Additive Manufacturing of Metals: Complex Microstructures and Architecture Design: Microstructure Evolution and Control
Sponsored by: TMS Additive Manufacturing Committee
Program Organizers: Yu Zou, University of Toronto; Hang Yu, Virginia Polytechnic Institute And State University
Wednesday 8:00 AM
November 4, 2020
Room: Virtual Meeting Room 6
Location: MS&T Virtual
Session Chair: Matteo Seita , Nanyang Technological University; Christian Leinenbach, EMPA
8:00 AM Invited
Alloy and Process Modification for Microstructure Control in Additively Manufactured Alloys: Christian Leinenbach1; Seth Griffiths1; Anthony De Luca1; Ariyan Arabi-Hashemi1; 1Empa, Swiss Federal Laboratories for Materials Science and Technology
Up until now, most of AM-related research has been focused on the optimization of the process parameters with the goal to produce equiaxed and defect-free microstructures. Only recently, several re-searchers started to study how the microstructure in AM fabricated parts can be manipulated by modifying the composition of the alloys.In this presentation, we will demonstrate how the combination of alloy and process modification can be used to manipulate the phase and microstructure formation and thus the properties of parts fabricated by laser powder bed fusion (LPBF). In particular, we will summarize the results of some ongoing projects at Empa such as the microstructure formation and manipulation during LPBF of a novel high-strength Al alloys, the site-specific control of microstructure and magnetic properties in a high-nitrogen stainless steel by in-situ alloy modification, or the mitigation of cracks in a Ni superalloy.
8:30 AM Invited
Engineering the Plasticity of SLM Steel via Crystallographic Texture Control: Sudarshan Raman1; Karl Sofinowski1; Matteo Seita1; 1Nanyang Technological University
Owing to its unique capability of forming materials point by point, at high spatial resolution, additive manufacturing enables the production of metal parts with spatially-varying microstructures. By controlling the distribution of different microstructures in the build, it is possible to produce materials with enhanced structural properties. In this work, we manipulate the local directional solidification of material during selective laser melting (SLM) to print near-single crystal "blocks" with specific textures. The blocks can be arranged to create builds with site-specific texture and properties. We apply this strategy to control where plastic deformation initiates in SLM-produced bars of 316L steel. The results demonstrate that this strategy can be used to produce damage-tolerant structures. The strategy may also be extended to exploit other material properties that are affected by texture, such as corrosion resistance, fatigue strength, and magnetic susceptibility.
9:00 AM
Microstructure of Alloy 247LC Manufactured by Laser Powder Bed Fusion: Olutayo Adegoke1; Joel Andersson1; Robert Pederson1; Håkan Brodin1; 1University West
Alloy 247LC is a γ’ precipitation strengthening nickel-based superalloy which displays cracks during laser powder bed fusion (L-PBF). More research is needed for increasing the understanding of the microstructure in order to solve this problem. This study presents the influence of process parameters on the microstructure and defects in L-PBF manufactured Alloy 247LC. High energy density, for example high laser power, low scanning speed and low hatch distance, produced high crack density. Low energy density produced high void content. High resolution scanning electron microscopy (SEM) of as-built samples displayed cell structures of approximately 400 nm. These cell structures have bright microconstituents containing mainly Hf and Ta in between the boundaries. γ’ was not observed in the as-built condition but may be present due to the relatively high hardness obtained. After hot isostatic pressing (HIP) the cracks were closed and relatively large γ’ was revealed. The γ’ reduced in size and displayed adequate hardening after solution heat treatment and ageing.
9:20 AM
Evaluation of Microstructure in Multi Bead Ti-6Al-4V: Amaranth Karra1; Ali Guzel1; Hangman Chen1; Amit Kumar Verma1; Anthony D. Rollett1; 1Carnegie Mellon University
Ti-6Al-4V printed by laser-hot-wire robotic welding is used for calibrating a model predict the properties based on machine parameters and this contains the thermal, microstructural and strength mode. Different geometries such as multi-beads, T-sections and overhangs produces different thermal histories. The microstructure contains fine Widmanstätten colony and basketweave α with coarse columnar β grains. The thermal cycles produced by multiple passes result in approximately equidistant bands and a transient region in the top. This work primarily quantified the banding and α morphologies using optical and scanning electron microscopy. XRD was used for the variation of c/a ratio and lattice parameters. An automated technique was developed using python to calculate α lath thickness from SEM images. The results of, and methodology developed for data acquisition and analysis will be discussed.