Automated image mapping and quantification of microstructure heterogeneity in additive manufactured Ti6Al4V

Zhao, Hao; Ho, Alistair; Davis, Alec; Antonysamy, Alphons Anandaraj; Prangnell, P.B.

doi:10.1016/j.matchar.2018.10.027

Cited by 32 publications

(22 citation statements)

References 40 publications

(157 reference statements)

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“…[3][4][5] In the WAAM process, following each deposition pass, the solidified material below the fusion zone is heated to above the b-transus temperature to a depth equivalent to that of about 4 to 5 added layers and transforms on cooling to a basket weave lamellar a microstructure, with a small volume fraction of retained b. [6,7] There is also typically a thin layer of grain boundary a which delineates the prior b-grain boundaries. Heat-affected zone (HAZ) bands, associated with a temperature rise from re-heating in the range from above~800°C to the b-transus temperature (~980°C [6] ), are also generated by each heat source pass.…”

Section: B Waam Microstructuresmentioning

confidence: 99%

The Effectiveness of Grain Refinement by Machine Hammer Peening in High Deposition Rate Wire-Arc AM Ti-6Al-4V

Hönnige

Davis

et al. 2020

Metall Mater Trans A

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Surface deformation, applied in-process by machine hammer peening (MHP), has the potential to refine the coarse columnar b-grain structures normally found in high deposition rate Wire-Arc Additive Manufacturing (WAAM) processes with Ti alloys like Ti-6Al-4V. Effective refinement, as well as a reduction in texture strength, has been achieved in relatively thick sections and to a depth that is greater than that expected from the surface deformation induced by MHP. By application of MHP to each deposition track, the average b-grain size could be reduced from cm's to less than 0.5 mm. Systematic experiments have been performed to investigate the origin of this interesting effect, which included 'stop-action' trials and separation of the strain and temperature gradients induced by the two process steps. The maximum depth of the plastic deformation from MHP required to generate new b-grain orientations was determined by electron backscatter diffraction local average misorientation analysis to be < 0.5 mm, which was less than the melt pool depth in the WAAM process. Nevertheless, new b-grain orientations were observed to form within the peened layer ahead of the approaching heat source as the peak temperature rose above the b transus, which then grew into the less deformed core of the wall as the temperature rose. This allowed the new grain orientations to penetrate deeper than the melt pool depth and survive to act as substrates for epitaxial growth at the fusion boundary during solidification, resulting in significant grain refinement.

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Section: B Waam Microstructuresmentioning

confidence: 99%

The Effectiveness of Grain Refinement by Machine Hammer Peening in High Deposition Rate Wire-Arc AM Ti-6Al-4V

Hönnige

Davis

et al. 2020

Metall Mater Trans A

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“…Ti6Al4V is designed for a good balance of strength, ductility, fatigue and fracture properties. Ti6Al4V has been used as an important structural material in advanced aircraft since the 1960s [14]. Nippon Steel and the Sumitomo Metal Corporation acquired qualifications in 1985 from Rolls-Royce and started commercial production of titanium alloys for aircraft engines.…”

Section: General Informationmentioning

confidence: 99%

“…Alloying elements in titanium can be categorized into α-stabilizers, β-stabilizers or neutral additions, depending on which phase the elements tend to stabilize, or whether they effectively increase or decrease the solid-state α-β transus temperature of titanium [14]. α-stabilizers, including the substitutional element (aluminum) and the interstitial elements (oxygen, nitrogen and carbon), strongly increase the threshold temperature at which the α phase is stable, even if the solute content increases.…”

Section: Crystal Structurementioning

confidence: 99%

“…β-stabilizers, including isomorphous elements (vanadium, molybdenum, niobium and tantalum) and eutectoid elements (ferrous, manganese, chromium and nickel), stabilize the β phase at lower temperatures. In addition, some neutral elements (zirconium, hafnium and tin) have no significant influence on the β transus temperature [14,17].…”

Section: Crystal Structurementioning

confidence: 99%

“…The addition of alloying elements to Ti leads to an increase of the β transus temperature from 882 • C of pure titanium to 980 • C, and approximately 9 ± 2 wt.% of the β phase is retained at room temperature. The majority of the diffusion transformation occurs within the temperature range between 850 and 950 • C at a transformation cooling rate between 5 and 50 • C/s [14]…”

Section: Crystal Structurementioning

confidence: 99%

See 2 more Smart Citations

Laser Metal Deposition of Ti6Al4V—A Brief Review

et al. 2020

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Laser metal deposition (LMD) is one of the most important laser additive manufacturing processes. It can be used to produce functional coatings, to repair damaged parts and to manufacture metal components. Ti6Al4V is one of the most commonly used titanium alloys, since it features a good balance of the mechanical properties of strength and ductility. The LMD of Ti6Al4V is attracting more and more attention from both science and engineering. The interest in processing Ti6Al4V with LMD in industry, especially in aerospace and medical branches, has been increasing in the last few years. In this paper, the state of the art for LMD of Ti6Al4V is reviewed. In the first part, the basics for Ti6Al4V, including, for example, the development history, the material properties, the applications, the crystal structure, the heat treatment and the mechanical properties, are introduced. In the second part, the main emphasis is on state of the art for LMD of Ti6Al4V. Initially, the process parameters of the current state of the art in the last years and their effects are summarized. After that, the typical microstructure after LMD is discussed. Then, the conducted heat treatment methods and the achievable mechanical properties are presented. In the end, some of the existing, current challenges are mentioned, and the possible research directions for the future are proposed.

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Data‐driven modeling of heterogeneous viscoelastic biofilms

Matouš

Nerenberg

2022

Biotech & Bioengineering

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Biofilms are typically heterogeneous in morphology, structure, and composition, resulting in nonuniform mechanical properties. The distribution of mechanical properties, in turn, determines the biofilm behavior, such as deformation and detachment. Most biofilm models neglect biofilm heterogeneity, especially at the microscale. In this study, an image‐based modeling approach was developed to transform two‐dimensional optical coherence tomography (OCT) biofilm images to a pixel‐scale non‐Newtonian viscosity map of the biofilm. The map was calibrated using the bulk viscosity data from rheometer tests, based on assumed maximum and minimum viscosities and a relationship between OCT image intensity signals and non‐Newtonian viscosity. While not quantitatively measuring biofilm viscosity for each pixel, it allows a rational spatial allocation of viscosities within the biofilm: areas with lower cell density, for example, voids, are assigned lower viscosities, and areas with high cell densities are assigned higher viscosities. The spatial distribution of non‐Newtonian viscosity was applied in an established Oldroyd‐B constitutive model and implemented using the phase‐field continuum approach for the deformation and stress analysis. The heterogeneous model was able to predict deformations more accurately than a homogenous one. Stress distribution in the heterogeneous biofilm displayed better characteristics than that in the homogeneous one, because it is highly dependent on the viscosity distribution. This study, using a pixel‐scale, image‐based approach to map the mechanical heterogeneity of biofilms for computational deformation and stress analysis, provides a novel modeling approach that allows the consideration of biofilm structural and mechanical heterogeneity. Future research should better characterize the relationship between OCT signal and viscosity, and consider other constitutive models for biofilm mechanical behavior.

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Automated image mapping and quantification of microstructure heterogeneity in additive manufactured Ti6Al4V

Cited by 32 publications

References 40 publications

The Effectiveness of Grain Refinement by Machine Hammer Peening in High Deposition Rate Wire-Arc AM Ti-6Al-4V

The Effectiveness of Grain Refinement by Machine Hammer Peening in High Deposition Rate Wire-Arc AM Ti-6Al-4V

Laser Metal Deposition of Ti6Al4V—A Brief Review

Data‐driven modeling of heterogeneous viscoelastic biofilms

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