In-situ Visualization and Modeling of Microstructure Evolution in Metallic Alloys under Additive Manufacturing Conditions

A.J. Clarke, Colorado School of Mines (Principal Investigator)

A. Karma, Northeastern University (Co-Principal Investigator)

Many potential benefits exist to using additive manufacturing (AM) - also known as three-dimensional (3D) printing - for making metal parts, rather than conventional manufacturing processes. AM is highly customizable, can produce complex structures, and can be used for the economical production of low numbers of metal components. To achieve the strict specifications needed for some applications, the microscopic structure of printed metal objects must be controlled. Also, 3D printing is still in its infancy. There is a need for new approaches that combine AM with other processing methods to provide flexible architectural control over a wide range of length scales, from the nanoscale up to the macroscale, of AM builds. This project seeks to enhance our understanding of the relationships between the structure of materials produced by AM, which determine material properties, and the methods by which those materials are processed. The research uses a combination of novel experiments and state-of-the-art computational models that provide unprecedented capabilities to visualize and predict microstructural development. The experiments are performed both in the laboratory and at U.S. DOE national user facilities using thin films and bulk samples in binary and ternary alloys. Three main aims are being pursued. The first aim is to gain novel insights into fundamental mechanisms of microstructure formation under conditions far from thermodynamic equilibrium associated with the high solidification rates of AM processes with particular focus on dendrite orientation transitions and grain texture evolution. The second aim is to unambiguously determine the genesis of grain refinement, by constitutional supercooling during solidification or by eutectoid formation in the solid state during thermal cycling in Ti-Cu-based alloys designed for AM. The third aim is to explore a new, promising avenue that combines AM and dealloying for scalable manufacturing of nanocomposites. This builds upon preliminary computational modeling results that reveal rapid melting and re-solidification of a single-phase intermetallic provides a powerful new dealloying method to make nanoscale interpenetrating-phase bi-continuous structures for typical AM melting conditions. This combined AM-dealloying approach will be investigated in a variety of experimental configurations that explore both fundamental aspects of the dealloying process under far from equilibrium conditions and the scalability of this approach for practical applications.