Ultrafine-grained and Heterostructured Materials (UFGH XII): Processing, Microstructure & Property I
Sponsored by: TMS: Shaping and Forming Committee
Program Organizers: Penghui Cao, University of California, Irvine; Xiaoxu Huang, Chongqing University; Enrique Lavernia, University of California, Irvine; Xiaozhou Liao, University of Sydney; Lee Semiatin, MRL Materials Resources LLC; Nobuhiro Tsuji, Kyoto University; Caizhi Zhou, University of South Carolina; Yuntian Zhu, City University of Hong Kong

Wednesday 2:00 PM
March 2, 2022
Room: 262A
Location: Anaheim Convention Center

Session Chair: Megumi Kawasaki, Oregon State University; Klaus-Dieter Liss, Guangdong Technion – Israel Institute of Technology; Hang Yu, Virginia Polytechnic Institute and State University

2:00 PM  Invited
Solid-state Additive Manufacturing of Ultrafine-grained Alloys via Additive Friction Stir Deposition : Hang Yu1; Hunter Rauch; 1Virginia Polytechnic Institute and State University
    Offering a deformation processing route to metal additive manufacturing, additive friction stir deposition is able to produce fully-dense, ultrafine-grained alloys with wrought-like mechanical properties in the as-printed state. Compared to other solid-state metal additive manufacturing technologies, which only involve local deformation, here the plastic deformation is global: the entire feed material undergoes severe plastic deformation at elevated temperatures. This leads to dynamic recrystallization during printing, resulting in a relatively uniform and significantly refined microstructure. In this presentation, I will provide an overview of the process-microstructure linkages for several alloys in additive friction stir deposition, such as Al, Cu, Ti, and steel. We show that the contact state at the tool-material interface and the material intrinsic properties, such as stacking fault energy, govern the recrystallization type (i.e., continuous or discontinuous) and texture development. Ultrafine grained alloys with complex hierarchical microstructures can be printed by engineering the mesostructure of the feed material.

2:30 PM  
Influence of Strain Gradients in Heterostructured Nanomaterials: Daniel Goodelman1; Andrea Hodge1; 1University of Southern California
    Heterostructured nanomaterials have been shown to be a promising solution for the age-old strength-ductility tradeoff issue. Since these materials feature both hard and soft domains that deform at different rates, a plastic gradient is formed that enhances strain hardening. Recently, we have shown that these materials demonstrate complex microstructures after heat treatment, specifically in Inconel 725. Several features such as abnormally large grains sandwiched between nanocrystalline and nanotwinned regions, as well as delta phase, rafted structures, and precipitates were observed. It is expected that the strain gradient in the film drives the mechanisms that lead to such complexity. However, the details of the strain gradient have yet to be fully understood. In this work, nanotwinned Inconel 725 films were synthesized using magnetron sputtering techniques to understand the effect of strain gradients within the film. Extensive characterization before and after heat treatment is evaluated for microstructural complexity for various strain values.

2:50 PM  
Control of Layer Instabilities during ARB Processing of Iron-based FCC/BCC Metallic Laminates: Thomas Nizolek1; Rodney McCabe1; Cody Miller1; Yifan Zhang1; Nan Li1; Daniel Coughlin2; John Carpenter1; 1Los Alamos National Laboratory; 2United States Steel Corporation
    Accumulative roll bonding (ARB) is a severe plastic deformation technique capable of producing bimetallic laminates with layer thicknesses ranging from the millimeter scale to the sub-micron scale. However, in order to enable refinement of the layered structure to the nanoscale, it is necessary to preserve layer continuity and the associated constraints on co-deformation during processing. Here we show that ARB processed iron-copper, iron-silver, and iron-aluminum laminates all exhibit layer length scale instabilities, including necking and shear banding, at ARB processing strains between 2.2 and 4.5. The effects of ARB process modifications, including intermediate annealing steps, on the microstructure, phase-resolved mechanical properties as determined through nanoindentation, and flow stability of these laminates will be discussed. Ultimately, for the iron-copper and iron-silver systems, ARB synthesis routes are obtained that preserve layer continuity by minimizing constituent phase flow-stress mismatch, allowing material with sub-100 nanometers layer thicknesses to be produced.

3:10 PM  
Effect of Nanostructuring in Additive-manufactured 316L Stainless Steel on Structural Relaxation Examined by In-situ Heating Neutron Diffraction Analysis: Jae-Kyung Han1; Xiaojing Liu2; Yusuke Onuki3; Yulia Kuzminova4; Stanislav Evlashin4; Klaus-Dieter Liss2; Megumi Kawasaki1; 1Oregon State University; 2Guangdong Technion - Israel Institute of Technology; 3Ibaraki University; 4Skolkovo Institute of Science and Technology
    The present report describes the structural changes and relaxation upon heating in an additive-manufactured 316L stainless steel examined by in-situ heating neutron diffraction analysis after nanostructuring by high-pressure torsion. The nanostructured austenitic steel with an average grain size of 60 nm improves the Vickers microhardness to HV = 500 which is twice higher than the as-printed sample. The in-situ examination provides linear thermal lattice expansion and stress relaxation of the material during heating. Together with ex-situ hardness testing, the structural relaxation behaviors upon heating of the austenitic steel are observed in a sequence of (i) recovery with slow strain relaxation up to 873K, (ii) recrystallization with accelerated strain relaxation at 873-973K, and (iii) grain growth above 973K with completing strain relaxation in lattices up to 1023K. The present in-situ heating neutron diffraction analysis successfully visualizes the sequential structural evolution in the additive-manufactured 316L stainless steel on time and temperature scales.