Additive Manufacturing of Metals: Complex Microstructures and Architecture Design: Microstructure and Mechanics in Metal AM
Sponsored by: TMS Additive Manufacturing Committee
Program Organizers: Yu Zou, University of Toronto; Hang Yu, Virginia Polytechnic Institute And State University
Tuesday 2:00 PM
November 3, 2020
Room: Virtual Meeting Room 6
Location: MS&T Virtual
Session Chair: Yu Zou, University of Toronto; Hang Yu , Virginia Tech
2:00 PM Invited
Modeling of Grain Growth in Metal Printing: Tarasankar DebRoy1; Tuhin Mukherjee1; 1The Pennsylvania State University
Prediction of grain growth and solidification morphology is important since they affect the mechanical properties of printed metal parts. Here we combine a well-tested 3D heat transfer and fluid flow model with a Monte Carlo method based grain growth model to predict three-dimensional grain structure, texture, columnar to equiaxed transition, and solid-state grain growth during directed energy deposition of nickel alloys. The effects of multiple thermal cycles during the deposition process on the solid-state grain growth are examined through modeling. We explain the origin of spatial non-uniformity of microstructure based on the transient temperature field and molten pool geometry. We also show how modeling can help to predict appropriate processing conditions to achieve customized texture and columnar to equiaxed transition to prevent solidification cracking.
2:40 PM Cancelled
Material Flow and Microstructure Evolution during Additive Friction Stir Deposition: Hang Yu1; 1Virginia Polytechnic Institute and State University
Additive friction stir deposition is an emerging large-scale, solid-state additive manufacturing technology that results in high-quality metals with refined equiaxed microstructures in the as-printed state. The overall thermomechanical history of the deposited material can be divided into three stages, preheating, rapid and severe plastic deformation, and cooling. Extreme thermomechanical processing and intensive material flow occur in the second stage, wherein dynamic phase evolution and dynamic recrystallization are dictated by the interplay of total strain, strain rate, and temperature. In this talk, we characterize the internal material flow during additive friction stir deposition and examine the microstructure evolution along the flow path. Using X-ray tomography and tracer-based feed materials, the 3D shape evolution of the deposited material is revealed with the accumulated strain level estimated. Correlation of the strain and the recrystallized microstructure gives rise to new physical insights into the dynamic microstructure evolution during additive friction stir deposition.
3:10 PM Cancelled
Complex Microstructures in Cold-spray Additive Manufactured Materials: Yu Zou1; 1University of Toronto
Cold spray, initially a coating technique, is being touted as a ‘near-net shape’ manufacturing technology that minimizes material waste by virtue of the high rate of deposition. During the cold spray process, metallic bulk components can be produced by spraying metal powders at high velocity, generating bonding through severe plastic deformation at temperatures well below the melting point of the powders. To fully understand the cold spray processing of metal powders, we systematically compare and study the microstructure evolution in Cu, Ni, Al, Ti, Ti-6Al-4V samples prepared by cold spray using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and nanoindentation. We show complex microstructure in these powder particles after cold spraying: nanocrystalline, nanotwins, annealing twins, gradient grains, deformation bands, dynamic/static recovery and recrystallization. The effects of gas temperature and powder velocity on the microstructure and mechanical properties in the cold sprayed samples are also discussed.
3:40 PM
Cracking in Additively Manufactured Refractory Metals: Elizabeth Ellis1; Yousub Lee1; Michael Kirka1; 1Oak Ridge National Laboratory
Additive manufacturing of refractory metals is an area of growing interest and may open new design avenues in energy production technologies such as nuclear fission and fusion. However, refractory metals such as tungsten and molybdenum are difficult to process using additive techniques due to their high melting point, high thermal conductivity, and brittle nature. While previous work has shown that it is possible to produce fully dense material via additive manufacturing by careful control of process parameters, cracking has proven more difficult to eliminate. In this work, molybdenum is used as a model material to explore cracking behavior in powder bed fusion of refractory metals, with a special focus on electron beam melting. Cracking mechanisms are summarized, and process-structure-property relations exploring the effects of build parameters on cracking behavior are presented. Recommendations for crack reduction in additively manufactured refractory metals are given.