Multi-material Additive Manufacturing: Processing and Heterogeneous Materials Design: AM of Functionally Graded & Dissimilar Materials
Sponsored by: TMS Additive Manufacturing Committee
Program Organizers: Hang Yu, Virginia Polytechnic Institute And State University; Steven Boles, Hong Kong Polytechnic University; Michael Gibson, Desktop Metal; Lonnie Love, Oak Ridge National Laboratory; Leon Prentice, SDI Ltd

Wednesday 2:00 PM
November 4, 2020
Room: Virtual Meeting Room 5
Location: MS&T Virtual


2:00 PM  Invited
Experimental -- Computational Approach for The Design of Functionally Graded Materials by Additive Manufacturing: Allison Beese1; Zi-Kui Liu1; Brandon Bocklund1; Lourdes Bobbio1; 1Pennsylvania State University
    Directed energy deposition (DED) additive manufacturing (AM) can be used to fabricate compositionally graded functionally graded materials (FGMs) by varying the volume fractions of powder metal feedstock fed into the melt pool during fabrication. However, when grading between dissimilar alloys or metals, detrimental phases (e.g., brittle intermetallics) may form, resulting in weak location within the FGM or complete failure of the FGM by cracking. This talk will detail our approach for combining experiments and computations to develop and validate computational databases and modeling tools needed to design FGMs that avoid detrimental compositions. Both equilibrium and Scheil solidification calculations for phase prediction were performed, and the limitations of equilibrium calculations as well as benefits of Scheil solidification calculations will be discussed in light of their ability to predict the experimentally observed phases in a Ti to Invar-36 FGM and a Ti-6Al-4V to Invar FGM.

2:30 PM  Cancelled
Gradient Microstructure and Local Mechanical Properties of a γ-TiAl/〖Ti〗_2AlNb Dual Alloy Produced by Laser Direct Metal Deposition: Haoxiu Chen1; Yu Zou1; 1University of Toronto
    TiAl/Ti_2AlNb dual alloys exhibit potential applications on aerocraftengines, but manufacturing of such alloys needs to achieve an appropriate gradient transition between these two alloys. Here, we deposited γ-TiAl alloy on a Ti_2AlNb substrate using the direct metal deposition (DMD) technique and analyzed their graded zone near the interface. Our results show that the transition zone mainly consists of three characteristic layers: the first layer possesses a small amountof α_2, B_2 and γ phases dispreading in the β matrix. In the the second layer, directional dendrites (α_2 phases as dendrite core and γ phases as dendrite arms) are developed in β matrix. The third layer exhibits equiaxial (α_2+ γ) colony with fully lamellar microstructure, which is similar to the microstructure of the γ-TiAl alloy. We also preformed nanoindentation tests on different phases and layers to revel their mechanical properties. The relationship between nanoindentation results and characteristic microstructure has been identified.

2:50 PM  
Additive Manufacturing Design of Functionally Graded Materials: Noah Sargent1; Xin Wang1; Kun Li1; Wei Xiong1; 1University of Pittsburgh
    Directed Energy Deposition is one of the powder-based additive manufacturing techniques with the advantage of fabricating Functionally Graded Materials (FGMs) through a dynamic variation of composition in consecutive layers along the building direction. FGMs have recently gained attention for their potential to enhance the performance of components that require a combination of material properties not available in traditional monolithic alloys. While the concept of FGMs shows promise, difficulties combining dissimilar materials such as segregation of alloying elements, residual stress, and precipitation of brittle intermetallic phases have limited their application. In this work, (CALPHAD-based: CALculation of PHAse Diagrams, ICME: Integrated Computational Materials Engineering) modeling techniques are used to design FGMs. Two case studies on SS316/HSLA (Stainless Steel 316/High Strength Low Alloy Steel) and Steel/Superalloy FGMs will be presented.

3:10 PM  
Precision Forming of FGMs via Directed Energy Deposition and Alloy Development Feeder: Kevin Luo1; 1FormAlloy
    Directed Energy Deposition (DED) has long been a technology suited for the formation of functionally graded material (FGM) systems due to its ability to use multiple materials within the same build, open source parameters, and low material consumption. However, combining dissimilar materials can be a challenge. To reduce residual stresses between the materials, a gradient transition can be used. In the past, the DED process relied on on-the-fly blending or introducing additional feeder to deposit the transitions. But for intricate transitions, this is not a viable long term solution. With that in mind, FormAlloy developed their ADF Alloy Development Feeder. Within the ADF, up to 16 different compositions can be deposited quickly. A revolver style hopper systems enables rapid transition from 1 hopper to another, and feeder operation features help prevent cross-contamination between materials. Discover how the ADF and DED process looks to provide the means for detailed FGM systems.

3:30 PM  
Wire-arc Additive Manufacturing of Inconel 740H Superalloy – P91 Steel Bimetallic Structures: Microstructure Characterization and Post-Heat Treatment Design: Soumya Sridar1; Xin Wang1; Michael Klecka2; Wei Xiong1; 1University of Pittsburgh; 2United Technologies Research Center
    Multi-material structures with varying functionality can offer unique solutions to engineering problems. However, joining two materials using additive manufacturing involves perplexing challenges such as cracking and segregation. In this study, bimetallic structures of Inconel 740H (IN740H) superalloy and P91 steel were fabricated using wire-arc additive manufacturing. The gradient zone was found to be devoid of any deleterious phases. Intergranular cracks were observed in the gradient zone if P91 is printed on top of IN740H, possibly due to the mismatch in thermal conductivity. Therefore, the deposition of IN740H over P91 is the optimum printing sequence for obtaining a defect-free build without an observable brittle phase. Further, the post-heat treatment schedule was designed for IN740H deposited over P91, using experiments and thermodynamic calculations.