Advanced Solid Phase Processing Symposium: Additive Approaches
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Mechanical Behavior of Materials Committee, TMS: Shaping and Forming Committee
Program Organizers: Suveen Mathaudhu, Colorado School of Mines; Cynthia Powell, Pacific Northwest National Laboratory; Kester Clarke, Los Alamos National Laboratory; Anthony Reynolds, University of South Carolina; Mostafa Hassani, Cornell University

Tuesday 2:00 PM
February 25, 2020
Room: Balboa
Location: Marriott Marquis Hotel

Session Chair: Mostafa Hassani, Cornell University; Paul Allison, University of Alabama


2:00 PM  Invited
Fatigue Mechanisms of Aluminum Alloys Fabricated by Additive Friction Stir Deposition: Ben Ruthford1; Dustin Avery1; Luke Brewer1; Paul Allison1; J. Brian Jordon1; 1University of Alabama
    Additive manufacturing is generally associated with powder-based beam melting or sintering methods. However, recent innovations in solid phase additive methods such as additive friction stir deposition (AFS-D) provide unique capabilities to additively repair or manufacture new components. The AFS-D process is a novel method that exploits high-shear and severe plastic deformation to produce fully-dense, near net-shape structures with wrought-like properties. While the feasibility of the AFS-D process has been demonstrated on various materials, the fatigue mechanisms of this new manufacturing process remains largely unknown. As such, in this talk, we present an in-depth investigation of the fatigue mechanisms of 6xxx and 7xxx aluminum alloys fabricated from the AFS-D process. In particular, fatigue crack nucleation and crack propagation mechanisms associated with the longitudinal and build directions of the AFS-D process are discussed. In addition, the effect of heat treatment on fatigue behavior is also presented.

2:25 PM  Invited
Smoothed Particle Hydrodynamic Simulations of Solid-phase AA6061 Additive Friction Stir Depositions: George Stubblefield1; Kirk Fraser2; B. J. Phillips1; D. Z. Avery1; N. Zhu1; Luke Brewer1; J. Brian Jordon1; Paul Allison1; 1University of Alabama; 2National Research Council Canada
    Additive Friction Stir-Deposition (AFS-Deposition) provides a rapid, flexible, and robust metal recycling option that may be applied to manufacture large-scale multi-material components and/or repair damaged structures (i.e. vehicles, armor systems, etc.). AFS-Deposition is a solid-phase process negating normal issues associated with fusion-based processes, such as porosity and hot cracking. Here, the first simulations of the process are presented, which are crucial to elucidate the thermomechanical processing during depositions. Computer simulations quickly reveal important information such as temperature gradients and grain morphology. However, due to the excessive deformation in the AFS-Deposition process, traditional finite element schemes are insufficient. In this work, a meshfree coupled thermomechanical approach is used to model the AFS-Deposition process. The meshfree method, Smoothed Particle Hydrodynamics (SPH), is used to discretize the set of continuum conservation equations. Simulation results from over-fed, optimal, and starved builds are compared to real-time temperature experimental data and X-ray residual stress data.

2:50 PM  
Microstructure and Mechanical Properties of Solid-State Additive Friction Stir Processed Alloy 600 on 304L Stainless Steel: Biswajit Dalai1; Jie Song2; Syeda Somaiya2; Benjamin Sutton3; Nicholas Mohr3; Seetha Mannava2; Matthew Steiner2; Vijay Vasudevan2; 1Lulea University of Technology; 2University of Cincinnati; 3EPRI
    Additive Friction Stir (AFS), also called MELD, is a novel, high deposition, solid state additive manufacturing process developed that is receiving considerable interest and attention for additive manufacturing of metallic materials with refined microstructures and enhanced mechanical properties. In this study, alloy 600 claddings on 304L stainless steel were produced using controlled process parameters and the microstructure (gran size, texture, etc) characterized using an arsenal of electron microscopy tools. The residual stress distributions, hardness and mechanical properties were also characterized. The results show that AFS leads to refined hierarchically graded microstructures and exceptional mechanical properties, which will be presented and discussed.

3:10 PM  
Advances in Deformation and Microstructure Evolution Understanding in Additive Friction Stir Deposition: Robert Griffiths1; Mackenzie Perry1; David Garcia1; Jenny Sietins2; Yunhui Zhu1; Hang Yu1; 1Virginia Polytechnic Institute; 2Army Research Laboratories
    Additive Friction Stir Deposition (AFSD) is a solid-state additive manufacturing process that can be used to deposit metals and composites in a freeform near-net shaping manner. Similar to other friction stir processes, there is a work space or “stir zone” within which material undergoes severe plastic deformation. However, during AFSD, this work space has different constraints than other friction stir processes, resulting in different directions and rates for material flow. Understanding the key behavior of material deformation and flow is vital for process optimization. Several key concepts are discussed including: material flow paths, tooling influence, resulting interfaces and part quality, and variability with material chemistry. X-ray computed tomography is employed to identify the material flow path and characterize the interfacial mixing; electron backscattered diffraction coupled with rapid cooling is used to identify localized strain and deformation during AFSD; high speed imaging is used to characterize the surface material flow .

3:30 PM Break

3:50 PM  Invited
Elucidating the Role of Flash Heating in Ultrasonic Consolidation of Powder and Foils: Zachary Cordero1; Austin Ward1; 1Rice University
    Ultrasonic consolidation of powders and foils is a promising approach for manufacturing bulk materials with non-equilibrium structures and exotic properties. In this processing route, a punch presses on the feedstock and oscillates at ultrasonic frequencies perpendicular to the loading axis. These ultrasonic vibrations shear the surface asperities and disrupt the oxide overlayer on the feedstock to achieve metallurgical bonding. The ultrasonic vibrations have been observed to decrease the flow stress of the feedstock, making it easier for the feedstock to bond under a low normal stress; however, the physical mechanism that drives this softening is still a matter of debate. Some researchers attribute softening to frictional heating while others argue for an acoustic softening effect where elastic waves increase the mobility of glissile dislocations. Here we resolve this controversy by combining heat transfer theory and plasticity models to show that flash heating drives junction growth in ultrasonic consolidation processes.

4:15 PM  
In-situ Studies of Impact-Induced Deformation and Solid-State Bonding in Cold Spray: Mostafa Hassani1; David Veysset2; Keith Nelson2; Christopher Schuh2; 1Cornell University; 2Massachusetts Institute of Technology
    Solid phase processes have garnered increasing attention in the domain of metal processing. They can not only bypass metallurgical constraints and challenges associated with melt-based processing approaches but also lead to enhanced mechanical properties compared to the melt-based counterparts. Cold spray is one of the emerging solid phase processes with applications in structural coatings, structural repair, and additive manufacturing. In cold spray supersonic impacts of power particles induce extreme conditions of strain rate, pressure, and shear at the contacting interfaces the result of which is solid-state bonding at micron scale. This talk will survey our work using an in-situ platform to study impact and bonding of individual powder particles and the associated phenomena in real time. We discuss new insights on impact-induced bonding mechanism, adiabatic plastic deformation, jetting, and microstructural evolution at the interfaces. We review in detail the conditions under which we observe solid-state bonding, impact-induced melting and erosion.

4:35 PM  
Designer Additive Manufacturing Powders for Solid State Additive Manufacturing Processing: Kyle Tsaknopoulos1; Jack Grubbs1; Danielle Cote1; 1Worcester Polytechnic Institute
    Commercially available powders designed specifically for additive manufacturing (AM) are becoming more ubiquitous. In an effort to determine if these designer alloys are also advantageous to use for non-traditional AM processes, such as the solid-state cold spray process, research was conducted using various AM designed alloys as feedstock. As powder properties are a function of their internal microstructure, it is therefore important to understand the microstructure in order to optimize the properties of the final parts. Powder properties can be controlled through the use of thermal treatment and analyzed through microstructural evolution. Heat treated AM powder was also tested as feedstock for the cold spray process. The internal microstructure of the feedstock powder was analyzed using scanning and transmitting electron microscopy, energy dispersive x-ray spectroscopy, and nanoindentation and guided through the use of computational thermodynamic and kinetic models. Mechanical properties were also determined.

4:55 PM  
Laser Assisted Cold Spray of AISI 4340: Dallin Barton1; Venkata Satish Bhattiprolu1; Clio Batali1; Gregory Thompson1; Luke Brewer1; 1University of Alabama
    This presentation will discuss cold spray deposition of ferritic AISI 4340 steel through the assistance of in situ laser heating. Cold spray is widely applied to additive repair and manufacturing of metallic components, but good deposition efficiency and quality are difficult to achieve in high-strength materials because of the powder’s inability to undergo sufficient deformation upon impact. We have combined high-pressure helium gas cold spray with a 4 kW, infrared laser under closed-loop feedback control to enhance the spray characteristics of 4340 steel. Laser assisted cold spray (LACS) was able to successfully deposit 4340 steel powders into a fully-consolidated material. Substantial increases in mass deposition efficiency were observed as a function of increasing surface temperature. Using electron microscopy, we are examining the changes in material microstructure as a function of heat input during LACS, including the amount of martensite formed.