Additive Manufacturing of Titanium-based Materials: Processing, Microstructure and Material Properties: Ti-processing
Program Organizers: Ulf Ackelid, Freemelt AB; Ola Harrysson, North Carolina State University
Wednesday 2:00 PM
October 12, 2022
Room: 305
Location: David L. Lawrence Convention Center
Session Chair: Sneha Prabha, Carnegie Mellon University
2:00 PM Cancelled
Correlating Laser Based Powder Bed Processing Conditions to the Fatigue Behavior of Additively Manufactured Ti-6Al-4V with As-built Surfaces: Jayme Keist1; Nickolas Sotiropoulos1; Scott Tokarz1; Edward Reutzel1; 1Pennsylvania State University
The fatigue of additively manufactured (AM) Ti-6Al-4V components varies widely depending on the surface condition. Although AM within a powder bed fusion (PBF) process allows for greater design freedom, the presence of as-built surfaces makes components prone to premature failure. Therefore, machining is usually employed to help improve the fatigue performance. Machining all surfaces, however, may be unrealistic for components with complicated geometries and with internal features. Instead, optimizing the PBF processing conditions can help improve the resulting fatigue performance of components with as-built surfaces. In this research, the impact of processing conditions such as layer thickness and contour scanning strategies were investigated on the resulting roughness and high cycle fatigue performance. In addition, the resulting surface roughness was also correlated with the build angle. Critical processing parameters and build design considerations were revealed that could be optimized to assure improved fatigue performance for components with as-built surfaces.
2:20 PM
Direct-Ink Writing of Hierarchically Porous Titanium for Enhanced Osseointegration: John Misiaszek1; David Dunand1; 1Northwestern University
Titanium has experienced clinical success as a bone implant material due to its high fracture toughness, excellent corrosion resistance, and favorable biological integration properties. However, titanium has demonstrated drawbacks in implant reliability via stress shielding and poor osseointegration. In this work, direct-ink writing (DIW) of a Ti + NaCl powder blend - followed by dissolution of NaCl space holder and Ti powder sintering – generates microlattices with porous struts. The millimeter-wide channels within the printed lattice (macroporosity) allows for nutrient transport and vasculature growth; the space-holder microporosity within the struts provides a size (~100 m), roughness, and morphology enabling colonization of osteoblastic cells, thus increasing osseointegration while also reducing implant stiffness (and stress shielding), e.g., for the application of intervertebral implants.
2:40 PM
Effect of Surface Finish on Fatigue Behavior of Laser Powder Bed Fusion Processed Hydride-Dehydride Ti-6Al-4V Powder: Mohammadreza Asherloo1; Ziheng Wu2; Muktesh Paliwal3; Anthony Rollett2; Amir Mostafaei1; 1Illinois Institute of Technology; 2Carnegie Mellon University; 3Kymera International
Non-spherical hydride-dehydride Ti-6Al-4V powder with particle size distribution of 50-120 μm is used for additive manufacturing parts using optimum processing parameters in laser powder bed fusion to achieve a relative density of >99.9%. Microstructural observations are performed and show a columnar and equiaxed grain structure in vertical and horizontal cross-sections, respectively. Surface roughness measurement show an average roughness of Ra = 15.71±3.96 μm in the as-build specimens, while the mechanically ground surfaces show an average roughness of Ra = 0.19±0.04 μm. Fatigue tests results show comparable fatigue life with spherical powders, and fractography analyses show crack initiation from the rough surface in the as-built specimens, while the subsurface defects in the mechanically ground specimens are responsible for crack initiation and failure. μ-CT results show transition of inner large pores to subsurface region after the mechanical griding, which acts as stress concentrators and decrease fatigue life of mechanically ground samples under high stress amplitude.
3:00 PM
Influence of Substrate Condition and Initial Residual Stresses on Wire Fed Electron Beam Additive Deposition: Fatih Sikan1; Priti Wanjara2; Javad Gholipour Baradari2; Mathieu Brochu1; 1McGill University; 2National Research Council Canada
Additive repair of aerospace components is gaining ever-increasing attention due to strategic material cost and manufacturing sustainability issues. This research evaluated the feasibility of an experimentally simulated electron beam wire fed (EBWF) additive repair using Ti-6Al-4V thin walls (3 mm) to emulate fan blade repair. The focus of this work was to understand the effect of the initial substrate microstructure and residual stress profile on the final deposit properties. The research included several substrate sample conditions with different initial microstructures and residual stress profiles that were manufactured by both additive and conventional manufacturing methods. Residual stress and distortion profiles of each substrate condition were analyzed pre-and-post-EBWF deposition. Alterations in the grain structure of the substrate plates were investigated through microstructural characterization. Mechanical properties and deformation behaviors were characterized to allow a comprehensive understanding of the inter-relationships between process, structure, and performance.
3:20 PM Break
3:40 PM
Modelling the Additive Manufacturing of a Titanium-based Hip Implant: Lakshana Mohee1; 1ANSYS Granta
Ti64 is one of the optimal materials used for producing hip implants and additive manufacturing (AM) can facilitate the production of such patient-specific medical devices, providing precision-fitting and reducing post-operative problems. Metal AM, however, is expensive and in-silico testing is increasingly used as a cost-effective and time saving alternative to physical experiments, helping to print-first-time-right. Our proposition is hence the development of an innovative finite-element modelling framework in which the geometry of the Ti-based implant is topologically optimized first to achieve light-weighting. This work will then explore the effect of processing parameters and build setup on the stress and distortion generated during the AM process, as well as the possibility of build failure. We will finally explore an AM digitalization strategy in which using a data management platform can help in capturing, structuring and then capitalizing on the vast amount of material and process data generated in the AM process.
4:00 PM
Process Window Approach for Qualification of Laser Powder Bed Fusion: Anthony Rollett1; Jack Beuth1; John Lewandowski2; Sneha Narra1; Kenji Shimada1; Craig Brice3; Frank Medina4; Ryan Wicker4; Elizabeth Holm1; Albert To5; Kirk Rogers6; Ayman Salem7; 1Carnegie Mellon University; 2Case Western University; 3Colorado School of Mines; 4University of Texas El Paso; 5University of Pittsburgh; 6Barnes Global Advisors; 7Materials Resources LLC
Under support from the NASA ULI program, CMU has partnered with other institutions and companies to develop a qualification methodology for Laser Powder Bed Fusion (LPBF) based on determining a process window (PW) for Ti-6Al-4V. The PW is based on a space of the main parameters such as power, speed, hatch etc. Fatigue samples have been printed in multiple printers at three different universities, as well as a NASA research center. The PW is quantified via porosity and 4-point bend fatigue, both of which show PW boundaries for keyhole and lack-of-fusion porosity and a minimum porosity approximately in the center of the PW. Although fatigue cracks normally start at defects, for optimal printing conditions, cracks instead start in a microstructural feature. The methodology has been transferred successfully to a small company printing an advanced aluminum alloy.
4:20 PM
Role of Build Orientation and Layers on Microstructure and Multi-scale Mechanical Properties of Wire Arc Additive Manufactured Commercially Pure Titanium: Tanaji Paul1; Blanca Palacios1; Tyler Dolmetsch1; Cheng Zhang1; Benjamin Boesl1; Arvind Agarwal1; 1Florida International University
Wire arc additive manufacturing (WAAM) is a promising technology for manufacturing large scale structural components with complex geometries. However, a dearth of understanding of the dependence of their structure and mechanical performance on the build orientation and additive layers restricts WAAM of metallic structures. This paper presents a comprehensive understanding of the structure and mechanical properties in WAAM-ed commercially pure titanium in three mutually orthogonal build directions. A bimodal structure, with grain sizes in the range of 100 micrometer to 1.5 mm resulted in a microhardness of 166 HV, about 80% of cast titanium. Tensile strength was weakest in the normal direction due to residual heat from pre-solidified layers. These correlations of microstructure and multi-scale mechanical properties as a function of WAAM build routine is a significant advancement in the large-scale additive manufacturing of commercially pure titanium structural components.
4:40 PM
Spatially Resolving Structure-Behavior Relations in Additive Manufactured Adaptive Materials: Arnab Chatterjee1; Reginald Hamilton1; 1Penn State
Shape Memory Alloys (SMAs) are a class of adaptive materials that undergo reversible solid state crystallographic and microstructural phase change with the application of stress or temperature. Conventional fabrication generates a uniform alloy structure to customize SMA response. In this work, we fabricated Nickel-Titanium based SMAs using the now well-known advanced fabrication method, additive manufacturing (AM). The layer-by-layer manufacturing allows customizing extrinsic geometrical shapes and dimensional scales and intrinsic composition and structure. We employ the Laser Directed Energy Deposition (LDED) AM technique using pre-blended elemental powder feedstock for depositing NiTi SMAs with Titanium-rich composition. As a result of layer/pass wise buildup, the intrinsic structural scales will vary spatially. We spatially resolve structure-behavior relations using a combined study of X-Ray and electron diffraction, optical microscopy, and microhardness. Signatures of layer/pass wise build are revealed and we produce spatial maps for contrasting the degree heterogeneity of differential LDED AM build plans.
5:00 PM
Manipulating Fatigue Life in L-PBF with Contour Control: Christian Gobert1; Austin Ngo2; David Scannapieco2; John Lewandowski2; Jack Beuth1; 1Carnegie Mellon University; 2Case Western Reserve University
Poor fatigue life of laser powder bed fusion (L-PBF) components limits complete adoption for aerospace applications. Contour scan vectors in L-PBF print at or near the free surface of parts, a fatigue critical zone, and can therefore influence component fatigue life.In this research the influence of developed contour strategies on TiAl6V4 4-pt bend fatigue specimens is studied. Designed contour strategies were parameterized with respect to remelt width-into-part and depth, defining a contour remelt zone. Cross-section optical microscopy was used to observe porosity content of contour remelt zones. To isolate the impact of contour selection and remelt zone size on fatigue life,various surface finishes and infill strategies were incorporated during testing.