Additive Manufacturing of Metals: Establishing Location-Specific Processing-Microstructure-Property Relationships: Materials, Methods, and Microstructures
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: High Temperature Alloys Committee, TMS: Shaping and Forming Committee, TMS: Additive Manufacturing Bridge Committee
Program Organizers: Eric Lass, NIST; Judy Schneider, University of Alabama-Huntsville; Mark Stoudt, National Institute of Standards and Technology; Lee Semiatin, AFRL; Kinga Unocic, Oak Ridge National Laboratory; Joseph Licavoli, Michigan Technological University; Behrang Poorganji, YTC America Inc.

Monday 8:30 AM
February 27, 2017
Room: 7B
Location: San Diego Convention Ctr

Session Chair: Eric Lass, NIST; Anthony Rollett, Carnegie Mellon University

8:30 AM Introductory Comments

8:35 AM  Invited
Influence of Feedstock Characteristics in Additive Manufacturing: Todd Palmer1; 1Penn State
    Significant efforts are being undertaken to develop process-structure-property (P-S-P) relationships in additive manufacturing (AM) processes to predict localized performance and establish certification protocols for AM components. However, the role of feedstock materials, to include metallic powders and wire, in these P-S-P relationships and the resulting performance of AM components is not well established. Optimized metal powder characteristics, such as size distribution and morphology, are commonly used in traditional press and sinter powder metallurgy processing but are not well defined for either powder bed fusion (PBF) or directed energy deposition (DED) AM processes. Comprehensive relationships identifying powder characteristics directly related to the AM process and resulting performance of components are under development. A review of recent work in this area involving common alloy systems used in both PBF and DED processes is provided as well as an understanding of how powder feedstock fabrication methods impact AM processing and performance

9:05 AM  Invited
The Origin and Effect of HAZ Banding in Large Scale Wire-Arc Additive Manufacture with Ti-6Al-4V: Alistair Ho1; Jack Donoghue1; Thays Machry2; Jialuo Ding3; Filomeno Martina3; Stewart Williams3; Phil Prangnell1; 1The University of Manchester; 2Airbus Group Innovations; 3Cranfield University
    Wire arc-based additive manufacture (WAAM) is a high deposition rate process suitable for building large-scale aerospace components. However, the large heat source and relatively thick layer height can cause significant microstructural heterogeneity. In particular, overlap of the thermal field from sequential passes leads to the formation white etched bands in optical images of the transformation microstructure. The origin of these bands and their consequences for mechanical performance are still not fully understood. In the work presented the local microstructure, texture, phase chemistry and strain distribution across added layers has been studied in the steady state region of a WAAM deposit, using quantitative microstructure data and image correlation. It is shown that the white bands primarily result from variation in composition of the α and β phases, and strain localisation can occur due to the appearance of a local microstructure comprised of larger domains with a single α variant.

9:35 AM  
Investigation on the Effect of Process Parameters on the Grain Structures Formed during Wire-arc Additive Manufacture (WAAM) of 2xxx Series Aluminium Alloys: Joseph Fixter1; Philip Prangnell1; Eloise Eimer2; Jialuo Ding2; Stewart Williams2; 1University of Manchester; 2Cranfield University
    Wire-Arc Additive Manufacturing (WAAM) is highly efficient, can achieve high deposition rates and does not rely on expensive equipment. WAAM thus has the potential to produce large scale, close to net-shape components, with greater design flexibility than conventional processing and at a lower cost than by other AM techniques. However, the deposition of material in layers, involving repeated moving melt pool solidification, can lead to a complex process history and non-ideal heterogeneous microstructures that exhibit microsegregation, columnar grain structures and banded heat affected zones, resulting from the overlapping thermal fields of individual melt tracks. In the work presented the grain structure of aluminium 2xxx series formed in the WAAM process is investigated and the effect of altering the process parameters, such as wire feed speed, energy input and wire travel speed is explored. This is achieved using a variety of techniques such as hardness testing, SEM imaging and EBSD.

9:55 AM  
Investigation into the Different Behavior of Gas and Water Atomized 316L Stainless Steel Powders in Selective Laser Melting: Umberto Scipioni Bertoli1; Alexander Wolfer2; Manyalibo Matthews3; Saad Khairallah3; Kevin Wheeler4; Dogan Timucin4; Jean-Pierre Delplanque2; Julie Schoenung1; 1University of California, Irvine; 2University of California, Davis; 3Lawrence Livermore National Laboratory; 4NASA
    Lower costs due to higher material usage efficiency are among the many advantages of additive manufacturing (AM). The production routes for powders used in AM also play an important role in its overall cost: it is known for instance that water-atomized powders are usually less expensive than gas-atomized powders. Although previous studies suggest that AM parts produced with water-atomized powders have inferior mechanical properties than their gas-atomized counterparts, an in-depth understanding of how different powder characteristics affect laser absorption and melt pool solidification is still lacking. With the help of both experimental and numerical simulation results, we show how the chemical and physical differences between two types of 316L stainless steel powders – one gas- and one water-atomized – influence melt pool behavior and final morphology in single track samples obtained by selective laser melting.

10:15 AM Break

10:35 AM  Invited
Selective Electron Beam Melting: A Powder Bed Based Additive Manufacturing Technology for High Performance Materials: Carolin Körner1; 1Universität Erlangen-Nürnberg
    Generally, additive manufacturing of metallic alloys is focused on selective laser melting (SLM). Selective electron beam melting (SEBM) is an alternative to SLM, where the laser beam is replaced by an electron beam. SEBM works under vacuum conditions at temperatures higher than 1000 °C. Thus, SEBM is especially suitable for high performance materials since it provides perfect protection against contamination. In addition, materials showing a high susceptibility to crack formation can be processed. In this contribution, the characteristics of SEBM are reviewed. The focus will be on the processing of nickel-base superalloys with a high g’-content which are generally hard to weld. Based on experimental and numerical results, the relationship between process, microstructure and resulting properties are discussed. The challenges and prospects of SEBM are critically analysed.

11:05 AM  
Additive Manufacturing of Metals: Differing Microstructures with Varying Builds: Roberta Beal1; Veronica Livescu1; Manny Lovato1; 1Los Alamos National Laboratory
     Additive manufacturing (AM) of metals is attractive due to its customizability, energy efficiency, and lower cost compared with conventional manufacturing methods. AM materials impose a new complexity through the build pattern of the particular additive process used, in addition to the polycrystalline microstructure within that pattern.Significant microstructural differences may be obtained for changes in the deposition process or the shape of the deposited material. This project is aimed at comparing microstructures of stainless steel built using three different deposition methods starting from the same stock powder material. There are several differing possible parameters used in each build process from each site and build direction. Steel samples deposited using LENS, electron beam powder bed, and laser powder bed are used to evaluate microstructural changes depending on deposition process and direction. Post-mortem metallographic analysis will be used to compare each sample microstructure and unveil connections between differing microstructures.

11:25 AM  Invited
Small Features and Microstructures in 3D Printed Heat Exchangers: Samikshya Subedi1; Erfan Rasouli2; Eric Truong2; Vinod Narayanan2; Anthony Rollett1; 1Carnegie Mellon University; 2University of California Davis
    Work is described that is focused on building small heat exchangers in IN718 for use with supercritical CO2. Conventional design is based on diffusion bonding whereas 3D printing allows considerably more freedom of design. The constraints and advantages of additive forming in a laser based powder bed machine are described, as they influence the changes in design that have been implemented. Residual stress is significant, for example. The current limits of resolution are described in terms of the smallest feature that can be built such as thin columns or tubes. The microstructures exhibit irregular grain shapes, low densities of annealing twins and substantial orientation gradients. Overall it is already clear that additive printing of small heat exchangers is a viable forming route.

11:55 AM  
Fundamental Study of the Effect of Process Variables in LMD Repairs with Inconel 718: Faye McCarthy1; Chris Heason2; Gavin Baxter2; Phil Prangnell1; 1The University of Manchester; 2Rolls Royce Plc
    Laser Metal Deposition is an attractive process for repair of aerospace components. To optimise the quality of repaired parts it is essential to understand the effect of the process conditions on the microstructure of the deposited material, which is controlled by the local solidification conditions and thermal history the material experiences. Here, work has been carried out to study the effect of process parameters on the melt pool size and shape, powder capture efficiency, and microstructure of single and multiple overlapping LMD tracks. The data has been used to fit an FE model to the melt pool profile which has subsequently been used to understand the effects of raster strategy and sample geometry. This has revealed that there is a significant influence of beam path and sample edge, in thin walled components, on the melt pool surface and consequently the local grain structure that develops during solidification.