reacting monomer enriching the high light intensity regions. A variety of kinetic differences capable of producing a stratified film will be presented including inherent monomer reactivity, number of functional groups per monomer, oxygen inhibition, thiol-ene chemistry, and Norrish type two initiation. Additionally, parameters that control the degree of stratification, such as methods of varying polymerization rate and the light gradient, will be examined. Changes in surface properties (such as contact angle, surface hardness, adhesion) and bulk properties (such as mechanical properties measured by dynamic mechanical analysis and polymer swelling) are studied as a function of stratification. Finally, a mathematical model which describes and predicts the production of stratified films via photopolymerization is presented. Photopolymerization allows for a facile, single step method of generating stratified films with controllable surface chemistries.

A compositionally graded Ti-xCr (10≤x≤30 wt%) alloy has been fabricated using Laser Engineered Net Shaping (LENSTM) to study the microstructural phase evolution along a compositional gradient in both as-deposited and heat treated conditions (1000°C followed by furnace cooling or air cooling). The alloys were characterized by SEM BSE imaging, XRD, EBSD, TEM and micro-hardness measurements to determine processing-structure-property relations. For the as-deposited alloy, α-Ti, β-Ti, and TiCr2 (C15 Laves) phases exist in varying phase fractions, which were influential in determining hardness values. With the furnace cooled alloy, there was more homogeneous nucleation of α phase throughout the sample with a larger phase fraction of TiCr2 resulting in increased hardness values. When compared to the air cooled alloy, there was absence of wide scale nucleation of α phase and formation of ω phase within the β phase due to the quicker cooling from elevated temperature. At lower concentrations of Cr, the kinetics resulted in a diffusionless phase transformation of ω phase with increased hardness and a lower phase fraction of TiCr2. In contrast at higher Cr concentrations, α phase separation reaction occurs where the β phase is spinodally decomposed to Cr solute-lean β1 and solute-rich β2 resulting in reduced hardness.