Additive Manufacturing of Metals: Microstructure, Properties and Alloy Development: Additive Manufacturing: Poster Session II
Program Organizers: Prashanth Konda Gokuldoss, Tallinn University Of Technology; Ulf Ackelid, Freemelt AB; Andrzej Wojcieszynski, ATI Specialty Materials; Sudarsanam Babu, University of Tennessee, Knoxville; Ola Harrysson, North Carolina State University

Tuesday 4:45 PM
October 1, 2019
Room: Exhibit Hall CD
Location: Oregon Convention Center

P3-18: Melt Pool Dynamics in Continuous Wave Laser Heating of Bulk and Powder Metal Targets: Deepak Shah1; Alexey Volkov1; 1University of Alabama
    Continuous wave laser heating of metal targets is used in various material processing applications, from deep laser drilling of bulk materials to selective laser melting of powders. In these applications, the complex melt pool shapes are formed and balanced by various interfacial effects, including surface tension, Marangoni stresses, recoil vapor pressure, and material removal due to evaporation. In the present work, the deep laser drilling and selective laser melting of powders are studied using a hybrid numerical method combining smoothed particle hydrodynamics (SPH) for melt pool dynamics and ray tracing (RT) technique for propagation, absorption, and scattering of laser radiation. The transient melt pool shapes and mechanisms of material removal from the molten pool in the targets of stainless steel are studied in single-track simulations as functions of laser intensity, scan speed, beam diameter, and powder particle size. This work is supported by NSF (projects CMMI-1554589 and CMMI-1663364).

P3-20: Off-line Quantification of in-build Cracking Susceptibility during AM Processing: Shubhra Jain1; Timothy Prost2; Ralph Napolitano1; 1Iowa State University; 2Ames Laboratory, DOE
    One of the most important issues currently limiting widespread AM implementation across the broad spectrum of high-performance alloys is the issue of cracking during localized and repetitive melting and freezing. In-build cracking may be attributed to solidification hot-cracking, liquation cracking, transformation-induced cracking, or simply to thermal stress induced cracking. Full-scale build trials are inefficient for alloy/process development, and there is a critical need for a reliable off-line methodology for benchmarking and screening alloys with respect to their potential AM processability. The work presented here involves the use of a new laboratory-scale localized melting method for rapid quantification and benchmarking of the in-build crack susceptibility. Test results are used in conjunction with thermodynamic and microsegregation models to characterize the behavior in various aluminum-based and nickel-based alloys, and relevant comparisons are made with existing models and other microsegregation-based indicators of hot cracking susceptibility.

P3-21: Optimizing Laser Parameters for Selectively Laser Melted Maraging Steel Using Deposited Energy Density: Ryoya Nishida1; Asuka Suzuki1; Naoki Takata1; Makoto Kobashi1; Masaki Kato2; 1Nagoya University; 2Aichi Center for Industry and Science Technology
    The effect of laser power and scan speed on the relative density, melt pool depth, and Vickers hardness of selectively laser melted (SLM) maraging steel were systematically investigated. The change in these structural parameters and hardness could not be always clarified by the volumetric energy density, which is widely used in the SLM processes. The deposited energy density, wherein the thermal diffusion length is considered as a heat-distributed depth, could express the change in these structural parameters and the hardness more precisely. In addition, the fabricated sample exhibited characteristic microstructural morphologies consisting of melt pools corresponding to the locally melted and rapidly solidified regions. The changes in features of developed microstructures (martensite structure and retained austenite) by laser parameters will be presented.

P3-22: Single- and Double-Track Simulations of Melt Flow and Pore Formation in Powder-bed Fusion Additive Manufacturing using Smoothed Particle Hydrodynamics and Ray Tracing: Deepak Shah1; Alexey Volkov1; 1University of Alabama
    Simulations of selective laser melting of metal powder are performed with a novel hybrid computational approach, which combines two-phase smoothed particle hydrodynamics (SPH) for material melting, melt flow, and solidification with ray tracing technique for predicting the laser radiation propagation in the powder. The interfacial terms in the SPH method account for surface tension, Marangoni stresses, recoil effect of vapor pressure, and direct material removal due to evaporation. The melting and solidification are taken into account based on the enthalpy formulation approach. The single- and double-track simulations are performed for powders of stainless steel in broad ranges of particle size dispersion, laser scan speed, and laser power. The conditions leading to the formation of pores due to incomplete melting, as well as due to pore trapping inside the solidified materials after transient collapse of the molten pool, are identified. This work is supported by NSF (projects CMMI-1554589 and CMMI-1663364).

P3-23: The Role of Extraneous Oxygen in the Formation of Oxide Inclusions in Laser Powder Bed Fusion: Pu Deng1; Bart Prorok1; Xiaoyuan Lou1; Vijaya Rangari2; 1Auburn University; 2Tuskegee University
    Oxide inclusions in stainless steel act as initiation sites for microvoids which result in significant effects on mechanical properties particularly, impact toughness. In the case of additive manufacturing (AM) 316L stainless steel, oxide inclusions can nucleate during laser melting and remain in the solidified microstructure. This work is aimed at assessing whether extraneous oxygen in process environment contributes to inclusion formation. The stainless-steel alloy 316L was employed and fabricated under series of different oxygen content environments. The characterization of oxide inclusions in fresh powder and AM processed materiel were conducted using scanning electron microscopy (SEM). Inert gas fusion (IGF) was used to measure oxygen content before and after AM processing. Results indicated that extraneous oxygen from the process environment played a role in oxide inclusion formation. Furthermore, the inclusion size and distribution analyses suggested that the oxide inclusions contained in the fresh powder were melted and regenerated during AM processing.

P3-114: Laser Powder Bed Fusion of Iron-based Bulk Metallic Glass Alloys: Thinh Huynh1; Holden Hyer1; Sharon Park1; Le Zhou1; Yongho Sohn1; 1University of Central Florida
    Additive manufacturing of several iron-based amorphous bulk metallic glass (BMG) and partially amorphous alloys were examined using laser-based powder bed fusion. Given the unique capability of laser-based powder bed fusion including production of complex geometry and rapid cooling rate, ferrous BMGs and ferrous partial BMGs have a good potential to be additively manufactured for engineering applications with due respect for critical thickness associated with cooling rate. In this investigation, characteristics of the as-gas-atomized starting powders were first documented. Then, the buildability/printability of ferrous BMGs and partial BMGs were examined by using SLM 125HL powder bed fusion unit as functions of laser power, laser scan speed, and slice thickness. Results of microstructural characterization will be presented with emphasis on the correlation among the as-built density, flaw formation, amorphousness, sample thickness, and mechanical behavior.