Nanoparticle Dispersion Mechanisms in Additively Manufactured Metal-matrix Composites and Functionally-graded Materials

Oregon State University, Corvallis OR

Investigators

Abstract

This grant supports research to fill the scientific gap pertaining to full utilization of three-dimensional printing to make metal-matrix composites and functionally-graded materials that either can have a complex composition or spatial gradation in composition. In this work, a metallic alloy is reinforced by nanoparticles delivered by an ink-jet module to a powder bed and fused by a laser beam. The process of jetting nanoparticles and melting with a laser beam is repeated layer-by-layer to create a three-dimensional metal-matrix composite or functionally-graded structure. This research identifies the mechanisms of nanoparticle dispersion and re-distribution inside the melt pool and, after solidification, inside the metallic structure during three-dimensional printing. The research outcomes are used in controlling or varying the composition of the alloy during the build and reducing the number of steps involved in conventional manufacturing of metal-matrix composites and graded structures. The resulting simplification and reduction in time, cost and energy consumption drives transformational change for innovative material designs for high-temperature applications, such as, heat exchangers and combustion chambers, which promote the national economy, drive energy-efficient manufacturing, and secure the national defense. This work contributes to education and outreach through mentoring of undergraduate and graduate students, and engaging high school students with hands-on experience through campus summer programs with focus on increasing and retaining the participation of underrepresented minorities in science, technology, engineering, and math. Current technical and economic challenges in powder-bed fusion additive technologies, such as selective laser melting, prevent adding reinforcement particles to the melt during the build in order to produce metal-matrix composites or varying chemical composition to form functionally-graded alloys. Ball-milling as a means to produce the powder mixture as feedstock for laser powder-bed processes presents nanoparticle dispersion and distribution challenges. Ball-milling changes the morphology of the powder and reduces flow, spreading, packing and wetting behavior leading to higher porosity and cracking in the as-built components. To overcome this challenge, a jetting system is integrated into the powder-bed to selectively and controllably add reinforcement nanoparticles to the laser melt pool. Mechanisms for nanoparticle distribution and redistribution are determined through coupled experiment and sequential reduced-order modeling of the thermal and hydrodynamic phenomena within the nanoparticle-injected melt pool. With increasing reinforcement content, stronger thermo-capillary convection within the melt pool can accelerate the re-arrangement of particles inside the melt pool. This contribution is significant because it is expected to revolutionize the use of selective laser melting as a means of in-situ composition variation and control to achieve targeted microstructures and properties while simplifying manufacturing steps and reducing cycle time and cost. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.