Additive Manufacturing: Processing Effects on Microstructure and Material Performance: Porosity
Sponsored by: TMS: Additive Manufacturing Committee
Program Organizers: Eric Lass, University of Tennessee-Knoxville; Joy Gockel, Wright State University; Emma White, DECHEMA Forschungsinstitut; Richard Fonda, Naval Research Laboratory; Monnamme Tlotleng, University of Johannesburg; Jayme Keist, Pennsylvania State University; Hang Yu, Virginia Polytechnic Institute And State University
Thursday 8:30 AM
February 27, 2020
Room: 6E
Location: San Diego Convention Ctr
Session Chair: Emma White, Ames Laboratory; Jayme Keist, Pennsylvania State University
8:30 AM
Synchrotron Validated Simulations of Pore Formation During Laser Powder Bed Fusion of Nickel Superalloys: Chu Lun Alex Leung1; Dawid Luczyniec2; Enyu Guo3; Sebastian Marussi1; Robert Atwood4; Benjamin Saunders2; Peter Lee1; 1University College London; 2Rolls Royce plc.; 3Dalian University of Technology; 4Diamond Light Source Ltd
The defect evolution mechanisms in powder bed fusion (PBF) additive manufacturing remains unclear owing to the fast laser-material interaction. Here, we reveal defect dynamics inside single-layer Inconel 625 melt tracks during PBF using high-speed synchrotron X-ray radiography (SXR). All melt tracks were post-examined by X-ray computed tomography (XCT). We applied advanced image quantification techniques to extract real-time defect statistics from the SXR data and deduced the melt volume and defect population in 3D from the XCT data. Experimental results were used to inform a 3D multiphase fluid flow simulation, resolving thermophysical phenomena at the solid-liquid-gas interface, from powder melting to material evaporation at high-resolution. The simulation results uncover distinctive melt flow and defect dynamics as well as their influence on track morphology under different build conditions. This study demonstrates that the combination of multiphase model and X-ray imaging can help understand and control the processing effects on microstructure.
8:50 AM
Effect of Process Parameters on the Porosity of IN718 Produced by Laser Powder Bed Fusion: Lonnie Smith1; P. Chris Pistorius1; 1Carnegie Mellon University
Laser powder bed fusion (LPBF) is a major process used to produce additively manufactured parts. One of the main issues with this process is the possibility for introduction of porosity into the parts built. These microscopic holes reduce the overall density of the part and can become sites for crack initiation and fatigue. Therefore, it is important to establish a connection between the process parameters used and the percentage of porosity found within these parts. Using dynamic x-ray radiography (DXR), the porosity of IN718 samples built using an EOS M290 was quantified. Samples were built using process parameters across PV space, including regions of expected keyholing and regions with predicted lack of fusion (LOF) porosity. Data gathered from the reconstructions of samples shows interesting results regarding the operating window of PV space for IN718.
9:10 AM
Strain-age Cracking of Nickel-base Superalloys Processed by Laser Beam Melting: David Grange1; Bruno Macquaire1; Jean-Dominique Bartout1; Christophe Colin1; 1Safran SA
Laser Beam Melting (LBM) offers new possibilities to produce parts with a higher geometrical complexity but also raises new challenges to process materials initially designed for casting. IN738LC is a nickel-base superalloy interesting for its high creep resistance and high temperature corrosion resistance. This alloy is made of an austenitic γ matrix reinforced by a high fraction of 𝛾′ - Ni3 (Al,Ti) precipitates, that confer interesting mechanical properties at high temperatures but that also complicate its shaping by the LBM process. Samples in IN738LC exhibited macroscopic cracks after heat-treatment. Interrupted thermal cycles proved that cracking occurs during the heating phase of the solution heat treatment. Microstructural characterizations and stress measurements with X-ray diffraction allowed to better understand the simultaneous phenomena at stake: precipitation of hard phases, stress relaxation and cracking mechanism. The study is enriched with a comparative microstructural analysis between IN738LC and another material with a close composition.
9:30 AM
Optimization of Pore-free Additive Manufacturing of Composites Utilizing Selective Laser Melting: Eugene Olevsky1; Andrey Maximenko1; 1San Diego State University
Numerical assessment of pore-filling time during Selective Laser Melting (SLM) of metal matrix composites is conducted based on the theory of liquid-phase sintering. Modeling of 3D bi-modal packings of spherical metal and ceramic particles indicates the existence of clusters of ceramic reinforcements with various volume concentrations. During SLM the pores between ceramic particles have to be filled with liquid metal, and the pore-filling duration can be considered to be the minimum necessary time of the successful pore-free SLM processing. Based on the results of the modeling an analytical criterion for the pore-free additive manufacturing of composites utilizing SLM is developed.
9:50 AM
Physics and Comparison of Complex Melt Flow and Defect Formation During Pulsed and Continuous Selective Laser Melting: Ian Mccue1; Steven Storck1; Morgan Trexler1; 1Johns Hopkins University Applied Physics Laboratory
Laser powder bed fusion additive manufacturing is a rapidly growing technology to produce components with unique and complex geometries. However, a major obstacle to its wide-spread use is defect formation during fabrication. High energy densities, fast laser-scan speeds, and rapid cooling can introduce a variety of defects, such as lack-of-fusion and keyhole porosity. It is experimentally challenging to capture defect formation, but significant insights have been garnered using continuum modeling techniques. Here, we use a high fidelity fluid dynamics model – that uses laser ray tracing, recoil pressure, surface tension, and evaporative cooling – to compare and contrast melt pool dynamics during continuous and pulsed selective laser melting. We find that continuous laser scanning produces elongated melt tracks that are susceptible to instabilities within a given melt layer, whereas pulsed laser scanning produces deep melt tracks that are susceptible to defects forming in previously melted layers.
10:10 AM Break
10:30 AM
Quantification of Porosity and Topology Influences on the Mechanical Behavior of Additively Manufactured Metallic Lattice Structures: Behzad Babamiri1; Joe Indeck1; Kavan Hazeli1; 1University of Alabama in Huntsville
The focus of this research is to delineate the interplay between porosity and topology on the mechanical behavior of Additively Manufactured Lattice Structure (AMLS) made of Inconel 718 manufactured using selective laser melting technique with two different topologies: (1) stretching-dominated and (2) bending dominated. In addition, the strain rate effect on the mechanical behavior is investigated. To achieve this, quasi-static and dynamic compression testing was performed on the as-built AMLS-Inconel 718 and the results are compared with stress relieved (SR), hot isostatic pressed (HIP), and HIPed plus solution aged (SA) heat-treatment conditions. X-ray computed tomography was used to map and quantify porosity size and distribution of each heat treatment conditions. As a result, a correlation between underlying microstructure, porosity, topology, and the rate of deformation on the mechanical behavior is established.
10:50 AM
Directed Energy Deposition of Al 5xxx Alloy Using Laser Engineered Net Shaping (LENS®): David Svetlizky1; Baolong Zheng2; Tali Buta1; Yizhang Zhou2; Oz Golan3; Uri Breiman1; Rami Haj-Ali1; Julie Schoenung2; Enrique Lavernia2; Noam Eliaz1; 1Tel Aviv University; 2University of California, Irvine; 3Afeka – Tel-Aviv Academic College of Engineering
Successful additive manufacturing of aluminum-based alloys has focused on near-eutectic AlSi and AlSiMg alloys. Here, we present directed energy deposition of Al 5xxx alloy using Laser Engineered Net Shaping (LENS®). The effect of processing parameters such as powder flow rate and laser scan speed on the density of the material is shown. A relative density higher than 99% was achieved. The pore shape and size distribution are analyzed by X-ray micro-computed tomography (µ-CT). A mean hardness of 65 VHN was measured in as-deposited samples. This value is slightly lower than that of wrought Al 5083, which is attributed to the observed reduction in Mg concentration in the printed material compared to the gas atomized powder feedstock used. The results of tensile tests combined with digital image correlation (DIC) are also reported. This study paves the way for process optimization toward printing of Al 5083 alloy by LENS®.
11:10 AM
Microstructure and Mechanical Properties of Porous Mg Scaffolds Fabricated by Additive Manufacturing for Biomedical Applications: Muzi Li1; Thomas Derra2; Alexander Kopp2; Jon M. Molina-Aldareguía1; Javier Llorca3; 1IMDEA Materials Institute; 2Meotec; 3IMDEA Materials Institute & Technical University of Madrid
Magnesium alloys exhibit promising properties as bone implant materials due to their biodegradability, non-toxicity and mechanical properties. Porous scaffolds are ideal structures for bone regeneration as they allow tissue growth. Lattice structures of Mg-RE alloy with different strut sizes were manufactured by Laser Powder Bed Fusion (LPBF) process. After processing and heat treatments, the lattices were protected against corrosion by plasma electrolytic oxidation. The relationship between processing conditions and the microstructure was carefully analysed by XCT, SEM, EBSD and TEM. In addition, the mechanical properties and the fracture mechanisms were ascertained by means of in situ compression tests within an X-ray µtomography system in lattices that have been immersed in simulated body fluids for different time periods. These results were used to ascertain the influence of processing parameters, lattice dimensions and heat treatments on the mechanical properties and corrosion resistance of lattice structures of Mg-RE alloys manufactured by LPBF.
11:30 AM
From Single Scan Tracks to 3D Samples: Effect of Process Parameters on Quality of Ti-6Al-4V Produced by Means of Direct Energy Deposition: Alessandro Carrozza1; Alberta Aversa1; Federico Mazzucato2; Abdollah Saboori1; Giulio Marchese1; Anna Valente2; Mariangela Lombardi1; Paolo Fino1; Sara Biamino1; 1Politecnico di Torino; 2SUPSI
Direct Energy Deposition (DED) is an additive manufacturing technique suitable for producing big size metallic components and their repairing. Titanium alloys are suited for being processed using this technology, especially Ti-6Al-4V. Different combinations of laser power and scanning speed were used to build single scan tracks to evaluate the most suitable process window for this material. Then geometrical features, for example melt pool height and width, were considered to avoid undesired phenomena, such as keyhole and inter-layer pores formation. Some of the best parameters’ combinations were then used to carry on an in-depth investigation on cubic samples, in which different parameters, related to melt pools interaction, were varied (hatching distance and Z-step). Overall porosity, microstructure and hardness were evaluated to determine final component quality and process feasibility for this alloy. Once determined the optimum combination of parameters, tensile tests were carried out to assess mechanical properties.
11:50 AM
Study on Multiple Beam Interaction for Laser Powder Bed Fusion: Wenxuan Zhang1; Luc Deike1; Craig Arnold1; 1Princeton University
Industrial powder bed fusion techniques often utilize a single laser beam to melt powders, however more recent advances have taken advantage of multiple beams to increase processing speed and control energy input. Despite these developments, there is a lack of fundamental research on how the multiple beams interact with each other to form different molten pools, affecting various performance metrics of the final products. In this work, we use two synchronized laser beams to study the proximity of two melt tracks with different spatial and temporal displacements between the laser beams. In particular, we examine the laser affected areas where two nearby tracks coalesce and where a single track splits into two separate ones. We determine the critical distance required for two melt tracks to merge together and study how the temporal displacement affects the coalescence and splitting behaviors of the two tracks.