Additive Manufacturing: Processing, Microstructure and Material Properties of Titanium-based Materials: On-Demand Oral Presentations
Sponsored by: TMS Titanium Committee
Program Organizers: Ulf Ackelid, Freemelt AB; Ola Harrysson, North Carolina State University; Peeyush Nandwana, Oak Ridge National Laboratory; Rongpei Shi, Harbin Institute of Technology
Friday 8:00 AM
October 22, 2021
Room: On-Demand Room 1
Location: MS&T On Demand
Laser Additive Manufacturing Under Reactive Atmosphere: An Approach to Fabricate Ultra-high Strength Commercially Pure Titanium Without Sacrificing Ductility: Dawei Wang1; Yangping Dong1; Ming Yan1; 1Southern University of Science and Technology
This study presents a novel approach for the additive manufacturing (AM) of commercially pure Titanium (CP-Ti). Through introducing the Ar−N2 reactive atmosphere into the laser powder bed fusion (LPBF) processing, the approach confers superb strength to CP-Ti without sacrificing its ductility. A yield strength of 807 MPa combined with a 19.15% elongation-at-fracture has been achieved by incorporating solute atoms from the Ar−N2 atmosphere. The mechanical performance and microstructure of the as-printed CP-Ti have been systematically investigated. Transmission electron microscopy, electron backscatter diffraction, and atom probe tomography have been employed to reveal the in-situ reaction mechanism between CP-Ti and reactive Ar−N2 atmosphere. Results suggest that nitrogen is generally dissolved in the α′-Ti matrix as interstitial solute atoms. The beneficial N content has a critical limit of ~0.43 wt.%. We believe our work has important significance in advancing the applications of CP-Ti/Ti alloys as biomedical or structural materials.
Additive Manufacturing of Shape Memory NiTi Alloys with High Building Rates: Jianing Zhu1; Evgenii Borisov2; Eduard Farber2; Marcel Hermans1; Vera Popovich1; 1Delft University of Technology; 2Peter the Great Saint-Petersburg Polytechnic University
Improving the productivity of Laser Powder Bed Fusion (L-PBF) received a lot of attention in recent years, which can contribute to manufacturing large-scale parts and saving time. The increased laser power improves L-PBF’s building rate, while also increases the risk for the formation of keyhole-induced pores. In this work, we adopt a strategy of coupling the high laser power (950 W) with a large beam size, enabled by implementing laser defocusing, to improve building rates and prevent from defect formation. Processing parameters were optimized based on the processing maps developed from analytical models predicting melt pool dimensions and defect formation criteria. Finally, the high-quality NiTi parts were fabricated with a 240% increase in productivity compared with a relatively low laser power (250 W) and a small beam size.
Influence of Thermal Treatments on the Microstructure and Mechanical Properties of Ti-6Al-4V Built by Electron Beam Melting (EBM): K.S.N. Sesha1; Kenta Yamanaka1; Kenta Aoyagi1; Akihiko Chiba1; 1Institute for Materials Research,Tohoku University
Effect of thermal treatments on the microstructure and mechanical properties of Ti-6Al-4V parts built by electron beam melting (EBM) additive manufacturing were investigated. As-built specimens were heat-treated at 800-980 °C for 2hrs followed by water quenching. As-built specimens showed acicular α phase with a small amount of β phase microstructure. The martensitic transformation from the β phase to α' phase at temperatures above 900 °C, while the retained β phase was observed after quenching from 800 °C and 850 °C. The improved yield strength and tensile strength were observed in specimens heat-treated above 900 ℃, while the lower yield strength and significant work-hardening and enhanced elongation-to-failure were attained in specimens heat-treated at 800 ℃ and 850 ℃. Formation of soft athermal α'' martensite and athermal ω phase was observed in specimen heat-treated at 850 ℃. The Correlation between phase formation and mechanical properties was studied in detail.
Effect of Pores Present in Very Low Volume Fraction on Tensile Properties of Additively Manufactured Titanium Alloys: Pankaj Kumar1; K.S. Ravi Chandran2; 1University of New Mexico; 2University of Utah
Additive manufacturing (AM) has emerged as a technique to manufacture complex geometry components in ready-to-use conditions. However, the major difficulty is the formation of geometrical defects such as pores of varying sizes, but in very low volume fraction, and their effect on the mechanical properties. In this study, the effect of residual pores (volume fraction <1%) on the tensile properties are rationalized by modeling the tensile deformation characteristics in the presence of pores in a PM manufactured Ti-6Al-4V alloy. This study demonstrates that tensile ductility is severely affected by the size of the largest pores present in the volume of the material. The strain localization and crack initiation due to the largest pore, limit the extent of uniform plastic deformation, thus, ductility. A simple analytical model is presented to elucidate how the ductility is influenced by the largest pores present in AM materials.
Surface Analysis and Microstructure Characterization of Electron Beam Melted (EBM) Ti-6Al-4V: Jared Darius1; Daniel Kenney1; Marcos Lugo1; 1Liberty University
Ti-6Al-4V (Ti64) samples obtained by electron beam melting (EBM) are studied to analyze as-built and polished surfaces and characterize the internal microstructure. We investigate the surface roughness, morphology, topography and chemical and phase composition. We first examine the Ti64 powder morphology pre-sintering or melting to characterize average particle size and any unique microstructures. Then the as-built EBM surface is inspected following the standard build procedure but without any machining or mechanical processing of the surface. It shall be noted that the ARCAM EBM machine naturally anneals the specimen at about 800°C during the build process. Next some specimens are machined and polished, and the resulting surface is studied in comparison to the as-built surface. The surfaces are characterized using confocal optical microscopy (including laser topography), scanning electron microscopy, electron dispersive spectroscopy (to verify chemical composition), and contact profilometry for standard measures of surface roughness.
Effect of High Oxygen Content on the Tensile and Fatigue Performance of Selectively Laser Melted (SLM) Ti-6Al-4V in the Hot Isostatic Pressed (HIP) Condition: Anne Osantowski1; Yuwei Zhai1; Oscar Quintana1; Weidong Tong1; 1Depuy Synthes
In this study, tensile and fatigue properties where investigated in SLM Ti-6Al-4V printed vertically and horizontally and in the HIPed condition. High (0.26 wt.%) and low (0.13 wt.%) oxygen contents were investigated. The ultimate tensile strength (UTS), yield strength (YS), and elongation (Elong.%) for low oxygen content samples printed in the vertical and horizontal direction were on average UTS 1037 MPa/YS 938 MPa/Elong.% 16.6, and UTS 1036 MPa/YS 936 MPa/Elong.% 16.9, respectively. For high oxygen content samples printed in the vertical and horizontal directions were on average UTS 1147 MPa/YS 1053 MPa/Elong.% 15.6, and UTS 1148 MPa/YS 1056 MPa/Elong.% 14.9, respectively. Clearly, the high oxygen content samples had higher UTS (p<0.00), YS (p<0.00), and marginally lower elongation (p<0.0002). Fatigue performance was evaluated depending on the oxygen content and metallurgical analysis was evaluated in relation to the mechanical properties.
Microstructural Instability in Additively Manufactured Gamma-TiAl Alloy: Johnson Jacob1; Darren Fraser1; Stefan Gulizia1; 1CSIRO
In this work Ti–48Al–2Cr–2Nb alloy has been manufactured by the Electron Beam Melting (EBM) process with a desire to homogenise the microstructure and avoid cracking. In the case of EBM, it has unique processing characteristics like high preheating temperature and a complex thermal history - a sequence of temperature cycles with a peak value close to the melting point, decreasing in intensity with every additional layer. Microstructural features including lamellar colony size, lamellar thickness and phases present were characterised and correlated to AM conditions and we have shown how it affected the microstructural evolution. A sequential change in composition and morphology was tracked in various layers during the course of EBM, which was identified as being due to microstructural instability of the primary lamellar structure that formed after rapid solidification during the layer by layer deposition.