Sudarsanam S Babu

Sudarsanam S Babu
University of Tennessee | UTK · Department of Mechanical, Aerospace and Biomedical Engineering

PhD

About

432
Publications
114,631
Reads
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14,717
Citations
Citations since 2016
119 Research Items
10696 Citations
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201620172018201920202021202205001,0001,5002,000
201620172018201920202021202205001,0001,5002,000
Additional affiliations
July 2013 - present
The University of Tennessee Medical Center at Knoxville
Position
  • UT/ORNL Governor's Chair and Professor

Publications

Publications (432)
Article
Magnitude and distribution of residual stresses in additively manufactured Ni-based superalloys may impact the mechanical performance of as-fabricated parts. Though electron beam powder bed fusion (E-PBF) can produce components with minimal defects and residual stresses compared to laser powder bed fusion and directed energy deposition, variations...
Article
In nature, materials and designs are smart i.e., they achieve the desired shape or size to optimize different processes without needing external devices. However, in the design of mechanical metallic structures, gaining such behavior without using special materials or external sources is still a visionary thought. Here the concept of lifelike metal...
Article
A unique microstructural feature often referred to as “fish-scale” has been reported in 316L austenitic stainless steel parts made by laser powder bed fusion (L-PBF) technique. Because the final microstructure is predominantly austenitic, with a face-centered cubic (γ-fcc) crystal structure, the “fish-scale” structures were originally assumed to be...
Article
Full-text available
Fluctuations in energy distribution during additive manufacturing (AM) can result in spatial and temporal thermal transients. These transients can lead to complexities, most significantly when alloys with multi phases are subjected to AM. Here we unveil such complexities in a duplex stainless steel, where we report an unanticipated formation of a N...
Article
A major goal in printing soft magnetic Fe-Si steels using additive manufacturing is to take advantage of the potential for complex geometric designs and site-specific grain control. One major step in the processing of these alloys is understanding how processing parameters might impact how the as-built microstructure responds to annealing (i.e. the...
Article
Fluctuating energy distributions experienced during Additive Manufacturing yield an evolution of spatial and temporal transients within a part. In general, the in-situ monitoring of these transients is near to impossible during manufacturing. In order to then gain perspective into the impact on these localized thermo-mechanical transients on the in...
Article
Full-text available
While there exists in nature abundant examples of materials with site-specific gradients in microstructures and properties, engineers and designers have traditionally used monolithic materials with discrete properties. Now, however, additive manufacturing (AM) offers the possibility of creating structures that mimic some aspects of nature. One exam...
Chapter
This article introduces the definition of metal manufacturing with an overview of the different processes. Then, a case study is presented to illustrate the methodology for selecting appropriate process by asking series of questions based on the Heilmeier Catechism, data from published literature and legacy knowledge. A case study is presented whic...
Article
Full-text available
Research on powder-based additive manufacturing of aluminium alloys is rapidly increasing, and recent breakthroughs in printing of defect-free parts promise substantial movement beyond traditional Al–Si–Mg) systems. One potential technological advantage of aluminium additive manufacturing, however, has received little attention: the design of alloy...
Article
Spatial control of microstructure within a three-dimensional component has been a dream of materials scientists for centuries. However, limitations in traditional manufacturing processes prevent detailed control over the distribution of microstructures in a single part. Here, we demonstrate the ability to control grain structure and crystallographi...
Article
Electron beam powder bed fusion (E-PBF) can produce nickel-based superalloy components with minimal cracking and post-processing. This is due to the reduced thermal gradients and high print temperatures accessible through innovative beam scanning strategies compared to other AM processes. However, variations in thermal signature along the build dir...
Article
The design of additively manufactured metallic alloys with tailored mechanical properties requires a detailed understanding of the microstructural evolution throughout the printing process. In Ti-6Al-4V, this involves a complex combination of phase transformations, leading to microstructural and property variations within a single as-fabricated bui...
Article
Dissimilar metal welds (DMWs) made between ferritic steels and austenitic alloys are used extensively in high-temperature power plant components. These DMWs experience premature creep failure in the ferritic steel’s heat affected zone (HAZ), close to the weld interface. Steep variations in microstructure and chemical composition across the dissimil...
Article
Full-text available
Additive manufacturing of aluminum alloys is largely dominated by a near-eutectic Al-Si compositions, which are highly weldable, but have mechanical properties that are not competitive with conventional wrought Al alloys. In addition, there is a need for new Al alloys with improved high temperature properties and thermal stability for applications...
Article
Samples of aluminum alloy 6061 produced via ultrasonic additive manufacturing (UAM) were irradiated in the High Flux Isotope Reactor (HFIR) up to 17.3 dpa at ∼70°C while in contact with water using perforated rabbit capsules. The irradiation campaign included as-received (AR) material, specimens subjected to various post-weld heat treatments (PWHTs...
Article
This paper reports evidence for enhanced elemental interdiffusion during ultrasonic additive manufacturing (UAM) across metal boundaries of copper-aluminum, nickel-gold, and nickel-gold-aluminum. The high solute interdiffusion measured by energy dispersive X-ray spectroscopy line scans is rationalized with calculated vacancy concentrations orders o...
Article
This research paper evaluated three pathways for qualification of 316L stainless steel components made by laser powder bed fusion additive manufacturing (AM). Comprehensive and consistent process flows with computational modeling, in-situ measurements, ex-situ characterization and mechanical testing with simple- and complex- geometries were explore...
Article
Distortion and residual stresses are major challenges that limit the ability to fabricate large scale structures using Additive Manufacturing (AM). Researchers worldwide are evaluating techniques to induce compressive residual stress in the parts via intermittent rolling. While reasonable success has been documented, the idea of lowering the marten...
Chapter
Manufacturing based on thermo-mechanical processing (TMP) is critical to many of the engineered products. In this article, the evolution of TMP processes is discussed from the historical perspective based on early days of processing steels and solid-state joining. Then, TMP is discussed as an industrial system with sub-systems based on material fee...
Chapter
Alloy design is an important step in realizing the optimal microstructure in a manufactured metallic component. Attaining the right microstructure distribution within a component is necessary for ensuring mechanical and functional performances that is expected in service. The inspiration for alloy design by empirical experimental observations has a...
Article
Full-text available
This work investigated the linear thermal expansion properties of a multi-material specimen fabricated with Invar M93 and A36 steel. A sequence of tests was performed to investigate the viability of additively manufactured Invar M93 for lowering the coefficient of thermal expansion (CTE) in multi-material part tooling. Invar beads were additively m...
Article
Full-text available
Published literature shows defect formation during laser powder bed fusion additive manufacturing (AM) of nickel base superalloys are sensitive to alloy chemistry, processing conditions, and geometry. In this work, ability to detect spatial distributions of defects is explored using in-situ monitoring of thermal signatures and surfaces. Simple and...
Article
There is a synergy between welding and additive manufacturing with reference to spatial and temporal variations of heat transfer. In this research, in-situ measurements of heat transfer conditions are considered as a viable qualification methodology for additive manufacturing (AM). Infrared imaging (IR) was performed within a laser powder bed fusio...
Article
As an effective dimension reduction and feature extraction technique, manifold learning has been successfully applied to high-dimensional data analysis. With the rapid development of sensor technology, a large amount of high dimensional data such as image streams can be easily available. Thus, a promising application of manifold learning is in the...
Article
Additive manufacturing (AM) promises a major transformation for manufacturing of metallic components for aerospace, medical, nuclear, and energy applications. This perspective paper addresses some of the opportunities for alloy and feedstock design to achieve site-specific and enhanced properties not attainable by conventional manufacturing process...
Article
Full-text available
Additive manufacturing is a promising alternative method for fabricating components of Ni-based superalloys which are difficult to cast, form and join. However, typical thermal cycles associated with laser powder bed-fusion techniques suppress the formation of desirable microstructures containing γ′ particles, necessitating long-time post-process h...
Article
The Effect of Beam Scan Strategies on the Microstructure of EBM Additively Manufactured Inconel 738 - Chris Blackwell, Meiyue Shao, Sriram Vijayan, Sabina Kumar, Sudarsanam Babu, Joerg Jinschek
Article
To understand the process-microstructure relationships in additive manufacturing (AM), it is necessary to predict the solidification characteristics in the melt pool. The present study investigates the influence of Marangoni driven fluid flow on the predicted melt pool geometry and solidification dynamics using a continuum finite volume model (FVM)...
Article
Metallic materials produced by additive manufacturing experience complex stress and thermal gyrations along the build direction. This has the potential to produce complicated heterogeneous microstructures that may exhibit a wide variety of mechanical properties. There remains a paucity of studies on the nature and the formation mechanisms of the mi...
Article
Ultrasonic additive manufacturing (UAM) is a solid-state 3D printing technology. Steels can be welded with UAM at reduced ultrasonic power, achieving half the shear strength of bulk material. A higher weld power is demonstrated by using a cobalt-based sonotrode coating, achieving shear strengths comparable to bulk 4130 material. In-situ temperature...
Article
Recent results have shown that the strength of resistance spot-welded joints made from advanced high-strength steels (AHSS) do not increase linearly with their base metal strength. While the martensite tempering and subsequent softening in a narrow heat affected zone (HAZ) of these joints has been reported as a primary cause for this degradation, t...
Article
Spatter particles, created during laser powder-bed-fusion (L-PBF) additive manufacturing process of 316 L stainless steel, solidified as single-crystal, non-equilibrium, body-centered cubic (BCC) ferrite, which has not been reported before. This phenomenon is unusual considering that the composition of stainless steel 316 L typically ensures primar...
Article
Traditionally, reactive gases such as oxygen (O2) and carbon dioxide (CO2) have been avoided during laser powder bed fusion (L-PBF) of metals and alloys based on the notion that it may lead to defect formation and poor properties. Here we show that instead, these gases can be used to form sub-µm-sized oxide particles in-situ during the L-PBF proces...
Article
Full-text available
This paper focuses on the mechanisms of phase transformations in additively manufactured Ti–6Al–4V during cooling. In particular, the goal is to understand if the imposed thermal cycles during fabrication results in the complete transformation of the α′ to the β phase or the sub-transus decomposition of α′ (martensite) to α + β. To this effect, sam...
Article
Effects of local plastic instabilities in the form of yield point phenomena (YPP) were investigated on local and global deformation and failure behavior of resistance spot-welded tension–shear (TS) samples made from M1700 advanced high-strength steel (AHSS) by means of finite element (FE) simulations. Material models with and without YPP were used...
Article
Recycling metal powders in the Additive Manufacturing (AM) process is an important consideration in affordability with reference to traditional manufacturing. Metal powder recyclability has been studied before with respect to change in chemical composition of powders, effect on mechanical properties of produced parts, effect on flowability of powde...
Article
The Fe–Cr–Al–Nb ferritic alloys strengthened by A2B Laves phases, with superior oxidation and corrosion resistance, are being considered for high temperature operation within fossil-fired steam power plants to increase process efficiency and reduce CO2 emissions. In this study, new sets of alloys based on Fe–30Cr–3Al–1Nb (in weight percent) were de...
Article
Ultrasonic additive manufacturing (UAM) is a solid-state manufacturing technology for producing near-net shape metallic parts combining additive ultrasonic metal welding and subtractive machining. Even though UAM has been demonstrated to produce robust metal builds in Al–Al, Al–Ti, Al-steel, Cu–Cu, Al–Cu, and other material systems, UAM welding of...
Article
Quantitative Study on the Effect of Thermal Gradients on the Microstructure of Additively Manufactured Ti-6Al-4V Builds - Volume 25 Supplement - Meiyue Shao, Chris Blackwell, Sriram Vijayan, Sabina Kumar, Sudarsanam S. Babu, Joerg R. Jinschek
Article
Graded Microstructure of Additive Manufactured Ti-6Al-4V via Electron Beam Melting - Volume 25 Supplement - Hansheng Chen, Christopher Cooper, Cameron Durrant, Yingluo Li, Sophie Primig, Xiaozhou Liao, Sudarsanam Suresh Babu, Simon P. Ringer
Article
Titanium carbide-nickel aluminide (TiC-NixAly) intermetallic matrix composite materials were fabricated with additive manufacturing and pressureless melt infiltration for applications intended for high-wear and corrosive environments while maintaining low density. Here, two compositions of nickel aluminide are infiltrated into porous, printed TiC p...
Article
Additively manufactured Ti-6Al-4V has columnar β grains along the build direction with a 〈001〉 fiber texture. Because of Burgers Orientation Relationship, the resulting α phase becomes textured albeit less strongly than the β phase. Microtexture zones have been identified in the α phase in laser-based systems. There have been limited studies on α p...
Article
Ultrasonic additive manufacturing (UAM) is a solid-state manufacturing process for making complex components. However, fabrication of ferritic (body centered cubic) steels has been challenging for UAM due to its high hardness. This research successfully joined AISI 4130 steel sheets by using soft Ni (face centered cubic) interlayers. The localisati...
Article
Full-text available
Atom probe tomography (APT) has been used to understand the redistribution of solutes during the isothermal cascading phase transformations from supersaturated austenite resulting in the formation of inverse bainite. Different cascading reactions resulting in the formation of inverse bainite, namely the cementite midrib formation, ferrite formation...
Article
Full-text available
Recent publications have shown that the load-bearing capability of advanced high-strength steel (AHSS) spot welds do not scale linearly with the tensile strength of the base metal. Although this unexpected degradation of welds has been linked to the tempering of the martensite phase in the heat-affected zone (HAZ), the detailed elastic–plastic stre...
Article
Traditional design and qualification methodologies for parts manufactured by traditional methods are being applied to Additive Manufacturing (AM) without understanding the nuances of the machines. While mapping process variables and tracking build data is helpful, some variables such as build geometry, support structure, and part melt order have no...
Article
Dissimilar metal welds between ferritic and austenitic alloys are common in high-temperature applications in the energy industry. Under service conditions, these welds experience carbon diffusion and concomitant detrimental microstructural changes that can render them susceptible to premature creep failure. Therefore, it is helpful to identify a fi...
Article
Dissimilar Metal Welds (DMWs) made between ferritic low alloy steels and austenitic alloys are widely used in high temperature components of nuclear and fossil energy power plants. Literature shows that these bimetallic welds fail prematurely by creep mechanism close to the interface of the ferritic (BCC) and austenitic regions (FCC), with lifetime...
Article
Carbon diffusion and the associated microstructural changes in dissimilar metal welds at elevated temperatures lead to a microstructure that is susceptible to premature failure. Graded transition joints (GTJs) can potentially provide a viable replacement to prolong the service life of these components. The purpose of the current investigation is to...
Article
Full-text available
Additive manufacturing (AM) is being considered as a primary manufacturing process for heat pipes. The Savannah River National Laboratory is researching AM to fabricate a hydrogen isotope separation unit for a thermal cycling absorption process that cycles from cryogenic to moderate temperatures and is a pressure boundary. AM is being explored as a...
Article
In laser powder bed additive manufacturing processes, feedstock materials are often recycled after each build. Currently, a knowledge gap exists regarding powder reuse effects on powder size distribution, morphology, and chemistry as a function of part geometry and processing conditions. It was found during selective laser melting (SLM) of 316 stai...
Article
This paper presents recent developments in statistical image processing to demonstrate feasibility of layer-by-layer nondestructive inspection for selective laser melting (SLM) of metallic parts. A matrix of 10 mm × 10 mm stainless 316 squares was deposited with the first row consisting of just the sintered surface, Row 2 a single layer, Row 3 with...
Article
Solidification conditions experienced during Selective-Electron Beam Melting (S-EBM) of Nickel-Base superalloys generally lead to epitaxial grain growth from previous layers, resulting in highly textured columnar grain structures, and consequently, highly anisotropic mechanical properties. However, in recent work, researchers have been able to prod...
Article
Purpose The purpose of this paper is to introduce the multi-solution nature of topology optimization (TO) as a design tool for additive manufacturing (AM). The sensitivity of topologically optimized parts and manufacturing constraints to the initial starting point of the optimization process leading to structures with equivalent performance is expl...
Preprint
Full-text available
Resistance spot welds made from Advanced High Strength Steels (AHSS) exhibit Heat Affected Zone (HAZ) softening due to the tempering of pre-existing martensite phase and the consequent decomposition into a mixture of ferrite and cementite. Despite the high strength level for the base metal, the occurrence of HAZ softening may lead to inferior joint...
Article
Components made by laser powder bed fusion (L-PBF) additive processes require extensive trial and error optimization to minimize defects and arrive at targeted microstructure and properties. In this work, in situ infrared thermography and ex situ surface roughness measurements were explored as methodologies to ensure Inconel® 718-part quality. For...
Article
High gamma prime (γ′) nickel-based alloys produced by selective electron beam melting are of interest to the turbine industry which requires control of microstructure in relation to loading conditions within complex component geometry. Welding literature predicts cracking and microstructure evolution as a function of alloy composition and process p...
Article
In-situ TEM Heating Experiment to Study Effects of Cyclic Thermal Gradients on Ti-6Al-4V under Additive Manufacturing Growth Conditions - Volume 24 Supplement - Meiyue Shao, Cheng-Han Li, Curtis L. Frederick, Sudarsanam S. Babu, Joerg R. Jinschek
Article
A metallic hybrid structure, consisting of an Inconel-718 matrix and a Co-Cr internal structure, was successfully manufactured using laser direct energy deposition process. Characterizations were performed using energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), neutron-computed tomography (nCT), and electron back-scatter diffraction (E...
Article
In the electron beam powder bed fusion (EB-PBF) process, a substantial number of high-gamma prime Ni-based superalloys are considered as non-printable due to a high propensity to form cracks. In this research, we focused on computational modeling framework to predict solidification-related cracking phenomena in EB-PBF processes. The cracking analys...
Article
Full-text available
Quenching and partitioning (Q&P) and a novel combined process of hot straining (HS) and Q&P (HSQ&P) treatments have been applied to a TRIP-assisted steel in a Gleeble®3S50 thermomechanical simulator. The heat treatments involved intercritical annealing at 800 °C and a two-step Q&P heat treatment with a partitioning time of 100 seconds at 400 °C. Th...
Article
Full-text available
Near-net fabrication techniques are highly beneficial to minimize rare earth metal usage to fabricate dense fully functional magnets. In this study, feasibility of using the directed-energy deposition technique for fabrication of magnets is evaluated. The results show that despite the ability to fabricate highly reactive materials in the laser depo...
Article
Innovative designs for turbines can be achieved by advances in nickel-based superalloys and manufacturing methods, including the adoption of additive manufacturing. In this regard, selective electron beam melting (SEBM) and selective laser melting (SLM) of nickel-based superalloys do provide distinct advantages. Furthermore, the direct energy depos...
Conference Paper
This paper overviews recent advances in developing novel alloy design concepts of creep-resistant, alumina-forming Fe-base alloys, including both ferritic and austenitic steels, for high-temperature structural applications in fossil-fired power generation systems. Protective, external alumina-scales offer improved oxidation resistance compared to c...