Controlling interdependent meso-nanosecond dynamics and defect generation in metal 3D printing

Science ◽  
2020 ◽  
Vol 368 (6491) ◽  
pp. 660-665 ◽  
Author(s):  
Saad A. Khairallah ◽  
Aiden A. Martin ◽  
Jonathan R. I. Lee ◽  
Gabe Guss ◽  
Nicholas P. Calta ◽  
...  
Keyword(s):  
Defect Formation ◽  
State Of The Art ◽  
Operational Reliability ◽  
Formation Mechanisms ◽  
High Fidelity ◽  
Melt Pool ◽  
3D Printers ◽  
Metal 3D Printing ◽  
Nanosecond Dynamics ◽  
Control Complex

State-of-the-art metal 3D printers promise to revolutionize manufacturing, yet they have not reached optimal operational reliability. The challenge is to control complex laser–powder–melt pool interdependency (dependent upon each other) dynamics. We used high-fidelity simulations, coupled with synchrotron experiments, to capture fast multitransient dynamics at the meso-nanosecond scale and discovered new spatter-induced defect formation mechanisms that depend on the scan strategy and a competition between laser shadowing and expulsion. We derived criteria to stabilize the melt pool dynamics and minimize defects. This will help improve build reliability.

scholarly journals High-Fidelity Simulated Players for Interactive Narrative Planning

2018 ◽  
Author(s):  
Pengcheng Wang ◽  
Jonathan Rowe ◽  
Wookhee Min ◽  
Bradford Mott ◽  
James Lester
Keyword(s):  
State Of The Art ◽  
Data Driven ◽  
High Fidelity ◽  
Interactive Narrative ◽  
Interaction Data ◽  
Convolutional Networks ◽  
Novel Approach ◽  
Adaptation Policies ◽  
Narrative Planning ◽  
Prior State

Interactive narrative planning offers significant potential for creating adaptive gameplay experiences. While data-driven techniques have been devised that utilize player interaction data to induce policies for interactive narrative planners, they require enormously large gameplay datasets. A promising approach to addressing this challenge is creating simulated players whose behaviors closely approximate those of human players. In this paper, we propose a novel approach to generating high-fidelity simulated players based on deep recurrent highway networks and deep convolutional networks. Empirical results demonstrate that the proposed models significantly outperform the prior state-of-the-art in generating high-fidelity simulated player models that accurately imitate human players’ narrative interactions. Using the high-fidelity simulated player models, we show the advantage of more exploratory reinforcement learning methods for deriving generalizable narrative adaptation policies.

scholarly journals Geomorphometry: Today and Tomorrow

2018 ◽  
Author(s):  
John P Wilson
Keyword(s):  
Content Knowledge ◽  
State Of The Art ◽  
High Fidelity ◽  
Terrain Modeling ◽  
Actionable Knowledge ◽  
Digital Terrain ◽  
Current State ◽  
Digital Terrain Modeling ◽  
Key Innovations

This paper summarizes the current state-of-the-art in geomorphometry and describes the innovations that are close at hand and will be required to push digital terrain modeling forward in the future. These innovations will draw on concepts and methods from computer science and the spatial sciences and require greater collaboration to produce “actionable” knowledge and outcomes. The key innovations include rediscovering and using what we already know, developing new digital terrain modeling methods, clarifying and strengthening the role of theory, developing high-fidelity DEMs, developing and embracing new visualization methods, adopting new computational approaches, and making better use of provenance, credibility, and application-content knowledge.

scholarly journals Multiscale analysis of crystalline defect formation in rapid solidification of pure aluminium and aluminium–copper alloys

2022 ◽  
Vol 380 (2217) ◽  
Author(s):  
Tatu Pinomaa ◽  
Matti Lindroos ◽  
Paul Jreidini ◽  
Matias Haapalehto ◽  
Kais Ammar ◽  
...  
Keyword(s):  
Rapid Solidification ◽  
Crystal Plasticity ◽  
Phase Field ◽  
Multiscale Analysis ◽  
Defect Formation ◽  
Formation Mechanisms ◽  
Pure Aluminium ◽  
Crystalline Defects ◽  
Dislocation Densities ◽  
Phase Field Crystal

Rapid solidification leads to unique microstructural features, where a less studied topic is the formation of various crystalline defects, including high dislocation densities, as well as gradients and splitting of the crystalline orientation. As these defects critically affect the material’s mechanical properties and performance features, it is important to understand the defect formation mechanisms, and how they depend on the solidification conditions and alloying. To illuminate the formation mechanisms of the rapid solidification induced crystalline defects, we conduct a multiscale modelling analysis consisting of bond-order potential-based molecular dynamics (MD), phase field crystal-based amplitude expansion simulations, and sequentially coupled phase field–crystal plasticity simulations. The resulting dislocation densities are quantified and compared to past experiments. The atomistic approaches (MD, PFC) can be used to calibrate continuum level crystal plasticity models, and the framework adds mechanistic insights arising from the multiscale analysis. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.

Entropy of Nanostructures

2017 ◽  
pp. 600-614
Author(s):  
Ottorino Ori ◽  
Franco Cataldo ◽  
Mihai V. Putz
Keyword(s):  
Mechanical Properties ◽  
Free Energy ◽  
Gibbs Free Energy ◽  
Defect Formation ◽  
Vacancy Concentration ◽  
Structural Evolution ◽  
Point Of View ◽  
Structural Defects ◽  
Formation Mechanisms ◽  
Topological Invariants

Recent advances in graphene studies deal with the influence of structural defects on graphene chemical, electrical, magnetic and mechanical properties. Here the complex mechanisms leading to the formation of clusters of vacancies in 2D honeycomb HD lattices are described by a pure topological point of view, aiming to correlate the variation of specific topological invariants, sensible to vacancy concentration, to the structural evolution of the defective networks driven by the topo-thermodynamical Gibbs free energy. Interesting predictions on defect formation mechanisms add details on the topological mechanisms featured by the graphenic structures with defects. Future roles of bondonic particles in defective HD materials are also envisaged.

scholarly journals Review of Laser Powder Bed Fusion of Gamma-Prime-Strengthened Nickel-Based Superalloys

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 996
Author(s):  
Olutayo Adegoke ◽  
Joel Andersson ◽  
Håkan Brodin ◽  
Robert Pederson
Keyword(s):  
Defect Formation ◽  
State Of The Art ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Cast Material ◽  
Creep Properties ◽  
Powder Bed ◽  
Gamma Prime ◽  
Cracking Mechanisms ◽  
Nonequilibrium Solidification

This paper reviews state of the art laser powder bed fusion (L-PBF) manufacturing of γ′ nickel-based superalloys. L-PBF resembles welding; therefore, weld-cracking mechanisms, such as solidification, liquation, strain age, and ductility-dip cracking, may occur during L-PBF manufacturing. Spherical pores and lack-of-fusion voids are other defects that may occur in γ′-strengthened nickel-based superalloys manufactured with L-PBF. There is a correlation between defect formation and the process parameters used in the L-PBF process. Prerequisites for solidification cracking include nonequilibrium solidification due to segregating elements, the presence of liquid film between cells, a wide critical temperature range, and the presence of thermal or residual stress. These prerequisites are present in L-PBF processes. The phases found in L-PBF-manufactured γ′-strengthened superalloys closely resemble those of the equivalent cast materials, where γ, γ′, and γ/γ′ eutectic and carbides are typically present in the microstructure. Additionally, the sizes of the γ′ particles are small in as-built L-PBF materials because of the high cooling rate. Furthermore, the creep performance of L-PBF-manufactured materials is inferior to that of cast material because of the presence of defects and the small grain size in the L-PBF materials; however, some vertically built L-PBF materials have demonstrated creep properties that are close to those of cast materials.

scholarly journals Beta Fleck formation in Titanium Alloys

2020 ◽  
Vol 321 ◽  
pp. 10001
Author(s):  
K. Kelkar ◽  
A Mitchell
Keyword(s):  
Titanium Alloys ◽  
Formation Mechanism ◽  
Defect Formation ◽  
Melting Rate ◽  
Vacuum Arc ◽  
Formation Mechanisms ◽  
Alloy Development ◽  
Vacuum Arc Remelting ◽  
Freckle Formation ◽  
Nickel Base

Beta fleck is a troublesome segregation defect in many titanium alloys. It has previously been investigated by several authors and appears to have two formation mechanisms, one similar to that of “freckle” in steels and nickel-base alloys, the other arising in the “crystal rain” effect seen in conventional steel ingots. The freckle defect has been extensively studied and several theories developed to account for its formation in both remelted ingots and directional castings. In this work we compare the findings of investigations into the nickel-base freckle formation mechanism to similar conditions in the vacuum arc remelting of titanium alloys. We find that there are strong similarities between the beta fleck formation conditions and the parameters related to the Rayleigh Number criterion for freckle formation. In particular, the dendritic solidification parameters and the density dependence on segregation coefficients both fit well with the conditions proposed to characterise freckle formation. The second formation mechanism arises in the columnar to equiax transition in solidification. The condition for the avoidance of the defect in the two cases is the shown to be the same, namely the use of a very low VAR melting rate, but that it is unlikely to be 100% successful in preventing defect formation. We propose that the techniques presently in use for alloy development in the superalloy field through optimising the composition for minimum sensitivity to freckle formation should be applied to the formulation of future titanium alloys; also that attention should be paid to developing the PAM process to provide suitable solidification conditions for defect absence in a final ingot.

Defects and Their Control in SiO2 Films Prepared by D2 –Lamp Photochemical Vapor Deposition

1988 ◽  
Vol 131 ◽  
Author(s):  
Hidehiko Nonaka ◽  
Kazuo Arai ◽  
Shingo Ichimura
Keyword(s):  
Vapor Deposition ◽  
Defect Formation ◽  
Film Growth ◽  
Film Surface ◽  
Formation Mechanisms ◽  
Silica Films ◽  
Activated Oxygen ◽  
Surface Modified ◽  
Photochemical Vapor Deposition ◽  
Vacuum Uv

ABSTRACTAmorphous silica films deposited from the mixture of gases (Si2 H6 and Si2F6) by deutrium-lamp CVD were studied by IR, vacuum UV, EPR and Auger electron (AE) spectrometries. The F-doping enhanced the film growth and removed defects in the film such as -H, -OH, and E' centers. A model on deposition and defect formation mechanisms was proposed based on the thermodynamic Stabilities of resultant HF in the reactions. The AES study showed that the film surface modified by activated oxygen had an increased hardness against electron beams.

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